Browsing by Browse by SEO 2020 "100504 Non-cereal crops (non-cereal crops for hay/silage/green feed)"

Smallholder crop-livestock systems are critical to future food security and meeting rapidly rising demand for livestock products. Yet, increasing competition for resources and high levels of soil degradation means farmers must produce more agricultural outputs without using more land, water or other inputs. Herbaceous forage legumes are one strategy for intensifying crop-livestock systems. However, current adoption levels are low and there is great uncertainty over the benefits, trade-offs and constraints of integrating forage legumes into farming systems at a farm and household level. Forage legume research has largely focused on agronomic performance and, consequently, the socio-cultural and economic factors which define the potential role of forage legumes in smallholder farming systems are poorly understood. Critically, little consideration has been given to the impact of gender roles on forage legume adoption and the distribution of impacts within a household. This thesis identifies potential opportunities for integrating forage legumes into smallholder crop-livestock systems in West Timor, Indonesia, and the benefits and trade-offs at a farm and household level.

The impact of forage legumes on farm production depends on the allocation of legume nitrogen (N) to crop and livestock enterprises. In Chapters 2 and 3, the impact of forage legume biomass management (retained vs. cut and removed) on inputs of fixed N, soil N and subsequent maize yield was assessed for an irrigated field experiment. While retaining shoot biomass contributed equivalent to 100-150 kg urea-N/ha and increased maize yield by 6-8 t/ha, there was little or no yield benefit when legume biomass was removed. The N fixation efficiencies (9-27 kg fixed-N/t shoot DM) and maize yield responses (5.8-7.9 t/ha higher yield compared to a maize control) were also double what is commonly achieved under dryland systems, indicating effective soil N and water management and sufficient yield potential are required to realise meaningful production benefits. As large trade-offs exist between allocating legume N to crop or livestock enterprises, alternative management options, such as grazing or partial biomass removal, may be required to achieve dual soil N-fodder benefits. Good agronomic practice is required to maximise the yield benefits of forage legumes. In Chapter 4, simulations for six case study sites in West Timor indicated that increases in maize yield of up 3.5 t/ha could be achieved if legume shoot biomass was retained, maize was planted at high densities (4-6 plants/m²) and weed control was effective. Critically, in West Timor, plant available water rather than soil N constrained crop production in poor years. Thus, the largest and most consistent yield responses from forage legume production are likely to be achieved for years and sites with low soil N fertility and high rainfall.

Despite the yield benefits of green manuring legume biomass, farmers often favour allocating biomass to increasing livestock production, as it provides more substantial economic benefits. In Chapter 5, whole farm and participatory modelling quantified the production and economic impacts of forage legumes for six case study farms. When used as fodder, forage legumes can more than double farm income, although they must be integrated with staple crops or planted on unutilised land to achieve such substantial benefits. The marginal value of feed increased with herd size from 0.9-1.0 M Rp/t TLU^-1 for smaller herds (≤2 TLU) to 1.8-3.1 M Rp/t TLU^-1 for larger herds (>2 TLU), indicating there were larger economic benefits for larger herds (TLU; Tropical Livestock Unit). Participatory scenario analysis indicated that livestock focused farmers favoured larger areas of legumes than other farm types. This indicates that farmers with sufficient incentive, land, labour and capacity to invest are likely to benefit most from forage legumes.

While forage legumes can provide large economic benefits, the impacts of technologies are often unevenly distributed between men and women. In Chapter 6, participatory onfarm evaluation assessed the potential benefits and constraints of forage legume production for male and female farmers. Preferences reflected gender roles; women favoured integrating forage legumes with food crops to increase soil fertility and crop yield, while men favoured permanent stands as they provided the largest economic benefit. Labour was identified as the key constraint to adoption, with unequal distribution of household labour suggesting that forage legumes may increase women's labour requirements but maintain or decrease men's labour requirements. Thus, forage legume adoption requires labour saving options and more equitable distribution of benefits and labour inputs between men and women.

This research demonstrated that integrating forage legumes into smallholder croplivestock farming systems can provide significant production and economic benefits. Yet, there are also large trade-offs associated with legume management, labour, land use and the inequitable distribution of household impacts. Further research is required to validate these potential impacts and how they may differ for a broader range of farmers and farming systems.

Atmospheric nitrogen (N) is fixed by symbiotic root-nodule bacteria (rhizobia) associated with pasture and pulse legumes and has a national value of about $3.5 billion annually.

This is based on nitrogen fixation rates of about 70 kilograms per hectare per year, crop and pasture legume areas of close to 50 million ha and fertiliser N costed to the grower at $0.76/kg, which equates to $1.00/kg plant-available N in the soil after accounting for N losses. The price of carbon-based fossil fuels, used in the production of nitrogenous fertilisers, is expected to increase in the future which will push fertiliser costs higher. Added to that are the environmental costs associated with the production, distribution and application of nitrogenous fertilisers. Therefore, the historical and ongoing interest by Australian farmers in using legumes which fix nitrogen in their farming systems makes good economic and environmental sense and needs to be sustained into the future.

We write this commentary in response to a recent paper by Barros et al. (2020) which reports rates of N₂ fixation of 0–265 kg ha^-1 (above-ground biomass only with no accounting of fixed N in the roots) by 15 sorghum (Sorghum bicolor (L.) Moench) genotypes at four sites in Brazil. The high values reported require careful consideration because they are up to ten times higher than observed elsewhere in Brazil on sorghum inoculated with diazotrophs specifically selected from parallel glasshouse experiments (dos Santos et al. 2017). Sorghum is a widely-grown poaceous grain crop, but one not known for its N₂-fixing capability. Based on the data presented, we calculate the rate of N₂ fixation would have needed to exceed 3 kg ha^-1 day^-1 during the first 90 days of growth for the highest fixing sorghum genotype, a rate higher than observed for most N₂-fixing legumes (e.g. soybean, Glycine max (L.) Merrill; La Menza et al. 2020). Barros et al. (2020) used a methodology that relies on small natural differences in ¹⁵ N abundance (usually expressed as δ¹⁵N; parts per thousand relative to atmospheric N₂) which generally occur between atmospheric N₂ and plant-available N in the soil, the latter sampled with a known non-N₂-fixing plant. The N₂-fixing plants, partly or wholly rely on atmospheric N₂ as an N source for growth, display significantly lower δ¹⁵N than plants with lesser or no dependence on N² fixation. At the two sites at which sorghum δ¹⁵N were significantly different to the δ¹⁵N of the non-N₂-fixing reference plants, the median Ndfa was calculated to be 52% and shoot N fixed 45 kg N ha^-1.