Management of organic resources for soil fertility improvement in low-input cropping systems

Kwabiah, Allan B.
Journal Title
Journal ISSN
Volume Title
University of Guelph

Plant litters are the prime source of energy and nutrients affecting soil biological, chemical and physical processes, including soil organic matter (SOM) formation. Due to cost and other socioeconomic constraints to the use of inorganic fertilizers in low input systems in the tropics, litter-derived nutrients are considered as sustainable alternatives to the use of inorganic fertilizers. In a laboratory incubation study using 18 litter materials, the relationships between litter quality (defined in terms of the concentration of total carbon (C), nitrogen (N), phosphorus (P), lignin (LIG), polyphenol (Pp), and their ratios) and litter decay, and release of N and P were explored. Initial release of residue P was more rapid than at later stages of laboratory incubation. This was attributed to leaching of the water soluble P content of the litter. In the longer term (>28 days), changes in microbial biomass N and P during incubation illustrated its capacity to act as a major source-sink of energy and mineral N and P in the transformation of organic matter. Under laboratory conditions, litter P explained between 42 to 69 percent ('p' < 0.001) of the variation in resin-P and also correlated with net mineral N (r = 0.59 to 0.70; 'p' < 0.001). Net mineral N released correlated with litter N (r = 0.70 to 0.93; 'p' < 0.001) and C/N ratio (r = -0.75 to -0.94; 'p' < 0.001). The critical level of quality parameters, defined as the level which separates N or P releasing from immobilizing litter were time-dependent. The single exponential function (Yt = Y0*e -kt) best fitted the data on percent of initial litter mass, N and P that remained during the decomposition of six plant species under field conditions. The decay rate constants ('k') of loss of litter mass, and release of N and P strongly correlated with litter P (r = 0.90 to 0.96; 'p' < 0.01). On-farm studies examined the effects of P inputs from litter and inorganic fertilizer sources on P availability and maize grain yield (MY) in the highlands of western Kenya. (Abstract shortened by UMI.)

organic resources, soil fertility improvement, low-input cropping systems, phosphorus, P availability, maize grain yield, Kenya