Biodisponibilité de l'azote et du phosphore dans les sols de bleuetières du Québec

Abstract

A better understanding of nitrogen (N) and phosphorus (P) bioavailability in blueberry soils is essential to establish fertilizer recommendations. The objectives of this study were: (i) to evaluate different methods to determine soil ammonium and phosphorus bioavailability to the crop, (ii) to determine the best N and P bio-indicator for blueberry fruit yields and nutrient leave concentrations, and (iii) to establish soil fertility classes. The treatments consisted of four N rates (0, 30, 60 and 90 kg N ha-1) and four P rates (0, 30, 60 and 90 kg P2O5 ha-1). Ammonium in soil was extracted with KCl (N-NH4KCl) and water (N-NH4W) and also determined using cation exchange membrane (N-NH4MEC).The soil phosphorus was extracted with Mehlich 3 (PM3) and water (PW) and using anion exchange membrane (PMEA). Soil N and P concentrations decreased during the season with an accumulation of available soil P in the soil surface layer. Soluble fractions of soil N (N-NH4W and N-NH4MEC) were significantly correlated with leaf N concentration (0.28BrB 0.78) and fruit yields (0.38BrB0.48). The bioavailable P fraction (PM3) was significantly correlated with leaf P concentration (r=0.30) and fruit yield (r=0.36). Soil water extractable ammonium and PM3 are the best indicators of the availability of soil N and P to blueberry crops. From these indicators, critical values beyond which fertilization is no longer required were established at 3.1 mg kg-1 for the N-NH4W, 52 mg kg-1 for PM3 and 0.028 for the molar ratio PM3/(Fe+Al)M3.