EFFECT OF PLANT-MATERIAL PARAMETERS ON NITROGEN MINERALIZATION IN A MOLLISOL

The introduction of plant materials into a soil can impact the nitrogen (N) status and the fertilizer requirement for agronomic crop production. Consequently, an accurate estimate of N mineralization from soil organic matter and incorporated plant material is necessary to adequately make a N fertilizer recommendation. The purpose of this study was to evaluate the effect of plant parameters including type, size, incorporation rate, and time after incorporation on N mineralization and to derive localized values for parameters in a widely used potential N mineralization model. Soil from the Ap horizon of a Latahco silt loam was amended with alfalfa (Medicago saliva L.), spring pea (Pisum sativum L.), and winter wheat (Triticum aestivum L.) plant materials sized to either <1, 1 to 2, or > 2 mm at rates of 0, 2, 4, and 6%. The soils were incubated at 35 degrees C for 20 weeks. The inorganic N in soils was removed by leaching with 100 mt 0.001M CaCl2 in 5- to 10-mt intervals followed by 25 mt of a nutrient solution devoid of N (0.002M CaSO4; 0.002M MgSO4; 0.005M Ca(H2PO4)2; and 0.0025M K2SO4) at 0, 2,4, 6, 8, 12, 16, and 20 weeks. The main effects of plant material type (PM), size (S), incorporation rate (R), and incubation time (T) and many 2-, 3-, and 4-factor interactions on N mineralization were statistically significant at P=0.05. Based on w(2), incubation time (T), and incorporation rate (R) were the two most important factors affecting N mineralization. The amount of N mineralized increased exponentially with increasing time and linearly with the incorporation rate. In addition, the incorporation of plant material not only increased potentially mineralizable N by as much as 5.1 times bur also accelerated N mineralization in soil by increasing the N mineralization rate constant 75%.