A Conservation Cropping System to Enhance Profitability of Sorghum in Rotation with Cotton in the Rolling Plains

John Sij, Jason Ott, Todd Baughman, and David Bordovsky

INTRODUCTION

Dryland production in the Semiarid Rolling Plains is practiced on more than 90% of the crop land. Water is the major environmental factor limiting crop production. Hence, drought- and heat-tolerant crops like sorghum and cotton are well-suited to this region. Effectively capturing, storing, and utilizing the limited rainfall is key to profitability. Conservation tillage systems have the greatest potential to improve water-use efficiency. In high rainfall years, sorghum yields can exceed 5000 lbs/acre, but typically average less than 2500 lbs/acre. Raising yields 20%, a goal of PROFIT, to 3000 lbs/acre is achievable if sufficient rainfall can be captured and stored. Conventional production systems do not have this capability.

METHODOLOGY

The study was initiated on 17 December 2001 at the Texas Agricultural Experiment Station in Chillicothe. Plots consisted of 8 rows on 40 in centers with a length of 315ft per plot. Treatments were composed of four crop rotation systems; continuous sorghum (CS), continuous cotton (CC), 1 Yr sorghum – 1Yr cotton (1S1C), and 1Yr sorghum – 2 Yr cotton(1S2C). The four crop rotation schemes were randomly assigned to plots and replicated three times.

The study site was prepared by tandem disking and chiseling once. Bates rye was interseeded in two rows on 10-in centers into the furrows of 40-in rows at 90 lb/ac on 4 January 2002. Rye growth was terminated in April at 50% heading with an aerial application of 2 pt/ac Roundup Ultra. All plots were strip-tilled without shanks before planting sorghum. Sorghum hybrid, Pioneer Brand 8500, was planted on 24 April between strips of terminated rye. Likewise, on 13 May, cotton variety, Paymaster Brand 2280 BtRR, was planted between strips of terminated rye. Dual herbicide was applied to the plots prior to planting at a rate of 1.5 pt/ac for preemergence weed control. After plant emergence plots were maintained and kept weed-free either through chemical weed control or hand hoeing.

After crop establishment, Watermark soil moisture sensors were placed in each plot at 12- and 36-in depths. Sensors were monitored weekly throughout the growing season to observe changes in soil moisture in each cropping system. The readable soil moisture range with Watermark soil moisture sensors is 0 to -2 atmospheres; the more negative the reading, the drier the soil.

Twenty feet of the middle two rows of each plot planted to sorghum were hand-harvested and yield (13 % moisture) expressed in bushels per acre (60 lbs/bu). A cotton stripper was used to harvest 315 ft of the middle two rows in plots planted to cotton. Lint yields were calculated in lb/ac based on 18% turnout.

Data were subjected to analysis of variance for a randomized complete block arrangement of treatments. Means were separated using protected LSD and were considered different at P < 0.05.

Results and discussion

No differences in soil moisture availability were detected during the 2002 growing season at the 1-ft depth (Fig. 1). Significant differences (P < 0.05) in soil moisture between the three treatments planted to grain sorghum and the CC treatment developed at a 3-ft depth after the sorghum plots were harvested on 9 August (Fig. 2).

Figure 1. Soil moisture at 1 ft for the 2002 and 2003 growing seasons.

Figure 1. Soil moisture at 1 ft for the 2002 and 2003 growing seasons.

Figure 1. Soil moisture at 1 ft for the 2002 and 2003 growing seasons.

Figure 2. Soil moisture at 3 ft for the 2002 and 2003 growing seasons.

Figure 2. Soil moisture at 3 ft for the 2002 and 2003 growing seasons.

Figure 2. Soil moisture at 3 ft for the 2002 and 2003 growing seasons.

Grain sorghum yields during the first trial year averaged 78 bu/ac (4700 lb/ac, Fig. 3). No significant differences among treatments were detected. The estimated lint yield for the CC plots was 430 lb/ac.

Figure 3. Grain sorghum yields for the 2002 and 2003 growing seasons.

Figure 3. Lint yields for the 2002 and 2003 growing seasons.

The authors believe the 2002 study went well despite a slow start due to early season drought. In the first year of study, end of season moisture at the 3-ft depth was greater in the sorghum plots than in the continuous cotton plots. Sorghum was harvested and shredded earlier than cotton, thus conserving deep soil moisture. This could benefit a subsequent cotton crop. Sorghum and cotton yields in 2002 were exceptionally good due to a high summer rainfall event the first week of July.

In 2003 persistent, season-long drought and high temperatures resulted in crop loss for sorghum and substantially reduced cotton yields (Fig. 3). Rainfall was only 58% of normal with no rainfall event in July through mid August, a critical period for sorghum.

The value of this system will not be fully known for several years, since it normally takes a number of cropping seasons to realize overall benefits from cover crops and reduced-till management systems. This is especially evident with the two extremely diverse cropping seasons experienced in 2002 and 2003.

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