11-1051 May 1966 pRotutions in the Brazos River Valley TEXAS A8cM UNIVERSITY TEXAS AGRICULTURAL EXPERIMENT STATION R. E. Patterson, Director, College Station, Texas SUMMARY The influence of l4 cropping systems on the physical and chemical soil characteristics of Miller clay was studied from 1952 to 1963. Determination of the influence of the rotations on yield also was made. The index crops used were cotton and corn. The soil properties studied were bulk density, field capacity, moisture percentage, permanent wilting per- centage, percent available water, noncapillary pore space, capillary pore space, organic matter, aggrega- tion, total nitrogen and available phosphorus. Yields of cotton and corn were influenced little by the cropping systems. There were , differences in soil properties after some of the tions, but these changes were ihot serious enou influence the yield of cotton or corn. v If cotton or corn is to be grown on Mille it should be grown continuously-not in rota ' with adequate rates of commercial fertilize maximum profit. f CONTENTS Summary ........................................................................................................ .. 2 Introduction ................................................................................................. .- 3 Review of Literature .................................................................................. .. 4 Materials and Methods .............................................................................. .- 5 Permanent Wilting Percentages ...................................................... -. 6 Noncapillary Pore Space ..................... ..'. .......................................... .. 6 Capillary Pore Space ..................... ................................................... .. 6 Bulk Density and Percent Available Water ................................ .. 6 Organic Matter Determination ........................................................ .. 6 Aggregate Analysis .............................................................................. -. 6 Infiltration Rates ................................................................................. .- 7 Statistical Analysis ................................................................................ .- 7 Results ........................................................................................................... .. 7 Cotton Yields ....................................................................................... .. 7 Corn Yields ........................................................................................... .. 7 Forage Yields ........................................................................................ .. 9 Soil Organic Matter .......................................................................... .- 9 Total Nitrogen .................................................................................... ..l0 Phosphorus ........................................................................................... .. l0 Soil Physical Properties .................................................................... ..l0 Capillary Pore Space .......................................................................... _.1l Percent Available Water .................................................................. ._l2 Bulk Density ...................................................................................... Field Capacity ...................................................................................... __l8 Permanent Wilting Percentage ........................................................ ..l4 Aggregate Analysis .............................................................................. _-1l} Infiltration ............................................................................................ -. 16 Discussion of Results ................................................................................ -_l6 Summary and Conclusion ........................................................................ __l7 Literature Cited ........................................................................................... __l8 Crop Rotations the Brazos River Valley Eli L. Whiteley and Billy W. Hipp* I ‘HE ROTATION OF CROPS may be defined as the growth of different crops in recurring sequence as contrasted t0 continuous culture of one crop- on the same land or haphazard sequence of crops. Crop rotations have classically been designed to aid in maintenance or improvement of soil productivity and reduction of insect, disease and weed problems. Changes in modern agriculture, however, warrant a closer look at this classical concept to determine if crop rotations are necessary in all locations. Maintaining soil productivity is, foremost in every farmer’s plans. This usually is achieved by finding the best combination of fertilizer practices, crop rotations and other management factors. Rota- tions unsupported by fertilization will not maintain the high yields demanded by modern agriculture. All products removed from the land contain es- sential mineral elements. oSome or all of these ele- ments probably will be removed by crops or animals at a rate faster than the natural rate of release into available forms in the soil. Thus, the soil must be supplemented with additional nutrients if pro- ductivity is to be maintained or improved. Nitrogen- fixing legumes, when properly inoculated, can add nitrogen to the soil but phosphorus, potassium and some minor elements must be returned as fertilizers if productivity is to be maintained. In recent years many research workers and farm- ers have questioned the necessity of including a legume in the rotation. The nitrogen supplied by a legume also could be added to the soil in the form of commercial fertilizers which may cost less than nitrogen supplied by legumes. Where livestock are a part of the farm enterprise, legumes may be used as a source of hay or for grazing. This will reduce the cost of nitrogen supplied by the legumes because of the double utility of the plants. The organic matter produced by grasses and legumes in a rotation is one of their most important products. Many soils with a fairly low clay content can be maintained at a high level of productivity by the use of commercial fertilizers and crop residues. The effect of deep-rooted legumes on internal drainage in soils with tight subsoils must be con- sidered. Farm observations of improved internal drainage after growing deep-rooted legumes have been frequent but are subject to considerable error. Much work needs to be done on the effect of legumes on aggregation, infiltration and tilth. *Respectively, associate professor and research associate, De- partment of Soil and Crop Sciences. REVIEW OF LITERATURE Soil scientists and others have conducted experi- ments 0n crop rotations for many years and various answers and theories have been developed. Many of these rotation experiments were conducted in the northern United States and on soils very different from Miller clay. A review of the literature dis- closes findings quite different in some areas and quite similar in others. Mills (7) made measurements of some physical properties of Miller clay following a 3-year rotation with six cropping systems. He found that sweet- clover in rotation with corn increased the percent pore space and permeability and decreased volume weight as compared with winter peas in rotation with corn. There was no improvement in perme- ability in the 5 to 8-inch zone under any rotation. Myers and Myers (8) proposed that the favor- able effects of legumes upon small grain yields may occur through their effect on soil structure rather than their influence on soil nitrogen. In a study of rotation and tillage treatments in the Rolling Plains of Texas, Perdomo (l4) found a relationship between rotation, tillage practices and soil physical properties. He found that wheat and a forage sorghum in rotation with sub-tillage had a definite beneficial effect on soil physical properties. Smith et al. (l9) found that on Austin clay, water-stable aggregates larger than 2 mm. in diameter were most abundant in soil horizons that contained the most organic matter, but the quantities of smaller aggregates were essentially unchanged in horizons of higher organic matter. Van Bavel and Schaller (25) showed that a significant positive correlation existed between ag- gregation and corn yields on Marshall silt loam. Pillsbury (l5) indicated that decayed organic matter can increase the rate of water entry into a Yolo loam. Patrick et al. (l3) found that winter cover crops on Commerce loam had a significant influence on organic matter, total nitrogen, aggrega- tion index, bulk density, noncapillary porosity, field capacity and wilting point but had no significant effect on permeability. Gish and Browning (2) made a study of the factors affecting the stability of soil aggregates and found that soil and crop management practices had a marked effect on the size, distribution and stability of soil aggregates. They also determined that under four rotation systems on Marshall, Belinda and Clarion soils, the best aggregation was achieved with bluegrass. This was followed by rotation meadow 4 and rotation corn, while continuous corn prod the least aggregation. " Laws and Evans (4) investigated the effe g long-period cultivation on some of the ph properties of Houston Black clay and Bell They concluded that: cultivation for 50 to 90 had decreased the pores drained under tensio’ 30 cm. of water in Houstoni; Black clay; H0 f Black clay contained a much larger percent to 5 mm. aggregates under virgin conditions =2 under cultivation; more total aggregates were. served under virgin soil; and there was a in organic matter in the upper 18 inches of i, ton Black clay which had been cultivated for w? years. Olmstead (ll) had similar findings under. land conditions in Kansas. He found that the in aggregation was approximately 80 percent a 40 years cultivation. In another portion of the g experiment, however, he showed that cropping ‘ terns which included continuous small grains, g tinuous row crops and rotations including fa caused no significant differences in aggregation. p’ Further investigations involving cropping j i terns and soil properties were made by Page Willard (12). They made various physical u‘ surements after cropping systems on a Nappa silty clay loam in Paulding County, Ohio. Of v, various physical measurements made, only determi tions of the air space porosity and degree of ag tion showed satisfactory correlation with yield lev McVickar et al. (6) compared five cropp“ systems on an Onslow fine sandy loam. The tr) ments were fallow, rye grass, crimson clover, v I and Austrian winter peas. After 4 years under th’ treatments results showed: organic matter cont was not increased enough by the different crops , be significant and water holding capacity was influenced by the cropping systems. a Neher (l0) investigated the effect of croppi systems and soil treatments on the water-stable gregates of a clay pan soil in Kansas. He f0 t. that alfalfa apparently caused an increase in A amount of water-stable aggregates in the soil. the residual effect of alfalfa on aggregation appea 1 to last as long as 8 years after the alfalfa was turn under. l An extensive study 0n a number of soils. Missouri, Illinois, Ohio, Georgia and California ' volving the modification of physical properties - soil by crops and management was made by Uhla A (22). He reported that (1) plants with deep a well-developed root systems, such as alfalfa and ku A” ixpected to increase porosity and permeability 11m prove soil structure and (2) crop residues _ kept on the soil surface improve the in- ‘rate of the surface soil and also improve ‘infiltration rate at lower depths. a study of crop rotations on a Lufkin fine “am, Naqvi (9) found no change in soil A conditions after a 4-year rotation involving d corn in combination with five legumes. i ta by Reynolds et al. (17) from these same .~< indicated that the effect of legumes and i on corn production was not enough to be vlcally important. j investigation by Raut (16) on a comparison Yrs of Yellow beardgrass and of continuous "on Miller clay showed that: (1) Yellow ‘Wss did not increase infiltration capacity and 4- to 7-inch layer in Miller clay was the 3.; factor in water infiltration. p; varying responses of soil properties to crop- tems previously mentioned may need to be for each individual area to determine how ‘('1 responds to various crops in cropping sys- “ i many cases the cost of obtaining desirable from crop rotation may cause them to lose “neficial nature, resulting in a liability rather =1: asset. If this is the case, crop rotations could pinated and replaced with a sound fertilizer ' ll MATERIALS AND METHODS i? is study was established on the Texas A8cM ity Plantation in the Brazos River valley in in Miller clay. This soil is very fertile and “inatural state is well aggregated. The internal is very slow and crusting is sometimes a I after heavy rains. The area selected for I was used as pasture from 1935 to 1950, planted f) on in 1951 and the rotation study was started fall of 1951. Grasses and legumes were planted ; fall of 1951, and the index crops- cotton and 1 A were planted in the spring of 1952. .» _g e design of the experiment was a randomized I with three replications. The design was such ch crop in each rotation appeared in each ition every yearf; iThus, in a 4-year rotation, plots were includied in each replication for that ‘n. Each plot was eight rows (40-inch) wide 0 feet long. The rotations used are listed in l. Standard varieties of the crops were _used ahout the study. These included Texas 30 TABLE l. ROTATIONS USED TO STUDY THE EFFECT OF ROTATIONS ON SOIL PRODUCTIVITY AND PHYSI- CAL PROPERTIES OF MILLER CLAY. First Second Third Fourth Rotation* year year year year C Cotton Continuous Cr Corn Continuous C, O Cotton Oats C, O-sc Cotton Oats- sweetclover C, O-sc, Sc Cotton Oats- Sweetclover sweetclover C, A Cotton Alfalfa C, O-a Cotton Oats- alfalfa C, O-a, A Cotton Oats- Alfalfa alfalfa C, A-f, A-f Cotton Alfalfa- Alfalfa- fescue fescue C, C, A-f, A-f Cotton Cotton Alfalfa- Alfalfa- fescue fescue C, C, A-f, A-f Cotton Cotton Alfalfa- Alfalfa- fescue fescue Cr, Cr, A-f, A-f Com Corn Alfalfa- Alfalfa- fescue fescue Cr, Cr, A-f, A-f Corn Com Alfalfa- Alfalfa- ' fescue fescue Cr, O-sc, Sc Corn Oats- Sweetclover sweetclover *In these rotations, the italicized symbol represents the crop in question. Preceeding and following symbols represent preceed- ing and following crops; the sequence remains unchanged. corn, Deltapine cotton, Mustang oats, Kentucky 31 fescue, common alfalfa and Madrid sweetclover. During the first 4 years (one cycle) of the study, the equivalent of 9 pounds of phosphorus (P) per acre per year was applied to the rotation containing legumes. The P was applied at the time of seeding of the legumes as a broadcast application. In a 2- year rotation the plot received 18 pounds of P, while a 4-year rotation received 36 pounds of P. At the end of the first 4 years, the rate of application of P was changed to 13 pounds per acre per annual application. After 8 years the plots were split and 40 pounds per acre of nitrogen was applied in a band to the corn and cotton plots. The cotton and corn yields were taken from the two center rows of the plots or subplots (after the split). The forage yields were taken from randomly selected areas within the plots. Standard farming practices were used through- out the study. Regular two or four-row equipment was used to prepare the land, plant and cultivate the crops. The corn was hand harvested. The cotton was hand harvested the first 4 years and machine picked the last 8 years. During the first 4 years of the study, the forage produced on the grass-legume plots was removed 5 as hay. To return more organic material to the soil, all forage produced was returned to the soil during the last 8 years of the experiment. All plots were sampled at the beginning of the experiment in 1951. Organic matter determinations were made only on these samples, since the experi- ment was designed to measure differences between the cropping systems and their effect on the soil as compared with the effects of the index crops in continuous culture. Soil samples for physical analysis were taken in February 1961. Duplicate samples were taken in copper rings 2 inches in diameter and 3 inches in length. Sampling depths were O-3, 3-6, 6-9 and 9-12 inches. Samples were trimmed in the field with a cheese cutter and stored in pint ice cream cartons previously coated with paraffin to reduce moisture evaporation. Duplicate samples for chemical anal- ysis were taken with a spade at depths of 0-6 inches and 6-l2 inches. In preparing soil cores for moisture retention characteristics, cheesecloth was placed over the bottom of the ring containing the samples and secured with a rubber band. The samples were then saturated with water. The saturated samples were allowed to drain briefly and then were weighed. Next, samples were placed in a pressure plate appartus (18) and sub- jected to a pressure of 1/ l0 atmosphere. When the samples reached moisture equilibrium at this pressure they were removed, weighed and their water loss recorded. Later, when all determiniations were com- pleted, the samples were ovendried. Calculation of the field capacity then was made by determining the percentage of moisture remaining in the soil at l /10 atmosphere pressure. (A l/ l0 atmosphere percent- age was considered as field capacity for this study instead of the usual 1/3 atmosphere percentage.) Permanent Wilting Percentages The 15 atmospheres moisture percentage normal- ly is termed the permanent wilting percentage and was determined by the pressure membrane (23). Samples were taken from the pressure plate and placed in the membrane, exposed to a pressure of l5 atmospheres (approximately 221 pounds per square inch) until moisture equilibrium was reached. They were determined to be at equilibrium when their weight remained constant for 3 days. When the samples were at equilibrium, they were removed, weighed and their weights recorded. The percent moisture at 15 atmospheres was determined and termed the permanent wilting percentage. 6 Noncapillary Pore Space After weights were recorded from the p membrane exposure, the samples again were sat ,1 with water. When saturation was complet samples were placed on a tension table (5), an pores were allowed to drain at 4O cm. water t for 48 hours. After 48 hours, the samples moved, weighed and their wleiights recorded. ' conclusion of the tension table determinatio ‘ samples were dried in an oven set at 105° C. days. Noncapillary pore space was determin subtracting sample weight at 40 cm. tension the saturated weight and dividing the differe ‘ the volume of the sample. Noncapillary pore i then was reported as percent by volume. a Capillary Pore Space Capillary pore space was determined by m ing the moisture lost between 40 cm. water te and ovendry weight and was expressed as perc ( volume as outlined by Baver (1). The calcu, is accomplished by subtracting the weight o ovendry sample from its weight at 4O cm. l tension and dividing the difference by the vo of the sample. It was assumed that the pores drained at 40 cm. were capillary pores. A Bulk Density and Percent Available Wa Bulk density and percent available water i calculated from data obtained in moisture rete determinations. Bulk density was determined’ dividing the ovendry weight of the soil core by‘) ring volume. Ring volume was 154.4 cubic cm.- ring, and the soil weight was in grams. The r_ ing weight per volume was in grams per cubic To determine an approximation of the p 7 water available to plants, the permanent wilting centage was subtracted from the field capacity » centage. The difference should have been the aml of water plants can take from this soil. i Organic Matter Determination Organic matter was determined by the or carbon content as described by the U. S. Sal'- Laboratory (23). This determination was n» from the loose soil taken with a spade. Each sal was duplicated, yielding twelve values per treat Two grams of ovendry soil were used for this anal‘ Aggregate Analysis The method used for aggregate analysis was l _ given by Van Bavel (24). A representative s n of about 500 gm. was passed through an 8- sieve. An air-dry sample of 25 gm. was taken -§ this and distributed evenly on a 5-mm. sieve i J ifof sieves underneath it descending in screen if he sizes used were 5 mm., 2 mm., 1 mm., 25 1| .125 IIIIII. We screens were moved in an up and down ’ in a container of water for 10 minutes. The t remained on each sieve size was ovendried, Id until only the primary particles remained hed through their corresponding screens again. imaining particles were ovendried and the L of water-stable aggregates was determined. egree of aggregation was expressed as a per- i‘ of the ovendry sample. j ltion Rates ‘(filtration rates were determined on six selected ns. These measurements were made in the ith cylinder infiltrometers (he heavy metal cylinders ranged from 10 to ches in diameter. The cylinders were driven es into the soil with a thick, steel-driving plate. were built outside the infiltrometers and filled water to reduce lateral movement of the water » the cylinders. Water was furnished to the ers by a garden hose attached to a water trailer. if each infiltrometer was filled, a gunny sack laced on the soil surface to avoid disturbance isoil. Water depth in the cylinders was main- in as near as possible to 5 inches. Periodic mea- ents of water depth were made to determine, i‘ ation rates. Measurements were made for 6 " l after a constant infiltration rate was obtained. 'tical Analysis iStatistical analysis of this experiment was by w sis of variance as outlined by Snedecor (20) in ters 11 and 12 and Steel and Torrie (21) in RESULTS Cotton Yields The yields of cotton in the various rotations are presented in Table 2. The (C, O-sc, Sc) rota- tion produced the most cotton, 1,314 pounds per acre, and the continuous cotton rotation produced the lowest yield, 1,099 pounds per acre. The difference is 215 pounds of seed cotton per acre. (C, C, A-f, A-f and (C, A) produced 171 and 161 more pounds of cotton per acre than continuous cotton. No other rotations produced yields statistically different from each other at 5_percent levels of significance. In view of the economics of cotton production based on yields alone, it would not pay to rotate dryland cotton on Miller clay unless the other crop (s) could be utilized for a profit. In 1960 the plots were split, and nitrogen was added at the rate of 40 pounds per acre per year to half of each plot. Yields are shown in Table 3. The yield of the rotations receiving nitrogen was significantly higher than the rotations not receiving nitrogen. The 4-year period during which additional nitrogen was applied to the plots was sufficient to establish a trend showing an increase in cotton yields. (C, A) and (C, C, A-f, A-f) had the highest yields from 1960 to 1963 and continuous cotton and (C, O) had the lowest yields. All rotated cotton produced higher yields than continuous cotton when all plots were averaged over all years. There was a greater difference between years than between rotations. Corn Yields Corn yields were erratic during this 12-year study. Averages varied from a high of 67.7 bushels per acre ter ll. in 1955 to a low 11.8 bushels per acre in 1956. (Cr, i E 2. COTTON YIELDS IN POUNDS OF SEED COTTON PER ACRE, 1952-1963 ‘ Lint z 37.5 percent Yelr 1952 1953 1954 1955 1956 1957 1958 1959 1960 1961 1962 1963 Average — — — -- - - - - - - — — — Pounds — — — — — — — — — — - — — g. .~ , Ss 1,547 2,017 1,200 2,230 798 557 1,562 1,430 1,732 1,320 476 907 1,314a* tA-f, A-f 1,360 2,240 1,387 2,465 857 462 1,198 1,222 1,582 1,133 300 1,040 l,270a 1,270 1 ,947 1,253 2,023 760 355 1 ,584 1,247 2,335 880 695 800 1 ,260a a, A 1,013 2,128 1,227 2,543 507 402 1,322 1,575 1,505 960 560 907 1,221ab l, a 1,147 2,415 1,227 2,050 545 753 1,240 1,428 1,555 733 507 907 1,209ab ‘a 987 1,973 1,413 2,230 758 447 1,358 1,505 1,358 1,000 405 880 1,l93ab I .~ a 1,147 1,680 1,253 1,997 760 570 1,220 1,453 1,658 880 530 1,013 1,180ab l , A-f, A-f a 1,760 1,147 2,358 508 455 1,058 1,505 2,133 693 543 933 1,17 lab -f, A-f 1,120 2,133 1,013 1,972 527 435 1,512 1,298 1,455 1,080 555 853 1,163ab i 1,173 2,338 1,120 2,022 603 493 1,138 1,090 1,482 653 230 847 1,099 b i Average 1,168 2,063 1,224 2,189 662 493 1,319 1,375 1,680 933 479 909 d a cd a f g cd c b e g e ge Test. ans followed by different letters are significantly different from each other at the 0.05 level according to Duncan’s Multiple 7 O-sc, Sc) and (Cr, Cr, A-f, A-f) were significantly rotations. Table 5 shows the influence of 40 poi higher than (Cr, Cr, A-f, A-f) and continuous corn. of nitrogen on corn yields. (C, O-sc, Sc) and . However, (Cr, Cr, A-f, A-f) was significantly higher Cr, A-f, A-f) were significantly higher than (Cr, than continuous corn. These data are presented in A-f, A-f) and continuous corn. Corn yields I Table 4. The corn in rotations (Cr, O-sc, Sc) and (Cr, Cr, A-f, A-f) were significantly higher than y (Cr, Cr, A-f, A-f) followed 2 years of a grass-legume from Cgntinugug Com, . mixture and would be expected to yield more than _ _ _ _ I continuous corn or corn following corn in a rotation. A Comparlson of ylelds. £20m nonfemhzed ' of (Cr, Cr, A-f, A-f) and (‘C13 Cr, A-f, A-f) s‘ that the (Cr, Cr, A-f, A-f) rotation yielded more i (Cr, Cr, A-f, A-f) in every year after 1955. The I difference between these rotations is that the, When the plots were split in 1960, the addition in (CT, CI‘, A-f, A-i) fOIIOWEd 2 years 0f alfalfa-f of 40 pounds of nitrogen per acre increased the while the corn in (Cr, Cr, A-f, A-f) followed 1 yields of the fertilized rotations over the nonfertilized in the same sequence of crops. All rotations " Corn gave good yields in only 2 of the 12 years. In 1955 and 1962 the yields of some plots were ap- proximately 70 bushels per acre. TABLE 3. COTTON YIELDS FROM THE ROTATION PLOTS THAT RECEIVED NO NITROGEN AND THE ROTA u PLOTS THAT RECEIVED 40 POUNDS NITROGEN PER ACRE FOR THE PERIOD 1960163 ' No nitrogen 40 pounds nitrogen per acre 1960 1961 1962 1963 Average 1960 1961 1962 1963 Average Mean ‘ — — — — — — — — — — — — — Pounds — — — — — — — — — — - I C, A 2,335 880 695 800 1,178 2,238 800 650 720 1,102 l,l04a C, C, A-f, A-f 2,133 693 543 933 1,076 2,112 1,053 538 933 1,159 I C, O-sc, Sc 1,732 1,320 425 970 1,096 1,857 1,227 577 773 1,108 C, O-sc 1,658 880 530 1,013 1,020 2,085 1,160 667 800 1,178 C, C, A-f, A-f 1,582 1,133 300 1,040 1,014 1,935 1,093 340 1,013 1,095 C, O-a, A 1,505 960 560 907 983 1,653 1,240 550 773 1,054 C, O-a 1,555 733 507 907 925 1,778 760 523 907 992 C, O 1,358 1,000 405 880 911 1,550 987 447 747 933 921 X C 1,482 653 230 847 803 1,985 813 357 800 989 896 Average 1,680 933 475 909 999b 1,885 1,016 522 837 1,065a *Means having different letters beside them differ at the 5 percent level of significance. TABLE 4. CORN YIELD IN BUSHELS PER ACRE 0F EAR CORN FOR THE ROTATION PLOTS THAT RECEIVED‘ NITROGEN FROM 1952 TO 1969 " Rotation 1952 1959 1954 1955 1956 1957 1959 1959 1960 1961 1962 1969 - — — — — — — — — — — — — — Bushels — — — — — — — — — — Cr, O-sc, s6 42.6 99.1 90.2 67.6 9.0 94.2 90.9 97.7 99.7 49.9 72.5 24.6 Cr, Cr, A-f, A-f 95.6 27.7 27.4 56.5 9.9 95.5 92.9 42.0 97.1 94.5 77.5 91.7 Cr, m, A-f, A-f 41.6 92.4 25.6 70.9 7.6 90.7 27.9 97.9 95.7 15.6 99.1 21.9 Cr 46.2 99.9 29.1 75.7 22.5 90.7 17.9 22.4 19.9 19.1 10.9 19.9 Average 41.5 99.0 26.6 67.7 11.9 92.9 27.4 94.9 99.0 27.9 49.9 24.2 *Means having different letters beside them differ at the 5 percent level of significance. TABLE 5. CORN YIELD IN BUSHELS PER ACRE OF EAR CORN FOR THE ROTATION PLOTS THAT RECEIVED’ NITROGEN AND THE PLOTS THAT RECEIVED 40 POUNDS PER ACRE OF NITROGEN FROM 1960 TO 1963 No nitrogen 40 pounds nitrogen per acre ‘_ Rotation 1960 1961 1962 1963 Average 1960 1961 1962 1963 Average M — — — — — — — — — — — — — — Bushels — — — — — — — — — — - I I Cr, O-sc, Sc 39.7 48.3 72.5 24.6 46.3 44.1 53.9 67.7 30.7 49.6 Cr, Cr, A-f, A-f 37.1 34.5 77.5 31.7 45.2 37.5 34.1 72.5 32.1 44.1 Cr, Cr, A-f, A-f 35.7 15.6 39.1 21.8 28.1 38.6 24.2 53.0 33.5 37.3 Cr 19.3 10.3 17.1 12.8 14.9 13.1 18.9 45.2 30.3 26.9 Average 33.0 27.2 51.6 22.7 33.6 33.3 32.8 60.1 31.7 39.5 *Means having different letters beside them differ at the 5 percent level of significance. 8 Q FORAGE YIELDS, 1956 TO 1963. YIELDS ARE IN POUNDS PER ACRE ON AN OVENDRY BASIS I 1956 19572 1958 1959 1960 1961 1962 1968 M646 8,810 8,800 8,800 9,880 7,578 6,628 4,445 627651 8,710 2,965 11,298 5,588 6,984 5,015 4,861 5,695ab 2,988 2,650 9,178 6,718 5,490 5,822 4,175 5,288 b6 4, A-f 8,070 8,247 7,240 7,602 9,968 8,102 1,985 5,178 b6 8,990 8,880 6,580 8,705 4,860 4,512 8,274 5,086 b6 8,148 2,608 6,868 9,028 6,250 4,219 8,107 4,960 6 -. 2,798 2,898 8,288 7,428 6,612 2,020 4,588 4,987 6 14,41 8,460 8,070 8,480 8,122 5,218 2,015 2,787 4,727 cd 1 2,577 2,668 9,222 7,551 5,422 2,765 2,428 4,665 6d 4, A-f 8,280 8,200 8,847 5,487 8,005 2,915 2,448 4,168 a ' A-f A-f 8,580 8,867 6,468 6,708 8,918 2,895 1,898 4,119 a i 8,240 8,222 1,860 8,855 2,765 8,492 2,277 2,887 6 8,262 ' 8,125 7,710 7,176 5,688 - 8,782 8,105 d8 due to floods. ‘g nitrogen yielded more than the rotations not 'ng nitrogen except (Cr, Cr, A-f, A-f). 7,6 Yields ‘he forage yields are shown in Table 6. This A- amount of ovendry material returned to the 4r acre each year except 1957. That year the ‘L. river backed water on the plots; all forage if were killed and no data were taken. The ] were reseeded in the fall of 1957. In the rota- ' (C, O-sc, Sc), (C, O-a, A), (C, A-f, A-f) and O-sc, Sc) the yields in Table 6 are averages 3;; was returned t0 the soil. (C, O-sc) produced the greatest amount of i- ial to be returned to the soil. This rotation uced an average of 6,276 pounds of ovendry rial each year. The (C, O-sc, Sc) rotation pro- I1 the second largest amount, 5,695 pounds per per year. The lowest production was in (C, O) ' it was significantly lower than all other rotations. ; alfalfa-fescue mixture did not produce as much iige as expected. It was difficult to maintain a 01m mixture of the grass and legume. In most i it tended to be mostly alfalfa or fescue. How- no difficulty was encountered in establishing _..- crops. f Organic Matter f The percent organic matter in the 0-6 inch depth i-the soil is shown in Table 7. The organic matter ; eased under every’ rotation. The amount of i‘; nic matter in the 26611 at the start of the experi- nt was relatively high for soils in this area of Texas. wever, it decreased rapidly in the l2 years of the idy. The smallest decrease occurred in the (C, , A-f) rotation, and the largest occurred in (C, _i c). This decrease is quite interesting when the 5e forage production for the 2 years that the“ I having different letters beside them differ at the 5 percent level of significance. forage yields are considered. (C, O-sc) had the high- est average forage yield (Table 6) and (C, A-f, A-f) produced about a ton less. The greatest decrease in organic matter occurred under the rotation produc- ing the largest amount of ovendry forage. In the (C, A-f, A-f) rotation the soil was cultivated in a row crop 1 year out of 3, while in (C, O-sc) the soil was cultivated in a row crop 1 year out of 2. This is believed to be one reason for the decrease in organic matter in the soil under the (C, O-sc) rotation. More cultivation in combination with high tempera- tures increased the rate of decomposition under (C, O-sc) which was. much greater than that under (C, A-f, A-f), and although more material was re- TABLE 7. SOIL ORGANIC MATTER CONTENT IN THE TOP 6 INCHES OF SOIL IN THE BEGINNING AND AT THE END OF THE ROTATION STUDY Percent organic matter Start End Amount of 1952 1963 decrease Cotton, Alfalfa-fescue, alfalfa-fescue 2.46 2.l8a* 0.28 Cotton, alfalfa-fescue, alfalfa-fescue, cotton 2.49 2.09b 0.40 Cotton, oats-sweetclover, sweetclover 2.50 2.08bc 0.42 Corn, oats-sweetclover, sweetclover 2.46 2.07c 0.39 Cotton, oats 2.42 2.07c 0.39 Cotton, alfalfa 2.47 2.06c 0.41 Com, corn, alfalfa-fescue, alfalfa-fescue 2.38 2.05c 0.33 Cotton, oats-alfalfa, alfalfa 2.44 2.050 0.39 Cotton, oats-alfalfa 2.43 2.0lc 0.42 corn, alfalfa-fescue, alfalfa-fescue,‘ corn 2.38 2.000 0.38 Cotton, cotton, alfalfa-fescue, alfalfa-fescue 2.39 2.000 0.39 corn continuous 2.36 1.90de 0.46 cotton, oats-sweetclover 2.47 1.89e 0.58 Cotton continuous 2.18 l.88e 0.30 Average 2.42 2.02 0.40 *Means not having the same letter beside them differ sig- v nificantly at the o percent level. ous rotations is shown in Table 8. TABLE 8. PERCENT. TOTAL NITROGEN IN MILLER CLAY AFTER VARIOUS CROP ROTATIONS Rotation 0-6 inch 6-12 inch Average C, A 0.16 0.161 0.161 a* C, O-sc, Sc 0.190 0.122 0.156 ab Cr, Cr, A-f, A-f 0.147 0.137 0.142 abc C, O-a 0.164 0.119 0.142 abc C, A-f, A-f 0.142 0.139 0.141 bc C, C, A-f, A-f 0.159 0.118 0.138 bc C 0.164 0.110 0.137 bc C, C, A-f, A-f 0.151 0.122 0.136 bc Cr, O-sc, Sc 0.143 . 0.124 0.134 c C, () 0.143 0.123 0.133 c Cy, C1‘, A-f, A-f C C, O-sc 0.136 0.119 0.127 c (11- 0.134 0.118 0.126 c C, 9-3, A 0.140 0.109 0.124 c Avgrage 0.15121 0.1241) *Means not having the same letter beside them differ sig- nificantly at the 5 percent level. turned t0 the soil, the organic matter decreased more rapidly and was reduced t0 a lower level 1n the (C, O-sc) . The rotations (C, O), (C, A) and (C, O-a) also were cultivated 1 year out of 2. The decrease in organic matter was 0.35, 0.41 and 0.42 percent, re- spectively. The rotations involving 2 years of culti- vated crops and 2 years of sod cro-ps followed the same pattern as the rotations with a 1:1 ratio of cultivated to sod crops. The percent decrease in organic matter varied from 0.33 to 0.40 percent. This indicates that it is somewhat fruitless to try to maintain a high organic matter content in these soils. Total Nitrogen The total nitrogen in the soil under the vari- Total nitrogen TABLE 9. PARTS PER MILLION PHOSPHORUS EX- TRACTED FROM MILLER CLAY AFTER VARIOUS CROPPING SYSTEMS Rotation 0-6 inch 6-12 inch Mean Cr 34.05 16.2 253 a* C, O 32.5 13.3 22_9 ab C1", Cr, A-f, A-f 31.7 13.0 223 ab‘: C, C, A-f, A-f 31.0 13.7 223 abc c t 29.8 14.2 _ 22,0 abc C, O-a 29.8 13.7 21.8 abc C, O-a, A 26.5 15.2 20.8 abcd C, A 29.0 11.8 20.4 bcd Cr, Cr, A-f, A-f 25.8 12.2 19.0 bcde C, O sc 25.3 12.0 18.7 bcde C, O-sc, Sc 25.8 10.5 18.2 (jdgf c, A-f, A-f 22.7 11.0 16.8 def Cr, O-sc, Sc 19.7 10.2 14.9 ef C, C, A-f, A-f 15.8 12.3 14.2 f Average 27.1 12.8 a b was significantly higher in the 0-6-inch dep in the 6-12-inch depth. The total nitrogen from 0.161 to 0.124 percent. t Phosphorus The available P in the soil at two d0 shown in Table 9. There was a significant ence between depths. The 0-,6-:'inch depth ficantly higher in available P than the depth. This was to be expected, since all 1 applied as a broadcast application to the and then disked into the top 6 inches of s; Soil Physical Properties When all four depths were combined ( had a significantly less noncapillary pore sp_ all other rotations. All rotations involvi, produced a greater percentage of noncapill i than the other rotations. Row crops seemed) influenced the noncapillary pore spacem" close-growing crops such as alfalfa, oats an clover. The range in noncapillary pore sp, from 6.23 percent for (C, O-sc) to 12.49 ” for the (ct; Cr, A-f, A-f) rotation, Table The 0-3-inch depth showed effects of on noncapillary pore space similar to the i‘- profile discussed previously. The corn r, again had larger amounts of pore space, (C, O-sc) rotation had the least amount t. capillary pore space. This low value for (C may have been caused by the decrease in- ,_ matter under this rotation, Table 7. A difference in the effect of 2 years of versus l year of cotton following 2 years of i fescue was found at this depth. The sec cotton had 13.00 percent noncapillary pore, TABLE 10. NONCAPILLARY PORE SPACE IN V‘ CLAY AFTER VARIOUS ROTATIONS ‘ Rotation Mean (percent by v01, C, O-sc 6.23a* C, C, A-f, A-f 8.20 b C, A-f, A-f 8.23 b C, O-sc, Sc i 8.79 bc C, O-a 8.80 bc C, O 8.98 bc C, A 9.24 bc C, O-a, A 9.48 bc C, C, A-f, A-f 10.14 bcd C 10.36 cd Cr, Cr, A-f, A-f 10.50 cd Cr, O-sc, Sc 11.44 dc 11.79 de C1", Cr, A-f, A-f 12.49 e *Means not having the same letter beside them differ sig- nificantly at the 5 percent level. 10 *Means not having the same letter beside them nificantly at the 5 percent level. .j 1 it-year cotton had 22.68 percent noncapillary 'e. inuous cotton was midway between these "lions. This was thought to be caused by the -, both aggregation and root channels. Many channels may have been produced through ears of continuous cotton which increased Alary pore space in that rotation. Apparently, ’ati0n of large aggregates was induced by _icue which increased the noncapillary pore der first-year cotton. In the second-year co-t- l; egation may have been reduced by natural tion; furthermore, a large number of root had not had time t0 develop from only 2 if cotton, resulting in a small amount of non- pore space for the (C, C, A-f, A-f) rotation. rn also increased the amount of noncapillary ‘ace at 3-6 inches and 9-12 inches, but there \ difference in noncapillary pore space due on at the 6-9-inch depth. This effect was it to be caused by the many root channels (ed by corn in the 3-6-inch and 9-12-inch zones. “ck of increase in noncapillary pore space at i es may have been caused by the poor root i’ in that zone because of a compacted layer at l, es. Evidence of this compacted layer will be it ted later. he increase in noncapillary pore space brought J by corn was attributed to the intensiveroot s}. of corn in the top 12 inches of the soil. Less ive cultivation also was a possible factor in sed pore space as a result of corn rotations. l was a significant difference in noncapillary f space at each of the four depths from all rota- f: combined (Table 11) . ‘a In a simple correlation of all variables at the ch depth, noncapillary pore space was found ve r values of .403 with field capacity, -.827 with density, -.711 with capillary pore space and with aggregates 2-5 mm. in diameter. An r e of .325 was required for significance at the ircent level. Correlation with all other variables listed was not significant at the 5 percent level. An analysis of the effects of cotton versus corn l’ made concerning noncapillary pore space. This lysis was based on 1 degree of freedom. Comparison of Qotton and corn indicated that I produced significantly more noncapillary pore _ce than cotton at 3-6 and 9-12-inch depths. F ues obtained were 19.08 and 4.15, respectively. F value of only 3.91 was required for significance the 5 percent level. This noncapillary-pore-space ease, brought about by cropping systems con- TABLE ll. PERCENT NONCAPILLARY PORE SPACE MEANS FROM l4 ROTATIONS AT FOUR DEPTHS Depth Mean 0-4 inches l6.66a* 3-6 inches 6.986 6-9 inches 4.47d 9-12 inches l0.38b “Wleans having different letters differ significantly at the 5 percent level of significance. taining corn, was thought to be caused by the intensive fibrous root system of corn. This root system makes many channels, allowing passage of water, whereas the cotton taproot has fewer roots in the top 12 inches of soil. Consequently, fewer channels are produced. Capillary Pore Space Corn tended to promote smaller amounts of capillary pore space than did rotations involving cotton. The (C, O-sc) rotation had consistently more caapillary pores than all other rotations. This effect was obviously again caused by the lack of organic matter under this rotation. Although corn and oats have similar root systems, the oats did not seem to prevent compaction as well as corn. Compaction was highly correlated with capillary pore space; there- fore, capillary pore space also increased under the (C, O-sc) rotation. The rotations involving corn had consistently less capillary pore space at all depths but were not significantly less at the 6-9 inch depth. There were no significant differences in capillary pore space in the 6-9-inch zone (Table 12) . These changes in capillary and noncapillary pore space due to a certain rotation were balanced by each other, so that the total pore space remained practically constant. When capillary pore space and noncapillary pore space were added together for each rotation, the range of total was from 55.50 to 58.28 percent. The extreme rotations were (C, O-a) , and (C), respectively. This indicated a difference of Only 2.71 percent in total pore space. It appears that either of these two types of pore space was in- creased only at the expense of the other, Figure 1. TABLE l2. PERCENT CAPILLARY PORE SPACE MEANS FROM l4 ROTATIONS AT FOUR DEPTHS DePth Mean 0-3 inches 4l.l5a* 3-6 inches 47,72 b 6-9 inches 51,89 q; 9-12 inches 50,26 d *Means having different letters differ at the 5 percent levels of significance. 11 ______ Noncapillary pore space 51 - ._.._.___Capillary pore space m 50 — U as S‘ 49 — o H O o. p, 48 - "', H m r-I r-I ‘H g- 47 — - U ‘é OJ n- -|' U , s-t (I) m 45 — - 44 — '- I - I I I I I I I I I I I I Q1 Cr Cr Cr C C C Q C C C C C C Cr O-sc Q3; O-a 0-a C O A O-sc _C_ A-f O-sc A-f Sc A-f A A-f Sc A-f A-f A.-f A-f A-f A-f Figure I. Capillary and noncapillary pore space as influenced by crop rotation. This could well be caused by differences in sizes of aggregates dominant in each rotation. In all rota- tions combined, there was a difference in the amount of capillary pores at each of the four depths. Table 12 shows these differences at four depths. The two values at 6-9 and 9-12 inches were higher than those at the 0-3 and 3-6-inch layer. This indicates that cultivation practices, which nonnally do not exceed - a depth of 6 inches, tend to keep the particles separated and prevent reorientation, so that pore spaces remain larger in the surface 6 inches than in the next 6 inches. Simple correlation with other measured variables shows that capillary pore space was significantly cor- related with percent available water (r I -.579) and bulk density (r I -.907) . Percent Available Water The (C) rotation had the least amount of avail- able water (7.75 percent) and (C, O-sc) had the second least amount (7.91 percent) (Table 13). The low amounts of available water in these two rotations was due to their high percentage of capil- lary pores. Evidently, the pores were small enough that water could not be removed as readily as from soils that had high amounts of large pore spaces. Another possibility for the low amount of available water in these two rotations is the “sea1ing off” of the routes of water removal by the large number 12 of tiny aggregates present under these rotati tems. The (c, c, A-f, A-f) rotation“ had the amount of available water (8.97 percent) f entire 0-12-inch depth. The remainder of the‘? tions were very similar to each other in amou available water for all depths combined. I At the 0-3-inch depth, the (c) rotation h exceptionally small amount of available water; percent, which was significantly less than all rotations. Rotations involving corn had more I able water than the other cropping systems. , was a difference of 4.13 percent available wat tween continuous cotton and continuous corn. v is an approximate amount of water equal to .37) inches. i’ Rotation systems seemed to react differen t’; the 6-9-inch depth in this phase of the experim g well as some of the other phases. At this depth corn rotations had the least available water. _i_ parently, the corn roots did not penetrate or this zone. Alfalfa-fescue seemed to be less eff‘ in disturbing the compacted layer than sweete because (C, O-sc, Sc) and (Cr, O-sc, Sc), both f taining sweetclover, increased the amount of I able water. Apparently, the roots from sweetc; disturbed this compacted layer and gave it the a’: to release more water when subjected to pre '_ from .10 to 15 atmospheres. I 2,13. PERCENT AVAILABLE WATER IN MILLER toLLowlNc VARIOUS CROPS IN ROTATION Percent available water 7.75a* 7.9lab -f, A-f 8.02abc - , A-f 8.l4abcd 8.l8abcd 8.20abcd 8.32abcde , 8.32abcde ‘ Cr, A-f, A-f 8.36abcde fosc, Sc 8.56 bcde O-sc, Sc 8.72 cde O-Ja ' 8.76 de "joa, A sas de C, A-f, A-f 8.97 f A‘ not having the same letter beside them differ sig- atly at the 5 percent level. it is possible that the increase in release of water f»: rotations is due to the size of pores and - tes created by certain cropping systems. Those ons causing large pore spaces tend to release ;water to plants than rotations with large amounts gillary pore space. The very small aggregates t contribute to capillary pore space have a shell fter around them not removed at 15 atmospheres i e, and the water inside the small pore space limited amount; therefore, the available water La eased. J Density rn decreased bulk density more than any crop. Over the entire 0-l2-inch depth the bulk ' of corn rotations ranged from 1.14 for con- ‘r corn to 1.18 for (Cr, Cr, A-f, A-f) , and the _~| ranges were from 1.21 for continuous cotton - 8 for (C, O-sc) , Table 14. l4. BULK DENSITY OF MILLER CLAY FOLLOW- VARIOUS ROTATIONS Mean (grams per cc.) _ otation (0-12 inch depth) i» l.l4a* yr, Cr, A-f, A-f l.l6ab V, O-sc, Sc l.l8abc p, Cr, A-f, A-f l.l8abc 1.21 bcd O-a, A 1.21 bcd -, C, A-f, A-f 1.22 cde i O-a 1.23 cde A I 1.24 de A-f, A-f 1.24 de _ 0 i 1.25 de V’ , C, A-f, A-f 1.25 de O-sc, Sc 1.25 de O-sc 1.28 e J.- not having the same letter beside them differ sig- I antly at the 5 percent level. 5 TABLE 15. BULK DENSITY AT FOUR DEPTHS AND l4 COMPOSITED ROTATIONS Depth, inches Mean in gms/cc 0.3 l.02a* 3-6 1.276 b 6-9 1.339 c 9-12 1.257 b *Means not having the same letter differ significantly at the 5 percent level. At the 0-3 and 3-6-inch depths, the corn rotations had the lowest bulk densities, but there was little difference in the cotton rotations at 0-3 inches. At 6-9 inches, continuous corn had the least bulk den- sity but there was no difference in the other rotations. Apparently, a compacted layer is developing at 6-9 inches under all rotations. Bulk density values are higher at this depth than either of the other three depths, Table 15. Simple correlation shows that the bulk density values determined coincide with capillary and non- capillary pore space. High bulk density samples had high percentages of capillary pore space and low bulk density samples had high noncapillary pore space percentages. Table 16 indicates these correlations. When a linear contrast of cotton and corn was made, F values obtained were 15.37, 4.38, .13 and 1.00 for the 0-3, 3-6, 6-9 and 9-12-inch depths, respectively. The required significant F value is 3.91. In a comparison of cotton and corn, corn was found to cause a much lower bulk density than cotton, especially in the surface 6 inches. This difference probably was due to the difference in root growth and tillage practices on cotton and corn. It appears that there has been little alteration of the soil physical properties accomplished in the 6-12-inch zone. Field Capacity The 14 cropping systems used in this study had no significant effect on the amount of water retained by the soil at field capacity; however, field capacity was correlated with bulk density and noncapillary pore space as shown previously. TABLE l6. A SIMPLE CORRELATION OF VARIABLES THAT WERE SIGNIFICANTLY CORRELATED WITH BULK DENSITY least significant r Measured variable r value found value at 5 percent level Field capacity _.56l .325 Percent available water _.52l .325 Noncapillary pore space _.827 .325 Capillary pore space .907 .325 l3 TABLE l7. PERCENT WATER IN MILLER CLAY AT PERMANENT WILTING FOLLOWING VARIOUS ROTA- TIONS Rotation Mean (Percent water) Cr, O-sc, Sc 30.02 a* C, C, A-f, A-f 30.02 a C, O 30.35 ab C, O-sc, Sc 30.38 ab C, O-a, A 30.48 ab C, O-a 30.52 ab Cr, Cr, A-f, A-f 30.60 ab Cr, Cr, A-f, A-f ' 30.73 ab C, A 30.74 ab Cr 30.76 ab C, A-f, A-f 30.99 ab C, O-sc 31.16 ab C, C, A-f, A-f 31.19 ab C 31.32 b *Means not having the same letter beside them differ sig- nificantly at the 5 percent level. Permanent Wilting Percentage There was little difference in wilting percent- age as a result of rotation. Continuous cotton had a significantly higher permanent wilting percentage than (C, C, A-f, A-f) and (Cr, O-sc, Sc), both of which contained legumes. The 15 atmospheres percentage (permanent wilting point) for the (C) rotation was 31.32 percent, and was 30.02 percent for both (C, C, A-f, A-f) and (Cr, O-sc, Sc), Table l7. 9o r- 66-12 inch depth g 0-6 inch depth '85 - w T“ 3 8Q .. :1. ~ — E 5g F- F. a, __ u-l Q 75 - J-J U) I H CU J-J q vi- 3 U 5 7Q .- L) H CU an 65 — 60 C Cr C,O-sc C,A C,A-f C,O-sc, Sc A-f Sc Figure 2. Effect of cropping systems on total water-stable aggregates. 14 At the 3-inch depth increments, the t? in rotations were minor. Rotations involvl clover or alfalfa had consistently lower valu, in the 0-3 inch depth where continuous y the lowest value. The (Cr) rotation had“ amount of noncapillary pore space which n.1, easily removed from its large pores when sub 15 atmospheres pressure. ' ' Aggregate Analysis Total aggregation was increased by (C, é and (Cr, O-sc, Sc) at the 0-6-inch depth, There was very little effect on total aggrega any of the cropping systems at the 6-l2-in q Linear comparison shows that rotations t, sweetclover increased total aggregation more at 0-6 inches than the other crops used rotations; however, the effect of sweetclover inches was not statistically significant. i Cropping systems did affect the amount mm. aggregates. Continuous cotton had t; amount of 2-5 mm. aggregates, Figure 3, and ( Sc) and (Cr, O-sc, Sc) had the largest aml this diameter aggregates in the 0-12 inch pro, Rotations involving sweetclover increased 5 centage of 2-5 mm. aggregates at 0-6 inches I‘. not increase them significantly at 6-12 inch the 0-6 inch depth (Cr, O-sc, Sc) and (C, O- both of which included sweetclover, had ll. 15.88 percent, respectively, Figure 4, and ( ] (C, A), which did not include sweetclover, h, least amounts, 1.65 and 3.75 percent, respecti (C, O-sc, Sc, and (Cr, O-sc, Sc), both con ‘l sweetclover, had the largest amount of 1-2 I, gregates at the 0-6 inch depth. They had 21.6, 22.12 percent, respectively. Continuous cott the least number of 1-2 mm. aggregates with percent. i? There was very little difference in eff cropping system on the amount of .25-1 m I, .l25-.25 mm. aggregates at any of the depths sured. However, continuous cotton did tend to; a larger number of small aggregates at all d The large number of small aggregates under tinuous cotton rotations was due to the large ber of small basic soil particles that did not together to form larger aggregates. It was t, noticed that the rotations with a high degr large aggregates had fewer small aggregates. i’ would indicate that the rotations causing 121;’ gregates did so at the expense of the small . gates. l g aggregates 2-5 mm. diameter U aggregates .25-1 mm. diameter m aggregates l-.2 mm.diameter ‘In aggregates .l25-i-.25 mm. diameter. F‘ t- i g h F? "'7 I _ T" T E 7 C ‘Cr C,o-sc,Sc* C,A i C,A-f,A-ff Cr,O-sc,Sc 1 A 3. Effect of cropping systems on water-stable aggregates at a depth of 0-12 inches. g aggregates 2-5 mm. diameter g aggregates 1-2 mm. diameter E O-6 inch depth U aggregates .2551 mm. diameter A‘ 5o _ aggregates .125-.25 mm. diameter __.1 "-7 ' 4O - . __ a 30 - i? f“ 20 '- 10 - b m T“ C Cr C,0-sc,Sc C,A C,A—f,A-f Cr,O-sc,Shc i re 4. Effect of cropping systems on water-stable aggregates at 0-6 inch depth. 15 1.1"’ 1.0 '- _o.s - 0.7 - 0.5 — Inches per hour 0.4 — l—l|-—1 C Cr C,0-sc, C,A C,A-f, CLO-SC, Sc A-f Sc Figure 5. Sustained infiltration rate on six cropping systems. Infiltration There was a highly significant increase over all other rotations in sustained rate of infiltration on the (Cr, O-sc, Sc) rotation, Figure 5. The high infiltration rate on this rotation was attributed to (1) the high amount of noncapillary pore space caused by corn, oats-sweetclover rotations; (2) the -~ increase in large aggregates caused by sweetclover; and (3) corn produced many fiberous roots in the topsoil which afforded a water path through the upper layers, under which the deeprooted sweet- clover furnished channels for water paths. In the cotton rotation there were few channels in the upper layer produced by the cotton taproot; consequently, the water could not get past the upper soil layers. DISCUSSION OF RESULTS The changes in soil physical properties as a result of rotations usually are large enough to be measurable but are very small when compared to the amount that they could change. One possible explanation for the lack of changes in soil physical properties is the nature of Miller clay itself. It is a soil that has good physical properties and will generally regain its original structure, regardless of treatment. This ~is evident when tillage practices are carried on and aggregates are bro-ken and crushed; 16 A rating effect on the physical properties of th'v in a short time they seem to be back to their state of aggregation. Apparently a change may be brought a, the physical properties of Miller clay when H1 such as organic matter or large amounts residue are introduced. i Another introduced mattersjwould be pl systems. This may cause thewmajor chan: occur in this soil due to crop rotation. In th’ iment the extensive fibrous root systems of the upper 6-inch layer of soil seemed to hav nificant effect on pore space, bulk density g filtration. Many small channels are created _ numerous roots in this layer; thus, air andf diffusion is enhanced. The soil below 6 i barely influenced by the fibrous root system because the roots are smaller below that therefore, smaller channels are produced, a smaller volume of air pores. Also, some c0 V, even turn and proceed horizontally at the endf top 6-inch layer and may never penetrate the inch layer in this soil. This might account for h of increased pore space at the 6 to 9 and 9 to A depths. The taproot of cotton, alfalfa and _-_ clover probably penetrated the compacted zo . the root system was so sparse that little eff measured. ' Continuous cotton, cotton-oats and other '- rotations that produced neither large amo organic matter to be returned to the soil g tensive fibrous root systems had the most of The amount of water available to plants apl decreased when large amounts of small capilla spaces were developed at the expense of the noncapillary pores because water is difficult A move from small capillary pore spaces. Bulk dd was increased in the surface 6 inches under rotation systems due to the lack of root and a consequent small amount of noncapillary. spaces. Effects of cultivation practices shoul be completely overlooked when evaluating th ton, nonlegume rotations because of the effect of extensive mechanical cultural practice/sag The unsolved mystery of aggregation be mentioned. Sweetclover promoted more d gation than other crops used in these rotati terns. Sweetclover did not produce more o’ matter to turn under nor did it have a larger, 1 extensive root system in the 0-6-inch zone whe primary aggregation increases were noted. Pe sweetclover or sweetclover roots secrete or con _ substance conducive to aggregation, either by i or through microbial stimulation. study was designed to determine the in- i crop rotation on the physical and chemical of Miller clay after l2 years of cropping d l4 crop rotations. The soil properties field capacity moisture percentage, per- ilting percentage, percent available water, 'ty, noncapillary pore space, capillary pore matter, aggregation and total nitrogen .ble P. experiment was conducted on the Texas ation in the Brazos River bottom. The systems were started in 1952 and concluded lts from the foregoing data warrant the i; conclusions regarding crop rotations on a av» SUMMARY AND CONCLUSION Rotations involving corn tended to result in more noncapillary pore space, less capillary pore space and lower bulk density. Rotations which included 2 continuous years of sweetclover increased the percent of large, water-stable aggregates. Yield was significantly correlated with only one soil physical property — total aggregation — and this correlation value was very low; however, if the present trend continues, yield may be critically in- fluenced by more than one physical property. A rotation system containing the ‘so-called soil- building crops used in this study would not be feasible. Instead of crop rotations, the continuous cropping of corn or cotton with adequate rates of commercial fertilizers probably would be the most profitable cropping alternative on Miller clay soil. L7! 10. ll. 12. LITERATURE Baver, L. D., Soil Physics. Third Edition. Sons, Inc., New York. 1956. John Wiley 8: Gish, R. E. and Browning, G. M. Factors affecting the stability of soil aggregates. Soil Sci. Soc. Amer. Proc. 13:51- 55. 1948. Haise, H. R., Doorman, W. W., Phelan, R. P. Lawhon, L. F. and Shockley, D. G. The use of cylinder infiltro- meters to determine the intake characteristics of irrigated soils. U.S.D.A.-A.R.S. Bul. P;41-47. 1956. Laws, D. W. and EvansyD. D. The effects of long-time cultivation on some physical and chemical properties of two rendzina soils. Soil Sci. Soc. Amer. Proc. 14:15-19. 1949. Learner, R. W. and Shaw, B. A. A simple apparatus for measuring non-capillary porosity on an extensive scale. Jour. Amer. Soc. Agron. 33:l003-1008. 1941. McVickar, M. H., Batten, E. T., Shulkcum, E., Pendleton, J. D. and Skinner, J. J. The effect of cover crops on certain physical and chemical properties of Onslow fine sandy 10am. Soil Sci. Soc. Amer. Proc. 11:47-49. 1946. Mills, J. F. The effect of cropping systems on the organic matter content and on certain physical properties of Miller clay. M. S. Thesis (Agronomy) A8cM College of Texas. 1953. Myers, H. E. and Myers, H. G. Soil aggregation as a factor in yields following alfalfa. Jour. Amer. Soc. Agron. 36:965-969. Naqvi, S. M. The effect of green manuring with winter legumes on some physical and chemical properties of Lufkin fine sandy loam. M.S. Thesis (Agronomy) A8cM College of Texas. 1954. Neher, D. D. The effect of cropping systems and soil treatment on the water-stable aggregates in a claypan soil in southeastern Kansas. Jour. Amer. Soc. Agron. 42:475- 477. 1950. Olmstead, L. B. The effect of long-time cropping systems and tillage practices upon soil aggregation at Hay, Kansas. Soil Sci. Soc. Amer. Proc. 11:89-91. 1946. Page, J. B. and ‘Villard, C. J. Cropping Systems and soil properties. Soil Sci. Soc. Amer. Proc. 11:81-88. 1946. 14. 15. 16. 17. l8. 19. 20. 21. 22. 23. 24. CITED 13. Patrick, W. H., Jr., Haddon, C. B. and Hendrix, effect of long-time use of winter cover crops ~- physical properties of Commerce loam. Soil Sci. v Proc. 21:366-368. 1957. i Perdomo. R. M. The effect of long-time croppi and tillage practices upon some physical pro Abilene clay loam soil. M. S. Thesis (Soil Physi College of Texas. 1961. '~ l; i Pillsbury, A. F. Factors influencing infiltration Yolo loam. Soil Sci. 64:171-181. 1947. Raut, G. N. Influence of a grass sod on infiltra‘ and pore space of Miller clay. M.S. Thesis -_{_ A8cM College of Texas. 1962. ‘l Reynolds, E. 1a., Rea, H. E., Whiteley, Eli., Rich, Y Roberts, J. E. Legumes for soil improvement f" and corn. Tex. Agri. Exp. Sta. Bul. 901. 1958.1 Richards, L. A. and Fireman, M. Pressure plate for measuring moisture sorption and transmission ' Soil Sci. 56:395-404. 1943. i Smith, R. M., Thompson, D. 0., Collier, J. Hervey, R. J. Soil organic matter, crop yields, if use in the Texas Blacklands. Soil Sci. 77:377-3 Snedecor, G. W. Press: Statistical Methods. Iowa State; Ames, Iowa. 1956. ' Steel, R. G. D. and Torrie, J. H. Principles and dures of Statistics. McGraw-Hill Book Co., In York, N. Y. 1960. Uhland, R. E. Physical properties of soils as by crops and management. Soil Sci. Soc. Amer 14:361-366. 1949. U. s. Salinity Laboratory Staff. The diagnosis f provement of saline and alkali soils. U.S.D.A. -l 60. 1954. f Van Bavel, C. M. H. Report of the committee on r analysis, 1951-1953. Soil Sci. Soc. Amer. Proc. l7: 1953. 5 Van Bavel, C. M. H. and Schaller, F. W. Soil if tion, organic matter and yields in a long-time ex as affected by crop management. Soil Sci. Soc. ._ Proc. 15:399. 1950. i [Blank Page in Original Bulletin] Texas ‘AGKM University Texas Agricultural Experiment Station College Station. Texas 77843 Director t Publication-Annual Report or Bulletin or Report of Progress Permit 1105 OFFICIAL BUSINESS y; i 4y- "ta Penalty tor pri payment at -