Sustainability indices from nutrient budgets of agro-ecosystems

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Classical measures of nutrient use efficiency at plant and plot scales based on yield, nutrient concentration, ratios, nutrient uptake, nutrient additions and nutrient budgets are distorted by spurious correlations and redundant information by not accounting for high-level interactions. A holistic approach arranged into balances can correct such distortions using the principle of orthogonality between subsets of components. Nutrient sustainability indices (NSI) are then computed as distances from reference compositions using tissue nutrient analyses at plant scale and nutrient budgets at plot scale. Nutrient use efficiency sustaining agroecosystem productivity could be synthesized thereafter into indices to facilitate making sound decisions and improve nutrient management practices. At plant scale, reference copmpositions are those of nutrients interacting at high-yield level using a Québec data set. At plot scale, long-term experiments are required to account for residual effects of cropping systems. Using isometric log ratios or orthonormal balances illustrated by a mobile with balances diagnosed at fulcrums and components appreciated in buckets, NSIs can be computed as multivariate distances from reference compositions. Our objective is to monitor the departure of agroecosystems from reference compositions at plant and plot scales. Foliar nutrients are diagnosed by calibrating the degree of nutrient imbalance in fertilizer trials and the long-term experiment. The long-term experiment established in 2008 allows monitoring the effect of maize (M)-soybean (S)-wheat (W) sequences and continuous forage (MMM, MSM, MSWFFF, FFF) on crop yield and soil quality started with M) or F. The setup also comprises two soil tillage methods (no-till and conventional), two types of residue management (residues left on soil or removed) and two fertilization regimes (mineral or organic based on local recommendations; control without fertilization), replicated 4 times (156 plots). Soils sampled initially at 5, 10, 20, 40, 60 and 100 cm were resampled in 2013 and 2015, and biomass and grain samples collected annually for nutrient budgeting. Soil quality metadata are aggregation and compactness indices, hydraulic conductivity, pH, and resistance to penetration, soil available nutrients. This novel management tool will allow decision makers and stake holders look holistically at nutrient management strategies ("what is measured can be managed wisely"), avoiding the usual hard-to-interpret holistically radial diagrams across myriads of ratios and individual components. These models will support the development of expert systems at local scale and fertilization strategies behind the 4R approach of the Canadian fertilizer industry (right rate, source, time, place). Four graduate students (M.Sc., Ph.D.) will frame novel systems of interpretable balances from design to innovation.