Fertilizer response and nitrogen use efficiency in African smallholder maize farms

Improving fertilizer recommendations for farmers is essential to increase food security in smallholder landscapes. Currently, blanket recommendations are provided across agro-ecological zones, although fertilizer response and nutrient use efficiency by maize crop are spatially variable. We aimed to identify factors that could help to refine fertilizer recommendation by analyzing the variability in fertilizer response (FR) and the agronomic nitrogen use efficiency (N-AE). A literature search for on-farm studies across Kenya and Sub-Sahara Africa (SSA), excluding Kenya, yielded 71 publications. The variability in FR was studied using a meta-analysis whereas key factors that influence FR and N-AE were studied with linear regression models. On average, the FR was 2, but it varied considerably from 1 to 28.5 (excluding outliers). In SSA, 18% of the plots were non-responsive plots with an FR < 1. The main factors affecting N-AE for Kenya were P-Olsen, silt content, soil pH, clay and rainfall, whereas only soil pH, exchangeable K and texture were important for SSA. However, our study indicates that available data on soil, climate and management factors could explain only a small part (< 33%) of the variation in FR and N-AE. Soil pH, P-Olsen, silt content, and rainfall had significant but low levels of power in explaining variation in FR and N-AE. Our findings indicate that strategies to refine fertilizer recommendation should include information on soil types and soil properties.</p

Spatial approach for diagnosis of yield-limiting nutrients in smallholder agroecosystem landscape using population-based farm survey data

Adept use of fertilizers is critical if sustainable development goal two of zero hunger and agroecosystem resilience are to be achieved for African smallholder agroecosystems. These heterogeneous systems are characterized by poor soil health mainly attributed to soil nutrient depletion. However, conventional methods do not take into account spatial patterns across geographies within agroecosystems, which poses great challenges for targeted interventions of nutrient management. This study aimed to develop a novel populationbased farm survey approach for diagnosing soil nutrient deficiencies. The approach embraces principles of land health surveillance of problem definition and rigorous sampling scheme. The advent of rapid soil testing techniques, like infrared spectroscopy, offers opportune avenues for high-density soil and plant characterization. A farm survey was conducted on 64 maize fields, to collect data on soil and plant tissue nutrient concentration and grain yield (GY) for maize crops, using hierarchical and purposive sampling. Correlations between soil test values with GY and biomass were established. The relationship between GY, soil NPK, and the tissue nutrient concentrations was evaluated to guide the setting up of localized critical soil test values. Diagnosis Recommendation Integrated System (DRIS) indices for total nitrogen (N), total phosphorus (P), and total potassium (K) were used to rank and map the prevalence of nutrient limitations. A positive correlation existed between plant tissue nutrient concentration with GY with R2 values of 0.089, 0.033, and 0.001 for NPK, respectively. Soil test cut-off values were 0.01%, 12 mg kg-1, 4.5 cmolc kg-1 for NPK, respectively, which varied slightly from established soil critical values for soil nutrient diagnostics. N and K were the most limiting nutrients for maize production in 67% of sampled fields. The study demonstrates that a population-based farm survey of crop fields can be a useful tool in nutrient diagnostics and setting priorities for site-specific fertilizer recommendations. A larger-scale application of the approach is warranted

Soil spatial variation to guide the development of fertilizer use recommendations for smallholder farms in western Kenya

A farm survey was conducted within a 100 km2 sampling block to collect data on the spatial variation in unfertilized maize biovolume and grain yields in relation to soil organic carbon (SOC), total nitrogen, phosphorus and extractable cations. Key soil factors associated with crop performance were identified using stepwise multiple linear regression modelling. The spatial variation of key soil factors and crop performance indicators (CPIs) was described in terms of spatial dependency. An analysis of variance indicated the variation explained by soil types, sampling units, and administrative units. Soil properties displayed high variability with coefficients of variation of in the range of 50% to 89% for extractable nutrients. Grain yield ranged widely from 0.1 to 11.3 t ha−1, with 31% of the variation being accounted for by measured soil properties. SOC was identified as key soil factor associated with variation in crop performance. SOC displayed moderate spatial dependency with a range of 523 m. Analysis of variation indicate that variation in SOC was sufficiently described by small spatial units (fields). These insights were used to provide a framework for determining an appropriate scale for developing digital soil maps or distance for soil sampling in heterogenous smallholder farming systems. Strategies aimed at refining fertilizer use recommendation can therefore use this guideline.</p

Digital Extension, Price Risk, and Farm Performance: Experimental Evidence from Nigeria

Despite decades of investment in agricultural extension, technology adoption among farmers and agricultural productivity growth in Sub-Saharan Africa remain slow. Among other shortcomings, extension systems often make recommendations that do not account for price risk or spatial heterogeneity in farmers' growing conditions. However, little is known about the effectiveness of extension approaches for nutrient management that consider these issues. We analyze the impact of farmers' access to site-specific nutrient management recommendations and to information on expected returns, provided through a digital decision support tool, for maize production. We implement a randomized controlled trial among smallholders in the maize belt of northern Nigeria. We use three waves of annual panel data to estimate immediate and longer term effects of two different extension treatments: site-specific recommendations with and without complementary information about variability in output prices and expected returns. We find that site-specific nutrient management recommendations improve fertilizer management practices and maize yields but do not necessarily increase fertilizer use. In addition, we find that recommendations that are accompanied by additional information about variability in expected returns induce larger fertilizer investments that persist beyond the first year. However, the magnitudes of these effects are small: we find only incremental increases in investments and net revenues over two treatment years

Threats to soil biodiversity - global and regional trends

Using the information provided on the main threats in the ten ecoregions present in the six world regions (Table of threats for Sub-Saharan Africa, South West Pacific, Latin America and Caribbean, North Africa and Near East, North America and Europe; FAOand ITPS, 2015), a summary table of the main threats common to these ecoregions was produced. This exercise showed that the most widespread threat to soil biodiversity in the world was the loss of SOM and SOC, and that this could be associated with other threats such as deforestation and agricultural intensification (both linked withland use change) and with climate change (particularly in tundra). This clearly shows the importance of sustainable management and conservation practices, to maintain this resource in soils, which represents one of the bases for the soils food webs. Deforestation and agricultural intensification were also major threats worldwide, being important intropical and temperate broad leaf and mixed forests and temperate and montane grassland sand boreal forests/taiga, although the level of available information on the topic was highly variable, depending on the particular world regions where these ecoregions occur. The ecoregions with the highest number of threats were the deserts and dry shrublands, the tropical and subtropical grasslands, and the temperate broad leaf and mixed forests. Invasive species also represented an important threat, particularly in Mediterranean and temperate forests and tundra.Fil: Brown, George. Ministerio da Agricultura Pecuaria e Abastecimento de Brasil; BrasilFil: Cooper, Miguel. Universidade do Sao Paulo. Escola Superior de Agricultura Luiz de Queiroz; BrasilFil: Kobayashi, Mónica. Food And Agriculture Organization Of The United Nations; ItaliaFil: Orgiazzi, Alberto. No especifíca;Fil: Domínguez, Anahí. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas Fisicoquímicas y Naturales. Instituto de Ciencias de la Tierra, Biodiversidad y Ambiente - Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Ciencias de la Tierra, Biodiversidad y Ambiente; ArgentinaFil: Dias Turetta, Ana Paula. No especifíca;Fil: Franco, André. No especifíca;Fil: Zaitsev, Andrey. No especifíca;Fil: Winding, Anne. No especifíca;Fil: Foereid, Bente. No especifíca;Fil: Singh, Brajesh. No especifíca;Fil: Guerra, Carlos. No especifíca;Fil: Rojas, Claudia. No especifíca;Fil: Spurgeon, David. No especifíca;Fil: Aksoy, Ece. No especifíca;Fil: Moreira, Fátima Maria. No especifíca;Fil: Bautista, Francisco. No especifíca;Fil: Xu, Jianming. No especifíca;Fil: Rousk, Johannes. No especifíca;Fil: Bedano, José Camilo. Universidad Nacional de Rio Cuarto. Facultad de Cs.exactas Fisicoquimicas y Naturales. Instituto de Ciencias de la Tierra, Biodiversidad y Ambiente. - Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Cordoba. Instituto de Ciencias de la Tierra, Biodiversidad y Ambiente.; ArgentinaFil: Bagyaraj, Joseph D.. No especifíca;Fil: Saxena, Krishna. No especifíca;Fil: da Silva, Laura Fernanda Simões. No especifíca;Fil: Tedersoo, Leho. No especifíca;Fil: Byrne, Loren. No especifíca;Fil: Callaham, Mac A.. No especifíca;Fil: Choudhary, Madhu. No especifíca;Fil: Aller, M. Fernanda. No especifíca;Fil: Delgado Baquerizo, Manuel. No especifíca;Fil: García Orenes, Maria Fuensanta. No especifíca;Fil: Tsiafouli, Maria. No especifíca;Fil: de Graaf, Marie. No especifíca;Fil: Hart, Miranda. No especifíca;Fil: Thuita, Moses. No especifíca;Fil: Karanja, Nancy. No especifíca;Fil: Fromin, Nathalie. No especifíca;Fil: Eisenhauer, Nico. No especifíca;Fil: Kaneko, Nobuhiro. No especifíca;Fil: Mele, Pauline. No especifíca;Fil: Pastor, Pilar Andres. No especifíca;Fil: Ochoa-Hueso, Raul. No especifíca;Fil: Kuperman, Roman. No especifíca;Fil: Ichami, Stephen. No especifíca;Fil: Fonte, Steven J.. No especifíca;Fil: Santillan, Vinisa Saynes. No especifíca;Fil: Tapia Torres, Yunuen. No especifíca