Crop-available water and agronomic management, rather than nitrogen supply, primarily determine grain yield of commercial chickpea in northern New South Wales

Abstract

Chickpea ('Cicer arietinum' L.) is considered an effective rotation crop in Australia's northern grains region; however, concerns exist that grain yields of commercial crops are reduced because of nitrogen (N) deficiency related to inadequate nodulation and N₂ fixation. As part of a program to address these issues, we report on the monitoring of 22 commercial fields around Moree, northern NSW, during 2005-07 that were designated for chickpea, and an associated farmer survey (81 respondents). Our objectives were to determine whether the monitored crops were limited by N and to develop recommendations that would optimise productivity for farmers growing chickpeas. In 2005, only soil water and nitrate data were collected from the six fields designated for chickpea. In 2006 and 2007, almost complete datasets were assembled from the 16 chickpea fields or crops, including soil water and nitrate at sowing, row spacing, plant density, plant height, stubble cover, weed density and composition, shoot biomass, grain yield, nodulation and N₂ fixation (%N derived from the atmosphere (%Ndfa) and total crop N fixed). The associated survey provided insights into farmer knowledge of, and practices related to, inoculation. Field monitoring indicated moderate-high levels of soil nitrate at sowing (averages 114, 126 and 110 kg N ha⁻¹ to 1.2 m depth for 2005, 2006 and 2007, respectively) and generally low plant nodulation (0.11-1.16 g fresh wt plant⁻¹) and N₂ fixation (0-62%Ndfa and 0-87 kg N ha⁻¹). Grain yield varied between 0.53 and 2.91 t ha⁻¹ across the 14 monitored crops, with averages of 1.89 t ha⁻¹ in 2006 and 1.02 t ha⁻¹ in 2007. Although total crop N and grain yields were highly correlated with total (i.e. soil + fixed) N supply, there was no evidence that the monitored chickpea crops were N-limited. Rather, we conclude that soil N and biologically fixed N were complementary in supplying N to the crops, the grain yields of which were primarily determined by the supply of plant-available water (PAW) and water-use efficiency (WUE). Simple and multivariate regression analyses showed that stubble cover during the fallow (positively correlated with sowing PAW) and sowing date (positively correlated with crop WUE) were significant determinants of grain yield. We conclude that farmers could improve inoculation practice by ensuring the time between seed inoculation and sowing is always <24 h.