A Comparison of Early and Recommended Soybean Production Systems in Tennessee

The Early Soybean Production System (ESPS) is based on a favorable relationship between local weather conditions and the planting, growth, and development of soybean [Glycine max (L.) Merr.] plants. Most researchers in the southern region (Kentucky, Arkansas, Mississippi, Texas, and Florida) have found ESPS to be equal or superior to recommended production systems. However, several studies in Kentucky have shown decreased yields in ESPS. Also, poorer seed quality has been associated with ESPS. The first objective was to compare seed yield and quality of soybeans planted in ESPS and the recommended system. The second objective was to study the phenological aspects of the ESPS and recommended system using crop development and weather data. The recommended system in this study was MG IV and V (two cultivars each) with four planting dates from 29 April to 10 June and the ESPS was defined as MG III (two cultivars) with three planting dates 18 March to 15 April. The study was conducted at Springfield, Spring Hill, and Milan, TN, from 1992 to 1994. Results indicate that ESPS led to lower yields than the recommended system for Tennessee, even in the hottest and driest environment that occurred during the study. In general, ESPS soybeans were exposed to cooler and moister conditions than the recommended system, but the more favorable conditions did not result in increased yields. There was no difference in oil content between ESPS and the recommended system. The percentage protein was higher in ESPS, but the seed score was higher (poorer). Based on this study, ESPS does not appear to hold much potential as an alternative production system in Tennessee. Research QuestionThe Early Soybean Production System (ESPS) is based on a more favorable relationship between local weather conditions and the planting, growth, and development of soybean plants. It has been shown to be a viable alternative to the standard production system in many states in the southern USA. However, since Tennessee is in a climatic transition zone between Kentucky and Mississippi, it is unclear how ESPS would perform in our state. Since cultivars that best fit Tennessee growing conditions are from MG IV, V, and IV and are planted from 25 April to 15 June, the recommended system in this study was MG IV and V planted in late April to early June and the ESPS was MG III planted from mid-March to mid-April. The objectives of this study were to evaluate the ESPS vs. the recommended soybean production system in Tennessee, and to study some phenological aspects of the two systems. Literature SummaryThe primary advantage of early-planted, early-maturing indeterminate soybean production is that reproductive development will generally coincide with periods of favorable precipitation and subsequent soil moisture availability. The primary advantages to ESPS are (i) to avoid drought stress that commonly occurs during seed development in humid southern regions, (ii) to spread out the harvest period, and (iii) to facilitate fall planting of winter crops. Most researchers in the southern region (Kentucky, Arkansas, Mississippi, Texas, and Florida) have found ESPS to be equal or superior to recommended production systems. However, several studies in Kentucky have shown decreased yields in ESPS. Also, poorer seed quality has been associated with ESPS. Study DescriptionThe study was conducted from 1992 to 94 at three locations, Springfield, Spring Hill, and Milan, TN. The plot design was a factorial, split-plot arrangement in randomized complete blocks with four replicates. The main plot was planting date (18 March, 1 April, 15 April, 29 April, 13 May, 27 May, and 10 June) and the sub-plot was cultivar (MG III—‘Williams 82’, ‘Resnik’ MG IV—TN4-86, Asgrow A4715; MG V—Asgrow A5979, ‘Hutcheson’). No-till production practices were used. The harvested area consisted of two 30 in. by 30 ft center rows. The harvested grain was threshed, weighed, and sampled for moisture content. A 1.5 lb sample was collected for seed quality analysis (oil and protein content, seed score). A GLMM (Generalized Linear Mixed Model) analysis was completed for seed yield, oil and protein content, and seed score. Dates of beginning bloom and fidl maturity were collected in the field during the growing season. Climate data were obtained from NWS Cooperative Climate Stations at Springfield and Spring Hill, and from an automated weather station at Milan. Applied QuestionsDoes the ESPS system result in equal or better yields than soybeans planted in the recommended system? Results (Table 1) from the 3-yr, three-location study indicate that ESPS led to lower yields than the recommended system for Tennessee, even in the hottest and driest environment that occurred during the study. In general, ESPS soybeans were exposed to cooler and moister conditions than the recommended system, but the more favorable conditions did not result in increased yields. Do the phenology data provide any insight as to why ESPS did not perform as well as it has in other studies in the southern USA? The primary advantage of ESPS is that reproductive development will generally coincide with periods of favorable precipitation and subsequent soil moisture availability. Our study showed that ESPS did, in fact, have generally more favorable precipitation regimes during the reproductive phase. However, there was also more temperature stress during the vegetative phase for the ESPS at every location and year except one. Table 1Results of single degree-of-freedom contrasts for the Early Soybean Production System (ESPS) and recommended soybean production system at Springfield, Spring Hill, and Milan, TN, 1992–1994. ContrastVariableESPSRecommendedFSeed yield24.5 bu/acre35.0 bu/acre38.48***Protein38.2%36.7%27.84***Oil18.3%18.5% 2.48Seed Score † 3.5 2.914.12******Significant at the 0.001 level. †1 = very good, 2 = good, 3 = fair, 4 = poor, 5 = very poor.