Leaching losses from Kenyan maize cropland receiving different rates of nitrogen fertilizer

© The Author(s), 2017. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Nutrient Cycling in Agroecosystems 108 (2017): 195–209, doi:10.1007/s10705-017-9852-z.Meeting food security requirements in sub-Saharan Africa (SSA) will require increasing fertilizer use to improve crop yields, however excess fertilization can cause environmental and public health problems in surface and groundwater. Determining the threshold of reasonable fertilizer application in SSA requires an understanding of flow dynamics and nutrient transport in under-studied, tropical soils experiencing seasonal rainfall. We estimated leaching flux in Yala, Kenya on a maize field that received from 0 to 200 kg ha−1 of nitrogen (N) fertilizer. Soil pore water concentration measurements during two growing seasons were coupled with results from a numerical fluid flow model to calculate the daily flux of nitrate-nitrogen (NO3−-N). Modeled NO3−-N losses to below 200 cm for 1 year ranged from 40 kg N ha−1 year−1 in the 75 kg N ha−1 year−1 treatment to 81 kg N ha−1 year−1 in the 200 kg N ha−1 treatment. The highest soil pore water NO3−-N concentrations and NO3−-N leaching fluxes occurred on the highest N application plots, however there was a poor correlation between N application rate and NO3−-N leaching for the remaining N application rates. The drought in the second study year resulted in higher pore water NO3−-N concentrations, while NO3−-N leaching was disproportionately smaller than the decrease in precipitation. The lack of a strong correlation between NO3−-N leaching and N application rate, and a large decrease in flux between 120 and 200 cm suggest processes that influence NO3−-N retention in soils below 200 cm will ultimately control NO3−-N leaching at the watershed scale.Earth Institute, Columbia University; National Science Foundation IIA-0968211; Bill and Melinda Gates Foundatio

The effect of mineral and organic nutrient input on yields and nitrogen balances in western Kenya

Author Posting. © The Author(s), 2015. This is the author's version of the work. It is posted here by permission of Elsevier for personal use, not for redistribution. The definitive version was published in Agriculture, Ecosystems & Environment 214 (2015): 10-20, doi:10.1016/j.agee.2015.08.006.Soil fertility declines constrain crop productivity on smallholder farms in sub-Saharan Africa. Government and non-government organizations promote the use of mineral fertilizer and improved seed varieties to redress nutrient depletion and increase crop yields. Similarly, rotational cropping with nitrogen (N)-fixing legume cover crops or trees is promoted to improve soil fertility and crop yields. We examined maize grain yields and partial N balances on 24 smallholder maize farms in western Kenya, where interventions have increased access to agricultural inputs and rotational legume technologies. On these farms, mineral fertilizer inputs ranged from 0 to 161 kg N ha-1 (mean = 48 kg N ha-1), and maize grain yields ranged from 1-7 tons ha-1 (mean = 3.4 t ha-1). Partial N balances ranged from large losses (-112 kg N ha-1) to large gains (93 kg N ha-1)with a mean of -3 kg N ha-1. Maize grain yields increased significantly with N inputs (from fertilizer and legumes) in 2012 but not in 2013 when rainfall was lower. Nitrogen inputs of 40 kg N ha-1 were required to produce 3 tons of maize ha-1. N balances varied both among farms and between years, highlighting the importance of tracking inputs and outputs on multiple farms over multiple years before drawing conclusions about nutrient management, soil fertility outcomes and food security. The addition of N from legume rotations was a strong predictor of grain yields and positive N balances in lower-yielding farms in both years. This suggested that legume rotations may be particularly important for buffering yields from climate variability and maintaining N balances in low rainfall years.This research was funded by an Earth Institute at Columbia University Cross-Cutting Initiative Grant, a National Science Foundation PIRE grant (IIA-0968211), and by the Bill and Melinda Gates Foundation (Gates Special Initiative Grant)

Effects of fertilizer on inorganic soil N in East Africa maize systems : vertical distributions and temporal dynamics

Author Posting. © Ecological Society of America, 2016. This article is posted here by permission of Ecological Society of America for personal use, not for redistribution. The definitive version was published in Ecological Applications 26 (2016): 1907–1919, doi:10.1890/15-1518.1.Fertilizer applications are poised to increase across sub-Saharan Africa (SSA), but the fate of added nitrogen (N) is largely unknown. We measured vertical distributions and temporal variations of soil inorganic N following fertilizer application in two maize (Zea mays L.)-growing regions of contrasting soil type. Fertilizer trials were established on a clayey soil in Yala, Kenya, and on a sandy soil in Tumbi, Tanzania, with application rates of 0–200 kg N/ha/yr. Soil profiles were collected (0–400 cm) annually (for three years in Yala and two years in Tumbi) to examine changes in inorganic N pools. Topsoils (0–15 cm) were collected every 3–6 weeks to determine how precipitation and fertilizer management influenced plant-available soil N. Fertilizer management altered soil inorganic N, and there were large differences between sites that were consistent with differences in soil texture. Initial soil N pools were larger in Yala than Tumbi (240 vs. 79 kg/ha). Inorganic N pools did not change in Yala (277 kg/ha), but increased fourfold after cultivation and fertilization in Tumbi (371 kg/ha). Intra-annual variability in NO−3-N concentrations (3–33 μg/g) in Tumbi topsoils strongly suggested that the sandier soils were prone to high leaching losses. Information on soil inorganic N pools and movement through soil profiles can h vulnerability of SSA croplands to N losses and determine best fertilizer management practices as N application rates increase. A better understanding of the vertical and temporal patterns of soil N pools improves our ability to predict the potential environmental effects of a dramatic increase in fertilizer application rates that will accompany the intensification of African croplands.Earth Institute at Columbia University Cross-Cutting Initiative Grant; National Science Foundation PIRE Grant Grant Number: IIA-0968211; Bill and Melinda Gates Foundation Grant Number: OPP1023542-0

Mineralisation Patterns of Selected Organic Materials

Abstract Thirty-two standard organic materials were mixed with a sandy soil (at 40% field capacity) at a rate equivalent to 5 t ha -1 and incubated aerobically under controlled conditions at 25°C for 28 days. Sampling for mineral N determination and CO 2 evolution was conducted at 3, 7, 14 and 28 days. Released CO 2 was related to resource quality, with those materials high in N, low in lignin and low in polyphenol concentrations releasing higher percentages of their initial C. In vitro dry matter digestibility (IVDMD) was linearly correlated with carbon breakdown, with correlation coefficients of 0.91, 0.92, 0.92 and 0.84 for sampling times of 3, 7, 14 and 28 days, respectively. Initial N concentration was significantly positively correlated with C breakdown at all sampling times. Nitrogen mineralisation was influenced mainly by initial N concentration of the materials, with materials having at least 2.3% N releasing N throughout the 28-day period

Nutrients in the nexus

Synthetic nitrogen (N) fertilizer has enabled modern agriculture to greatly improve human nutrition during the twentieth century, but it has also created unintended human health and environmental pollution challenges for the twentyfirst century. Averaged globally, about half of the fertilizer-N applied to farms is removed with the crops, while the other half remains in the soil or is lost from farmers’ fields, resulting in water and air pollution. As human population continues to grow and food security improves in the developing world, the dual development goals of producing more nutritious food with low pollution will require both technological and socioeconomic innovations in agriculture. Two case studies presented here, one in sub-Saharan Africa and the other in Midwestern United States, demonstrate how management of nutrients, water, and energy is inextricably linked in both small-scale and large-scale food production, and that science-based solutions to improve the efficiency of nutrient use can optimize food production while minimizing pollution. To achieve the needed large increases in nutrient use efficiency, however, technological developments must be accompanied by policies that recognize the complex economic and social factors affecting farmer decision-making and national policy priorities. Farmers need access to affordable nutrient supplies and support information, and the costs of improving efficiencies and avoiding pollution may need to be shared by society through innovative policies. Success will require interdisciplinary partnerships across public and private sectors, including farmers, private sector crop advisors, commodity supply chains, government agencies, university research and extension, and consumers

Nutrients in the nexus

Synthetic nitrogen (N) fertilizer has enabled modern agriculture to greatly improve human nutrition during the twentieth century, but it has also created unintended human health and environmental pollution challenges for the twentyfirst century. Averaged globally, about half of the fertilizer-N applied to farms is removed with the crops, while the other half remains in the soil or is lost from farmers’ fields, resulting in water and air pollution. As human population continues to grow and food security improves in the developing world, the dual development goals of producing more nutritious food with low pollution will require both technological and socioeconomic innovations in agriculture. Two case studies presented here, one in sub-Saharan Africa and the other in Midwestern United States, demonstrate how management of nutrients, water, and energy is inextricably linked in both small-scale and large-scale food production, and that science-based solutions to improve the efficiency of nutrient use can optimize food production while minimizing pollution. To achieve the needed large increases in nutrient use efficiency, however, technological developments must be accompanied by policies that recognize the complex economic and social factors affecting farmer decision-making and national policy priorities. Farmers need access to affordable nutrient supplies and support information, and the costs of improving efficiencies and avoiding pollution may need to be shared by society through innovative policies. Success will require interdisciplinary partnerships across public and private sectors, including farmers, private sector crop advisors, commodity supply chains, government agencies, university research and extension, and consumers

Ecological Approaches to Human Nutrition

Objective. To describe the role that ecological knowledge plays in alleviating hidden hunger, considering human nutrition as an overlooked ecosystem service. Methods. We review existing literature and propose a framework that expands on earlier work on econutrition. We provide novel evidence from case studies conducted by the authors in western Kenya and propose a framework for interdisciplinary collaboration to alleviate hidden hunger, increase agricultural productivity, and improve environmental sustainability. Results. Our review supports the concept that an integrated approach will impact human nutrition. We provide evidence that increased functional agrobiodiversity can alleviate anemia, and interventions that contribute to environmental sustainability can have both direct and indirect effects on human health and nutritional well-being. Conclusions. Integrated and interdisciplinary approaches are critical to reaching development goals. Ecologists must begin to consider not only how their fiel

Farm management, not soil microbial diversity, controls nutrient loss from smallholder tropical agriculture

© The Author(s), 2015. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Frontiers in Microbiology 6 (2015): 90, doi:10.3389/fmicb.2015.00090.Tropical smallholder agriculture is undergoing rapid transformation in nutrient cycling pathways as international development efforts strongly promote greater use of mineral fertilizers to increase crop yields. These changes in nutrient availability may alter the composition of microbial communities with consequences for rates of biogeochemical processes that control nutrient losses to the environment. Ecological theory suggests that altered microbial diversity will strongly influence processes performed by relatively few microbial taxa, such as denitrification and hence nitrogen losses as nitrous oxide, a powerful greenhouse gas. Whether this theory helps predict nutrient losses from agriculture depends on the relative effects of microbial community change and increased nutrient availability on ecosystem processes. We find that mineral and organic nutrient addition to smallholder farms in Kenya alters the taxonomic and functional diversity of soil microbes. However, we find that the direct effects of farm management on both denitrification and carbon mineralization are greater than indirect effects through changes in the taxonomic and functional diversity of microbial communities. Changes in functional diversity are strongly coupled to changes in specific functional genes involved in denitrification, suggesting that it is the expression, rather than abundance, of key functional genes that can serve as an indicator of ecosystem process rates. Our results thus suggest that widely used broad summary statistics of microbial diversity based on DNA may be inappropriate for linking microbial communities to ecosystem processes in certain applied settings. Our results also raise doubts about the relative control of microbial composition compared to direct effects of management on nutrient losses in applied settings such as tropical agriculture.SAW, MA, CN, and CAP were supported by NSF PIRE grant OISE-0968211. GeoChip analysis was supported by the Office of the Vice President for Research at the University of Oklahoma and NSF MacroSystems Biology program EF-1065844 to JZ

Socioecologically informed use of remote sensing data to predict rural household poverty

Tracking the progress of the Sustainable Development Goals (SDGs) and targeting interventions requires frequent, up-to-date data on social, economic, and ecosystem conditions. Monitoring socioeconomic targets using household survey data would require census enumeration combined with annual sample surveys on consumption and socioeconomic trends. Such surveys could cost up to $253 billion globally during the lifetime of the SDGs, almost double the global development assistance budget for 2013. We examine the role that satellite data could have in monitoring progress toward reducing poverty in rural areas by asking two questions: (i) Can household wealth be predicted from satellite data? (ii) Can a socioecologically informed multilevel treatment of the satellite data increase the ability to explain variance in household wealth? We found that satellite data explained up to 62% of the variation in household level wealth in a rural area of western Kenya when using a multilevel approach. This was a 10% increase compared with previously used single-level methods, which do not consider details of spatial landscape use. The size of buildings within a family compound (homestead), amount of bare agricultural land surrounding a homestead, amount of bare ground inside the homestead, and the length of growing season were important predictor variables. Our results show that a multilevel approach linking satellite and household data allows improved mapping of homestead characteristics, local land uses, and agricultural productivity, illustrating that satellite data can support the data revolution required for monitoring SDGs, especially those related to poverty and leaving no one behind.</p