Long-Term Study of Planting Date Effects on Seed Yield in Soybean

Abstract

Planting date in relation to subsequent crop development and yield are important determinants in realizing crop yield potential. This study was conducted to determine optimum planting dates for Oklahoma adapted maturity groups of soybean [Glycine max (L.) Merr.]. Effects of planting date on yield were investigated at Bixby, OK, in tbe Uniform Soybean Tests for Southern States. Field experiments were conducted from 1958 through 1994. Planting dates across years ranged between 10 May and 1 July, and were assigned to 5-d, planting intervals. Maturity groups IV, V, and VI were evaluated. Soil type was a Wynona silty clay loam (fine-silty, mixed, thermic Cumulic Haplaquoll). Significant interaction occurred between maturity group and planting interval for yield. Highest average yields produced by maturity group IV (2248 lb/acre) occurred with 9 to 18 May and 8 to 22 June planting intervals. Lowest average yields for maturity group IV (1524 lb/acre) occurred with 19 May to 7 June planting intervals. Highest average yields for maturity group V (2573 lb/acre) occurred with 14 to 18 May and 13 to 22 June planting intervals, and lowest average yields (1950 lb/acre) with 19 May to 12 June planting intervals. Maturity group VI produced highest average yields (2501 lb/acre) with 14 to 18 May, 3 to 7 June, and 13 to 22 June planting intervals. Maturity group VI yields for all other planting intervals averaged 2073 lb/acre. During the range of planting dates available from early May to early July, for maturity groups IV, V, and VI, definite optimum planting dates occur for highest yields. Knowledge of optimum planting dates can be one crop management tool applied to enhance crop productivity, facilitate cropping patterns, and better utilize environmental conditions. Problem Determining optimum planting dates for maximum seed yield is fundamental for successful crop production. This study was conducted to identify optimum planting dates based on seed yield for adapted maturity groups. Background Growers have a relatively long period between early May and early July for planting soybean in Oklahoma. Different maturity groups may produce different seed yields and change in relative rank for various dates of planting. This requires evaluation of maturity groups within planting dates and planting dates within maturity groups rather than considering either maturity group or planting date alone. Identification of optimum planting dates for different maturity groups would enable minimizing the effects that temperature, water stress and photoperiod may have on seed yield. Study Description This study was conducted from 1958 through 1994 on a Wynona silty clay loam at the Oklahoma Vegetable Research Station in Bixby, in the Uniform Soybean Tests for Southern States. Genotypes used each year were dependent upon entries in the Uniform Soybean Tests. Maturity groups IV, V, and VI were included. Maturity group IV contained both determinate and indeterminate genotypes. Maturity groups V and VI consisted of only determinate genotypes. All maturity groups were planted on the same date in a particular year, but planting dates changed from year to year. Planting dates ranged between 10 May and 1 July across the years. Planting periods between 9 May and 2 July were assigned to groups of 5-d intervals. Experiments were conducted under normal dryland conditions using cultural practices considered standard for the region. Seed yield was measured on each entry for the planting date in each year. Applied Questions Using genotypes representing maturity groups grown in Oklahoma, when are optimum planting dates for each maturity group? For each maturity group in this study, mid-May and mid- to late June plantings produced highest average seed yields. Lowest yields obtained for all maturity groups generally occurred for plantings between 19 May and 7 June. An exception was maturity group VI producing a high yield at the 3 to 7 June planting interval (Fig. 1). Figure 1Open in figure viewerPowerPoint Mean seed yield of each maturity group for each planting interval at Bixby, OK, from 1958 through 1994. What maturity groups produced highest yields for the various planting dates? For several planting intervals, maturity groups V and VI tended to produce higher seed yields than maturity group IV, but statistical significance did not exist at all planting intervals. Maturity group VI genotypes produced better seed yields than maturity group IV when planted in very late May or early June.