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, mag improve NUE while reducing soil N losses. A two-par study was conducted in an ongoing five-gear held experiment (1992-1996) on a Brandon loam soil (fine-loamy, mired, mesic Typic Endoaquoll) (Orthic Humic Gleysol) at the Central Experimental Farm, Ottawa, ON, Canada (45 degrees 23' N, 75 degrees 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 (NH4+ plus NO3-) of approximate to 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 mineral ized 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 preplanting that reached a plateau at approximate to 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.