Effect of Crotalaria rotation and trash removal in soil N transformations and sugarcane response to N fertilization

Abstract

Sustainability of sugarcane based biofuel production is affected by nitrogen use efficiency (NUE). The challenge is to increase sugarcane yield while decreasing synthetic N fertilizer usage towards improving NUE. One option is to adopt a legume-based rotation, such as sunn hemp (Crotalaria). The cost is the main limitation, but it can be overcome by increases in yield and reduction of N application at planting. Previous research indicates also a potential reduction in ratoon N fertilization, but studies are still needed under Brazilian conditions. The goal is to evaluate the effect of sunn hemp rotation in reducing N fertilizer demand by sugarcane ratoon. Four field trials will be set up in areas that received (i) or not (ii) previous rotation with sunn hemp. The trials will be set up after cane-plant harvest by means of application of the followings treatments: control, 50, 100, and 150 kg ha-1 N, as well as two additional treatments: 50 or 100% of straw removal (with 100 kg ha-1 N - allowing evaluate the effect of straw removal on sugarcane yield and NUE). In one local, 15N fertilizer will be applied in order to quantify NUE and recovery in the soil. Field trials will be set up in 2014 and measurements of soil N transformations, sugarcane yield and quality, N uptake, and NUE will be performed in the following harvests (2015, and 2016). The final objective is to evaluate the potential of sunn hemp rotation in reducing N fertilizer requirements for sugarcane based biofuel production. (AU)