Phosphorus fertilizer placement and tillage affect soybean root growth and drought tolerance

Abstract

Tillage system and P fertilizer placement can affect plant root growth and therefore water and nutrient uptake. The objective of this study was to evaluate the effect of P fertilizer placement and tillage system on soybean [Glycine max (L.)] root growth and grain yield under induced drought stress. A field study was performed at two locations in southern Brazil, during the 2014/2015 season. Phosphorus fertilizer placement and tillage combinations were evaluated using triple superphosphate at 31 kg P ha-1. Treatments included: (i) strip-tillage with deep band (ST–DB); (ii) strip-tillage with band-applied 5 by 5 cm (ST–B); (iii) no-till with broadcast (NT–BR); (iv) no-till with band-applied 5 by 5 cm (NT–B); and (v) no-till with surfaceband (NT–SB). Root length density (RLD) and root diameter were evaluated at 0- to 25-cm depth in 5-cm intervals. Yield was evaluated under rainfed as well as under induced drought conditions. The ST–DB treatment showed increased total RLD among treatments, with about 58% greater RLD than the NT– BR treatment, and 46% greater RLD than the NT–B treatment at the 15- to 25-cm soil depth. Furthermore, the soybean yield penalty with the ST–DB treatment was lower than any other treatment with a yield reduction of about 9 and 0.3% at respective locations under induced drought stress. Results from our study showed that the ST–DB treatment contributed to enhance soybean root growth at deeper soil layers and improved overall resilience to induced drought.