B-1 May 1 % LIBRARY NOV16 197a; ‘Texas! “i varsity in PECAN OR CHARDS The Texas Agricultural Experiment Station I. E. Mill Director, College Station, Texas Texas A University Forage Production \~»»» Contenlzr Summary .............................................................................. --2 Introduction ......................................................................... --3 Shade Patterns ..................................................................... ..3 Light Reduction and Quality .............................................. .. 5 Forage Production ............................................................... ..5 Grass Varieties and Species ......................................... --5 Nonproducing Orchards ............................................. --6 Producing Orchards .................................................... ..6 Mature Orchards .......................................................... ..8 Acknowledgments ............................................................... --8 Sunnmary The production of Coastal and NK-37 bermudagrass and hybrid sudangrass was evaluated in irrigated and dry- land pecan orchards of varying ages. Young pecan trees, even if closely spaced, shade a relatively small percentage of the ground, especially during the critical midday period. Producing trees spaced 50 x 50 feet shaded 36 percent of the total area during a midday period between 10:00 a.m. and 2:30 p.m. Light is reduced under full grown trees as much as 90 percent, which essentially eliminates grass growth. Light reduction under young trees is less than under mature trees apparently because of greater light reflectance through and around the smaller canopy. Coastal and NK-37 bermudagrass in a young irrigated pecan orchard produced yields in excess of 5 tons per acre at Brownwood and Mineral Wells. 2 grass growth being dependent on tree size and spa -%, Coastal bermudagrass and hybrid sudangrass n: yields of 2 to 3 tons of dry forage per acre in a d 2f orchard of 12- to 16-year-old trees in the Brazos bottom near College Station. In general, 200 poun nitrogen per acre gave maximum forage production. I and NK-37 survived in an orchard of mature trees in“ not shaded between 10:00 a.m. and 3:00 p.m., but, duction was very limited. r 1 As trees increase in size, both the extent and in ' of shade increases, and grass production decreases. ; major effect is in midday, and not all the area is so at this time. Tree spacing is a major determining p on the length of time forage production is practical‘ pecan orchard since this determines the percentage l: total area shaded by trees at any stage of develop Pasture shade trees would likely have similar eff - grass growth as pecan trees, the amount of reducti, age Production ECAN OR (211.4121); Ethan C. Holt* Ki The Texas Agricultural Experiment Station (Soil and "-- iences Department). A of a trademark name or a proprietary product does not a guarantee or warranty of the product by The Texas , ral Experiment Station and does not imply its approval to usion of other products that also may be suitable. FOR SEVERAL YEARS FOLLOWING ESTABLISHMENT of pecan trees, no economic returns are realized from nut pro- duction. This is overcome to some extent by closer tree spacing initially, but other practices such as hay production may provide an alternative source of income during this period. However, information is needed on the effects of understory crop competition on tree growth and de- velopment and nut production. Also, trees as they develop compete with interplanted crops both directly and indirectly. The tree roots compete for nutrients and moisture, while the overstory competes for light and carbon dioxide. This publication, based on research concerned with tree effects on forage production, provides information on production levels at various stages of tree development. Tree shade patterns, light reduction under trees and sub- sequent grass production and survival were evaluated. Shade Patterns Grass requires light for growth, and plants compete for available light. Light intercepted by the leaves of one plant is not available for use by another plant. In compe- tition for light between pecan trees and interplanted grass, the tree has the advantage since the canopy of the tree is always above that of the grass. Not all light is intercepted since the tree cover is usually not complete, and the canopy may be open enough to pennit some light penetration to the ground level. Both tree size and tree spacing influence the proportion of light intercepted for a fixed area. When the trees are small, a relatively small percentage of the total light is intercepted, and interplanted grass would be affected little. Also, there are no areas continuously or completely shaded when trees are small. As the trees increase in size, the potential for grass production is dependent on tree spacing. The area directly under the tree canopy may be continuously shaded which limits grass growth; thus production is re- stricted to the area between canopies. Shade patterns were plotted for 6-year-old trees spaced 35 x 35 feet at Brownwood (Figure 1). The observations were made in August at intervals during the day. The area shaded during the midpart of the day represented no more than 10 percent of the total area. Thus, even if grass growth is affected by shade in young orchards, the total effect would be small since, at most, grass growth is reduced but not stopped by partial shade. Shade patterns in July were plotted for 12-year-old trees spaced 50 x 50 feet at College Station (Figure 2). The trees averaged 28 feet tall with a canopy spread of 21 feet. The total shaded area represented approximately 36 per- cent of the area assigned to each tree. The severest effect of shade appeared to be during midday or from about 10:00 a.m. to 2:30 p.m. The midday shaded area was considerably less than the total shaded area. Obviously tree spacing would have a major effect on the proportion 3 8:30 10:30 12:30 2:30 4:30 Figure 2. Shade pattern of 12-year-old pecan tree spaced 50 A x 5O feet, 8:30 a.m. to 4:30 p.m. i Figure l. Shade patterns of 6-year-old pecan tree from 9:30 a.m. ‘_> to 3=30 p.m. 911mm I \ S. c . l | I n I I '0 I t a I a I l. "'1 a o. I '1‘ "f Q. ' ' l’. v" .~~ ."¢;"\ w;\n0u\np ~~o°" '. .... c u n LIGHT I I a n M i-l E .1 -4,¢,|' Figure 3. Shade pattern of 33-year-old pecan trees spaced 25 feet x 70 feet (area inside dotted 4 line occupied by light grass receiving shade. If the trees had been spaced I eet, the shaded area would have represented 75 of the total area. Even closer spacing would L» ted in more complete shade. Thus, not only but also tree spacing determines light interception riod of time during which grass production may acceptable level. patterns for mature pecan trees (33 years old) wood are shown in Figures 3 and 4. The trees lished originally on 35-foot centers, but alternate c removed later to provide a 35 x 70-foot spacing. ival was staggered in alternate rows which pro- 1,35x7O-foot spacing in perpendicular directions ‘if I uniform distribution of the trees over the area. sunlight reached the ground level under the tree ~ een approximately 10:00 a.m. and 3:00 p.m. _ entage of the area shaded between 10:00 a.m. and l} was not determined, but it would appear to be l» tely 50 percent, even with this tree spacing. 5 the length of time any area received direct light be no more than 2 to 3 hours. i Light Reduction and Quality amount and quality of light reaching the ground er the canopy of both mature and young pecan a e measured and related to full sunlight measure- it the same area. Photosynthetically active light is considered as that with wave length between 400 diometer at 5O mlu. intervals between 380 and 700 at 100 my. intervals between 750 and 1050 m”, the l5. g in the far-red and infrared range and having " effect on photosynthesis. The results of light ents under mature trees are given in Table 1 tage reduction from full light. Little photosyn- active light is transmitted through the canopy of ees, and, therefore, little or no grass growth could ed under such trees. Generally, it is found that a proportion of green light (500-560 mp.) as well as . 11$? 1. e 4. Shade in an orchard of mature pecan trees. millirnicrons (mp1,). Light was measured using a . TABLE 1. LIGHT QUALITY UNDER MATURE PECAN TREES, U.S. PECAN FIELD STATION, BROWNWOOD Percent of full sunlightl Wave length Imp.) 8:30 a.m. 11=30 a.m. 2:30 p.m. 380 13.7 5.1 7.8 400 20.6 5.7 9.5 450 16.6 4.5 7.1 500 15.0 3.8 6.9 550 16.1 4.7 9.9 600 11.2 3.2 8.8 650 9.3 2.6 8.1 700 13.4 3.9 7.7 Average (400-700) 14.6 4.1 8.3 750 25.2 9.9 15.4 850 27.7 10.9 18.5 950 25.0 10.1 17.9 1050 24.4 11.0 22. Average (750-1050) 25.6 10.5 18.5 lReadings were made for each wave length in full light and under the tree canopy and the readings under the canopy expressed as percent of full light. the far-red and infrared light is transmitted through trees; however, in this case, the only change in proportion of wave lengths was in the far-red and infrared range which was transmitted to a greater extent than the other wave lengths. Thus, light quality is changed to some extent under tree cover, and light intensity is drastically reduced. The degree of reduction is apparently related to canopy spread and density. Light under small trees (6 years old) was reduced only about 45 percent as contrasted to 9O percent under the mature trees -— evidently because of light reflectance through and around the smaller canopy. Shade effects of small trees are limited, then, because the total shaded area is restricted, the length of time any area is shaded is limited and light reduction in the shade is less than with larger trees. _ Forage Production Grass Varieties and Species Crops may be interplanted in pecan orchards to pro- vide income during the establishment and early production years, to reduce weed competition and the necessity of cultivation, to provide improved footing for harvesting equipment and to prevent erosion. The grass should en- hance harvesting and nut recovery. Annual grasses such as sudangrass have been used successfully in pecan orchards -—- they may be planted in the spring, harvested two or three times for hay and the soil completely tilled and leveled prior to nut harvest. Thus, these crops provide income and reduce the need for weed control during the summer but do not provide for soil I stabilization during harvest or the ensuing winter period. The finer-stemmed and shorter grass-type or sudan hybrids would seem to be more suitable for use in orchards than the robust types. The shorter stems would make them less competitive with young trees, and the finer stems would not only make better hay, but the stubble would be easier to destroy before harvest. Bermudagrass is the most widely grown sod crop in pecan orchards, and any of several varieties is probably satisfactory. This research has been concerned largely with Coastal because of its superiority over common for hay and with NK-37 in the more northern and western locations because it can be established rapidly from seed. NK-37 is susceptible to leaf diseases and is less suitable for use in East and South Texas. The bermudagrasses produce a sod which can be mowed closely prior to harvest and which provides footing for harvesting equipment, thus enhancing harvest. Since they are perennials, they provide soil pro- tection year round and reduce weed competition. Because the bermudagrasses are deep rooted, they compete with the tree crop for moisture and nutrients; both must be in adequate supply if good grass production is expected and if nut production is maintained. It seems unlikely that a noncompetitive yet productive grass will be found that would meet the other requirements for an interplanted crop. Nonproducing Orchards Coastal and NK-37 bermudagrasses were established in a young breeding orchard at the U.S. Pecan Field Station at Brownwood in 1966. Each grass was fertilized at two nitrogen rates: 100 and 300 pounds nitrogen per acre. Each treatment was replicated four times. The main plots were 55 x 35 feet with the tree in the center. Yields were determined from four mower strips 3 x 10 feet in each main plot. Since the trees shaded no more than 1O per- cent of the plot area at the beginning of the experiment, tree competition for light was assumed to be a minor factor. NK-37 became established from seed rapidly, whereas Coastal required the entire growing season to pro- duce a cover even with limited irrigation. Hay yields of 5 to 7 tons per acre were obtained in 1968 (Table 2), depending on variety and nitrogen level. Yields have been somewhat less since 1968, but generally satisfactory. Yield is increased with added nitrogen, and nitrogen in excess of 100 pounds probably is needed to avoid undue effect on the trees. Coastal and NK-37 yields have varied but with no consistent difference between the TABLE 2. BERMUDAGRASS FORAGE YIELDS IN AN IRRIGATED PECAN ORCHARD (5-YEAR OLD TREES IN I968) AT THE U.S. PECAN FIELD STATION, BROWNWOOD Pounds of dry forage per acre‘ Nitrogen Variety (lb/acre) I 968 I 969” I970 I971 COGSICII I00 l0,060b 3,6900 8,5901) 6,707‘: 300 l3,8l0a 4,5l2b I l,3l0a 1065c NK-37 l00 7,2900 2990c 6,7200 8,402!’ 300 I l,450b 5,3203 11,220“ I0,629a ‘Values in a column followed by the same letter are not significantly different. 2Yields are for two cuttings only which represent approximately 50% of the total production in I969. 6 TABLE 3. COASTAL AND NK-37 BERMUDAGRASS STAND DE q IN AN IRRIGATED PECAN ORCHARD (5-YEAR OLD TREES IN I AT THE U.S. PECAN FIELD STATION, BROWNWOOD Nllmge" Relative density ratingl Grass treatment , variety (lb./acre) I968 I969 I9’ Coastal I00 I .75 I .00 I, 300 1.00 1.00 1. NK-37 100 2.50 2.50 2. 300 3J0 3.50 2.1 lGround cover density was rated on a scale of I to 5 with I dense and 5 being open sod. i two. NK-37 sod is more open than Coastal sod (TaISIl-l but its density should be adequate for soil protection ‘ equipment footing. Young pecan trees were established in a Coastal in the Brazos River bottom near Mineral Wells (H. L. Farm) on 50 x 5O feet centers. Forage yields were termined from four mower strips per plot, each 3 x 10 All treatments were replicated four times. Very high f 1 yields were obtained the first and fifth years (Table 4) yields of approximately 5 tons in other years. Res to nitrogen was essentially maximum at 200 nitrogen per acre. However, it was not determined w I this was adequate for both the grass and the trees. " experiment included a treatment involving clean culti I in the tree row to reduce effects of grass competiti the trees. Such a practice should favor the trees and r grass production proportionately. A 12-foot clean-tilleclf was maintained representing approximately 2O perc i: the area; thus, production was reduced about 2O p L In later years as the trees increase in size and shade become more severe, the influence of a clean-tilled“- on forage production would be decreased. Since th mary shade effects are in the area surrounding thef removal of grass in this area by cultivation wouli reduce yields in proportion to the cultivated area. _ Producing Orchards ., A forage production study was started in 1966,. 12-year-old dryland orchard in the Brazos River l. near College Station. Coastal bermudagrass (Figure 5 . TABLE 4. COASTAL BERMUDAGRASS PRODUCTION IN , PECAN ORCHARD IN BRAZOS RIVER BOTTOM NEAR MINERAL i Pounds dry forage per acre2 Nitrogen (lb./acre) 1967 1968“ 1969‘ 1970 200 18,960“ 9,283” 3,636“ 11,000“ 1 400 20,640“ 9,613“ 4,343“ 10,750" 600 20,720“ 9,124” 4,808" 10,955“ 1 lTrees were planted in I966. 2Values in a column followed by the some letter are not signi different. l 3One cutting was lost which would have increased production, least 50 %. I 4One cutting on May 28, I969. istal bermudagrass in a dryland pecan orchard i er bottom near College Station, Texas. 1966, hybrid sudangrass (Figure 6) was seeded and each was fertilized with 0, 100, 200 and of nitrogen per acre. Each main plot was I with the tree in the center, with four repli- IQieIds were determined from eight mower strips I in each plot, four strips being taken around of the plot and four underneath the tree. I production (Table 5) was highest the first iximately 3% tons per acre, and declined each ter. Increasing tree size and shade effects no I ibuted to the decline. Also, extended dry periods ings of 1970 and 1971 delayed planting and Figure 5. Sudangrass in a dryland orchard in the Brazos River bottom near College Station, Texas. seedling emergence and further reduced or limited pro- duction. Production at the 1971 level is economically questionable, but this was due in part to late planting and not entirely to tree competition. Coastal bermudagrass produced up to 21/2 tons of hay annually in two or three cuttings and has declined to some extent with time (Table 5). However, Coastal pro- duction in 1971 exceeded 2 tons even with the dry spring and the increased shade effects. Measurements and observations have indicated that grass growth is affected most by shade in the 4- to S-hour PRODUCTION IN DRYLAND PECAN ORCHARD, BRAZOS RIVER BOTTOM NEAR COLLEGE STATION (TREES ESTABLISHED Pounds of dry forage per acrez Sudangrass Coastal bermudagrass Shaded Open Weighted Shaded Open Weighted a rea a rea total a rea a rea total 1957 3150 4320 4300“ 2150“ 3730 5150 4530“ 5390“ 5350 7730 7230“ 7540“ 5750 7140 5540“ 55903 1953 3195 3270 3240“ 2910 4170 3720“ 4130 5340 4920“ 4340 5720 5220“ 5710 5295 5030“ 4340 5540 5750“ 5715 5340 5440“ 4405 5145 5520“ 1959 2353 3233 2957“ 2042 3354 2333“ 2037 5040 4337“ 4143 5375 4933“ 3773 5999 5199“ 4570 5500 5905“ 4432 5534 5137“ 4500 5911 5433““ 1970 1754 2254 2030“ 2372 3233 2925“ 2131 2530 2500“ 3724 4072 3947“ 3034 3392 3253“ 4142 5105 4753“ 3118 C 4010 3537“ 3413 5073 4430““ 1 1971 1373 2751 2554“ 1754 3207 2435“ 1459 2531 2045“ 2752 4945 3343“ @ 1315 3123 2472“ 2957 5047 4507“ I 1792 3343 2557“ 2302 5143 3722“ I spaced 50’ x 50'. lthin a column for any I year followed by the same letter are not significantly different. midday period. In the College Station study, this shade area was estimated to represent 36 percent of the entire area, increasing to 48 percent in 1971. The weighted yields were calculated 0n the basis of production in the shaded and open areas and the proportion of the entire area represented by each. The effect of tree shade on grass growth is shown in Tables 5 and 6. The reductions in growth under the tree canopy reported in Table 6 are based on growth in the most open areas within the orchard. These areas may have received some shade during early morning and late after- noon; therefore, the estimates of shade effects may be lo-w. Estimates of reduction in growth have been somewhat erratic but are adequate to show that growth in areas re- ceiving midday shade is definitely reduced. This has ranged from asrlow as 18 percent in sudangrass to as high as 48 percent in Coastal bermudagrass. There is not a definite pattern in growth reduction in the shade. Further, while the midday shaded area increased gradually, the calculated weighted effect was based on‘ the same area until 1971 when the estimated area was increased because of increased canopy size. The increasing canopy size must have reduced light in the shade still further since production in the shade showed a drastic reduction in 1971. The influence of duration of shade and, possibly, intensity of shade may be seen in the contrast between growth on the north and south sides of the trees, both from areas receiving midday shade. The north side of the tree would be shaded a longer period, and the shade intensity probably would be greater because of less oppor- tunity for reflected light. The shade pattern in Figure 2 suggests these conclusions. Within a radius of 10 feet of the tree, production on the north side of the tree was 11, 11, 14, 21 and 4O percent less than on the south side in the years 1967 through 1971, respectively. If the north side is contrasted to unshaded area, the decrease was 6O percent in 1971. These data demonstrate the effect of increasing shade intensity as the canopy increases in size. Thus, production is restricted as orchards increase in age by both the total shaded area and the increased density of the shade (Figure 7). TABLE 6. EFFECT OF TREE SHADE ON DRpYLAND GRASS PRODUCTION (TREES ESTABLISHED IN 1954) Coastal bermudagrass Hybrid sudangrass °/., reduction in growth Weighted effect Weighted effect Under on to-tal Under on total Year canopy production canopy production 1967 23.7 9.2 1968 29.2 12.0 13.5 5.5 1969 27.3 11.9 36.3 15.8 1970 21.9 10.1 18.3 8.4 1971 48.7 23.9 45.7 22.4 Figure 7. Coastal bermudagrass in an orchard of 20-y pecan trees. i Mature Orchards y.‘ Coastal and NK-37 bermudagrasses were spri_ seeded, respectively, in an orchard of 33-year-old trees spaced 35 x 70 feet at Brownwood. The i planted in 1966, became established and surviv; in areas that received direct sunlight during a part it time between 10:30 a.m. and 2:30 p.m. According shade patterns shown in Figure 3, no area received light for more than 2 to 3 hours daily. Growth tenuated with narrow leaves and showed no tend, produce runners and rhizomes during the first year. were not determined, but would have been nil, an’ proximately 50 percent of the area was completely; Both Coastal and NK—37 bermudagrasses survived y . more open areas and increased in density in 1967 Growth approximately 10 inches high was present ine 1968 with an estimated production of 1,000 p0 n, acre in the open areas. Since this represented t’, duction for the growing season and no more than t’ total area was covered, acre production would has? too low to be of value. Thus, forage production feasible with mature trees even spaced as widely as 3 feet. Acknowledgments _, ]. Benton Storey, associate professor, The aw is cultural Experiment Station (Soil and Crop Sci partment) assisted in making arrangements for the mental locations. George D. Madden, U.S. 1’- Station, Brownwood, Texas, made orchard space a for the studies and provided irrigation and gene 3- tenance for the plot areas. H. L. Petty, Mineral‘; . Texas, made orchard space available and provided f: maintenance for the plot area on his farm south of . Wells.