Nutrient Uptake and Economics of Summer Greengram as Influenced by Residual Effect of Paddy Residues and Fertility Levels

The main obstacles preventing the current crop generation’s genetic potential from being fully realized are the low and falling productivity of many tropical soils. It is vital to take the necessary steps to stop this decline in soil productivity because if it is not stopped, it will have major consequences for future food demands of an expanding human population. The use of inorganic fertilizers for crop productivity has been constrained by their scarcity and high price (Tanimu et al., 2007). As a consequence, farmer uses the available organic sources. Several nations use the crop wastes that are produced as a result of agricultural activity in various ways. Depending on the final usage, they are used treated or unprocessed. In Indo-gangetic plains (IGP), farmers burn crop residue in open field that leads to not only emission of harmful gases and air pollutants into the atmosphere (Raghavendra et al., 2020), but also causes loss of nutrients. To minimize this problem, recycling of nutrients (Nitrogen, phosphorous and potassium) through crop residue retention is one of the desired options that may lead to effective disposal and help overcome the deficiencies of other nutrients, such as sulphur, zinc and boron deficiencies, which are widespread in the IGP region (Prasad, 2005). In an organic rice-wheat farming system, the potential for plant nutrition in rice and wheat straw is substantial. According to Sharma and Sharma (2004), these crops remove between 35% and 40% of the nitrogen, 10% to 15% of the phosphorous and 80% to 90% of the potassium from the system through the straw. Thus, using straw leads to the recycling of a significant proportion of plant nutrients.
       
Additionally, fields are kept fallow for 70 to 80 days in the summer following the harvest of the winter crops. In these situations, including a legume in crop rotations can be crucial for preserving soil fertility and crop productivity. Legumes are a valuable source of organic nitrogen due to their ability to fix atmospheric nitrogen, their nodulated roots and plant residues left after harvest. Conventional tillage delays the sowing of summer greengram by 7-10 days due to intensive tillage practices followed by farmers for optimum seed bed preparation (Chouhan et al., 2005). Consequently, under such condition resource conserving technologies (RCTs) like zero tillage have emerged over the past 2-3 decades as a means of achieving the optimum yields in intensive cropping systems (Sharma et al., 2012 and Almaz et al., 2017). About 40% of the crop land in India alone is grown using no-till techniques, with the majority of this practise occurring in North India. The soil benefits from this strategy in numerous ways, including erosion prevention, enhanced moisture, cooling effect and carbon supply. Keeping all these things in mind, an attempt has been made to determine the effect of crop residue incorporation on nutrient uptake and economics of summer greengram as influenced by residual effect of paddy residues and fertility levels.

Experimental site
 
A field study was carried out at the college farm of the Professor Jayashanker Telangana State Agricultural University, Hyderabad during kharif, rabi and summer seasons of 2020-21 and 2021-22. The site was located at 17°32'22"N latitude and 78°41'11"E longitude and 550 m above mean sea level (MSL). The plot of experiment was characterized by sandy clay loam soil with a pH of 8.33, an EC of 0.37 dS m-1and soil organic carbon content of 0.38%.  The analysis of soil prior to the commencement of the study revealed that the available nitrogen (N), phosphorus (P) and potassium (K) were 145.0 kg N ha^-1, 38 kg P₂O₅ ha^-1, 277 kg K₂O ha^-1, respectively.
 
Treatment and experimental design
 
The field trial was conducted using a strip plot design. The horizontal plot treatments consisted of eight residue management methods viz., R₁: Burning residue before sowing, R₂: Retention of residues, R₃: Removal of residues before sowing, R₄: Incorporation at 15 DAS, R₅: Incorporation at 15 DAS+SSP at equivalent to ‘P’ dose, R₆: Spraying consortia of decomposers @ 10% of residue weight+surface retention, R₇: Spraying consortia of decomposers @ 10% of residue weight+incorporation at 15 DAS, R8: Spraying consortia of decomposers @ 10% of residue weight+incorporation at 15 DAS + SSP at equivalent to ‘P’ dose. The vertical plot treatments involve three fertility management practice viz., F₁: 180:60:60 kg N, P₂O₅ and K₂O ha^-1 (75% RDF), F₂: 240:80:80 kg N, P₂O₅ and K₂O ha^-1 (100% RDF) and F₃: 300:100:100 kg N, P₂O₅ and K₂O ha^-1 (125 % RDF). Rice was sown during kharif season of 2020 and 2021, respectively. After harvesting, the residue was collected and weighed. Maize was sown during rabi seasons of 2020-21 and 2021-22 under zero tilled conditions and rice residue was applied as per the treatments. Recommended dose of fertilizer for rice and maize (120-60-40 and 240:80:80 kg N, P₂O₅ and K₂O ha^-1, respectively) was given according to the study. Greengram was sown by dibbling after the harvest of maize under residual conditions. The sowing was done on 9^th March and 28^th February during summer 2021 and 2022 respectively. The greengram variety used in this investigation was WGG-42 which was released in Telangana in the name of yadadri.
 
Data collection
 
Matured pods from the net plot area of 3.0×3.2 m² were picked manually and dried in the sun. The weight of cleaned grains obtained from each plot after threshing was recorded. The net plot seed and haulm yield of five plants which were marked for recording post harvest observations were added and the total yield was expressed in kg ha^-1. The nitrogen, phosphorous and potassium content of the plant samples were analyzed at harvest stage of the crop. The plant samples were dried in hot air oven at 60^oC and the dried samples were grinded in a willey mill. The powdered samples were then used for analysis.
 
Statistical analysis
 
Gross returns, net returns and B: C ratio were calculated for each treatment and analyzed statistically. Relationship of seed yield with nutrient uptakes was established by using regression analysis. While doing so, the parameters for which significantly high correlation was noticed were selected for regression studies. Plant seed yield (dependent variable) was assumed as a function of uptake of nutrients (independent variable) and the following straight line model was established by least square technique (Gomez and Gomez, 1984) as follows.
Where:
y= Seed yield (kg ha^-1).
a= Y-axis intercept.
b= Regression coefficient.
x = independent variable.

Yield
 
Among all the tested combinations, R₈F₃ (consortia+ incorporation+SSP with 125% RDF) recorded significantly higher seed yield and haulm yield (Table 1) which was comparable with R₈F₂ (consortia+incorporation+SSP with 100% RDF) and significantly superior over R₈F₁ (consortia+incorporation+SSP with 75% RDF) treatment combination. On the other hand, the significantly lower seed yield and haulm yield were recorded with the treatment combination of R₃F₁ (removal with 75% RDF) which was statistically comparable with that of R₁F₁ (in-situ burning with 75% RDF), R₂F₁ (retention with 75% RDF) and R₆F₁ (retention+consortia with 75% RDF). Paddy residues applied to maize crop released plant nutrients slowly to the greengram over time. Higher growth, greater absorption and better translocation of assimilates from source to sink could have resulted in increased yield as nutrients were available at more frequent intervals from residual sources in consortia + incorporation+SSP treatment. These results are also in consonance with the findings of Davari et al., (2012) and Shukla et al., (2022) in greengram and maize crops, respectively.
 

 
Nutrient uptake
 
The scrutiny of the data on nitrogen (N), phosphorous (P) and potassium (K) uptake of greengram revealed that in consortium+incorporation+SSP (R₈) plots there is significant increase in nitrogen uptake as compared to in-situ burning plots (Table 2). The nutrient uptake variation among the treatments showed the importance of microbial consortium application to hasten up the decomposition of residues at rhizosphere (Bargaz et al., 2018 and Singh et al., 2012). Naiyar et al., (2016) also found an increase in nitrogen uptake by grain and straw of wheat with incorporation of residues which might be due to better root establishment resulting in better translocation and the movement of nutrient in soil solution and ultimately their greater absorption and utilization by the growing plants.
 

       
Among the fertility levels, the increase in the fertility levels from 75% RDF to 125% RDF significantly influenced the NPK uptake. The maximum uptake of nutrients was recorded with 125% RDF and lowest values were recorded with 75% fertilizer application. In general, the overall absorption of a nutrient by a plant is proportional to the nutrient concentration and the amount of dry matter produced. Increased uptake at larger doses might have resulted in early plant vigour and a high photosynthetic rate resulting in greater nutrient uptake throughout the crop growth period. Similar results were reported by Brar et al., (2000) that application of 180 kg N ha^-1 during paddy straw incorporation in addition to recommended nitrogen fertilizer dose (120 kg N ha^-1) in two equal splits (at sowing and 3 weeks after sowing) significantly increased the nitrogen and phosphorous uptake by 14.8% and 10% as compared to recommended dose alone.
       
No significant differences were found among residue management practices and fertility levels with respect to nitrogen, phosphorous and potassium uptake.
 
Economics
 
Significantly higher gross returns, net returns and B:C ratio were recorded with R₈F₃ (consortia+incorporation+SSP with 125% RDF) than other combinations but statistically at par with that of R₈F₂ (consortia+incorporation+SSP with 100% RDF) and superior over R₈F₁ (consortia+incorporation+SSP with 75% RDF) treatment combination (Table 3). The treatment combination viz; R₇F₃ (consortium+ incorporation at 125 % RDF) also followed similar trend. On the other hand, significantly lower monetary returns were recorded with the treatment combination of R₃F₁ (removal with 75% RDF) and was in equivalence with that of R₁F₁ (in-situ burning with 75% RDF), R₂F₁ (retention with 75% RDF) and R₆F₁ (retention + consortia with 75% RDF) (Table 3).
 

       
The higher returns observed in consortia+ incorporation+SSP with 125% RDF and 100 % RDF could be due to higher seed and straw yields obtained in these treatment combinations. Badiger et al., (2019) also reported that application of 50 percent recommended dose of chemical fertilizers along with microbial consortia reduced the cost of inputs in greengram. Similar findings were reported by Singh et al., (2019).
 
Regression analysis
 
Regression between nutrient uptake and seed yield
 
The dependence of seed yield on the NPK uptakes was evident from significant (P=0.01) and positive correlation between yield and N uptake, P uptake and K uptake data (Table 4). Determination coefficient (R²) was observed to be 0.57 for N uptake, 0.53 for P uptake and 0.63 for K uptake which indicates that there is increase in nutrient uptake as a result of higher yield.
 

It can be concluded that paddy residue management and fertility levels to zero till maize had a significant impact on greengram yield, nutrient uptake and economics. When microbial consortia+SSP+incorporation was combined with 100% RDF, higher seed yield, haulm yield, NPK uptake, gross returns, net returns and B-C ratio were noticed. Therefore, under zero till rice-maize-greengram cropping system, crop residue incorporation at 6.5-7.0 t ha^-1 and application of microbial consortia in conjunction with fertilizers had a positive residual impact on boosting summer greengram uptake and resulting in higher yield and monetary returns.

We, the authors of the paper undersigned hereby declare that there are no conflicts of interest regarding the publication of the manuscript in Legume Research Journal.