Evaluation of sulfur mineralization potential of meadow soils and availability to alfalfa

Abstract

With the reduction in S inputs through atmospheric deposition and high analyses fertilizers, soil organic S will become a more important source of S to crops. Sulfur mineralization in 20 meadow soils was investigated using a long-term aerobic incubation and a greenhouse bioassay with alfalfa (Medicago sativa L.). The cumulative S mineralization (Sm) was linear with time for 13 soils whereas 7 soils showed an exponential phase over the first 10 wk followed by a linear release phase. Podzolic soils dominated the latter group. The data were described by an incremental zero-order model where an initial flush was accounted for. The total amount of mineralizable S (Sm), the amount of S mineralized in the first 1.4 wk (Se), the S mineralization potential (So) and the rate constant (k) were all very closely correlated to the N mineralization potential and to the amount of N mineralized in the first 1.4 wk of incubation (r = 0.64–0.85; P < 0.01). The S mineralization parameters were not significantly correlated to soil pH, total C, N, and S, C:S and N:S ratios and extractable P content. The Se and So mineralization parameters were significantly correlated to the soil sand content (r = 0.51 and 0.53; P < 0.05) suggesting the possible involvement of particulate organic matter as a pool of mineralizable S. Alfalfa yield response to S addition was observed only on seven soils with lowest cumulative S. Total S uptake of alfalfa represented, on average, 10% of Sm and was strongly correlated to Sm (r = 0.81**) and k (r = 0.78**). The effect of S fertilizer on plant S uptake was observed only for the third cut (P < 0.01), this being probably due to mineralizable S depletion in soils. The results of this study suggest that the initial potential of N mineralization is a good indicator of Sm and that a short term incubation could measure the S supplying power of Québec soils. Key words: S uptake, organic C, nitrogen and sulfur, texture, incremental zero-order equation