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

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 x 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 Ib/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 Iblacre. Solid plantings were more profitable than skip-row plantings from 1985 to 1987 with no difference in 1984. This variability produced significant year x 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 Ib/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.