Plant-available nitrogen in the soil: Relationships between pre-plant and pre-sidedress nitrate tests for corn production
2008
Ma, Bao-Luo | Wu, Tian-Yun
Corn (Zea mays L.) producers in the rainfed regions sometimes sidedress fertilizer N according to pre-plant-nitrate test (PPNT) results based on the assumption that there is a linear relationship between pre-sidedress nitrate test (PSNT) and the PPNT. There has been no report on such relationship in Ontario (Canada) and elsewhere in the nonirrigated corn-growing regions. A field study was conducted near Ottawa, Canada for 7 y to (1) determine changes in soil available N from pre-planting to shortly after the sidedress stage (late June) for corn and (2) establish a quantitative relationship between PPNT and PSNT. In each year, soil samples from fields of three to four plot experiments with different cropping histories, soil textures, and management levels, taken at 7 to 10 d intervals, and from on-farm trials taken at pre-planting and pre-sidedress, were extracted with 2 M KCl. The concentrations of NO$ _3^- $-N were determined colorimetrically. It was found that soil NO$ _3^- $-N concentration of PSNT was a linear function of PPNT with an average slope of 1.7. However, the slope of the regression equations differed dramatically among cropping sequences, and to a lesser extent, soil textures. The NO$ _3^- $-N concentration after planting to pre-sidedress was influenced by air temperature and precipitation during this period of time. Both PPNT and PSNT positively correlated with corn-grain yield. Our data suggest that cautions must be taken when deciding the rate of fertilizer N for sidedress application to corn based on PPNT test, especially under more humid northern climate conditions.
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