Effect of plant material parameters on nitrogen mineralization in a mollisol

Abstract

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 2 mm at rates of 0, 2, 4, and 6%. The soils were incubated at 35°C for 20 weeks. The inorganic N in soils was removed by leaching with 100 mL 0.001M CaCl₂ in 5‐ to 10‐mL intervals followed by 25 mL of a nutrient solution devoid of N (0.002M CaSO₄; 0.002M MgSC>₄; 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 but also accelerated N mineralization in soil by increasing the N mineralization rate constant 75%.