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Furthermore, our analysis corroborates previous research that found social networks to be relatively homophilous, with limited social interaction across socioeconomic strata within a village. Hence, if agricultural extension messages are primarily diffused through ‘progressive’ farmers, who usually belong to the better- off, better-educated, and higher-caste stratum, they have limited scope of reaching the poorer segments in a village. To further boost farmers’ awareness of the technology, extension messages should therefore be targeted to farmers representing different social strata.
Zero-tillage productivity impacts in wheat in the Eastern Indo-Gangetic Plains
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Our estimated ZT induced wheat yield gain of 498 kg ha−1 in farmers' fields is in line with findings from field trials: in seven on-station trials conducted in the Eastern IGP, the average ZT induced yield increase in wheat amounted to 15 %, or 460 kg ha−1 in absolute terms (Erenstein and Laxmi 2008); at 490 kg ha−1, the average yield gain reported from on-farm trials in Bihar is also very similar to our estimates of what farmers achieve with their own management (Dhiman et al. 2003). Since the yield benefits associated with ZT have been established ceteris paribus with factors such as differences in time of planting and fertilizer use controlled for in the analysis, the causal mechanisms for the estimated yield gains are likely to be associated with soil related factors. Intensive tillage typically increases evaporative losses of soil water (Schwartz et al. 2010), which in turn can reduce early plant growth under deficit irrigation conditions. Further, the higher levels of soil porosity and surface roughness following tillage increase the total volume of water applied with the first irrigation (Erenstein et al. 2007), which can result in growth reductions associated with wet field conditions and processes such as denitrification and root stunting.
In the context of the dominantly irrigated wheat production systems of Bihar without adoption of ‘full’ conservation agri- culture (i.e. ZT in combination with soil cover from crop residues), we conclude that farmers reap substantial yield and monetary benefits from ZT practices, both in upland and low- land ecologies. The practicality of early sowing of wheat varies across agro-ecological zones due to temporal differences in soil drainage, which needs to be considered when targeting extension messages. Nevertheless, our findings imply that the potential of ZT to facilitate an advancement of wheat sowing can be exploited in well-drained areas. Furthermore, the efficiency analysis indicates considerable scope to increase yields through better management of current levels of inputs, e.g., by improving the timing of field operations, with the caveat that there may be binding constraints that limit the ability of farmers to achieve the same level of TE in all fields. Additional work is required to identify the root causal factors of these inefficiencies and to prioritize differentiated intervention points matched to the needs of different farm types. To increase the number of ZT beneficiaries in the densely populated Eastern IGP and, hence, contribute to enhancing wheat productivity and food security in an environ- mentally sustainable manner, an expansion of the network of ZT service providers is required as tractor and drill ownership is not a tenable goal for most capital-constrained small and medium-sized farms. Furthermore, efforts are needed to raise farmers’ awareness of the ZT technology and to reduce the observed scale bias in its use, which is likely to be caused by the fixed costs associated with service provision in dispersed fields. Business models that include demand aggregation and service coordination may help overcome this bias by reducing transaction costs. Scale bias may also lessen with time as the number of service providers increases, and competition makes the providers less selective in marketing their services.
On the whole, this study provides strong evidence that ZT for wheat provides tangible and significant yield and economic benefits to adopters across a range of production ecologies and socio-economic settings in the Indian State of Bihar, while reducing environmental externalities commonly associated with extensive tillage. ZT technology could play a major role in making Bihar self-sufficient in wheat. Hence, BGREI and other development initiatives in the region should continue to provide an enabling environment for the accelerated spread of ZT as an important element of sustainable wheat intensification in Eastern India.