Soil Nitrogen Amendment Effects on Seasonal Nitrogen Mineralization and Nitrogen Cycling in Maize Production

Nitrogen use efficiency (NUE) is a measure of the extent to which a crop transforms available N to economic yield. Seasonal N mineralization of organic amendments increases available N and, depending on the timing of mineralization and crop requirements for N, may improve NUE while reducing soil N losses. A two‐year study was conducted in an ongoing five‐year field experiment (1992–1996) on a Brandon loam soil (fine‐loamy, mixed, mesic Typic Endoaquoll) (Orthic Humic Gleysol) at the Central Experimental Farm, Ottawa, ON, Canada (45°23′ N, 75°43′ W). Our objectives were to (i) quantify the effects of inorganic N fertilizer, stockpiled (SM), and rotted manure (RM) application on seasonal N mineralization and (ii) monitor the mineral N balance in the soil–plant system. Application of manure at the highest rate having a mineral N (NH + 4 plus NO − 3 ) of ≈100 kg N ha −1 and up to 800 kg N ha −1 of total N resulted in up to 120 kg ha −1 of net N mineralized. The potential loss of this mineralized N was minimized during the growing season compared with inorganic fertilizer application because of the synchronization of soil N release and uptake by maize ( Zea mays L.). In soil receiving 200 kg inorganic N ha −1 , the amount of net N mineralized over the season was between 130 and 170 kg ha −1 , but large losses of mineral N from the rooting zone occurred during the same period. The amount of net N mineralized over the season accounted for up to half of the plant N uptake in all treatments; for example, the amount of net N mineralized in manured soils represented about 30 to 60% of total plant N. It appears that a priming effect on soil mineral N occurred in all treatments during the vegetative period. This resulted in a curvilinear relationship between net N mineralization rate and soil mineral N levels at pre‐planting that reached a plateau at ≈140 kg N ha −1 . The rate of N mineralization during the grain‐filling period was approximately the same at both levels of inorganic N fertilizer, but was, on average, three times higher under manure treatments. Compared with N mineralization under the 200 kg N ha −1 fertilizer treatment, all manure treatments resulted in higher rates of net N mineralization during the grain‐filling period.