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Measurement of recovery of fertilizer N and soil mineral N by maize must be improved in the western semiarid tropics for maximizing crop yield and reducing environmental pollution. The relevant variables for characterizing this N use are the N uptake by the plant from the applied fertilizer (NdfF) and that from the soil (NdfS). The direct measurement of these two variables requires the use of 15N labeled fertilizer, a difficult and expensive technique. It would therefore be useful to have sensitive indicators for these variables. This study was conducted to measure the variability in the N use from soils. The experiments were carried out with maize at 24 sites in a 3000 ha area of village land with Luvisols located in the central zone of Burkina Faso. Each site had two treatments with two replicates: 0 and 80 kg N ha−1 applied as urea labeled with 15N. Statistical analysis of the results identified three groups of fields differing in soil fertility, each corresponding to a certain distance from the farmstead, and provided a relationship between the variables NdfF, NdfS, and easily measured indicators. The most pertinent indicators (r2>0.9) were: (a) for NdfS, the total N in plant without fertilizer (Nplt0) and the apparent crop recovery of N fertilizer (ACR %), and (b) for Nplt0, Nav (available N) as measured by the Waring Bremner test, exchangeable K, and (c) the clay content. The coefficients of determination improved when the regressions were calculated for each soil fertility group. These results have two important applications: (a) the possibility of estimating easily the part of N taken up by maize that comes, respectively, from the soil and the fertilizer; and (b) the identification of two factors limiting soil fertility, that is, the mineral N and exchangeable K+ content of the soil before cropping.
Institut de l'Environnement et de Recherches Agricoles (INERA), Saria, Burkina Faso 2:
CIRAD, Laboratoire Matières Organiques des Sols Tropicaux (MOST), Montpellier, France 3:
Centre National de la Recherche Scientifique et Technologique (CNRST), Ouagadougon, Burkina Faso