\ TEXAS AGRICULTURAL EXPERIMENT STATION R. D. LEWIS, Director, College Station, Texas flulletm 71/ LIBRARY A&M. COLLEGFr STUBBLE MULCH MANAGEMENT For Water Conservation and Erosion Control on Hardlands 0F the Southern Great P|ains in cooperafion wiih {he UNITED STATES DEPARTMENT OF AGRICULTURE The TEXAS AGRICULTURAL AND MECHANICAL COLLEGE SYSTEM GIBB GILCHRIST, Chancellor [Blank Page in Original Bulletin] l7 Preface This bulletin contains a resume 0f the stubble mulch tillage studies carried 0n the past 7 years at the Amarillo Conservation Experiment Station. The Amarillo station is located in the 15 to 20-inch rainfall belt in the Panhandle of Texas. Drouth years occur in which it is extremely diflicult to maintain a vegetative cover adequate to protect the soil from wind and water erosion. Much of the rainfall occurs as torrential showers so that maintaining the hardland soil in as permeable a condition as possible is a matter of considerable importance. Considerable information has been obtained in the Plains States during the past 10 years concerning the merit of stubble mulch farming. Cultivation by this method is done with sweeps which till the soil without turning it. Thus, as much plant residue as possible is kept on the surface» of the ground. Subtillage is compared with the oneway and moldboard plows in raising wheat in the studies made at the Amarillo station. Data are presented on grain yields, soil moisture, available nitrogen and organic matter. The Southern Great Plains are generally said to comprise Eastern New Mexico, Southeastern Colorado, Southwestern Kan- sas and the Panhandles of Oklahoma and Texas. CONTENTS Page Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 Specifications and Equipment for Land Preparation . . . . . . . . . . . . . . . . .. 6 Results in Grain Yield . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 7 Plow Sole . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 8 Precipitation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 8 Soil Moisture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 8 Available Nitrogen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 10 Organic Matter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 11 Straw-grain Ratio . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 11 Significance of Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 12 Summary and Recommendations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 15 P52-749-3M-L180 BULLETIN 711 JUNE 1949 STUBBLE MULCH MANAGEMENT For Water Conservation and Erosion Control on Harcllands oF the Southern Great Plains CHARLES J. WHITFIELD, C. E. VAN DOREN and WENDELL JOHNSON * EARNING t0 farm the heavy soils of the Southern Great Plains successfully has been the basis of investigations at the Amarillo Conservation Experiment Station for the past 7 years. a Conservation of the soil and water resources and dependable crop production are fundamental to successful farming in this 15 to 20-inch rainfall belt, an area susceptible to both wind and water erosion. The average annual precipitation on the Amarillo station, 1939 through 1948, has been 18.2 inches. The principal crops are winter wheat, grain and forage sorghums, Sudan, and native and introduced grasses. Detailed studies, most of which were initiated in 19-41, of stubble mulch tillage, cover crops, crop rotations, adapted crops, including grasses and legumes, and other conservation practices such as terracing and water spreading, have given helpful information on conservation of both soil and water. Definite progress has been made in con- trolling erosion and stabilizing crop production by the use of stubble mulch tillage. This report concerns studies made of stubble mulch practices in growing winter wheat on Pullman silty clay loam, a deep, fine textured, slowly permeable hardland soil, high in fertility and moderately high in organic matter under native conditions. There are some 11,750,000 acres of these deep, heavy soils in the Southern Great Plains. A group of 32 plots one-third acre in size Were established in 1941 and 1942. Four types of implements, two plows and two subtillage machines, were used on plots planted to wheat year after year. These were the oneway plow, the moldboard plow, the Noble cultivator, and a subtillage machine developed at the Amarillo station. Two types of implements, the oneway plow and the Amarillo subtillage machine, were used on plots planted to wheat one year and fallowed the next year. Each treatment was randomized and replicated 4 times. *Re_spectively, project supervisor, soil conservationist and soil scientist, Amarillo Conservation Experiment Station, Amarillo, Texas. 6 BULLETIN 711, TEXAS AGRICULTURAL EXPERIMENT STATION This study is a cooperative project between the Texas Agricul- tural Experiment Station and the Research Division, Soil Con- servation Service, U. S. Department of Agriculture, which operate the Amarillo Conservation Experiment Station. The station is 14 miles west of Amarillo. Specifications and Equipment for Land Preparation Performance requirements for a subtillage implement to be used for land preparation at the Amarillo station were set forth as follows: 1. Maximum amount of residue to be left on the surface (stubble mulch), with as many as four tillage operations within a 3-months period. 2. Cultivation of land at different depths to prevent plow sole formation, to aid in the deeper penetration of moisture, and to obtain a rapid, effective weed kill. 3. Fields to be left in suitable condition for planting crops. After considerable testing of various combinations of sweeps and other implements, it was found that to do a successful job of subsurface tillage a subtiller should: 1. Be capable of operating at fixed depths. 2. Be equipped with rolling coulters to cut residues and weeds ahead of the sweeps to prevent clogging. Figure "1. Subtillage machine employing five 30-inch sweeps de- signed for operation at controlled depths in Pullman silty clay loam soils with a minimum of clogging due to surface residues. STUBBLE MULCH MANAGEMENT 7 3. Have adequate weight and strength for penetration and operation under difficult soil conditions. 4. Cultivate the soil to kill weeds and volunteer crops, such as wheat, effectively. A machine embodying these requirements, determined by more than 3 years of study, was constructed at the Amarillo station in the spring of 1945. It consists of five 30-inch Dempster sweeps mounted on a heavily reinforced carrier equipped with a power lift and rolling coulters. The implement has been used the past 4 years with a high degree of success under a wide range of conditions. Trashy fields, some of which were covered with a heavy growth of volunteer wheat, have been worked suc- cessfully with no more difficulty, generally, than would be en- countered using the oneway. Results in Grain Yield Grain yields for each of the 7 years, 1942-48, are given in Table 1 for the plots in wheat year after year, along with the 7-year average. Table 1. Grain yields from stubble mulch plots in continuous wheat, 1942-48 Wheat yield—bushels, per acre Tillage —~ 7-year 1942 1943 1944 1945 1946 1947 1948 average Moldboardplow. 20.3 4.2 19.7 4.4 1.8 31.8 5.6 12.5 Onewayplow.... 20.1 6.0 24.5 6.3 2.6 28.4 4.6 13.2 Subtillage . . . . . .. 19.0 7.1 26.4 6.9 6.0 34.3 6.2 15.1 An average of 2.6 bushels more wheat per acre was obtained from the continuous wheat plots which were subtilled than was produced after the moldboard plow, and 1.9 bushels more than where the oneway was used. The fact that subsurface tillage gave increased wheat yields during the period these tests were in operation is in harmony with the effectiveness of stubble mulches in controlling erosion. It is also interesting to note that the average annual wheat yield on the subtilled plots was 15.1 bushels per acre. The grain yields for the 7-year period are shown in Table 2 where two implements, the oneway plow and the subtiller, were used on plots planted to wheat one year and fallowed the next. An increase of 2.8 bushels per acre was recorded in favor of the subsurface tillage implement over the oneway on plots in wheat and fallow. For any single crop year, wheat after a year of fallow consistently outyielded wheat planted year after year (compare Tables 1 and 2). This effect has been pronounced 25 BULLETIN 711, TEXAS AGRICULTURAL EXPERIMENT STATION Table 2. Grain yields in wheat and fallow system, 1943-48 Wheat yield——bushels per acre Average Tillage r- yield 0Y1 1943* 1944 1945 1946 1947 1948 fallow land Oneway . . . . . . . .. 11.9 28.4 16.7 8.5 33.1 13.9 18.8 Subtillage . . . . . .. 14.6 28.4 20.4 13.9 36.8 15.7 21.6 *Plots fallowed in 1942.- in dry years When the moisture stored during a year of fallow has meant the difference between crop success and failure. In addition, fallowing has made possible the production and maintenance of a stubble mulch to protect the soil from blowing regardless of the occurrence of periods of subnormal precipi- tation (Figure 2). Plow Sole There has been no indication of plow sole formation during these studies. Depth of plowing for all four implements for the first operation of the season, was 4 to 5 inches, for the second 2 to 3 inches, and for subsequent operations 1 to 2 inches. This is common practice throughout the area and there is no indi- cation that deeper plowing is necessary even at periodic intervals. Precipitation Four of the 7 years of this study had less than the Amarillo station average of 18.2 inches of precipitation (Table 3). Table 3. Precipitation, annual and by crop years for wheat, 1941-48 Year 1941 1942 1943 1944 1945 1946 1947 1948 Annual 32.6 18.5 17.1 21.7 12.9 15.9 14.4 20.4 Crop year (July-June). 26.5 17.3 ‘ 21.2 I 15.7 x 13.5 20.8 13.6 Soil Moisture Soil moisture samples taken on the continuous wheat plots have failed to show moisture to be consistently higher under subtillage than under the other cultural methods. In fact, soil samples taken in October 1948 showed that the subtilled plots in both the continuous Wheat and the wheat-fallow-Wheat system, after producing a crop of wheat in 1948, were somewhat lower in soil moisture than plots tilled with the oneway or moldboard plow (Table 4). l7 STUBBLE MULCH MANAGEMENT 9 Figure 2. Subtilled land showing wheat stubble re-sidue remaining on surface. Since the larger yields have been obtained on the subtilled plots, it would be difficult t0 assess the amount of moisture actually made available to the crop under different tillage systems by a consideration of soil moisture data alone Where a measure of the moisture used by the crop is not available. It is noteworthy, however, that when land has been in fallow for a year, more moisture is consistently found in sub- tilled than in onewayed land. This is convincing proof of the efficiency of the stubble mulch system in storing moisture. Of especial interest in this connection are the data which compare Table 4. Average moisture content to a depth of 3 feet of stubble mulch plots, October 1948 and March 1949 Moisture content, percent Oct. 1948 Mar. 1949 Tillage method Land in: Continuous wheat Moldboard plow Wheat . . . . . . . . . . . . . . . . . . 16.0 18.1 Oneway Wheat . . . . . . . . . . . . . . . . . . 16.3 17 .2 Subtillage Wheat . . . . . . . . . . . . . . . . . . 15.1 20.1 Wheat-fallow-wheat system Oneway Fallow . . . . . . . . . . . . . . . . . . 16.2 19.0 Subtillage Fallow . . . . . . . . . . . . . . . . . . 15.3 20.1 Oneway Wheat . . . . . . . . . . . . . . . . . . 18 . 1 17 .8 Subtillage Wheat . . . . . . . . . . . . . . . . . . 21 . 5 18.9 10 BULLETIN 711, TEXAS AGRICULTURAL EXPERIMENT STATION moisture reserves in the stubble mulch plots in late March 1949, about 5% months after the October sampling. It is apparent that the subtilled fallow and continuous wheat plots had been able to retain sufficient Winter precipitation to more than over- come the moisture deficiencies of the previous fall, and at this season of the year were able to surpass the oneway and mold- board plow plots in moisture content. Available Nitrogen Samples taken in October 1948 were analyzed for available nitrogen. They reveal (Table 5) that: 1. On the continuous wheat plots, nitrates were lower on sub- tilled than on oneway plots. 2. Nitrates were increased by fallowing and in general were lower on continuous wheat than on wheat-fallow rotation plots. This appeared to be true Where moisture was available for nitrification and where there were no crops to take up the nitrates. Essentially the same relationships were found to exist in late March 1949, at which time the mean nitrate-nitrogen content of the top 4 feet of soil in parts per million was 4.4 on moldboard plow plots, 5.9 where the oneway plow was used, and 3.0 with subtillage. In the relatively dry area of the South- ern Great Plains, moisture appears to be the limiting factor in crop production, rather than fertility. Table 5. Nitrate nitrogen determinations (p.p.m.) on stubble mulch plots, October 1948 Depth of sample Cultural practice l 0-3 3-6 inches inches Continuous wheat Oneway . . . . . . . . . . . . . . . . . . . . . . . 22.6 7.4 Subtillage . . . . . . . . . . . . . . . . . . . . . 8.6 3.3 Wheat and 1 year of fallow (wheat 1947-48) . . 21. 5 14.6 Oneway (fallow 1947-48). . 30.9 11.8 (wheat 1947-48) . . 12.8 4.7 Subtillage (fallow 1947-48) .. 40.0 11.7 STUBBLE MULCH MANAGEMENT 11 Organic Matter Organic matter determinations made in October 1948 showed slightly higher percentages in stubble mulch tillage when com- pared with the conventional oneway method of tillage (Table 6). Also, wheat-after-wheat plots were slightly higher in organic matter than were the plots in wheat-fallow rotation. Table 6. Percent of organic matter in stubble mulch plots, October 1948 Depth of sample Cultural practice 0-3 3-6 inches inches Continuous wheat Oneway . . . . . . . . . . . . . . . . . . . . . . . 2.05 1.46 Subtillage . . . . . . . . . . . . . . . . . . . . . 2.09 1. 58 Wheat and 1 year of fallow (wheat 1947-48) . . 1.90 1. 53 Oneway (fallow 1947-48) . . 1.96 1. 52 (wheat 1947-48) . . 2.03 1.66 Subtillage (fallow 1947-48). . 2.08 1. 54 Straw-grain Ratio Ratios of the weight of grain and the weight of straw pro- duced on continuous wheat and on wheat-fallow-wheat plots are given in Table 7. Straw to grain ratios on continuous wheat plots were con- sistently highest where the moldboard plow was used as the tillage implement and lowest where subtillage was practiced. The highest ratio, 7.64, was obtained on the moldboard plow plots in 1946, the year of least precipitation in this study. In a given year, lower ratios were observed on fallow plots than where continuous wheat had been grown using the same tillage treatment. This is an indication that the yield advantage gained by subtillage over other methods of seedbed preparation may also be due to an improved moisture-fertility balance. This could be the case if the lower nitrification rate often observed under subtillage has the effect of avoiding overstimulation. In this connection, on the subtilled continuous wheat plots the light-green color of foliage associated with a meager supply of available nitrogen was distinctly in evidence on May 1, 1949. This was in marked contrast with the darker-green color of wheat on the oneway and moldboard plow plots. Conditions for nitrification and non-symbiotic nitrogen fixation are regarded 12 BULLETIN 711, TEXAS AGRICULTURAL EXPERIMENT STATION as being very favorable on the soils 0f the Southern Great Plains and more than the optimum amount of nitrates may at times be present in the soil. Support for this theory is found in the data presented in the discussion of soil moisture and available nitrogen. In late March 1949, the greatest amount of available nitrogen and the least amount of soil moisture were found in the one- wayed continuous wheat plots, and the largest amount of soil moisture combined With the smallest amount of available nitrogen occurred in the subtilled plots. It is likely that sub- tillage through the agency of lower temperature and higher sur- face moisture content, inhibits nitrification in early spring and thereby retards vegetative growth to a point more compatible with climatic conditions. As a result, more efiicient use as far as grain production is concerned is made of the rather scanty rainfall of the region. Table 7. Ratios of weight of straw to weight of grain on stubble mulch plots in continuous wheat and in wheat-fallow-wheat. Precipitation received during corresponding crop or crop and fallow seasons, 1943-47 Tillage practice 1 943 1 944 1 945 1 946 1 947 1 943-46 average Ratio of straw to grain-continuous wheat Moldboard plow... . . 5.26 2.98 2.74 7.64 2.02 4.66 Oneway . . . . . . . . . . .. 4.03 1.84 1.59 4.49 2.15 2.99 Subtillage . . . . . . . . .. 3.55 1.32 1.06 2.89 1.73 2.20 Precipitation, inches per crop year 17.3 21.2 15.7 13.5 20.8 16.9 Ratio of straw t0 grain—wheat-fallow-wheat Oneway . . . . . . . . . . .. 3.18 1.84 0.92 2.89 2.21 Subtillage . . . . . . . . .. 2.81 1.85 0.84 2.01 1.88 Precipitation, inches per crop and fallow 2 years 43.8 38.5 36.9 29.2 34.3 37.1 Significance of Data Analysis of variance of grain yields on the continuous Wheat plots (Table 2) showed that: 1. The differences in grain yields between implements are highly significant. STUBBLE MULCH MANAGEMENT 13 2. The yield differences between the subtilled and the plowed plots for 1942 and 1943 during the first 2 years of treatment are not significant. There is a significant difierence in yields favoring subtillage during the next three years, 1944, 1945 and 1946; and a highly significant difference for 1947 and 1948. In other words, the effects of stubble mulch tillage were ac- cumulative through the 7-year period of study. This favorable effect of subtillage appears to be due at least in part, to an improvement in the physical condition of the soil. Tables 4 and 5 do not show the accumulative beneficial effect of the stubble mulch to be due to stored moisture or enhanced con- ditions for nitrification. However, data on the ratio of weight Table 8. Analysis of variance; stubble mulch plots; continuous wheat, by years and for 7-year periodil! Source Degrees Mean square variation freedom 1942 1943 1944 1945 1946 1947 1948 Total . . . . . . . . . 15 Treatment... . . 3 1.89 14.30 *40.75 *5.32 T18.93 T31.14 T4.84 Replication.... 3 36.00 3.65 14.66 2.29 5.07 12.06 ' .30 Error.‘ . . . . . . .. 9 2.99 9.98 10.19 .91 3.24 .97 .54 Source variation Degrees Sum Mean freedom squares square Total . . . . . . . . . . . . . . . . . . . . . 111 12,955.91 Treatment . . . . . . . . . . . . . . . . . 3 149.54 T4985 Years . . . . . . . . . . . . . . . . . . . .. 6 12,177.89 Interaction . . . . . . . . . . . . . . . . 18 201.97 ~ T1.22 Replication . . . . . . . . . . . . . . . . 21 222. 1o 3' Exp. error . . . . . . . . . . . . . . . . . 63 204.41 3.24 Treatment total . . . . . . . . . . . . 3 149. 54 T49.85 Noble blade vs. sweep machine . . . . . . . . . . . . . . . .. 1 5.16 5.16 Noble blade & sweep machine vs. oneway & moldboard plows . . . . . . . . . 1 138.40 T138.40 Oneway vs. moldboard plow . . . . . . . . . . . . . . . . . . . . 1 5.94 5.94 *Data significant at the 5% level. TData highly significant at the 1% level. ITZAnalyses were made by K. B. Porter, Agronomist, Amarillo Experiment Station. 14 BULLETIN 711, TEXAS AGRICULTURAL EXPERIMENT STATION of straw to weight of grain produced on continuous wheat and on wheat-fallow-wheat plots indicate an improved moisture- fertility balance (Table 7). 3. There was no significant difference in grain yields be- tween the two subtillage sweep machines, the Noble cultivator and the station machine. The subtiller that works best under the conditions encountered may be used without loss of yield. 4. Differences in the grain yields between the oneway and the moldboard plow were not significant. 5. Analysis of variance of plots in wheat and fallow indicates that differences recorded between onewayed and subtilled plots have a high degree of significance (Table 9). Table 9. Analysis. of variance of yields of stubble mulch fallow plots, by years and for 6-year period Source Degrees Mean square variation freedom 1943 1944 1945 1946 1947 ; 1948 l TOtHl . . . . . . . . . . . . . 11 l Treatment . . . . . . . .. 2 *7.60 4.88 *42.80 *52.55 *16.17! 4.10 Replication . . . . . . .. 3 10.44 5.25 2.61 2.39 9.33% 2.81 Error . . . . . . . . . . . .. 6 1.68 4.94 5.06; 1.53 1.81; 1.53 l l Source variation Degrees Sum Mean freedom squares square Total . . . . . . . . . . . . . . . . . . . .. 71 5,729.74 Treatment . . . . . . . . . . . . . . . . . 2 170.77 185.39 Years . . . . . . . . . . . . . . . . . . . .. 5 5,275.72 Interaction . . . . . . . . . . . . . . . . 10 85.43 *8. 54 Replication . . . . . . . . . . . . . . . . 18 78.47 Exp. error . . . . . . . . . . . . . . . . . 36 99.36 2.76 Treatment total . . . . . . . . . . . . 2 170.77 $85.39 Noble blade & sweep mach- ine vs oneway plow . . . . . . . 1 165.77 T165.77 Noble blade vs sweep machine . . . . . . . . . . . . . . . . . 1 5.00 5.00 *Data significant at the 5% level. "fData highly significant at the 1% level. w“, STUBBLE MULCH MANAGEMENT 15 Summary and Recommendations 1. A subtiller constructed on the Amarillo station has been used with a high degree of success. It consists of five 30-inch Dempster sweeps mounted on a heavily reinforced carrier and is equipped with a power lift and rolling coulters. 2. An average of 2.6 bushels, or 21 percent more Wheat per acre was obtained from the continuous Wheat plots which were subtilled than was produced using the moldboard plow, and 1.9 bushels, or 14 percent more than when the oneway was used. ‘ 3. An increase of 2.8 bushels, or 15 percent, was recorded in favor of the subsurface sweep machine over the oneway in a wheat and fallow system. 4. Analysis of variance showed these differences on grain yields to be highly significant in favor of the subtilled plots. 5. The effects of stubble mulch tillage have been accumulative through the 7-year period» of study, the improvement being due in part at least to an improved physical condition and a better moisture-fertility balance in the soil. 6. Data have been presented which would indicate that the stubble mulch system of tillage for winter wheat production on the silty clay loam soils of the Southern Great Plains can be used to accomplish its intended purpose of moisture conserva- tion and erosion control without financial sacrifice by the farmer in reduced returns from the land.