Factors Affecting Microbial Formation of Nitrate-Nitrogen in Soil and Their Effects on Fertilizer Nitrogen Use Efficiency

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: soil clay content, bulk density, organic matter content, pH, temperature, and rainfall. Maximal rates of N mineralization require an optimal level of air-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- and air-filled space. A maximal rate of nitrate formation occurs at a pH of 6.7 and rather modest mineralization rates occur at pH 5.0 and 8.0. Predictions of the soil nitrate-N concentrations with a relative precision of 1 to 4 μg N g 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 >10%. Predicting mineralization in this manner allows optimal N applications to be determined for site-specific soil and weather conditions.

Predicting Nitrogen Availability in Irrigated Potato Systems

“…Mineralization is infl uenced by the type of tillage used, the source and quality of organic residues present, and inorganic fertilization strategies. Infl uential bio-physical environmental factors include soil organic matter, temperature, pH, soil moisture, soil texture (which infl uences aeration and diffusion of substrate for soil microorganisms) and soil community ecology (Olness et al, 2001). There are excellent reviews of the N transformation processes involved that can be consulted for in-depth discussion (Cassman et al, 2002;Jansson and Persson, 1982).…”

“…Efforts to predict N supply from soil include models based on mathematical functions that describe observed interaction of soil organic matter, aeration and soil texture (Olness et al, 2001) and temperature-based models (Griffi n and Honeycutt, 2000;Honeycutt and Potaro, 1990). Simulation models that predict N release generally incorporate two or more organic matter pools with different decay constants.…”

“…Controlled environment studies have shown excellent predictive capacity, where water fi lled pore space has been shown to be closely related to microbial respiration rate and nitrate formation, or thermal units used to accurately predict N mineralization from a range of organic sources (Griffi n and Honeycutt, 2000;Henricksen and Breland, 1999). The application of models to predict nitrate formation in the fi eld environment has had more variable success (Linn and Doran, 1984;Olness et al, 2001;Paz et al, 1999).…”

Simulation of Soil Temperature Dynamics with Models Using Different Concepts

“…Soil temperature ( T soil ) is one of the most important variables of the soil. It can significantly influence seed germination [ 1 ], plant growth [ 2 ], uptake of nutrients [ 3 ], soil respiration [ 4 , 5 ], soil evaporation [ 6 ], and the intensity of physical [ 7 ], chemical [ 8 , 9 ], and microbiological processes [ 10 , 11 ] in the soil.…”

Can reducing tillage and increasing crop diversity benefit grain and forage production?

“…Starter fertilizer was used for all corn plantings, and for all soybean plantings through 2005. In CT-2y corn, a side dress of ammonium nitrate (2002–2005) or anhydrous ammonia (2006–2009) was applied in early June at rates generated by the Nitrogen Decision Aid (Olness et al, 1999) using pre-plant soil tests; CT-4y corn received a single side-dress application of ammonium nitrate in 2002 (Table 2). Every year, wheat received a fertilizer application at planting that supplied N, P and K. Alfalfa did not receive additional fertilizer applications.…”