Pilar Muschietti-Piana1,2, Therese McBeath1,2, Ann M. McNeill1, Pablo A. Cipriotti3 and Vadakattu Gupta2,
1 School of Agriculture, Food & Wine, The University of Adelaide, SA5005, E mail: [email protected]
2 CSIRO Agriculture & Food, CSIRO Agricultural Systems, Waite Campus, PB 2, Glen Osmond, Adelaide SA, 5064
3 School of Agriculture, University of Buenos Aires, Av. San Martin 4453, Ciudad Autónoma de Buenos Aires, C1417DSE
In low-rainfall wheat cropping systems, low crop uptake of nitrogen (N) has been linked to asynchrony in soil-N supply through mineralisation. This is especially true on sandy soils of SE Australia which have a low-N supply capacity. When N released from soil and residues is insufficient, and/or the timing of biological supply is not well matched with crop demand, manipulating N supply using fertiliser applications becomes vital to achieve yield potential. The aim of this study was to measure the timing of N supply with crop N uptake for wheat following wheat-residues and wheat following lupin-residues under two N fertiliser rates in a low-rainfall sandy soil environment. In each residue-type site, plants and deep soil samples to rooting depth were collected at sowing and at 5 key wheat growth stages. Plants were analysed for N content, above-ground biomass and grain yield at maturity. All soil samples were analysed for gravimetric water content and mineral-N. The combination of lupin residues with a high fertiliser N rate increased soil mineral-N at the time of high demand, promoted plant growth and wheat N uptake. In a dry season, the additional N supplied as fertiliser at early stages was a key input to support an increase in wheat yield potential. Responses in N uptake throughout the growing season indicate that there remains a demand for fertiliser N following legume-N residue in this environment, but fertiliser N inputs remain risky as indicated by the lack of significant yield increase in a low rainfall growing season.