Economic trade-offs of biomass use in crop-livestock systems: Exploring more sustainable options in semi-arid Zimbabwe

In complex mixed crop-livestock systems with limited resources and biomass scarcity, crop residues play an important but increasingly contested role. This paper focuses on farming systems in the semi-arid areas of Zimbabwe, where biomass production is limited and farmers integrate crop and livestock activities. Conservation Agriculture (CA) is promoted to intensify crop production, emphasizing the retention of surface mulch with crop residues (CR). This paper quantifies the associated potential economic trade-offs and profitability of using residues for soil amendment or as livestock feed, and explores alternative biomass production options. We draw on household surveys, stakeholder feedback, crop, livestock and economic modeling tools. We use the Trade-Off Analysis Model for Multi Dimensional Impact Assessment (TOA-MD) to compare different CR use scenarios at community level and for different farm types: particularly the current base system (cattle grazing of maize residues) and sustainable intensification alternatives based on a CA option (mulching using maize residues ± inorganic fertilizer) and a maize–mucuna (Mucuna pruriens) rotation. Our results indicate that a maize–mucuna rotation can reduce trade-offs between CR uses for feed and mulch, providing locally available organic soil enhancement, supplementary feed and a potential source of income. Conservation Agriculture without fertilizer application and at non-subsidized fertilizer prices is not financially viable; whereas with subsidized fertilizer it can benefit half the farm population. The poverty effects of all considered alternative biomass options are however limited; they do not raise income sufficiently to lift farmers out of poverty. Further research is needed to establish the competitiveness of alternative biomass enhancing technologies and the socio-economic processes that can facilitate sustainable intensification of mixed crop-livestock systems, particularly in semi-arid environments

Optimizing Livelihood and Environmental Benefits from Crop Residues in Smallholder Crop-Livestock Systems in Southern Africa. Series Paper Number 11

Sustainable forms of intensification are needed to address the low and stagnant production of farming systems in southern Africa. More efficient use of crop-livestock interactions can contribute to this; in this context the effective use of crop residues is becoming increasingly important and also contested. Crop residues left on the field for mulching are expected to bring long-term environmental benefits but when fed to livestock they provide farmers with short-term livelihood benefits. This study aims at better understanding the diversity of farming systems and uses of crop residues, in particular the trade-offs in using the residues for soil amendment versus livestock feed. It is part of a global comparison with sites along a human and livestock population density gradient across sub-Saharan Africa and South Asia. This southern Africa study represents the most extensive case of semi-arid areas with lowest biomass production. Three sites were compared, at different levels of agricultural intensification, extent of crop-livestock integration and use of crop residues. 1. Mzimba in Northern Malawi – intensified crop oriented production. 2. Nkayi in southwest Zimbabwe – integrated crop-livestock systems. 3. Changara in Tete province in Central Mozambique – extensive crop-livestock farming. Across the three sites, crop residues are clearly needed as livestock feed. In Nkayi and Changara low crop yields and low biomass production against the existing demand from livestock prevents farmers from using residues for purposes other than livestock feed. The practice of collecting and kraal feeding residues in Nkayi illustrates that the pressure on residues is at a level where farmers start privatizing residues in order to ensure their individual benefits. When feeding crop residues in the kraal, farmers also increase the amount of manure for soil fertility improvement. Even in Mzimba, with higher residue production and lower livestock ownership, very few farmers retain the residues to achieve real impact on soil health. Although farmers see soil fertility as a critical constraint, they have limited residues to spare for mulching. The trade-offs of reallocating crop residues from livestock feed to mulching for soil amendment will be high as long as alternative feed technologies and access to input and output markets are not developed. The trade-offs will be lower in areas with higher biomass production and less competition with livestock. Technical options need to increase biomass on existing croplands, addressing feed shortages and the need for soil amendment concurrently. Viable institutional structures and appropriate policies need to support this intensification processes through better access to inputs, knowledge and markets. The pathways for sustainable intensification and more efficient crop residue utilization need to be developed within the local context. We found strong growth potential for livestock-oriented agricultural development in extensive areas (Changara), strengthening crop and livestock integration to support intensification in areas like Nkayi, and enhancing crop-livestock integration for more efficient resource utilization where biomass is less limiting (Mzimba)

Effect of increasing dietary proportion of plantain on milk production and nitrogen use of grazing dairy cows in late lactation

Context: Plantain has shown promise as a forage that can mitigate nitrogen (N) losses from farm systems, although adoption and regulation requires knowledge of the minimum amount of forage area or diet quantity to observe an effect. Aims: A grazing study was conducted to evaluate the effect of offering increasing proportions of spatially adjacent plantain (PL) and perennial ryegrass–white clover (PRGWC) on milk production and N utilisation of dairy cows. Methods: Forty-eight late lactating cows blocked into replicated (n = 3) groups of four cows were randomly allocated to one of the following four forage treatments based on percentage area of plantain: 0%, 15%, 30%, or 60%. Cows were allocated 25 kg DM/cow.day of forage above ground level daily on the basis of metabolisable energy requirements. Dry matter intake was estimated from the difference between pre- and post-grazing pasture mass, using a calibrated electronic rising-plate meter. Milk production was measured as yield and milk solids, while N use was estimated from total milk N excretion and spot subsamples of blood, urine and faeces. Key results: Offering cows spatially adjacent strips of PL increased apparent dry matter intake compared with PRGWC pasture alone (16.4 vs 15.1 kg DM/cow.day, P = 0.027) and apparent metabolisable energy intake (203 vs 188 MJ/kg.cow.day, P < 0.001). Milk yield (16.1 kg/cow.day), milk solids production (1.6 kg/cow.day) and fat concentration (5.69%) were unaffected by the proportion of plantain in the diet. PL offered at 60% of the area increased milk protein concentration compared with PRGWC (4.65 vs 4.36%, P < 0.01). There was no treatment effect on total apparent N intake (563 g N/cow.day), N excretion in milk (113 g N/cow.day) and N-utilisation efficiency (20 g milk N/100 g N consumed). However, total milk urea, blood urea and urine urea N concentrations declined with increasing plantain in the diet, reflecting an influence on urea metabolism. Conclusions: Offering plantain to grazing dairy cows did not improve milk yield or N-use efficiency, but influenced urea metabolism. Implications: Sowing plantain in spatially separate strips within perennial ryegrass–white clover pastures is a useful option to achieve target levels of plantain in the diet and, in conjunction with other mitigation strategies, can be used to improve the sustainability of pastoral dairy farming

Three ways to improve water productivity in Zimbabwe

A poster prepared for the ILRI Annual Program Meeting (APM) 2010, held at ILRI campus, Addis Ababa, Ethiopia, April 14-17, 2010