CONTRIBUTION OF GREEN MANURE INCORPORATION IN COMBINATION WITH NITROGEN FERTILIZER IN RICE PRODUCTION

An experiment was conducted at the Soil Science Field Laboratory of Bangladesh Agricultural University, Mymensingh during April to November, 2012 to study the combined effects of Sesbania green manure incorporation with different levels of nitrogen fertilizer on the growth and yield of BINA dhan7. There were five treatments for using Sesbania as pre-rice green manure (GM): Fallow (No GM), GM for incorporation at 40, 50, 60, and 70 days after sowing (DAS). T. Aman was planted after chopping the GM. For T. aman there were 9 treatments: Fallow plot received full dose (180 kg urea ha -1 ) of N fertilizer while plots with GM received 50 and 75% of recommended N fertilizer. The experiment was laid out in a Randomized Complete Block Design with three replications. The highest grain yield of 5752 kg ha -1 and straw yield of 6654 kg ha -1 were observed in the plot treated with 75%recommended dose of nitrogen (RDN) and green manure incorporated at 50 DAS. The lowest grain yield (4783 kg ha -1 ) and straw yield (5154 kg ha -1 ) were recorded with GM incorporated at 40 DAS + 50% RDN. The N content and uptake by the grain and straw were differed significantly due to different treatments and maximum uptake was recorded with the application of 75% recommended dose of nitrogen (RDN) and green manure incorporated at 50 DAS. The overall results indicate that application of Sesbania green manure incorporated at 50 DAS in combination with 75% recommended dose of nitrogen could be considered more effective for BINA dhan7 production.

-1 ) of N fertilizer while plots with GM received 50 and 75% of recommended N fertilizer.The experiment was laid out in a Randomized Complete Block Design with three replications.The highest grain yield of 5752 kg ha -1 and straw yield of 6654 kg ha -1 were observed in the plot treated with 75%recommended dose of nitrogen (RDN) and green manure incorporated at 50 DAS.The lowest grain yield (4783 kg ha -1 ) and straw yield (5154 kg ha -1 ) were recorded with GM incorporated at 40 DAS + 50% RDN.The N content and uptake by the grain and straw were differed significantly due to different treatments and maximum uptake was recorded with the application of 75% recommended dose of nitrogen (RDN) and green manure incorporated at 50 DAS.The overall results indicate that application of Sesbania green manure incorporated at 50 DAS in combination with 75% recommended dose of nitrogen could be considered more effective for BINA dhan7 production.

INTRODUCTION
Low soil fertility due to organic matter depletion is a major constraint severely affecting higher crop production in Bangladesh (BARC, 2012).Organic matter contributes to soil fertility and productivity through its positive effect on the physical, chemical and biological properties of the soil.But the organic matter content in many parts of Bangladesh soils has been seriously depleted due to intensive cropping with modern varieties, very little use of crop residues, little or no use of organic manures, absence of green manure etc.As a result, soil productivity, in general, has been degraded and stagnation in yield has occurred even with high dose of chemical fertilizers under rice based cropping patterns.
Adding inorganic fertilizers is a good way of correcting the deficiency of nutritional elements, but they not only add to the cost of production but often are not available to meet the demands of farmers.Although the fertilizers are very effective in increasing yield, they may deteriorate the soil structure and pollute the groundwater.In addition, chemical fertilizers are expensive due to the energy crisis and are unavailable to many farmers, particularly in developing countries like Bangladesh.In this situation, green manure can serve as a cheaper source of plant nutrition and has become popular with farmers.Green manuring is the process of growing leguminous crops and ploughing the same in soil.On decomposition, it results in increased soil fertility.At the same time, improving the organic matter content of soil also improves its water holding capacity, aeration, colloidal complex, and hence its ability to retain nutrients.
Although many green manure crops are available (Kerala Agricultural University, 2002), the N 2 -fixing leguminous crop Dhaincha (Sesbania aculeata) is particularly important because it can fix 56.2-150 kg ha -1 of nitrogen (Bin, 1983).Studies with Sesbania green manuring at Bangladesh Agricultural University have shown very promising contribution of S. aculeata in supplementing N requirement of the following T. Aman rice and also recycling of S and P for the next crops.Many workers suggested green manuring along with N fertilizer application for slow release of nutrient elements during the entire period of crop growth (Singh et al., 1990).It has also been reported that green manuring provides a substantial amount of nutrients for the next crop (BRRI, 1998;Elahi, 1991).It is evident that the application of Sesbania aculeata along with the recommended chemical fertilizers may ensure adequate supply of nutrients especially nitrogen to the transplanted rice over the entire growing season for better plant growth with higher grain production (Pervin et al., 1995) Although S. aculeata is known for long as a GM crop but there is a lack of adequate knowledge regarding the time and method of chopping and mixing the GM crop with the soil.Therefore, the present study was undertaken to find out the appropriate time for chopping and mixing Sesbania as a pre-rice green manure and to determine the optimum doses of N to be applied in combination with Sesbania green manure incorporated at different times for the production of BINA dhan7.

MATERIALS AND METHODS
The experiment was carried out at Soil Science Field Laboratory, Bangladesh Agricultural University, Mymensingh during April to November, 2012.The soil belongs to Sonatala series under the AEZ of the Old Brahmaputra Floodplain.The experimental soil was silt loam in texture.BINA Dhan7, a high yielding variety of rice was used in this experiment as test crop.The experiment was laid out in a randomized complete block design (RCBD) with three replications.The experiment comprised of 9 treatments: T 0 (No GM + 100%RDN), T 1 (GM incorporated at 40 DAS + 50%RDN), T 2 (GM incorporated at 40 DAS + 75%RDN), T 3 (GM incorporated at 50 DAS + 50%RDN), T 4 (GM incorporated at 50 DAS + 75%RDN), T 5 (GM incorporated at 60 DAS + 50%RDN), T 6 (GM incorporated at 60 DAS + 75%RDN), T 7 (GM incorporated at 70 DAS + 50%RDN) and T 8 (GM incorporated at 70 DAS + 75%RDN).Here, RDN = Recommended dose of nitrogen (180 kg urea ha -1 ) as per BARC Guide (BARC, 2005); GM = Green manure.
Green manuring crop, Sesbania aculeata was sown at a time on the same day but incorporated into the soil at different time interval i.e.40, 50, 60 and 70 DAS.Nitrogen, phosphorus, potassium and sulphur were supplied through urea, TSP, MoP and gypsum, respectively.The recommended fertilizer doses applied for the experiment were 180 kg urea ha -1 , 120 kg TSP ha -1 , 70 kg MoP ha -1 , 50 kg gypsum ha -1 .TSP, MoP and gypsum were applied as basal dose during final land preparation.Urea was applied in three instalments (the first instalment at 15 DAT, the second at 30 DAT and the third at 45 DAT).The seedlings of 25 day old were transplanted at a time in all the experimental plots maintaining a spacing of 20 cm x 20 cm although the green manure was incorporated into the soil at different time interval as per treatments.Intercultural operations such as irrigation and weeding were done as and when necessary.The crop was harvested at full maturity.Ten hills were randomly selected from each plot to record the yield contributing characters.Grain and straw yields were recorded plot wise and converted to kg ha -1 .Grain and straw samples were collected, dried, grounded, sieved and used for chemical analysis.Grain and straw samples were analysed for total nitrogen concentration following semi-micro Kjeldahl method (Bremner and Mulvaney, 1982).The N uptake by grain and straw was determined from the N content and yield data.All the data were statistically analyzed following F-test and mean comparison was made by Duncan's New Multiple Range Test (DMRT).

Grain yield
The highest grain yield of BINA dhan7 (5752 kg ha -1 ) was obtained in the treatment GM incorporated at 50 DAS + 75% RDN which was statistically similar to those observed in GM incorporated at 40 DAS + 75% RDN, GM incorporated at 60 DAS + 75%RDN and GM incorporated at 70 DAS + 75%RDN with the values of 5519, 5512 and 5448 kg ha -1 , respectively (Table 2).The increase of grain yield might be due to more availability of nitrogen to rice crop released by incorporation of green manure and due to other beneficial effects of GM.The lowest grain yield (4783 kg ha -1 ) was obtained in the treatment GM incorporated at 40 DAS + 50% RDN which was at par with No GM + 100% RDN, GM incorporated at 50 DAS + 50% RDN, GM incorporated at 60 DAS + 50% RDN and GM incorporated at 70 DAS + 50% RDN were identical with T 1 with grain yield of 5115, 5222, 5127 and 4875 kg ha -1 , respectively.Dekamedhi and Medhi (2000) reported that grain yield of rice was significantly increased due to application of green manure in combination with N fertilizer.These results are also in agreement with Miah et al. (2001), Paramanik et al. (2004), Sarkar et al. (2004) and Chaudhary et al. (2011).

Straw yield
The highest straw yield (6654 kg ha -1 ) was recorded in the treatment GM incorporated at 50 DAS + 75% RDN which was statistically similar to that recorded in GM incorporated at 60 DAS + 75% RDN) (6461 kg ha -1 ).The lowest straw yield (5154 kg ha -1 ) was recorded in the treatment GM incorporated at 40 DAS + 50% RDN (Table 2).Dekamedhi and Medhi (2000) found that straw yield of rice increased with the addition of green manure and urea-N.

Biological yield
The highest biological yield (12410 kg h -1 ) was recorded in the treatment GM incorporated at 50 DAS + 75% RDN which was statistically similar to those recorded in GM incorporated at 40 DAS + 75% RDN, GM incorporated at 50 DAS + 50% RDN, GM incorporated at 60 DAS + 75%RDN and GM incorporated at 70 DAS + 75% RDN (Table 2).The lowest biological yield (9937 kg ha -1 ) was noted in the treatment GM incorporated at 40 DAS + 50% RDN Which was on par with the treatments No GM + 100% RDN, GM incorporated at 60 DAS + 50% RDN and GM incorporated at 70 DAS + 50% RDN

Nitrogen content and uptake by rice grain and straw
N content and uptake both by grain and straw of BINA Dhan7 varied significantly due to application of green manure and N fertilizer.The N content in rice grain ranged from 1.037 to 1.430% and in rice straw from 0.532 to 0.644%.(Table 3).The highest N content both in rice grain (1.430%) and straw (0.644%) was observed in the treatment GM incorporated at 50 DAS + 75% RDN and the lowest value was noted in the treatment GM incorporated at 40 DAS + 50% RDN .
Nitrogen uptake by rice grain ranged from 49.54 to 81.54 kg ha -1 .The maximum N uptake 82.24 kg ha -1 by rice grain was observed in GM incorporated at 50 DAS + 75% RDN.The minimum N uptake of 49.54 kg ha -1 was observed in T 1 GM incorporated at 40 DAS + 50% RDN.The results are in agreement with Medhi et al. (1996) and Dekamedhi and Medhi (2000) who found that with the combined application of green manure and N fertilizer, N uptake by rice grain was increased.In case of rice straw, N uptake ranged from 27.39 to 42.86 kg ha -1 .The maximum N uptake 42.86 kg ha -1 by straw was observed in GM incorporated at 50 DAS + 75% RDN.The minimum N uptake by rice straw 27.39 kg ha -1 was recorded in GM incorporated at 40 DAS + 50% RDN.The results reveal that N uptake in rice grain was higher than that of straw.The total N uptake was the highest in GM incorporated at 50 DAS + 75% RDN and the lowest in GM incorporated at 40 DAS + 50% RDN which was statistically similar to that of GM incorporated at 70 DAS + 50% RDN.The results support the findings of Duhan et al. (2002) who found increased N uptake of rice with application of green manure along with N fertilizer.

CONCLUSION
On the basis of one year experimentation it can be concluded that incorporation of Sesbania green manure at 50 DAS along with the application of 75% of recommended N fertilizer is best for cultivation of BINA dhan7.

Figure
Figure (s) in a column having common letters does not differ significantly.GM = Green manure; RDN = Recommended dose of nitrogen; DAS = Day after sowing; SEm = Standard error of means; CV = Coefficient of variation

Figure
Figure (s) in a column having common letters does not differ significantly.GM = Green manure; RDN = Recommended dose of nitrogen; DAS = Day after sowing; SEm= Standard error of means; CV = Coefficient of variation