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The critical limit of nitrogen in soil and plant (CAU R-1) was determined through a pot culture experiment with twenty five soils of Imphal West district of Manipur, India for predicting the response of rice to nitrogen application. All the soil samples were clayey in texture and acidic in reaction with the mean pH value of 5.16, electrical conductivity ranged from 0.06 to 0.14 dSm -1 with an average of 0.1 dSm -1 , organic carbon content from 1.06 to 2.62 % with mean value of 2.03%, cation exchange capacity of the soils from 12.20 to 20.20 meq/100g with mean value of 16.06 meq/100g. Available nitrogen content in soils varied from 185.00 to 331.06 kg N/ha with an average value of 267.24 kg N/ha. Available nitrogen in the soils was positively and significantly correlated with plant N content (r=0.653**), dry matter yield (r=0.556**), plant N uptake (r=0.726**) in control pots. There was also a positive and significant correlation between available N and bray's per cent yield (r = 0.519**). The critical limit of available N was established at 257 kg N/ha for soil and 1.04 % for 45 days old rice plants. Soil containing N below this critical limit may respond economically to N fertilization for growing rice.

Evaluation of nutrient status in soil is important for nutritional, environmental and economical aspects. Phosphorus is a very important nutrient for leguminous crops. In order to evaluate the phosphorus availability, six soil test methods were carried out for predicting response of soybean to phosphorus application on twenty surface soils (0-15 cm) of Imphal East District, Manipur were studied. The suitability of these extractants was in the descending order: Bray P 1 > Mehlich P 1 > Bray P 2 > Troug P > Olsen P > Morgan P. Bray's P 1 extractable phosphorus showed the highest and positive correlations with phosphorus content (control), phosphorus uptake (control), Bray's percent yield and uptake. Therefore, this extractant may be used as an index of available phosphorus for soybean (JS-335) grown on acid soils of Imphal East District, Manipur, the critical level being 13 ppm (mg kg-1). The critical limit of phosphorus concentration in plant at 40 days of planting was 0.22%.

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