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Mesocosms containing lateritic soil from West Bengal, India and de-ionized water were treated with different amounts of nitrogen (N), phosphorus (P), and potassium (K) fertilizers. Concentrations of available N, P, and K in soils and gross primary productivity were measured for the mesocosms. Critical concentrations of the three nutrients were estimated by the graphical method of Cate and Nelson that has been used widely for establishing critical soil nutrient concentrations in fertilization research on terrestrial crop plants. Critical concentrations of the three nutrients were: available N, 200 mg kg−1; available P, 13 mg kg−1; available K, 80 mg kg−1. Ponds sited in red, lateritic soil in West Bengal were treated monthly with 20, 15, and 3 kg ha−1 application−1 of N, P, and K, respectively. There was an increase in gross primary productivity when the critical concentrations of available N, P, and K established in the mesocosm study were attained in the pond soils. Fish production in fertilized ponds is positively correlated with gross primary productivity. Thus, the concept of critical nutrient concentrations in soils could be a valuable tool in pond fertilization research.

In view of the growing awareness about vermicomposting technology in recycling a wide range of organic wastes, the behaviour of phosphorus during mineralization of different organic wastes in the absence and presence of epigeic earthworms was studied. The magnitude of the transformation of phosphorus from the organic to inorganic state, and thereby into available forms was found to be considerably higher in the case of earthworm-inoculated organic wastes, showing that vermicomposting may prove to be an efficient technology for providing better P nutrition from different organic wastes. The transformation of P into three major inorganically bound forms; Al-P, Fe-P and Ca-P also tended to change substantially during the process of vermicomposting.