Are soil mineralizable nitrogen pools replenished during the growing season in agricultural soils?

Dessureault-Rompré, J., Zebarth, B.J., Burton, D.L., Gregorich, E.G., Goyer, C., Georgallas, A., and Grant, C.A. (2013). "Are soil mineralizable nitrogen pools replenished during the growing season in agricultural soils?", Soil Science Society of America Journal, 77(2), pp. 512-524. doi : 10.2136/sssaj2012.0328  Access to full text

Abstract

Seasonal changes in both environmental conditions and substrate quality and quantity determine the soil N supply to plants. The objective of this study was to evaluate seasonal changes in the quantity and quality of soil mineral N (SMN) and mineralizable N pools under a growing potato (Solanum tuberosum L.) crop that was preceded by three crop species (barley [Hordeum vulgare L.], Italian ryegrass [Lolium multiflorum Lam.], and red clover [Trifolium pratense L.]) that might be expected to affect soil N supply. Seasonal changes were small and expressed mainly through changes in SMN and Pool I, a labile mineralizable N pool, which decreased significantly from May to August and then subsequently increased in October. In comparison, potentially mineralizable N (N0) did not change during the growing season. The depth distribution of mineralizable N pools was also studied, and these were similar in size for the 0- to 15- and 15- to 30-cm layers but decreased for 30 to 45 cm. The estimated depletion of SMN and Pool I for the 0- to 30-cm layer from May to August was less than the supply of N to the potato crop, estimated as plant N uptake (N accumulation in tubers plus vines in late August). This suggests that mineralizable N pools are actively replenished during the growing season, which contradicts the use of a first-order equation in field prediction studies that assume N0 is depleted with time. These results highlight the need for better understanding of what controls the size and kinetics of the mineralizable N pools to accurately predict N mineralization during the growing season.

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