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Fertilizers, hybrids, and the sustainable intensification of maize systems in the rainfed mid-hills of Nepal

By: Devkota, K.P.
Contributor(s): McDonald, A | Khadka, L | Khadka, A | Paudel, G.P | Devkota, M.
Material type: materialTypeLabelArticlePublisher: Amsterdam, Netherlands: Elsevier, 2016Subject(s): Fertilizers | Conservation agriculture | Maize | NepalOnline resources: Access only for CIMMYT Staff In: European Journal of Agronomy v. 80, p. 154-167Summary: In the rainfed mid-hill region of Nepal, most fields receive 2–3 t ha−1of organic compost application everyyear. Despite efficient recovery and use of organics in the mixed crop-animal systems that predominantin the mid-hills, depleted soil fertility is widely understood to be a significant constraint to crop pro-ductivity, with most farmers achieving maize grain yields below 2 t ha−1. Increased use of fertilizer mayarrest and even reverse long-term soil quality degradation, but few farmers in the mid-hills use them atpresent and existing recommendations are insufficiently responsive to site, varietal, and managementfactors that influence the productivity and profitability of increased fertilizer use. Moreover, policy mak-ers and development practitioners often hold the perception that returns to fertilizer use in the mid-hillsare too low to merit investment. In this study, on-farm experiments were conducted at 16 sites in thePalpa district, Nepal to assess the responsiveness of a maize hybrid (DKC 9081) and an ‘improved’ open-pollinated maize variety (‘OPV’, Manakamana-3) to four nitrogen (N) rates, i.e., 0, 60, 120 and 180 kg ha−1,with each N rate response evaluated at 30:30 and 60:60 kg ha−1rates of phosphorus (P2O5) and potassium(K2O), respectively. With sound agronomy and high rates of fertilizer (180:60:60 kg N:P2O5:K2O ha−1),grain yields observed in the field experiments exceeded 8 t ha−1with hybrids and 6 t ha−1with OPV. Yieldlevels were lower for OPV than hybrid at every level of applied N, but both genotypes responded linearlyto N with partial factor productivity for N (PFPN) ranging from 14 to 19 for OPV versus 26–30 for hybrid,with improved N efficiencies obtained when P and K rates were significantly higher. Averaged acrossphosphorus (P) and potassium (K) levels, a $ 1 incremental investment in fertilizer increased the grossmargin (GM) by $ 1.70 ha−1in OPV and by $ 1.83 ha−1in the hybrid. For the full response of N, requireshigher rate of P2O5:K2O and vice-versa and full response to P2O5:K2O does not occur if N is absent. Theseresults suggest that, i) degraded soils in the mid-hills of Nepal respond favorably to macronutrient fer-tilizers – even at high rates, ii) balanced fertilization is necessary to optimize returns on investments inN but must be weighed against additional costs, iii) OPVs benefit from investments in fertilizer, albeit ata PFPNthat is 36–47% lower than for hybrids, and, consequently iv) hybrids are an effective mechanismfor achieving a higher return on fertilizer investments, even when modest rates are applied. To extendthese findings across years and sites in the mid-hills, crop growth simulations using the CERES-maizemodel (DSSAT) were conducted for 11 districts with historical weather and representative soils data.Average simulated (hybrid) maize yields with high fertilizer rate (180:60:60 kg N:P2O5:K2O ha−1) rangedfrom 3.9 t ha−1to 7.5 t ha−1across districts, indicating a high disparity in attainable yield potential. Byusing these values to estimate district-specific attainable yield targets, recommended N fertilizer ratesvary between 65 and 208 kg N ha−1, highlighting the importance of developing domain-specific recom-mendations. Simulations also suggest the potential utility of using weather forecasts in tandem with siteand planting date information to adjust fertilizer recommendations on a seasonal basis.
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In the rainfed mid-hill region of Nepal, most fields receive 2–3 t ha−1of organic compost application everyyear. Despite efficient recovery and use of organics in the mixed crop-animal systems that predominantin the mid-hills, depleted soil fertility is widely understood to be a significant constraint to crop pro-ductivity, with most farmers achieving maize grain yields below 2 t ha−1. Increased use of fertilizer mayarrest and even reverse long-term soil quality degradation, but few farmers in the mid-hills use them atpresent and existing recommendations are insufficiently responsive to site, varietal, and managementfactors that influence the productivity and profitability of increased fertilizer use. Moreover, policy mak-ers and development practitioners often hold the perception that returns to fertilizer use in the mid-hillsare too low to merit investment. In this study, on-farm experiments were conducted at 16 sites in thePalpa district, Nepal to assess the responsiveness of a maize hybrid (DKC 9081) and an ‘improved’ open-pollinated maize variety (‘OPV’, Manakamana-3) to four nitrogen (N) rates, i.e., 0, 60, 120 and 180 kg ha−1,with each N rate response evaluated at 30:30 and 60:60 kg ha−1rates of phosphorus (P2O5) and potassium(K2O), respectively. With sound agronomy and high rates of fertilizer (180:60:60 kg N:P2O5:K2O ha−1),grain yields observed in the field experiments exceeded 8 t ha−1with hybrids and 6 t ha−1with OPV. Yieldlevels were lower for OPV than hybrid at every level of applied N, but both genotypes responded linearlyto N with partial factor productivity for N (PFPN) ranging from 14 to 19 for OPV versus 26–30 for hybrid,with improved N efficiencies obtained when P and K rates were significantly higher. Averaged acrossphosphorus (P) and potassium (K) levels, a $ 1 incremental investment in fertilizer increased the grossmargin (GM) by $ 1.70 ha−1in OPV and by $ 1.83 ha−1in the hybrid. For the full response of N, requireshigher rate of P2O5:K2O and vice-versa and full response to P2O5:K2O does not occur if N is absent. Theseresults suggest that, i) degraded soils in the mid-hills of Nepal respond favorably to macronutrient fer-tilizers – even at high rates, ii) balanced fertilization is necessary to optimize returns on investments inN but must be weighed against additional costs, iii) OPVs benefit from investments in fertilizer, albeit ata PFPNthat is 36–47% lower than for hybrids, and, consequently iv) hybrids are an effective mechanismfor achieving a higher return on fertilizer investments, even when modest rates are applied. To extendthese findings across years and sites in the mid-hills, crop growth simulations using the CERES-maizemodel (DSSAT) were conducted for 11 districts with historical weather and representative soils data.Average simulated (hybrid) maize yields with high fertilizer rate (180:60:60 kg N:P2O5:K2O ha−1) rangedfrom 3.9 t ha−1to 7.5 t ha−1across districts, indicating a high disparity in attainable yield potential. Byusing these values to estimate district-specific attainable yield targets, recommended N fertilizer ratesvary between 65 and 208 kg N ha−1, highlighting the importance of developing domain-specific recom-mendations. Simulations also suggest the potential utility of using weather forecasts in tandem with siteand planting date information to adjust fertilizer recommendations on a seasonal basis.

Maize CRP FP1 - Sustainable intensification of maize-based farming systems

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