Title Sorghum/Cotton Rotation under Extreme Deficit Irrigation Conditions. Location Texas Agricultural Research and Extension Center, Halfway, TX

Transcription

1 Title Sorghum/Cotton Rotation under Extreme Deficit Irrigation Conditions Participants James P. Bordovsky, TAES, Lubbock/Halfway Calvin Trostle, TAEX, Lubbock Eduardo Segarra, Texas Tech, TAES, Lubbock Location Texas Agricultural Research and Extension Center, Halfway, TX Contact James P. Bordovsky, TAES, HCR1, Box 117, Plainview, TX (806) , Section 1 Contribution to goals of PROFIT and benefits to producers. This field experiment seeks to evaluate sorghum as a viable production option in a sorghum/cotton (1:2) rotation compared to continuous cotton under limited irrigation conditions. In theory, early planted sorghum can be irrigated more heavily at the beginning of the growing season, allowing limited mid- and late-season water supply to be concentrated on the cotton after sorghum yield potential (early dough stage) has been fulfilled. For producers, this strategy would allow longer irrigation periods in areas restricted by extremely limited pumping capacity. Long-term improvements in water use efficiency by using sorghum in rotation with cotton are also expected over time. This project established a sorghum/cotton rotation (1:2) on a 9-acre area under a 8-span center pivot with the crop irrigated by the LEPA method. Treatments include: CCC continuous cotton (3 reps), CCS cotton followed by cotton and sorghum (5 replications), CSC cotton followed by sorghum and cotton (5 replications), and SCC sorghum followed by two years of cotton (5 replications). An additional factor was irrigation capacity with treatments limited to 0.0, 1.25, or 2.5 gpm/acre. These levels are well below irrigation capacities needed to fully meet the evaporative requirements of either sorghum or cotton and are becoming quite common on the High Plains. The extremely low rainfall during the summer of 2001 resulted in more water being diverted from sorghum to cotton than was originally scheduled. This resulted in sorghum yields in the dryland, 1.25, and 2.5 gpm/acre treatments being lower that expect at 22.0, 36.5, and 72.2 bu/acre, respectively. Although irrigations were delivered at different times and slightly different amounts, there was no difference in cotton lint yield between continuous cotton (CCC) and rotation cotton (CCS and CSC) in the first year of this experiment. Cotton lint yields were high averaging 343, 746, and 1158 lb./acre in the dryland, 1.25, and 2.50 gpm/acre treatments, respectively. In this extremely dry year, looking at the short-term economic impact, irrigation water was better spent on cotton rather than sorghum production. Benefits to cotton from sorghum residue from previous years cannot be documented until next year.

2 Section 2 Research methodology, results, and technology transfer. Objective This field experiment seeks to evaluate sorghum as a viable production option in a sorghum/cotton (1:2) rotation compared to continuous cotton under limited irrigation and dryland conditions. In theory, early planted sorghum can be irrigated more heavily at the beginning of the growing season, allowing limited mid- and late-season water supply to be concentrated on the cotton after sorghum yield potential (early dough stage) has been fulfilled. Long-term improvements in cotton production due to rotation are expected over time. Methodology A sorghum/cotton rotation (1:2) was established in 2001 on a 9-acre area under a 8- span center pivot with the crop irrigated by the LEPA method. This area is adjacent to, and follows the same layout, as the rotation established by Trostle in Treatments include: CCC continuous cotton (3 reps), CCS cotton followed by cotton and sorghum (5 replications), CSC cotton followed by sorghum and cotton (5 replications), and SCC sorghum followed by Figure 1. Sorghum/cotton rotation field irrigated by LEPA center pivot at TAES, Halfway, June two years of cotton (5 replications). Primary treatment plots were inch rows wide and arced 70 o of the pivot circle (circular rows). The 70 o pivot arc was split into three smaller arcs having irrigation capacities limited to 0.0, 1.25, or 2.5 gpm/acre. The pivot nozzles were located in alternate furrows and were equipped with manual valves. Color coded valves and preplanned irrigation schedules allowed operators to irrigate specific plots at appropriate times. Cotton had been planted in this field from 1998 through On May 18, 2001, GA M3838 sorghum seed was planted at 7.7 lb. per acre in sorghum plots. Paymaster 2326RR cotton was planted at 60,000 seed per acre on May 17, Nutrients (liquid, ground application) were applied based on soil tests for appropriate crops and expected yields. Normal cultural practices were conducted through the growing season. Greenbugs were controlled in sorghum with one application of Lorsban. Irrigations were scheduled throughout the growing season subject to the three irrigation capacity limits. Table 1 gives the irrigation schedule by week for each treatment based on pumping capacity with the option of moving water between sorghum and cotton crops (in rotation treatments) during peak growth periods.

3 Table 1. Planned and optional weekly irrigation schedules for sorghum/cotton rotation at 1.25 and 2.50 gpm/acre irrigation capacities used in Irrigation Amounts (Inches) 1.25 gpm/ac 2.5 gpm/ac Crop Rotation CCC CCS CSC SCC CCC CCS CSC SCC Week of 4-Jun Jun Jun Jun Jul Jul Jul Jul Jul Aug Aug Aug Aug Sep Optional Optional Weekly Irrigation Distriubtions Results and Discussion Rainfall for the year totaled 8.49 inches prior to planting and 3.04 inches from planting through September resulting in good early growth and severe water stress late in the growing season. Irrigations were begun on June 7 and were terminated on August 29. Figure 2 displays cumulative seasonal irrigation totals for sorghum (SCC), continuous cotton (CCC), and cotton going into sorghum (CCS). The CCS and CSC (not shown) treatments were irrigated identically the first year of this rotation. Slopes of lines through data points indicate pumping rates and periods in which water was applied to sorghum, cotton, or both in the rotation treatments.

4 Pumping Capacity = 1.25 gpm/acre The extremely low rainfall during the summer resulted in more water being diverted from sorghum to cotton in the 1.25 gpm/acre treatments than was scheduled in Table 1. This resulted in sorghum yields in the dryland, 1.25, and 2.5 gpm/acre treatments being lower that expect at , and 72.2 bu/acre, respectively (Table 2). Although irrigations were delivered at different times and slightly different amounts, here was no difference in cotton lint yield between continuous cotton (CCC) and rotation cotton (CCS and CSC) in the first year of this experiment. Cotton lint yields were high averaging 343, 746, and 1158 lb./acre in the dryland, 1.25, and 2.50 gpm/acre treatments, respectively. Cumulative Seasonal Irrigation (inches) Cumulative Seasonal Irrigation (inches) 6 4 All water diverted from sorghum to cotton 2 CCC CCS SCC 0 6/7 6/21 7/5 7/19 8/2 8/16 8/ Date Pumping Capacity = 2.5 gpm/acre 0 6/7 6/21 7/5 7/19 8/2 8/16 8/30 Date Figure 2. Cumulative seasonal irrigation from planting for sorghum/cotton rotation treatments irrigated at 1.25 and 2.5 gpm/acre capacity at TAES, Halfway, TX, Technology Transfer and Education Activity This past growing season was the first year of this field experiment. A field tour of this site and an explanation of the experiment was made for the Texas Cooperative Extension Crop and Drip Irrigation Tour, Halfway, TX, September 11, 2001.

5 Table 2. Sorghum grain and cotton lint yield resulting from sorghum/cotton rotations under dryland conditions and at pumping capacities of 1.25 and 2.5 gpm/acre at TAES, Halfway, Yield Irrigation Capacity Treatment Name 2001 Crop Grain (bu/ac) Lint (lb/ac) Seasonal Irrigation (in.) Dry CCC Cotton 333c 1 0 CSC Cotton 341c 0 CCS Cotton 352c 0 SCC Sorghum gpm/ac CCC Cotton 723b 6 CSC Cotton 786b 5.4 CCS Cotton 730b 5.4 SCC Sorghum gpm/ac CCC Cotton 1160a 10.8 CSC Cotton 1163a 10.2 CCS Cotton 1152a 10.2 SCC Sorghum Yields followed by the same letter are not statistically significant (P<0.05, LSD)