Climate and Management Factors Influence Soybean Yield Potential in a Subtropical Environment

Abstract

Th e interactive infl uence of climate and management factors on soybean [Glycine max (L.) Merr.] yield potential has not been investigated in subtropical production environments. Such information can help fi ne tune current soybean management practices to increase yield and resource-use effi ciency and to minimize risk. Th e objective of this study was to identify key biophysical and management factors governing variation in soybean yield potential in southern Brazil. To accomplish that objective, we used a large database on soybean yield and phenology collected from a combination of on-farm and research-station experiments conducted during four crop growing seasons (2011)(2012)(2013)(2014)(2015) in Rio Grande do Sul (southern Brazil). Th e database portrayed a wide range of weather conditions, soil types, water regimes, sowing dates, and cultivar maturity groups (MGs). Water supply and photothermal quotient explained most of yield variation across site-years. A boundary function was derived for the relationship between soybean yield and water supply, and an attainable water productivity of 9.1 kg grain ha -1 mm -1 . A seasonal water supply of ?800 mm appeared suffi cient to maximize seed yield, and most late-sown crops fell short of this value. Late-sown crops were also exposed to a lower photothermal quotient during reproductive stages, and this explained the yield penalty of 26 kg ha -1 d -1 of sowing delay aft er 4 November observed for non-water-limited crops. Sowing date, accompanied by proper selection of cultivar MG and determination of soil water status at sowing time, appear to be the most cost-eff ective management practices to ensure a high photothermal quotient and low risk of water defi cit during reproductive stages and, therefore, a high yield potential in the subtropical environment of southern Brazil.

Performance of soybean in hydromorphic and nonhydromorphic soil under irrigated or rainfed conditions

“…Management practices should be intensified in soybean cultivation in hydromorphic soils, in order to minimize stresses such as the loss of cellular turgor (first effect of water stress), which causes reduction of leaf growth rate (Streck, 2004) and, consequently, loss of soybean yield potential (Zanon et al, 2016).…”

“…If, on the one hand, rotating soybean crops with irrigated rice have increased recently, on the other hand, there are few studies on the development and productivity of the used soybean cultivars in hydromorphic soils in Brazil (Zanon et al, 2015(Zanon et al, , 2016Sartori et al, 2016), Uruguay (Chebataroff et al, 2002;Castillo et al, 2013), and Argentina (Caride et al, 2011). These few studies do not completely explain the differences of the ecophysiological processes (photosynthetic rate, dry matter partition), and the development of soybean cultivated in hydromorphic and nonhydromorphic soils in an integrated way.…”

Two approaches to calculate TVDI in humid subtropical climate of southern Brazil

“…Considering that TVDI has the capacity of locating in time and space the occurrence of water restrictions in large producing regions, it is possible to use the statistics obtained from long time series of TVDI to quantify associated causes, for example, yield differences. The use of TVDI images allows to generate results more detailed than those currently available for southern Brazil (Sentelhas et al, 2015;Zanon et al, 2016). Only three periods with high TVDI were observed in northern Rio Grande do Sul in the 2009-2010 cropseason (Figure 8).…”

“…Similarly, soybean crops occupy most cultivated areas in Rio Grande do Sul (RS) State and, because it is cultivated mostly under non-irrigated conditions, the crop is highly dependent on rainfall, which is often insufficient to meet crop demands. Therefore, amount and distribution of water supply impose the upper limit of soybean productivity in the state (Zanon et al, 2016).…”

TVDI spatiotemporal pattern of a soybean growing area in humid subtropical climate

“…This results from the fact that, in a largely non-irrigated agriculture activity, rainfall is the only water supply to the system and, therefore, associated with water availability for the crop. Water restrictions, especially during blooming and grain filling, hinder crop development and yield (Zanon et al 2016).…”