Response of Cotton to Cropping and Tillage Systems in the Texas Rolling Plains

Cotton (Gossypium hirsutum L.) and wheat (Triticum aestivum L.) are the major agronomic crops grown in the Texas Rolling Plains, and sorghum [Sorghum bicolor (L.) Moench.] is an adapted high residue crop that is grown on a limited scale. Much of the cotton is grown in continuous monoculture (CC), largely because it is considered to be the most profitable crop for the area. Also, acreage bases restrict individual farms to a monoculture operation. High residue crops now are required in Conservation Compliance Plans. The primary objective of the present study was to determine the effects of combinations of cropping and tillage systems on cotton production. A study comparing the effects of tillage and crop rotations on cotton production was conducted for 8 yr (1985–1992) in the Texas Rolling Plains. Reduced (RT) and conventional (CT) tillage systems were used in combination with a wheat‐cotton rotation in a fallow system (WFC). Cotton was grown in rotation with sorghum (SC) in the RT system. Furrow diking was used in RT systems. Continuous cotton in the RT system produced yields equal to those from the SC rotation, and significantly greater than those from CC‐CT. Cotton in the WFC systems produced yields equivalent to those in the CC‐RT system. The CC‐RT system is a viable system on land not susceptible to erosion. The SC‐RT system provided the best alternative for highly erodible land because a crop is obtained each year. The WFC systems produce only two crops in 3 yr. Research Question Much of the cotton produced in the Texas Rolling Plains is grown in continuous, monoculture (CC) with conventional tillage (CT) systems that use multiple land preparation operations including chiseling, sweep‐plowing, and disking operations. Cotton can be rotated with grain crops that return more residue to the soil. Do rotational systems that return residue to the soil result in equal or higher cotton production? Do reduced tillage (RT) practices in combination with rotational systems that leave more surface residue conserve water and increase cotton production? Literature Summary Reduced tillage systems with furrow diking have been shown to increase yields and profitability of continuous, monoculture cotton in the semiarid Texas Rolling Plains. Rotational systems in many areas are reported to increase surface residue, reduce runoff, increase soil water accumulation, and increase yields of following crops. Rotational systems have received little attention in the Rolling Plains, and the combined effects of rotational systems with reduced tillage and furrow diking have not been reported for the area. This study was designed to determine the effects of reduced tillage and rotational systems of sorghum and wheat on cotton. Study Description The study was located at the Texas Agricultural Experiment Station in Chillicothe, Hardeman County (34.1° N lat, 99.3° W long, elev. 1406 ft). Mean annual precipitation is 24.87 in. (88‐yr mean). Soil type at the test site is an Abilene clay loam with a cross‐ and downslope of approximately 0.2%. Initial soil test data were typical of this and most soil types in the Rolling Plains, showing that N was very low, P was low, and K was very high: Calcium and Mg were high. Organic matter was < = 1% and pH was 7.9, mildly alkaline. Cotton was grown in RT and CT systems, in CC, and in rotation with wheat (WFC). A sorghum‐cotton rotation (SC) system with RT also was included in the study. The RT system used controlled traffic, subsoiling of furrows to disrupt compacted soil caused by wheel traffic, and simultaneous furrow diking during land preparation. The WFC rotational system produced two crops (one cotton and one wheat crop) in 3 yr, while the SC system produced one crop of cotton or sorghum each year. Rotational systems were repeated in the study so that a crop was obtained each year from each crop in the rotation. Data were obtained from cotton during 8 yr, 1985 to 1992. Fertilizer rates for all crops were based on soil test information and historical response. Rates for cotton ranged from 30 to 40 Ib N and P2O5/acre. Cotton was planted in late May or early June and harvested with a batt/brush stripper in November or early December. Soil water measurements were made with a neutron probe and used, along with yield, to calculate water‐use‐efficiency (WUE). Long‐term weather records were used in establishing regression equations for cotton yield and precipitation, and these were compared with regressions of yield on stored water. Applied Questions Did cropping and tillage systems affect the productivity of cotton under dryland conditions in the Texas Rolling Plains? Crop rotations produced no yield increase over continuous cotton in the RT system. Continuous cotton in the RT system produced yields equal to those from the SC‐RT, WFC‐RT, and WFC‐CT. The CC‐RT produced yields greater than those from CC‐CT. Yields of cotton from the WFC systems were significantly lower than those from CC‐RT in 1987 and 1990, 2 of the 3 yr in which CC‐RT produced the highest yields. The only year in which WFC produced a significantly higher yield was 1989 when yields were less than 100 lb/acre from the annual cropping systems. Did cropping and tillage systems affect the amount of water used and water use efficiency of cotton grown under dryland conditions in the Texas Rolling Plains? Cropping systems resulted in a significant difference in the amount of water used by cotton. Based on the 7‐yr mean (1985–1991), the SC rotation was significantly more efficient in water use (13.91 in.) than the WFC‐CT system (14.84 in.). Mean water use by all other systems was within the above range. Cropping and tillage systems both had a significant effect on WUE. Based on the 7‐yr mean, WUE was greater for CC‐RT and SC‐RT than for CC‐CT and WFC‐CT; WFC‐RT, CC‐RT, and SC‐RT did not differ from each other. Cumulative precipitation from 1 January through 31 May provided a better predictive value for cotton yields than did water stored in a 5‐ft profile at the beginning of the season. Regression analyses showed that the most responsive system to preseason precipitation was the CC‐RT system. Should continuous cotton be grown in the Texas Rolling Plains? The CC‐RT system is a viable system for the Texas Rolling Plains on soils that are not highly erodible. On highly erodible soils, crops producing significant amounts of residue should be used in rotations. The SC rotation offers an alternative to continuous cotton, depending on the comparative market price for the two crops. Due to lack of a positive response of cotton to the WFC systems, these do not appear to be viable alternatives if the crops are rotated on the basis of two crops in 3 yr.