Evaluation of some indices of potentially mineralizable nitrogen in soil

TLDR: In this paper, a series of soil N mineralization indices were evaluated using 153 samples chosen from arable fields representing a wide range of soil types, management practices, and climatic zones.

Abstract: A series of soil N mineralization indices were evaluated using 153 samples chosen from arable fields representing a wide range of soil types, management practices, and climatic zones. These indices were compared against potentially mineralizable N (No) determined by aerobic incubation at 25°C for 24 wk. Three different pools of mineralizable N were recognized: Pool I, the mineralization flush on rewetting in the first 2 wk; Pool II, gross N mineralization in the next 22 wk; and Pool III, the potentially mineralizable N, predicted from the fitted curve, that did not mineralize during the incubation period. Pool I was highly correlated with CaCl 2 -N, KCI-NH 4 , and KCl-NO 3 , which extract soil mineral N. Pool III was significantly correlated with ultraviolet absorbance of NaHCO 3 extract at 205 and 260 nm (NaHCO 3 -205 and -260), Illinois soil N test, NaOH direct-distillation N, and hot KCl-NH 4 , which mostly extract hydrolyzable organic N. All indices except the mineral N based methods, phosphate-borate buffer method, and microbial biomass C were significantly related to N 0 , which includes both Pools II and III. The NaHCO 3 -260, NaOH direct-distillation N, and Illinois soil N test had the highest correlations with No (r2 = 0.74, 0.61, and 0. 51, respectively). Total organic C and N represent long-term changes in N 0 and were almost as effective in predicting N 0 as the other indices (r 2 = 0.60 and 0.67, respectively); however, they would be expected to be less sensitive to short-term changes in N 0 due to changes in soil management practices and history.