The net contributions of fixed N by crop legumes in low rainfall farming systems

Michael Moodie1, Mark Peoples2, Laura Goward2, Nigel Wilhelm3

1Mallee Sustainable Farming, PO Box 843, Irymple VIC 3498; [email protected]

2CSIRO Agriculture and Food, Black Mountain Laboratories, Canberra, ACT 2601

3 South Australian Research and Development Institute, Glen Osmond 5064, South Australia

Abstract

The inclusion of grain legume crops in low rainfall farming systems of south-eastern Australia can improve subsequent cereal crop productivity where nitrogen (N) is a limiting factor.  However, little is known about either the productivity or the capacity of crop legumes to contribute N in this low rainfall environment.  Over three seasons (2013-2015) break crop comparison trials were sampled to measure dry matter (DM) production and symbiotic N2 fixation of chickpea, field pea, lentil, lupin, faba bean and vetch crops grown in the Victorian and South Australian Mallee.  On average, shoot DM produced across species and seasons was in the order of 3 – 4 t DM/ha while average grain yields for all species across the three years was around 1 t/ha.  Chickpea fixed significantly less shoot N than the other species, which on average fixed ~60 kg N/ha in the above-ground DM across the three seasons.  After taking account of the amount of N removed in harvested grain across the three seasons, and including estimates of the likely contributions of fixed N associated with the nodulated roots, 12 of the 15 crop by season combinations were calculated to have provided agronomically significant net inputs of fixed N for the potential benefit of following crops.  Therefore it was concluded that legume crops appear to be a viable mechanism to maintain or improve the N fertility of cropping soils in low rainfall Mallee farming systems.