2006/11/01 by Frédérique Duguet, Léon Etienne Parent, Léon Étienne Parent +2 · 1 citation
Agricultural and Biological Sciences · Environmental Science · #Soil Carbon and Nitrogen Dynamics #Soil and Water Nutrient Dynamics #Phosphorus and nutrient management
paper · doi:10.1097/01.ss.0000235233.47804.e6
Organic soils may mineralize large amounts of organic N annually. Total N, C/N ratio, and the light fraction (LF) of soil organic matter are common indices of net nitrification and N uptake by plants. Compositional analysis of C, N, and a filling value (R2) to unity as soil components requires computation of log-transformed multiratio (component concentration divided by geometric mean of components), standardization using log-ratio mean and standard deviation in high N mineralizing soils, and integration as χ32 variable. The objective of this article was to relate the χ32 value and LF to net nitrification and plant response to added N in organic soils. An independent subpopulation of 18 organic soils producing more than 1 kg mineral N ha−1 day−1 was obtained from the literature to compute compositional (C, N, R2) norms. Thirty-four organic soil materials showing wide variation in total N and soil organic matter were incubated for 240 days in the laboratory. Ryegrass was grown in the greenhouse using six soils of contrasting (C, N, R2) composition. Four vegetables (carrots, potatoes, celery, and onions) were also grown in commercial fields at 34 sites for testing the power of their response to added N. Organic soils showed zero-order kinetics and released −0.16 to 1.91 mg NO3-N kg−1 day−1. Using a Cate-Nelson partitioning technique, the critical χ32 value was found to be 10.8 for the incubation experiment. Within both χ32 groups, nitrification rate was higher when N content in LF increased. The greenhouse study showed a soil critical χ32 value between 6 and 12. In field experiments, crops grown in organic soils with χ32 values <5.9 showed little or no response probability to added N. The soil χ32 value could become a useful fertility index for N recommendations in organic soils.