ABSTRACT
The litter decomposition and nutrient release pattern of two dominant weeds in a shifting cultivation system were studied. The foliage and root litter of Ageratum conyzoides L. and Spilanthes paniculata Wall. ex DC. showed a biphasic weight loss pattern with a peak during the initial 60 d of incubation. The decay rate coefficient ('k') for foliage and root residues of Ageratum conyzoides (6.57 and 2.92) was lower than that of Spilanthes paniculata, which registered little difference between root (7.30) and foliage (7.67) residues. Release of nitrogen (N), phosphorus (P) and potassium (K) also followed a biphasic pattern and their release rate coefficients ranged from 3.65-8.03, 4.75-8.40 and 7.3-9.86, respectively. Rapid K release lasted for only 30 d of incubation. However, initial N and P release continued for about 60 d. In the case of Ageratum conyzoides' roots, N release was initially slower compared to the later stages. Initial lignin and cellulose concentrations showed a significantly negative correlation with the decay rate coefficient; whereas, N concentration showed a significantly positive correlation with the decay rate coefficient. The microbial population and fungal diversity varied with the decomposition period in the field and mainly depended on litter nutrient concentration. Diversity of fungal species was lowest in roots of A. conyzoides and was highest in foliage. Fungal species recorded during the study on plant residues mostly belonged to the Deuteromycetes group. Roots of Spilanthes paniculata and foliage of both species had a C:N of < 25 and released more than 90% of N, P and K within 150 d. They can be considered to be good resources for the improvement of soil fertility. Thus, these residues, particularly those of Spilanthes paniculata, can play a significant role in soil nutrient enrichment in poorly managed shifting cultivation systems.
