Submitted to: International Nitrogen Conference
Publication Type: Proceedings
Publication Acceptance Date: 10/15/2001
Publication Date: 11/1/2001
Citation: OLNESS, A.E., LOPEZ, D., ARCHER, D.W., CORDES, J., SWEENEY, C., MATTSON, N., RINKE, J.L., VOORHEES, W.B. FACTORS AFFECTING MICROBIAL FORMATION OF NITRATE-NITROGEN IN SOIL AND THEIR EFFECT ON FERTILIZER NITROGEN USE EFFICIENCY. THESCIENTIFICWORLD. 2001. V. 1(S2). P. 122-129. Interpretive Summary: On average, only about half of the N applied as fertilizer is found in the crop at harvest. The remainder of the applied N is leached to groundwater or lost back to the air as a gas. The value of the N lost each year is about $1.5 to $2 billion. Part of this loss is due to the fact that soil microbes produce nitrate-N from soil organic matter each year. The amount of microbially produced N depends on several factors. These are 1) soil temperature, 2) soil clay content, 3) soil pH, 4) soil bulk density, 5) spring rainfall, and 6) spring temperatures. The amount of microbially produced N can be predicted by these factors. By subtracting the predicted amount of microbially produced N and the amount of nitrate-N present at planting from the amount of N needed by the crop, we can estimate the amount of fertilizer N that needs to be added to get the best yields. The N fertilizer decision aid can be used by farmers, crop consultants, and scientists to improve N fertilizer use efficiency by greater than 10%.
Technical Abstract: Mineralization of soil organic matter is governed by predictable factors with nitrate-N as the end product. Crop production interrupts the natural balance, accelerates mineralization of N, and elevates levels of nitrate-N in soil. Six factors determine nitrate-N levels in soils. These are: soil- clay content, bulk density, organic matter content, pH, temperature and rainfall. Maximal rates of N mineralization require an optimal level of ai filled pore space. Optimal air filled pore space depends on soil-clay content, soil organic matter content, soil bulk density and rainfall. Pore space is partitioned into water-filled and air space. A maximal rate of nitrate formation occurs at a pH of 6.7 and rather modest mineralization rates at pH 5.0 and pH 8.0. Predictions of the soil nitrate-N concentrations with a relative precision of 1 to 4 ug N g**-1 of soil were obtained with a computerized N-fertilizer decision aid. Grain yields obtained using the N-fertilizer decision aid were not measurably different from those using adjacent farmer practices but N fertilizer use was reduced by greater than 10%. Predicting mineralization in this manner allows optimal N applications to be determined for site-specific soil and weather conditions.