Dry Weight and Leaf Area Production Rates of Irrigated Determinate Soybeans1

Abstract

AbstractQuantitative measurements are needed to determine the effects of irrigation on production rates of dry matter and leaf area of soybeans [Glycine max. (L.) Merr.]. A field experiment was conducted on a Typic Albaqualf (Crowley silt loam) and a Vertic Fluvaquent (Kobel clay) for three seasons. The objectives were to evaluate dry matter and leaf area production and to use growth analysis techniques to quantify these growth rates for irrigated (I) and nonirrigated (N) soybeans. Growth analysis parameters computed include crop growth rate (CGR), relative growth rate (RGR), net assimilation rate (NAR), leaf area ratio (LAR), leaf weight ratio (LWR), and specific leaf area (SLA). Little or no plant response to irrigation was found during the wetter than normal season in 1974. Differences in plant growth due to soil moisture regime were obtained in the two dry seasons (1975 and 1976). These differences initially were found during late vegetation and early bloom growth stages in both leaves and stems on or near the same date. Generally, the irrigated soybeans accumulated greater amounts of dry matter and leaf area and had higher seed yields than did the nonirrigated soybeans.Values of crop growth rate for I and N soybeans increased to a maximum during late July and early August of 1974 and declined thereafter. Similar results were found with the I soybeans in 1975. The period of maximum CGR corresponded to late vegetative and early reproductive growth. The maximum CGR of the N soybeans was found at mid‐August during 1975, the season when rainfall deficits were observed. This period of maximum CGR corresponded to mid‐podfill growth stages.Values of relative growth rate, net assimilation rate and leaf area ratio were highest during early vegetative growth and decreased as the season progressed. Generally, in a given year the I soybeans had greater values of the growth parameters during reproductive stages. The decline of LAR of the N soybeans during 1975 was attributed to the decrease in leaf weight ratio during vegetative growth and to the decrease in both LWR and specific leaf area during reproductive growth. The greater LAR values of the I soybeans during reproductive growth was due to the longer period during which the assimilates were converted to leaf area production.