Managing legume leys, residues and fertilisers to enhance the sustainability of wheat cropping systems in Australia: 1. The effects on wheat yields and nutrient balances

Farming activities practiced on many Australian soils have resulted in substantial losses of soil organic matter (SOM), nutrient loss, soil structural degradation and declines in cereal yield and quality. Field trials, consisting of a legume or fallow phase followed by three wheat (Triticum aestivum L.) crops, were established on a degraded Ferric Luvisol (Red Earth) soil in New South Wales to investigate the effect of crop residue and fertiliser management on wheat yield and nutrient balances. There were no effects of a chickpea (Cicer arietinum L. cv Amethyst), barrel medic (Medicago truncatula L. cv Sephi), or fallow phase on the grain yields of three subsequent wheat crops. Grain yield was depressed by 12% following a lucerne (Medicago sativa L. cv Trifecta) crop from which the plant residues had been removed, relative to when residues were returned or grazed. Consecutively, higher wheat grain yield losses of 7.4 and 8.6% in 1994 and 1995 were found on treatments from which wheat stubble was annually removed from the system. Grain yield losses of 6, 7 and 13% in three consecutive wheat crops were found where no fertiliser was applied at sowing. Nutrient balances, based on inputs of nutrients in fertilisers and residues, and the export of nutrients in grain and crop residue were found to be useful in describing the flow of nutrients in a farming system and predicting possible soil nutrient depletion. Fallow systems provide no nutrient inputs and result in N losses of up to −189 kg ha−1 over three wheat crops. The balance of nutrients such as potassium (K), which are contained in larger proportions in stubble, were found to be −102 kg ha−1 on the wheat stubble removed treatments and +8 kg ha−1 on the stubble retained treatments. Better recycling of crop residues and improving ley system to increase nutrient and C inputs have the potential to improve soil fertility and grain production.