Long term impact of tillage practices and biennial P and N fertilization on maize and soybean yields and soil P status

The benefits of no till (NT) management in the short to medium terms need to be examined over decades of continuous cropping. Our objectives were to (i) assess the long term effects of tillage practices (no-till (NT) and mouldboard plough [MP]) and biennial P x N fertilizer rates applied to the maize phase of a two-year maize-soybean rotation on grain yield, Mehlich-3 P (P-M3), and Olsen P (P-Ol), and (ii) determine whether NT practice affects the relationships between P-M3, P-Ol and P budgets. The study site was established in 1992 on a clay loam soil of the St-Blaise series (Dark Grey Gleysol). The experimental design is a split plot with NT and MP assigned to main plots and nine combinations of 3 P (0, 17.5, and 35 kg P ha(-1)) and 3 N (0, 80, and 160 kg N ha(-1)) additions assigned to subplots. Maize and soybean grain yield response to P additions was obtained only twice between 1992 and 2010. On average, grain yields were reduced by 10-25% in NT compared to MP treatments in 11 years. The dynamics over years of P-M3 and P-Ol (0-15 cm) in unfertilized P treatment was similar in NT and MP. In contrast, P fertilized NT maintained greater P-M3 and P-Ol than MP. This difference in soil tests P was due to greater P accumulation in the 0-5 cm and 5-10 cm soil layers of NT. Under MP, soil tests P and P budgets over the P treatments were linearly related and for this specific MP treatment, we calculated that a P budget of +/- 100 kg P ha(-1) would change P-M3 by 12 kg ha(-1) and P-Ol by 7 kg ha(-1). Under NT, a cubic model fitted closely to the experimental data due principally to a more than proportional change in soil tests P relative to P budgets in fertilized P treatments. We conclude that additions of P fertilizer in NT systems changes the dynamics of P in the rooting zone, suggesting the importance of approaches to monitor P dynamics specifically tailored for NT systems that integrates the variability caused by the absence of mixing the fertilizer, residues, and soil. Crown Copyright (C) 2012 Published by Elsevier B.V. All rights reserved.