Long term impact of tillage practices and biennial P and N fertilization on maize and soybean yields and soil P status
Résumé
The benefits of no till (NT) management in the short to medium terms need to be examined over decades ofcontinuous cropping. Our objectives were to (i) assess the long term effects of tillage practices (no-till (NT)and mouldboard plough [MP]) and biennial P × N fertilizer rates applied to the maize phase of a two-yearmaize–soybean rotation on grain yield, Mehlich-3 P (PM3), and Olsen P (POl), and (ii) determine whetherNT practice affects the relationships between PM3, POl and P budgets. The study site was established in1992 on a clay loam soil of the St-Blaise series (Dark Grey Gleysol). The experimental design is a splitplot with NT and MP assigned to main plots and nine combinations of 3 P (0, 17.5, and 35 kg P ha−1) and3 N (0, 80, and 160 kg N ha−1) additions assigned to subplots. Maize and soybean grain yield response toP additions was obtained only twice between 1992 and 2010. On average, grain yields were reduced by10–25% in NT compared to MP treatments in 11 years. The dynamics over years of PM3 and POl (0–15 cm)in unfertilized P treatment was similar in NT and MP. In contrast, P fertilized NT maintained greaterPM3 and POl than MP. This difference in soil tests P was due to greater P accumulation in the 0–5 cmand 5–10 cm soil layers of NT. Under MP, soil tests P and P budgets over the P treatments were linearlyrelated and for this specific MP treatment, we calculated that a P budget of ±100 kg P ha−1 would changePM3 by 12 kg ha−1 and POl by 7 kg ha−1. Under NT, a cubic model fitted closely to the experimental datadue principally to a more than proportional change in soil tests P relative to P budgets in fertilized Ptreatments. We conclude that additions of P fertilizer in NT systems changes the dynamics of P in therooting zone, suggesting the importance of approaches to monitor P dynamics specifically tailored for NTsystems that integrates the variability caused by the absence of mixing the fertilizer, residues, and soil.