Factors affecting microbial formation of nitrate-nitrogen in soil and their effects on fertilizer nitrogen use efficiency.
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 microg 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 >10%. Predicting mineralization in this manner allows optimal N applications to be determined for site-specific soil and weather conditions.
Olness
A
A
USADA-ARS-MWA, N. Central Soil Conservation REs. Lab, Morris, MN 56267, USA. Olness@morris.ars.usda.gov
Lopez
D
D
Archer
D
D
Cordes
J
J
Sweeney
C
C
Mattson
N
N
Rinke
J
J
Voorhees
W B
WB
D000383:Agriculture / Q000379:methods*; D001419:Bacteria / Q000378:metabolism; D002622:Chemistry, Agricultural; D005308:Fertilizers / Q000706:statistics & numerical data*; D006863:Hydrogen-Ion Concentration; D008910:Minnesota; D008962:Models, Theoretical; D009566:Nitrates / Q000737:chemistry / Q000378:metabolism*; D011237:Predictive Value of Tests; D015203:Reproducibility of Results; D012621:Seasons; D012987:Soil / Q000032:analysis; D012988:Soil Microbiology; D003313:Zea mays / Q000378:metabolism
D005308:Fertilizers; D009566:Nitrates; D012987:Soil