New soybean varieties for fallow cropping of sugarcane fields : SRDC final report

Abstract

Cropping of soybean has been shown by the yield decline joint venture to increase the yield of the following sugar crop by 15 to 30 percent. Part of the benefit occurs via provision of nitrogen to the following cane crop and part due to improvement in soil health. Soybean is unique among the tropical grain legumes in its ability to fix large amounts of nitrogen and maintaining reasonable fixation even in the presence of moderate levels of soil nitrogen. It also appears that the amount of nitrogen left behind for the following cane crop by a soybean green-manure crop is well in excess of requirements. Soybean may therefore be grown, grain harvested and sold for cash, whilst maintaining the rotational benefit to the following cane crop. The release of new soybean varieties by this project and its predecessor and work conducted by other researchers to help overcome yield decline in sugarcane cropping has seen a dramatic change in farming practice toward inclusion of soybean into the system. Availability of soybean grain harvested from crops grown on the coast has found a steady market. More recently several processing plants are planned for the tropics and at least one of these plants is contracting purchase of grain from the 2008 crop at good prices. This project sought to build on the recent release of variety Stuart by providing complimentary varieties suited to oilseed or human consumption use to coastal growers with a range of attractive traits, but focussing on high grain yield and biomass, strong lodging resistance, nematode and phytophthora resistance. In this way it was planned to provide a better and more profitable soybean rotation to benefit canegrowers.