Abstract
Efficient use of nutrients is a key requisite for a sustainable intensification of agriculture in order to meet the increasing global crop demand while minimizing deleterious environmental impacts. Agroforestry systems exhibit tree–crop interactions, which potentially contribute to nutrient-efficient agro-ecosystems. Our goal was to determine whether the conversion from cropland monocultures to alley-cropping agroforestry increases nutrient response efficiency (NRE), the ability of plants to convert available nutrients into biomass. We found that crop yield, plant-available nutrients and NRE were comparable between agroforestry and monocultures, but the trees in agroforestry had high NRE, contributing to nutrient retention of the agroforestry systems as a whole. The unimodal relationship of the crops’ NRE with plant-available nutrients suggests that NRE values were beyond optimum in both agroforestry and monoculture indicating nutrient saturation. This indicates that fertilizer inputs can be reduced (or optimized) without sacrificing crop yield or profit. Based on the NRE curves, we assessed that a reduction of plant-available N by 50% would lead to a decrease in crop yield by 17% and a concomitant increase in N response efficiency by 67%, whereas a similar reduction of plant-available P would lead to a decrease in crop yield by 8% with an increase in P response efficiency by 83%. An optimized fertilization to achieve such lower levels of plant-available nutrients will have beneficial effects on nutrient retention and redistribution. Optimizing fertilizer input will make alley-cropping agroforestry a productive and profitable agro-ecosystem that contributes to an ecologically sustainable agriculture.
Highlights
Global food production has increased in the past decades, following the demands of a growing world population (Food and Agriculture Organization of the United Nations 2015)
As the nutrient response efficiency (NRE) did not differ between crops in monoculture and in agroforestry systems (Table 4), we present one combined curve for both systems
These comparable NREs of crops in the two systems were a result of the similar grain yields between agroforestry crop row and monoculture treatments as well as their analogous soil nutrient availability, described above
Summary
Global food production has increased in the past decades, following the demands of a growing world population (Food and Agriculture Organization of the United Nations 2015). To meet the increasing global crop demand while minimizing environmental impacts, efficient use of nutrients is a key consideration, i.e. by maintaining or increasing yields on existing croplands while substantially lowering the use of fertilizers (Tilman et al 2002, 2011; Foley et al 2011). Improving the efficiency with which nutrients are converted into crop yield requires evaluation criteria of land-use systems that go beyond the traditional dose–response curves of fertilizer-yield relationships (Cerrato and Blackmer 1990). Maximizing productivity through chronic large fertilizer applications potentially leads to nutrient saturation and low NRE (e.g. Keuter et al 2013) which, in turn, can decrease nutrient retention in biomass and in the soil, and increase nutrient losses and their negative environmental impacts (e.g. Hoeft et al 2014)
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