Abstract
It has been demonstrated that soybean (Glycine max) produces lower yields at relay intercropping with wheat (Triticum aestivum) than if it is sown as a sole crop. However, most studies considered wider or irregular soybean row spacing, compromising its capacity to recover after wheat harvest. This work studied the stress effects in relay soybean intercropping and suggests narrowing row spacing to improve soybean performance. The aims were (i) to compare growth and yield of two planting patterns and (ii) to separate the effect of water stress (WS) from the effects of other stress factors (OSF) induced by wheat on intercropping soybean. WS was evaluated comparing above-ground dry and grain yield of irrigated and non irrigated intercropping soybean, and OSF was evaluated comparing intercropping soybean with another treatment in which wheat straw (aerial biomass) was eliminated at soybean emergence, both irrigated treatments. In wheat, similar yields were obtained in treatments with an intercropping planting pattern with two rows for wheat and one for soybean (2:1) compared to three rows for wheat and one row for soybean (3:1). However, intercropping soybean at narrow row spacing (52 cm; 2:1) improve yielded 23% more than intercropping at 70 cm (3:1). During wheat-soybean coexistence, OSF prevailed on soybean and this effect persisted in later stages. After wheat harvest, OSF reduced the amount of light interception from R1 to R5 and depressed the crop growth rate (CGR) in 34%. However, in this period, WS also affected the radiation use efficiencies (RUE) which explained the greater fraction (66%) of the total stress induced by wheat in soybean CGR. Intercrop soybean yielded 182 g m-2 less compared to the unstressed sole crop control. Considering the wheat effects on soybean growth, 63% (116.5 g m-2) of the total yield lost were due to WS. Therefore, most of the performance of relay intercropping soybean was linked with water disponibility since early stages. However, at optimum water condition wheat competition by light and resources also affected soybean yield (OSF: 37%).
Highlights
Wheat-soybean double cropping is well established in Argentine pampas north to 34oS (Calviño et al, 2003)
In order to assess and identify the effect of wheat competition on soybean intercrop, a particular form of treatment design was employed to separate the effect by water stress (WS) from the EOF effects of stress on soybean performance
Wheat yield was affected by row spacing, intercropping patterns yielded 11% less than normal planting
Summary
Wheat-soybean double cropping is well established in Argentine pampas north to 34oS (Calviño et al, 2003). Like many other similar regions in the world, latesown soybean grain yield is severely restricted by a shorter crop cycle and by an important drop in temperature, radiation and photoperiod during the reproductive stages. In the southern Argentine pampas, these conditions lead to drastic reductions in seed number and seed mass; a reduction of 56 kg ha-1 per day in yield was reported at a delayed planting date of soybean in double cropping after wheat, highlighting the importance of advancing the sowing date (Calviño et al, 2003). In the southern Argentine pampas, these conditions lead to drastic reductions in seed number and seed mass; a reduction of 56 kg ha-1 per day in yield was reported at a delayed planting date of soybean in double cropping after wheat, highlighting the importance of advancing the sowing date (Calviño et al, 2003). Monzon et al (2007), by means of simulation, estimated that the increase in temperature in the last three decades at Balcarce (a location in the south Argentine pampas), accelerated the development of wheat advanced wheat harvest and this could have allowed earlier sowing of double cropped soybean, increased soybean yield at a rate of 26.2 kg ha-1 year-1.
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