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Several new and existing short-term forage legumes could be used to provide nitrogen (N) inputs for grain crops in subtropical farming systems. The fixed-N inputs from summer-growing forage legumes lablab (Lablab purpureus), burgundy bean (Macroptilium bracteatum) and lucerne (Medicago sativa) and winter-growing legume species snail medic (Medicago scutellata), sulla (Hedysarum coronarium) and purple vetch (Vicia benghalensis) were compared over several growing seasons at four locations in southern Queensland, Australia. Available soil mineral N and grain yield of a following cereal crop were compared among summer-growing legumes and forage sorghum (Sorghum spp. hybrid) and among wintergrowing legumes and forage oats (Avena sativa). In the first year at all sites, legumes utilised the high initial soil mineral N, with <30% of the legume N estimated to have been derived from atmospheric N2 (%Ndfa) and legume-fixed N <30 kg/ha. In subsequent years, once soil mineral N had been depleted, %Ndfa increased to 50-70% in the summer-growing legumes and to 60-80% in winter-growing legumes. However, because forage shoot N was removed, rarely did fixed N provide a positiveNbalance. Both lablab and burgundy bean fixed up to 150 kg N/ha, which was more than lucerne in all seasons. Prior to sowing cereal grain crops, soil nitrate was 30-50 kg/ha higher after summer legumes than after forage sorghum. At one site, lablab and lucerne increased the growth and yield of a subsequent grain sorghum crop by 1.4 t/ha compared with growth after forage sorghum or burgundy bean. Of the winter-growing legumes, sulla had the highest totalN2 fixation (up to 150 kg N/ha. year) and inputs of fixedN(up to 75 kg N/ha), and resulted in the highest concentrations of soilN(80-100 kg N/ha more than oats) before sowing of the following crop. Wheat protein was increased after winter legumes, but there was no observed yield benefit for wheat or grain sorghum crops. New forage legume options, lablab, burgundy bean and sulla, showed potential to increase N supply in crop rotations in subtropical farming systems, contributing significant fixed N (75-150 kg/ha) and increasing available soil N for subsequent crops compared to non-legume forage crops. However, high soil mineral N (>50 kg N/ha) greatly reduced N2 fixation by forage legumes, and significantN2 fixation only occurred once legume shootNuptake exceeded soil mineralNat the start of the growing season. Further work is required to explore the impact of different management strategies, such as livestock grazing rather than harvesting for hay, on the long-term implications for nutrient supply for subsequent crops. [ABSTRACT FROM AUTHOR]

Highlights: [•] Mixing crops and livestock helps Australian farmers manage climate, price and soil variability. [•] Recent crop–livestock innovations can improve farm productivity, sustainability and reduce risk. [•] Potential for grazing dual-purpose cereal and canola crops or sacrificially grazing crops is unrealised. [•] Perennial pasture phases in grain crop rotations can provide multiple farm benefits. [•] Systems growing mixtures of crops and pastures and to utilise novel pasture species are evolving. [ABSTRACT FROM AUTHOR]

• Tropical forage legumes were grown in rotation or relays with maize and rice. • Subsequent maize yields increased by up to 80 % if legumes were retained as mulch. • Maize yield increased less (15−35% higher) after legume forage was harvested. • Forage legumes grown in rotation with rice increased subsequent yields by 40–70 %. • Clitoria ternatea proved the most beneficial forage legume for diverse systems. In temperate systems, it is well known that forage legumes can improve both nitrogen (N) supply and yields of subsequent cereal crops. While this is assumed to be true in tropical systems, it is less well tested, particularly in smallholder settings where forage is often cut and removed from the field. This paper confirms the potential of short phases of tropical forage legumes to provide N to subsequent crops in seasonally dry tropical farming systems. Across five experiments, maize and rice grain yields increased by up to 80 % after 4−8 month rotations of forage legumes, but the benefits were smaller when legume growth was reduced, biomass was removed for forage, or the yield potential of cereal crops was lower. We found that the additional N cycling from legumes can last for at least 2 years, although the benefit diminishes with time. When all legume material was retained as mulch, the estimated additional N provided to subsequent no-till maize crops was the equivalent of 9−15 kg urea-N per tonne of above-ground legume biomass produced but fell to 1.5−3 kg urea-N/t if forage was removed. After shoot removal, more legume N cycled to a subsequent rice crop (equivalent of 11–13 kg urea-N/t of legume biomass) than to a no-till maize crop, presumably because more below-ground material mineralised. Of the legumes tested, Clitoria ternatea grew best across a variety of environments and use patterns and provided the largest yield benefits to subsequent crops. This research demonstrates the potential to integrate short phases of tropical herbaceous forage legumes into smallholder crop-livestock systems in the seasonally dry tropics, and, in doing so, improve or maintain staple grain crop production and household food self-sufficiency. [ABSTRACT FROM AUTHOR]

Abstract: Australia has a long history of mixed farming. This paper examines the integration of Australian cropping and livestock production from three perspectives: as a factor in land use change, a consequence of individual management practices and a means of meeting farmers’ multiple objectives. Since about 1995, the proportion of cropped land has increased on Australian cropping farms while livestock numbers have decreased. Land use in the north-eastern, central and south-western regions of the cropping zone have diverged. Despite these changes, mixed farms still dominate Australia’s broadacre farming regions. Previous accounts of the dimensions in which farming enterprises are integrated can be simplified for Australian broadacre agriculture. For most purposes it is sufficient to consider a nested set of four integration options: “specialization” (not integrated organizationally), “separation” (integrated organizationally only), “rotation” (integrated organizationally and spatially, but not temporally) and “synchronization” (integrated in all three dimensions). We illustrate these integration options with a short survey of agronomic practices that affect crop–livestock integration. We review the farmer objectives that enterprise integration can meet and the constraints that limit it, seeking to balance social, economic and agronomic factors. We use a dynamic simulation model to make a first quantification of the economic risk reduction provided by enterprise diversification. Constraints imposed by limited labour, capital, and management attention cannot be overlooked; this is especially relevant in Australia where labour is increasingly in short supply. We characterize our surveyed set of agronomic practices with respect to the farmer objectives they affect. We find that farmers generally have the option of meeting a particular objective through different practices that affect different dimensions of integration. Practices that result in closer integration in time and space generally require greater management attention; practices that do not integrate in space typically require an increase in external inputs. History suggests that current commodity price ratios may be sufficient to slow or reverse the overall land use trend away from livestock production. In the longer term, forecast increases in worldwide demand for meat, energy costs and soil resource constraints will all encourage Australian cropping farmers to maintain mixed systems; however reduced availability of labour relative to capital will push land use toward specialized systems. Valuing the benefits and costs associated with differing degrees of enterprise integration is a major research challenge that will require insightful application of both biophysical and economic models. [Copyright &y& Elsevier]