Effect of Integrated Nutrient Management on Rice-Greengram Cropping Sequence

Rice based cropping is one of the most important cropping system of India and hence rice is the staple food of India. Coastal Gujarat heavy rainfall zone leaves no scope to replace kharif rice due to soil and climatic compulsions, hence rice dominates in kharif season. However, number of other agronomic crops can be profitably cultivated during rabi and summer season with proper field management. However, cultivation of rice under poor soil and crop management practices for longer periods continuously resulted in poor soil fertility through the evidence of multi nutrient deficiencies in soil and deteriorated physical properties of soil. This decline in soil quality resulted in reduced partial crop productivity and factor productivity (Jat et al., 2012). Due to scarcity of organic manures and heavy exploitation of high analysis fertilizers, nutrient-related stress are becoming a cause of concern. Continuous cropping of rice with two to three crops grown in a year, leads to more use of N fertilizer with yields often remained stagnant. Continuous cultivation of rice under wetland conditions resulted in low level of available nitrogen in soil and this N can be again recharged in soil through biological nitrogen fixation (Ghosh et al., 2007). In such types of soil one of the most crucial requirements for enhancing the crop yieldis the efficient utilization of applied fertilizer. Inorganic fertilizers along with integrated and judicious use of different organic sources like FYM, vermicompost, green manure etc. could be an effective choice for enhancing crop yield in such region. A synergistic effect on crop yield is reported through common use of fertilizer and organics has improved soil fertility in coastal soils (Dubey and Verma, 1999). Nutrient use efficiency, soil biological health and soil quality improved through use of combination of inorganic and organic sources of fertilizers as an integrated approach. Soil health can be conserved by employing organic sources through maintaining balance between soil microflora and soil organic matter, finally helps to boost soil properties. Regulation of soil microbial biomass, further mineralization of soil organic carbon and converting it into organic matter and ultimately its contribution to higher nitrogen availability to crops is regulated by organic productions addition in soil. Application of organic manures releases various native sources of nutrients by decreasing soil salinity, apart from addition of nutrients in soil, it smoothens soil microbial activity, as soil salinity is influenced by soil microbial communities and their activity (Mitran et al., 2017). Hence, major sources of plant nutrients such as mineral nutrients, organic and biological sources should be utilized judiciously for sustainable crop production in a cropping system. The residual effects of FYM applied to the succeeding rabi season crops lasted even up to third sequence of the crop. Pulses have the property of recharging soil fertility, which place pulses in a unique position in various cropping systems, especially in dryland agriculture (Mitra and Mandal, 2012). Rotation of legumes after cereals not only fix nitrogen, but also enhance nutrient availability, reduce disease incidence, improves soil structure and promotes mycorrhiza population (Singh et al., 2011). Therefore, this experiment was planned to throw light on the use of integrated nutrients through organic and inorganic sources on rice and its residual effect on succeeding green gram for the farming community in the coastal Gujarat plains of India.

The field experiment was conducted during 2012-15 at Navsari Agricultural University, Gujarat, India to find the effect of integrated nutrient management on growth, yield, quality, economics and soil properties of rice-greengram cropping sequence. The annual rainfall ranges between 1500-1700 mm. Soil of the experimental field was medium black and fairly drained. The textural class was clayey. A dominant type of clay was montmorillonite and grouped under order vertisol. The chemical composition indicated that the soil was low in available nitrogen (220.80 kg ha^-1), medium in organic carbon (0.45%) and available phosphorus (40.60 kg ha^-1) and high in available potassium (321.12 kg ha^-1). The soil was alkaline in reaction with pH 8.0. Kharif rice cv. Jaya experiment was laid down in randomized block design with 5 treatments with four replications and after the harvest of rice, each plot of rice was divided into three equal sub plots for sowing rabi greengram cv. Co-4 with three levels of fertilizers with four replications in split plot design to test the residual effect of rice treatments on greengram. Main plot treatments (kharif rice) were T₁- General RDF (RDF: 100-30-00 kg NPK ha^-1+ FYM at 10 t ha^-1), T₂- 75% RDN through chemical fertilizer+25% RDN through biocompost (BC), T₃-75% RDN through chemical fertilizer+25% RDN through vermicompost (VC), T₄- 75% RDN through chemical fertilizer + 25% RDN through FYM and T₅- Control. During rabi season each plot of rice was divided into three equal plots for three fertilizer levels as a sub plot treatments viz. control, 50% and 100% RDF were applied at 20:40:00 kg NPK ha^-1 to greengram during rabi season. Before rice planting soil was analyzed for available NPK before rice planting. Rice was transplanted at 20 cm × 15 cm and green gram at 30 cm × 10 cm spacings. The experimental plots were kept fixed for three years. All intercultural operations were done as per requirement. In order to analyze the influence of soil properties on agronomic performance and to assess the impact of organic and inorganic fertilizers on soil fertility, representative soil samples were taken from experimental plot and initial soil status was assessed. Rest all the soil samples were taken at the end of third year cropping season. Samples were taken from the cultivated soil layer (upper 15 cm), using an auger. The statistical analysis of the experimental data was done as per the methods suggested by Gomez and Gomez (1983).

Growth and yield of rice
 
Growth contributing characters (Table 1), grain yield (55.68 q ha^-1) and straw yield (75.87q ha^-1) were significantly highest by application of general RDF. Among all three INM treatment,75% RDN through CF + 25% RDN through VC  registered significantly highest growth and yield of rice. Perusal of yield of rice registered among integrated approach treatment of organic and inorganic sources the superiority trend is as follows vermicompost>biocompost>farm yard manure. Use of general RDF has increased rice grain yield by 85.66% and inorganic combination with vermicompost by 69.65%, biocompost by 58.72% and FYM by 50.82% over absolute control. Highest grain yield of rice was recorded by the application of full inorganic sources with recommended organic nutrients may have helped for immediate release and availability of nutrients as compared to other tried treatments. Integrated use of organicand inorganic sources of nutrient may have contributed for nice synchronization of nutrient availability to rice crop, which was reflected in highest rice grain yield and drymatter production. Comparable results were obtained by Gudadhe et al., (2011) in case of cotton. Higher yield of rice might be due to improvement in soil physical and chemical properties also and increased the availability of nutrients with the addition of FYM along with other sources of organics (Mitra and Mandal, 2012).
 

 
Nutrient content, uptake and protein content in rice
 
Looking to the data from Table 2 expressed that, application of general RDF has gave highest NPK content in grain (1.325, 0.297 and 0.390%, respectively), straw (0.688, 0.087 and 1.455%, respectively) and also the total NPK uptake (125.82, 23.02 and 131.44 kg ha^-1) of rice on pooled mean basis of three years. However it was found at par with NPK content in rice grain and N and P content in rice straw by application of 75% RDN through CF + 25% RDN through VC. Planting rice without any organic or inorganic fertilizer treatment gave lowest nutrient content in grain, straw and total uptake in rice. Application of organic manures in combination with chemical fertilizer has increased the activities of nitrogen fixing organisms and symbiotic association of mycorrhiza which enhanced nutrient availability for a longer period and also increased nutrient use efficiency of the crops and availability of more native nutrients to the plants resulting in a higher absorption of the nutrients (Banik and Sharma, 2009). Similar results were observed by Mitra and Mandal, (2012) in rapeseed-greengram-rice sequence. However, in case of protein, application of general RDF has gave significantly superior protein content (7.88%) and protein yield (4.59 q ha^-1) in rice, however protein content  was found at par with INM treatment 75% RDN through CF + 25% RDN through VC.
 

 
Growth and yield of greengram
 
In this experiment combination of organic and inorganic treatments were investigated on kharif rice, however on the same treatments,greengram treatments were superimposed with three levels of fertilizers and pooled data of three years (Table 3) showed that  general RDF has shown highest green gram growth parameters and seed yield per plant (5.58), also seed yield (9.79 q ha^-1), haulm yield (24.28 q ha^-1), harvest index (28.70) and rice equivalent yield (95.09 q ha^-1) were significantly highest with the application of general RDF and it was significantly at par with application of 75% RDF through CF + 25% through organic fertilizer vermicompost to rice. Significantly higher rice equivalent yield reflected the residual advantage of legume greengram crop on the succeeding rice (Gudadhe et al., 2011) besides contribution in total system productivity. Treatment details from 2 to 4 showed that one chemical fertilizer level i.e. 75% RDN through chemical fertilizer was tested with three sources of organic manures viz. biocompost, vermicompost and FYM with 25% contribution and their efficiency can be calculated by estimating their yield increase over absolute control. Thus, per cent yield increase of greengram over control is in the following order, general RDF (48.33%) > 75% CF + 25% VC (45.90%) > 75% CF + 25% BC (31.21%) > 75% CF + 25% FYM (21.81%). Least growth and yield parameters of greengram were observed with absolute control. The higher yields in greengram in the rotation might be due to improved  physico-chemical properties of soil and  more availability of nutrients with the addition of organic manures namely FYM, biocompost and vermi compost to the preceding rice crop and further mineralization of required nutrients to the succeeding greengram crop hence its  yield effect is reflected. Above results are closely related with the findings of Saha et al., (2007) in rice-greengram wet season rice cropping system. Gudadhe et al., (2016) also noticed the same findings in case of cotton-chickpea cropping sequence where general RDF and other fully organic treatment of vermicompost was given to cotton, however chickpea was sown with four levels and both these treatments (general RDF and 100% N through vermicompost) had given highest chickpea seed yield because of availability of residual nutrients which were applied to previous crop cotton.
 

        
In greengram subplots,where application of 100% RDF was supplied to greengram has registered significantly highest growth characters, yield contributing characters and seed yield (9.93 q ha^-1), haulm yield (24.61 q ha^-1), harvest index (28.80) and rice equivalent yield (86.10 q ha^-1) over 50% RDF. This may be due to the confluence residual effect of nutrients applied to rice and full package of nutrients applied to greengram. Least growth characters, yield contributing characters and yield were observed in control treatment.
 

 
Nutrient content, uptake and protein content in greengram
 
Rice residual treatments to greengram gave significantly higher NPK content in seed (3.448, 0.124 and 1.112%, respectively), haulm (0.902, 0.091 and 1.788, respectively) and total uptake (55.94, 3.42 and 54.36 kg ha^-1, respectively)through general RDF and which was found statistically equal with NPK content in seed, haulm and total uptake, except total P uptake by application of INM treatment 75% RDN through CF + 25% RDN through VC and which was also followed by 75% RDN through CF + 25% RDN through BC and the same trend was observed for protein content and protein yield. This might be due to the additional amount of nutrient supplied by organic manures, as well as advantageous effects of organic matter decomposition that positively influenced with physical and chemical properties of the soil. Similar outcome was recorded in rice-based crop sequences as reported by Khanda et al., (2005) under Gangetic plains of India. Integrated application of nutrients to previous crop rice became available to greengram, organic manures can supply various macro and micro nutrients and which became favourable for higher N fixation by green gram crop. Similar findings reported by Mitra and Mandal, (2012) in rapeseed-greengram-rice.
        
For subplot treatments to greengram, significantly highest NPK content in seed (3.510, 0.122 and 1.105%, respectively), haulm (0.891, 0.089 and 1.777%, respectively) and total uptake (56.97, 3.42 and 54.81 kg ha^-1, respectively), protein content (21.94%) and protein yield (2.19 q ha^-1) were by the highest level of fertilizer i.e. 100% RDF and it was statistically same with P and K content in seed and NPK content in haulm by application of 50% RDF to greengram. Least values of NPK content in seed and haulm and total uptake was found with absolute control.
        
Application of NPK through 100% RDF to succeeding crop and application of RDF + 10 t FYM to the preceding crop by mineral fertilizers also increased in the total uptake of N, P and K, protein content and protein yield. This might be due to higheravailability of nutrients and more efficient nutrient use of preceding season nutrients to the succeeding sequence in presence of FYM and vermicompost. The increased uptake of nutrient took place due to improvement in the soil conditions, which encouraged root growth luxuriously and the absorption of nutrients and moisture from a wider area. Sufficient nutrient reserves in soils helped for higher nutrient uptake and utilization by crops. Productivity and profitability of rice based cropping systems, cannot be sustained for long if we continue the practices of addition of less organic and more inorganic sources of nutrients at a time (Ghosh et al., 2007).
 
Economics of rice-greengram cropping sequence
 
After examining three years average data as summarized in Table 5 of rice-greengram cropping sequence among five main plots of rice and three subplots of greengram it is revealed that, highest gross monetary returns (Rs. 161582 ha^-1), net monetary returns (Rs. 76706 ha^-1) and benefit cost ratio (1.90) was obtained by application of general RDF to rice crop. This may be due to higher production potential of rice along with the good market price of greengram and luxuriant nutrient supply of organic and inorganic nutrients. It was closely followed by application of 75% RDN through CF + 25% RDN through VC. As vermicompost turned out to be costlier but it has its superiority by expressing higher yield both in rice and greengram, hence VC seems more nutrient rich and soil friendly and also shown its superiority on gross and net monetary returns over BC. These findings are in close confirmation with the study of Gudadhe et al., (2016).
 

        
Among three different subplots to greengram highest gross monetary returns (Rs. 147584), net monetary returns (Rs. 68589 ha^-1) and benefit cost ratio (1.86) were obtained by application of 100% RDF, next economic treatment was 50% RDF to greengram. Highest rice-greengram system profitability was due to application of 100% RDF to greengram which provided required nutrients for nitrogen fixation to greengram and residual effect of organic nutrients supplied to rice, which contains various micronutrients e.g. Mo, B, Co, Ca etc. which also helped to boost yield and economics of the greengram and of whole system also. 
 
Effect on bulk density, organic carbon and available nutrients
 
Outcome of results with respect to bulk density and organic carbon of the soil at 0-15 cm depth revealed that the values ranged between 1.35-1.48 g cm^-3 and 0.43-0.64%, respectively at the end of the 3^rd years investigation under different fertilization levels (Table 6). Significantly lowest values of bulk density (1.35 Mg cm^-3) and highest values of organic carbon (0.64%) were observed by general RDF, followed by 75% RDN + 25% RDN through FYM (1.38 Mg cm^-3 and 0.61%, respectively). These findings are superior over initial values of bulk density (1.38 Mg cm^-3) and organic carbon (0.45%). Kar et al., (2012) included legumes in rice-fallow during the season which supplemented the N requirement to the succeeding legume crop, but improved soil structure which was destroyed by puddled rice. In this experiment also application of organic manures has improved pore space, soil aggregation and soil organic carbon. Similar findings are also reported by Mirtan et al., (2017), Gudadhe et al., (2018) and Gudadhe et al., (2015).
 


It can be said that, with the application of organic manures along with chemical fertilizers to the preceding crop rice and chemical fertilizers application to succeeding greengram has enhanced the available NPK of the soil significantly. Utilisation of general RDF to rice brought about the maximum available NPK (254.31, 48.29 and 348.49 kg ha^-1, respectively) in the soil (Table 6) and which was followed by another organic inorganic combination treatment i.e. 75% RDN through CF and 25% through VC. Banik and Sharma, 2009 during winter crops-rice cropping system used organic and inorganic sources of nutrients and they also found that incorporation of the organic manures in the soil build up the available nutrients status (macro and micro both) and organic carbon. In this experiment enhancement available N in soil might be due to the release of NPK after decomposition of FYM, BC and VC and mineralization from native sources during decomposition processes again contributed to the maximum build up of available nutrients over control and initial soil nutrient status. Crop sequences with legume showed better available nitrogen in the soil due to their nitrogen fixing ability. Also it can be said that, biomass added through greengram, was also rich in nitrogen, which might have accelerated fixation of nitrogen by the free living organisms (Chauhan et al., 2001).

Experimental outcome revealed that application of general RDF has significantly increased growth, yield and economics of rice by decreasing soil bulk density and increasing soil organic carbon and improving available soil nutrients, which was followed by application of 75% RDF through CFand 25% through organics. Use of general RDF has increased rice grain yield by 85.66% and inorganic combination with vermicompost by 69.65%, biocompost by 58.72% and FYM by 50.82% over absolute control. Residual nutrients of rice have gave significantly higher greengram seed yield and application of general RDF has significantly increased greengram seed yield over control and  is in the following order, general RDF (48.33%) > 75% CF + 25% VC (45.90%) > 75% CF +25% BC (31.21%) > 75% CF + 25% FYM (21.81%). Use of 100% RDF to greengram gave significantly highest greengram seed yield over other two levels. Application of general RDF to rice and 100% RDF to greengram gave highest net monetary returns and benefit cost ratio to rice-greengram cropping sequence, also it has also improved soil physical and chemical properties and it was followed by 75% CF + 25% VC. Hence, if general RDF to rice-greengram is not available the application of 75% CF + 25% VC can compensate the yield.