MSc

An investigation was undertaken at the College of Horticulture, Vellanikkara, during 1993 – 1994 to study the utilization of phosphorus from green manure by rice. The main objectives of the study were to assess the contribution of phosphorus released from labeled green manure to the phosphorus nutrition of rice and to study the effect of incorporation of green manure on the utilization of applied fertilizer and native soil phosphorus. The effect of incorporated green manure on the dry matter yield of rice was also investigated.
The green manure used was Sesbania aculeate. 32p labelled green manure was produced by growing sesbania in sand culture for 50 days. When the plants were 15 days old 32p (carrier free) was applied with water at 30 µCikg-1 sand. The labeled plant material was used for the incubation study and pot culture experiment.
The results obtained from the incubation experiment conducted to study the dynamics of P mineralization from green manure revealed that the release pattern of Bray – 1 extractable P was similar both in 0.25 and 0.5 per cent green manure amended soil irrespective of the quantity of green manure added. The available P content of the green manure amended soil was relatively higher at the initial day of incubation, gradually decreased till 25th day and thereafter increased. The contribution of P from green manure and native soil also followed similar trend. As extracts of soil immediately after amending with labeled green manure showed 32p activity, it is possible that Bray – 1 reagent extracted inorganic P from the green manure. The P release from green manure and soil was the least at the 30th day of incubation and then showed an increasing trend for both levels of green manure incorporation. Till 30th day more P was released from 0.5 per cent green manure incorporation, later showed a reverse trend.
To study the effect of incorporation of green manure on P utilization by rice, a pot culture experiment was done with 32p labeled green manure and amophos. The results revealed that per cent P derived from fertilizer (% Pdff) increased upto 20 days after transplating and thereafter it decreased, whereas the per cent phosphorus derived from green manure (% Pdfg) was very low during the initial stages, and thereafter it increased considerably. So a combind application of green manure and inorganic P fertilizer will meet the P requirement of the crop throughout the growth period. ‘% Pdfg’ increased with increasing rate of application of green manure. Per cent utilization of P from amophos was high during the initial stages of crop growth, later it decreased while the per cent utilization of P from green manure increased considerably after 20 days of transplanting. The per cent utilization decreased with increasing rate of application of green manure.
With regard to crop growth characters, significant increase in plant height and tiller number were observed with the application of 0.25 per cent green manure along with amophos. Among the yield attributing characters, number of spikelets per panicle showed significant increase with the application of 0.25 per cent green manure in combination with amophos. Grain and straw yield were also the highest under the same treatment. Both grain and straw yield were significantly low when green manure alone was applied at the higher rate (0.5 per cent).