The uptake and use of nitrogen by paddy rice in fallow, cereal, and legume cropping systems

In a previous paper, we reported that prior crops either increased or decreased the yield of paddy rice ( Oryza sativa L.) and altered its response to fertiliser N. We considered that rice yield responses to prior crop might have reflected the uptake of crop residue N and the efficiency of its use to produce grain. Experiments consisted of dry-season grain or legume crops, or fallow, followed by wet-season rice (cv. Lemont); and wet-season grain or legume crops, or fallow, followed by dry-season rice. Urea at one-third of the rate required for optimum rice yield was applied at 3 stages of rice crop growth: sowing, permanent flood, and/or panicle initiation. Soil N supplied 4.1 to 6.5 g N/m 2 to the rice crop, depending on the season. Rice also recovered 0 to 0.25 of the N in the residue of a prior maize crop and 0.23 to 0.57 of the N in grain legume residues or a legume green manure crop; the fraction was greater if fertiliser N was not applied. Increased N uptake was the major contributor to heavier yield. The relationship between grain yield and crop N content was mostly linear, and thus physiological efficiency of N use for rice grain production was essentially constant across the range of environments provided by fertiliser N and cropping system treatments in this study. In experiments where fertiliser N was applied, there were small effects of prior cereal and legume cropping treatments on physiological efficiency. In contrast, without fertiliser N application, physiological efficiency was increased by prior cereal and legume crops, which likely resulted from a greater congruence between the N demand of the rice crop, and the N supply from the soil and incorporated residue, when compared with a fallow treatment. Keywords: fertiliser, nitrogen recovery, nitrogen use efficiency, Oryza sativa , prior crop. Australian Journal of Agricultural Research 50(6) 945 - 952 Full text doi:10.1071/AR98088 © CSIRO 1999