Grain Production and Economic Returns from Dryland Sorghum in Response to Tillage Systems and Planting Patterns in the Semi‐Arid Southwestern USA

Abstract

Sorghum [ Sorghum bicolor (L.) Moench.] is grown primarily under dryland conditions in the semi‐arid southwestern USA. Soils in the area are low in organic matter and are poorly structured. They are susceptible to compaction, surface sealing following rainfall, slow infiltration, and significant runoff and erosion. Management of these soils for efficient crop production requires different practices than those used on more productive soils. Skip‐row planting of row crops is common. The practice may consist of planting two or four rows and skipping one or more rows, but one of the more common patterns is planting two rows and skipping one. The practice of skip‐row planting is based upon the assumption that skipping rows between planted rows gives a yield advantage over planting in contiguous rows. A study was conducted from 1984 to 1987 to determine the effect of tillage systems and planting patterns on grain sorghum production and profitability. A reduced tillage system using subsoiling and diking of furrows (RT) was compared with a conventional tillage system (CT). The soil type at the study site varies from a Miles fine sandy loam (fine‐loamy, mixed, thermic Udic Paleustalf) on the east end to a Portales clay loam (fine‐loamy, mixed, thermic Aridic Calciustoll) on the west end. Grain sorghum was planted in solid (contiguous rows) and skip‐row (two rows planted and one skipped) patterns in 40‐in. rows in each tillage system. Tillage systems produced no significant mean yield effects, but there was a significant year × tillage system interaction for yield. Sorghum in the RT system produced a significantly higher yield than that in CT in 1986 and a significantly lower yield in 1987, when yields exceeded 5000 lb/acre. There was a perched water table within 4 ft of the surface during part of the crop year of 1987, making the test periodically subirrigated. As contrasted with yields, net returns from RT showed a significant advantage over CT from 1984 to 1986 and no difference in 1987. Sorghum in solid plantings produced significantly higher yields from 1985 to 1987. Sorghum in skip‐row plantings was competitive with solid planting only in the lowest yielding year, 1984, when yields were less than 1800 lb/acre. Solid plantings were more profitable than skip‐row plantings from 1985 to 1987 with no difference in 1984. This variability produced significant year × row pattern interactions. The RT system was more stable for yield than the CT system, and the RT solid system was the most profitable as well as the most economically stable of the four systems, as measured by CVs. The RT skip‐row system was the most stable for yield. Sorghum in skip‐row plantings produced the lowest economic returns and the lowest yields. Skip‐row plantings in RT and CT systems were the most stable for yield, and the CT skip‐row was the least stable economically. Sorghum production was profitable in 3 of the 4 yr when yields were about 2500 lb/acre or higher. Skip‐row planting showed no yield or economic advantage over solid planting, and the RT solid planting was the most profitable when the 4‐yr average is considered. Research Question Sorghum is grown primarily under dryland conditions in the semi‐arid southwestern USA. Soils of the area are low in organic matter and are poorly structured. They are thus susceptible to compaction, surface sealing following rainfall, and significant runoff and erosion. The result is that soil moisture usually is inadequate for optimum yields. Methods to offset moisture limitations are needed to increase yields, enhance stability of production, and increase economic returns from sorghum. A reduced tillage system (RT) using subsoiling and furrow diking as compared with conventional tillage (CT) has produced significant yield increases in cotton. Economic returns from cotton in the RT system have been greater than those attributable to yield increases because of reduced inputs. Skip‐row planting of sorghum and cotton in dryland production systems is used in the semi‐arid southwestern USA as a purported hedge against moisture limitations. This practice consists usually of planting two or four rows and skipping one or more rows between planted rows. The practice also affects acreage allotments and government payments. The objective of this study was to evaluate the combined effects of a reduced tillage system vs. conventional tillage in combination with skip‐row and solid planting patterns on yield and profitability from grain sorghum production. Literature Summary Subsoiling, furrow diking, and a combination of these practices in separate operations have given significant yield increases in cotton and grain sorghum production in the Rolling and High Plains of Texas. Results have not always been consistent in these locations, and have differed in other locations and with different crops. An RT system combining subsoiling and diking furrows has significantly reduced runoff, increased moisture storage, water use efficiency, yields, and profitability of cotton in the Rolling Plains. Differing results have been obtained in other areas and with other crops. Skip‐row planting of row crops, especially grain sorghum and cotton, in the semi‐arid southwestern USA is common. Results with cotton and sorghum have not been consistent, and there is little published information about sorghum. No information was found about the use of RT with skip‐row planting. Study Description This study was conducted for 4 yr (1984–1987) on a mixed soil consisting of Miles fine sandy loam on the east end of the site, grading to a Portales clay loam on the west end. Treatments consisted of two tillage systems: (i) reduced tillage (RT) (including subsoiling, furrow diking, and controlled traffic) and (ii) conventional tillage (CT) (including chiselling, sweeping, and disking), and two planting patterns: (i) solid (contiguous) 40‐in. rows, and (ii) skip‐row planting (two 40‐in. rows planted, one skipped). Land was prepared in the winter and spring as early as weather permitted using the operations described above. Treatment plots were maintained in the same location each year. Sorghum hybrid ‘ATx399 × Tx430’ was planted at 3 to 4 seed/ft of row in all treatments and all years. Planting dates were in late June and early July. A dry blend of fertilizer supplying 50 lb of N and 30 lb of P 2 O 5 /acre was applied in 20‐in. bands in the sides of beds each year before planting. This rate of fertilizer was based on soil tests from samples taken each year. Propazine was used for weed control, and a rodweeder was used to control volunteer sorghum before planting. Sorghum was harvested with a plot combine, and yield per acre determined. Economic analyses were done using enterprise budgets generated with a Microcomputer Budget Management System. Cost of inputs was based on local prices prevailing at the time of the study. Costs and net returns to land, management, and risk were calculated on per acre basis assuming 500 acres for each system. Price received for grain was based on government loan price plus deficiency payments and was $5.14/cwt. Applied Questions What was the effect of tillage treatments on yield and economic returns? The RT system had no significant yield advantage over the CT system based on the average of the 4 yr. Mean yields over the 4 yr (1984–1987) were 2977 and 2927 lb/acre for RT and CT, respectively. However, tillage systems did not respond the same each year. Sorghum in the CT system produced significantly higher yields in 1987, but no significant differences were present in the 3 other yr. The high yields in 1987 resulted from a high water table during part of the year. In contrast to yield, the RT system had a significant advantage in net returns over the CT system from 1984 to 1986, but not in 1987. Differences in net returns to tillage systems were magnified compared with yield as a result of lower production costs. The reduced costs were primarily in preharvest variable costs (fuel and labor for machinery operation and maintenance), and in fixed costs for machinery and equipment. While RT and CT were not different from each other in 1987, net returns in 1987 were at least twofold greater than for the next highest year, 1986. This difference was due to the high yield level in 1987 compared with other years. What was the effect of planting patterns on yield and economic returns? Sorghum in solid plantings produced significantly higher yields from 1985 to 1987. Sorghum in skip‐row plantings was competitive with solid planting only in the lowest yielding year, 1984, when yields were less than 1800 lb/acre. Solid plantings were more profitable than skip‐row plantings from 1985 to 1987 with no difference in 1984. What was the combined effect of tillage systems and planting patterns on yield and economic returns? Solid plantings produced higher yields and greater economic returns than skiprow. The RT solid system was the most profitable as well as the most economically stable system. Skip‐row plantings were the most stable for yield, but the CT skip‐row was the least stable economically. The only situation in which skip‐row planting was competitive was in 1984 when all systems lost money. Sorghum production was profitable in 3 of the 4 yr when yields were about 2500 lb/acre or higher. Grain yields averaged over tillage and row pattern treatments were 1703, 2625, 2983, and 4497 lb/acre from 1984 to 1987, respectively. Net retur

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