Interactive Effect of Potassium and Zinc on Growth, Yield, Quality and Economics of Green Gram (Vigna radiata L.) under Semi-arid Region of South-west Haryana

Pulses are one of the important segments of Indian agriculture after cereals occupying a key position in vegetarian diet and plays an immense role in economy (Singh et al., 2017). Green gram [Vigna radiata (L.) Wilczek] is third important conventional pulse crop next to chickpea and pigeonpea, having high nutritive value and is adopted and acclimatized over wide range of agro-climatic zones. It contains about 25% protein, 56.7% carbohydrates, 4.1% fibers, 3.5% minerals, 10.4% moisture, 1.3% fat and appreciable amount of riboflavin, thiamine and little amount of Vitamin B complex (Lokhande et al., 2018). India ranks first in both area and production of green gram in world with an area of 5.79 million ha, production of 2.50 million tonnes in 2019-20 with the average productivity 957 kg ha^-1 (INDIASTAT, 2022). In Haryana, during 2019-20 green gram was grown in an area of 20.17 thousand ha producing 12.00 thousand tonnes with an average productivity of 595 kg ha^-1 (INDIASTAT, 2022).
       
Fertilizers are one of the vital inputs for crop production as they supply nutrients in adequate amount and maintains soil fertility (Deb et al., 2016). Total K content of the earth crust is about 2.3 to 2.5% (Rao and Srinivas, 2017), but a very small proportion of it become available to plants. Potassium is widely regarded as the “quality element” (Usherwood, 1985) and it is absorbed in the form of K⁺ by the plants and play important role in stomatal movement, photosynthesis, protein synthesis, enzymes activation, grain development, biotic and abiotic stresses (Egila et al., 2001). Potassium application is rarely done in pulses despite field studies suggested that application of K₂O (20-40 kg ha^-1) helped in attaining higher production (Ali and Rao, 2001). Zinc is one of the essential micronutrients which activates many enzymes like tryptophan synthetase, superoxide dismutase and dehydrogenases as well as stabilization of RNA, DNA and ribosomes (Kumar et al., 2017; Kumar et al., 2016), which are involved in metabolic processes and biochemical pathways (Manisha et al., 2021b). About 43% of the soil samples collected from different parts of India were found to be deficient in zinc (Shukla et al., 2014). By the year 2025, it is assumed that the zinc deficiency is likely to increase from 49 to 63% as most of the cultivated soils are showing the symptoms of zinc deficiency (Manisha et al., 2021a). Zinc increases the productivity, nodule formation mechanism and N-fixation in roots of leguminous crops (Khan et al., 2004). Keeping the above views in mind the current studies were planned to decipher the effects of different levels of potassium and zinc application on growth, yield attributes, yield and quality of green gram.

The study was conducted in kharif 2018 at Research Area of Regional Research Station, CCS HAU, Bawal situated in district Rewari in the south-west Haryana which is located at latitude 28.10° N, longitude 76.50° E and 266 m above mean sea level. The climate of Bawal is semi-arid with average rainfall of 577 mm. Experimental site was sandy loam in texture containing 102.37, 11.18 and 170.10 kg ha^-1, KMnO₄ oxidizable N (Subbiah and Asija, 1956), 0.5 M NaHCO₃ extractable P (Olsen et al., 1954) and 1 N NH₄OAC extractable K (Jackson, 1973), respectively as macronutrients and 0.97, 7.64, 6.24 and 0.52 (mg kg^-1) DTPA extractable (Lindsay and Norvell, 1978) zinc, iron, manganese and copper, respectively as micronutrients in 0-15 cm depth with pH 8.17 (Jackson, 1973), EC 0.16 dS m^-1 (Jackson, 1973) and organic carbon 0.17% (Walkley and Black, 1934). The experiment was laid out in split-plot design consisting of 16 treatment combinations with three replications. Four potassium levels @ 0 (K₀), 10 (K₁₀), 20 (K₂₀), 30 kg ha^-1 (K₃₀) was applied through muriate of potash were kept in main-plot, while four zinc levels in kg ZnSO₄ ha^-1 @ 0 (Zn₀), 12.5 (Zn_12.5), 25 (Zn₂₅) and 37.5 (Zn_37.5) were kept in sub-plot. Green gram cultivar MH-421 was sown by maintaining spacing of 30 cm × 10 cm. The crop was raised and managed with all standard package of practices. Recommended dose of fertilizer (RDF) was 15:40 kg for N and P₂O₅ ha^-1 used (Anonymous, 2018b).
       
Green gram plants (5 from each plot) were uprooted with the help of the fork without damaging the roots at 40, 50 DAS and at harvesting and weigh the nodule after counting. The same plants were used for recording all growth and yield attributes and average of these observations were worked out. After harvesting and sun-drying of crop, seeds were separated in each plot and calculated it on the hectare basis (q ha^-1) for yield estimation. Straw yield was calculated by subtracting grain yield from biological yield of individual plot. Protein content in grain was determined by multiplying nitrogen content in seed (%) by a factor 6.25. Seed index is calculated by counting 100 seeds. The prices of the inputs prevailing at the time of their use were considered for working out the economics of treatments. Net monetary returns (Rs. ha^-1) was calculated by deducting the cost of cultivation from gross monetary returns (Rs. ha^-1). Benefit-cost ratio was worked out by dividing the gross monetary returns by cost of cultivation. The critical differences for all the parameters were calculated to compare the treatment means by proper methods using online statistical package OPSTAT developed by Sheoran et al., (1998).

Crop growth and yield attributes
 
Result revealed that (Table 1 and 2) the application of different potassium and zinc levels influenced growth and yield attributes of green gram significantly. Plant height (cm), number of branches per plant, dry matter production per plant (g), number of pods per plant were increased significantly at 40, 50 DAS and at harvest with every successive increase in potassium and zinc levels. Highest value of these parameters was recorded under K₃₀ and Zn_37.5 treatment that was statistically at par with the K₂₀ and Zn₂₅ treatment, respectively and minimum observations recorded in control treatments. It could be attributed to the fact that potassium enhances plant vigour and strengthens the stalk, further it has synergistic effect with nitrogen and phosphorous resulted in better plant growth and a greater number of branches per plant (Goud et al., 2014).
 

 

       
Results (Table 1) showed that the number of nodules and their fresh weight at 40 and 50 DAS were significantly influenced by the application of potassium but the effect of zinc was non-significant. Highest number of nodules and fresh weight of nodules were found under K₃₀ treatment (17.07 and 0.111g) followed by K₂₀ treatment (15.27 and 0.087g). Both the treatments were statistically at par but significantly superior over the K₀. This might be due to the fact that potassium in plant system enhances enzymes activity as well as activity of cytokinin. The results are in agreement with the findings of Ranpariya and Polara (2018).
       
Number of seeds per pod (Table 2) was significantly affected by different levels of potassium and zinc. Highest number of seeds per pod was observed under K₃₀ (9.43) and Zn_37.5 (9.32) treatments which were at par with K₂₀ and Zn₂₅ treatment, respectively. The results are in agreement with the findings of Sadaf and Tahir (2017).
 
Crop yield
 
Seed and straw yield (Table 2) of green gram was significantly affected with the application of potassium and zinc levels. Highest seed 11.42 and 10.38 q ha^-1; straw 13.36 and 11.89 q ha^-1 and biological yield 24.78 and 22.27 q ha^-1 recorded with K₃₀ and Zn_37.5 treatment, respectively, which was found statistically at par with K₂₀ and Zn₂₅ treatment, respectively and significantly superior over K₀ treatment. The positive effect of potassium and zinc in photosynthesis partitioning, cell elongation, higher nutrients uptake and more over biosynthesis of indole acetic acid resulted in higher plant height and number of branches per plant and ultimately helped in realization of higher crop yield. The above results found are in conformity with the results of Thesiya et al., (2013) and Ranpariya and Polara (2018). The interaction between of potassium and zinc was found non-significant in case of yield. No significant effects of different potassium and zinc application were observed on harvest index of green gram.
 
Effect on quality
 
Application of potassium significantly increased the protein content and seed index (Table 2). Maximum protein content (22.94%) and seed index (4.26 g) was recorded with K₃₀ treatment, followed by K₂₀ treatment and both were found statistically at par to each other but significantly superior over rest of the treatments. This might be due to the synergistic effect of potassium on nitrogen which facilitates uptake and assimilation of N into simple amino acids and amides, higher photosynthetic activity, followed by efficient transfer of metabolites and subsequent accumulation of these metabolites in the seed with the resultant increase in the size and weight of individual seed. The results are in agreement with the findings of Kurhade et al., (2015). Application of zinc increased the protein content (21.07 to 21.94%) and seed index (3.77 to 4.13) but effect was non- significant with successive increase in dose.
 
Economics
 
The perusal of data in Table 3 indicates that highest gross monetary returns (Rs. 83447 ha^-1) were fetched under K₃₀ Zn_37.5 treatment followed by K₂₀Zn_37.5 (Rs.83378 ha^-1) treatments. The net monetary return (Rs.31528 ha^-1) and the B:C ratio (1.61) was maximum found under K₂₀Zn₂₅ treatment.
 

Based on the research findings, it may be concluded that the application of 20 kg K₂O ha^-1 and 25 kg ZnSO₄ ha^-1 in green gram was found optimum in term of growth, yield attributes, yield, quality and economics (highest net benefit) in coarse-textured medium K status soil.

The necessary facilities and services provided by Regional Director, RRS Bawal and Head, Department of Soil Science, CCS HAU, Hisar is highly acknowledged.

The authors declare that they have no known competing financial interests that could have appeared to influence the work reported in this paper. The authors have no conflict of interest.