Sorghum Hybrid Selection and Planting Management under Moisture Limiting Conditions

Using the proper planting window and hybrid maturity for grain sorghum [ Sorghum bicolor (L.) Moench] under moisture‐limiting conditions would produce consistent yields of higher test weight grain. The main objective of the research was to determine the effect of planting date and hybrid maturity on sorghum grain yield. Study duration was 1993 through 1995 at the Sandyland Experiment Field, Stafford County, Kansas, on a Naron loamy fine sand (fine‐loamy, mixed, thermic Udic Argiustoll). Main plots were planting date (mid‐April through early July), subplots were hybrid maturities (early, medium, full), and sub‐subplots were individual hybrids. Planting prior to mid‐June did not separate bloom dates although planting dates were spread over 6 wk. The optimal planting period for consistent grain yield was 25 May through 5 June, regardless of maturity. Yields decreased with planting both earlier and later than this optimum, but early planting decreased yield less than late. Except at planting date extremes, hybrid maturity did not affect yield. Individual hybrid yield response within maturity groups interacted with planting date. Test weight was unaffected by early planting, but late planting was detrimental. An optimal planting window exists to produce consistent grain sorghum yields. Under conditions of moisture stress, individual hybrid characteristics, not maturity, are most important. Research Question Producers in areas of limited moisture plant grain sorghum during the later portion of the recommended planting period to permit mechanical weed control and move reproduction beyond heat and water stress. Full‐season hybrids are selected to optimize yield. These practices increase risk of low yield and quality. Early planting and use of early hybrids could improve yield consistency and quality. Determining sorghum grain yield response to planting date and hybrid maturity was the objective of this study. Literature Summary Planting date work has focused on no‐tillage, especially for corn. Unlike sorghum, corn plant development responds linearly to heat accumulation and increasing hybrid maturity increases hybrid yield under Corn Belt conditions. Unlike sorghum, corn maturity ratings use heat accumulation. Most sorghum is planted where corn production risk is high because of heat and moisture stress. Unlike corn, grain sorghum under stress delays reproduction. Because stress is typical in areas of sorghum production, full‐season hybrids are at greater risk with late planting. Limited work demonstrates the possibility of planting sorghum earlier. Data are needed across a number of planting dates and a range of maturities to determine the optimal planting period and hybrid maturity. Study Description Sorghum was planted following wheat from 1993 to 1995 at the Sandyland Experiment Field, Stafford County, Kansas, on a Naron loamy fine sand. Fertilization consisted of 20 lb P/acre and 143 lb N/acre. Metolachlor was used for grass control; broadleaf control was achieved with bromoxynil in 1993 and 1994, and atrazine plus dicamba in 1995. Treatments: Planting dates: five (mid‐April to early July). Split plots — hybrid maturity (early, medium, full). Subplots — individual hybrids (16 hybrids total). April–September moisture: 29.8 in.(1993); 12.3 in.(1994); 23.5 in.(1995); rainfall distribution varied markedly. Applied Questions Is there an optimal planting period and does hybrid maturity affect yield under moisture‐limiting conditions? During the study, across extremes in rainfall and temperature, consistent, optimal yields were achieved by planting from 25 May to 5 June regardless of maturity (Fig. ). Except at planting date extremes, hybrid maturity did not affect yield. The optimal planting window was widest with early hybrids and decreased as hybrid maturity increased. Abnormally wet, cool conditions shift the planting window into mid‐June, whereas dry, hot conditions favor mid‐May. Does planting early or late minimize risk to grain yield? Effect of planting date on grain sorghum yields in 1993, 1994, and 1995. LSD (0.05) = 10 (1993), 8 (1994), 6 (1995). image Planting early presents less risk, especially as hybrid maturity increases (Fig. ). Risks of early planting (cool, wet conditions; frost; seedling disease) are less in this region than those of late planting (dry, hot conditions; delayed maturity; freeze).