Response of Summer Mungbean [Vigna radiata (L.) wilczek] to Foliar Potash Fertilization under Different Moisture Regimes

Pulses are wonderful gift of nature, can be grown on wide range of climatic condition and soils. They are rich in protein and considered as main protein source for vegetarians. Pulses are the second major constituent of Indian diet after cereals. Among the pulses greengram constitutes 24.20% of protein and superior as compared to others (Imran et al., 2015). Greengram [Vigna radiata (L.) Wilczek] is locally called as mungbean belongs to family fabaceae/leguminaceae. It is annual in nature, generally short duration and drought resistant crop which can also be grown on low fertile soils. The symbiotic association was seen between roots of mungbean with Rhizobium bacteria and fixes the atmospheric nitrogen (58-109 kg ha^-1) into the soil (Ali, 1992). Mungbean is found rich in lysine, making its protein an exceptional supplement to rice in terms of balanced human nutrition (Yadav et al., 2009). Among the tools of crop production, irrigation turn out to be the most important factor in the changing global scenario. Day by day the requirement of water during summer months is increasing due to high temperature and higher evapotranspiration needs. Adequate water is required at all growth stages of mungbean, but it is very much susceptible to water stress during flowering and pod filling stage. Shortage of water during these sensitive stages will cause significant reduction in yield. Water stress negatively affects many plant processes including photosynthesis and transpiration (Ohashi et al., 2006) etc., which also cause substantial reduction in dry matter accumulation (Reddy et al., 2004). Scheduling of irrigation is the major factor which plays a key role in producing higher yields of summer crop. Foliar nutrition may be a useful option particularly for the areas where soil application of fertilizers often leads to locking or loss of nutrients. Potassium influences the water economy and crop growth through its effects on water uptake, root growth, maintenance of turgor, transpiration and stomatal regulation. Potassium is one of the macronutrients which plays a major role in plant growth and sustainable crop production. It involves in activation of more than 60 plant enzymes (Bushkh et al., 2011). It imparts resistance in plants against diseases and pests attack. It also helps in maintaining the turgor pressure of the cell which is necessary for cell expansion. It also helps in osmo-regulation of plant cell, support in opening and closing mechanism of stomata (Yang et al., 2004). Taken as whole, potassium is an enzyme activator, helps in synthesis of starch and protein, helps in metabolism, plays major role in stomatal regulation, also takes part in chlorophyll formation and grain development. Potassium (K+) is reported as an important element in reducing the ill effects of soil water stress. Foliar application of potassium increases the drought tolerance in mungbean plant (Thalooth et al., 2006). Application of potassium at the time of flowering showed the beneficial effect on all the growth characters (Beg et al., 2013). Hence, relation between potassium and water stress became an important aspect of research in Meerut, (U.P) to avoid adverse effects of higher temperature during summer season. Keeping this in view the following study was formulated to study the “Response of summer mungbean to foliar potash fertilization under different moisture regimes”.

The experiment was conducted at Technology Park, Sardar Vallabhbhai Patel University of Agriculture and Technology, Meerut (U.P.) during 2018. The soil of the experimental field was well drained, sandy loam in texture and slightly alkaline in reaction (7.73). It was low in organic carbon (0.46%) and available nitrogen (176.3 kg ha^-1), medium in available phosphorus (16.4 kg ha^-1) and potassium (149.2 kg ha^-1). The treatments consisted of 2 levels of irrigation I1 (0.6 IW/CPE) and I2 (0.4 IW/CPE ratio) in main plots and six levels of foliar potassium application viz., T₁-control, T₂-1% K by KCl at flowering stage, T₃-1% K by KNO₃ at flowering, T₄-1% K by (KCl + KNO₃) at flowering, T₅- 1% K by KCl at flowering and pod development stage, T₆-1% K by KNO₃ at flowering and pod development stage, were tested in split plot design replicated thrice. Seed rate of 25 kg ha^-1 of Pant Mung-5 variety was used for sowing. Five cm deep furrows were opened at a row distance of 30 cm with the help of furrow opener, manually. Recommended dose of fertilizer was applied @ 20 kg N ha^-1 and 40 kg P₂O₅ ha^-1 to all the treatments. The whole amount of nitrogen and phosphorous were given through DAP (18% N and 46% P₂O₅) and urea (46% N) as basal dose i.e. at the time of sowing and foliar potassium fertilizers were given as per treatments to each plot. During crop period, the irrigations were given based on climatological approach, at IW/CPE ratio of 0.6 and 0.4, as per treatments. The evaporation was recorded every day from USWB (United States Weather Bureau) Class A open pan evaporimeter installed at IIFSR, Modipuram. In totality five irrigations were scheduled to the treatment with 0.6 IW/CPE (on 6^th April, 22^nd April, 2^nd May, 19^th May and 28^th May) and 3 irrigations were scheduled to the treatment with 0.4 IW/CPE ratio (on 16^th April, 2^nd May and 24^th May). The data recorded during the course of investigation were subjected to statistical analysis as per method of analysis of variance.

Effect of irrigation regimes on growth and yield of mungbean
 
Growth parameters
 
The data pertaining to growth parameters indicated that plant height, number of leaves, drymatter accumulation plant^-1 and branches plant^-1 generally increased with increasing number of irrigations at all the stages of crop growth. Scheduling of irrigation at 0.6 IW/CPE ratio (I1) recorded significantly taller plants (55.1 cm), higher leaf area index (3.77), Number of leaves plant^-1 (5.36), Number of branches plant^-1 (4.88), drymatter accumulation (12.4 g plant^-1) at harvest as compared to 0.4 IW/CPE ratio (I2) (Table 1). This might be due to more availability of moisture and essential nutrients under frequently irrigated conditions, maintenance of higher water status in plants, which resulted into more absorption of PAR, higher rate of photosynthesis, cell division and cell enlargement that helps in the formation of taller, thicker stem and root system, which ultimately increased the number of branches plant^-1 and drymatter accumulation. Similar results were also found by Patel et al., (2011) and Chaudhary et al., (2015) in mungbean.


 
Yield and yield attributes
 
Irrigation scheduled at 0.6 IW/CPE ratio (I1) recorded significantly higher number of pods plant^-1 (16.8), grains pod^-1 (8.2), test weight (34.2 g), grain yield plant^-1 (4.3 g), grain yield (1100 kg ha^-1) and straw yield (2381 kg ha^-1) over 0.4 IW/CPE ratio (I2) (Table 2). The probable reason for increase in these yield attributing characters was due to frequent water supply that resulted in increasing uptake of water and nutrients. This helped in keeping larger photosynthetic green surface and provided the longer reproductive phase which in turn improved storage and translocation capacity to attain higher allocation of drymatter in grains. The highest grain and straw yield at 0.6 IW/CPE ratio (I1) were mainly due to sufficient moisture supply during the entire growth period, increased the soil moisture status which resulted into higher leaf water potential, higher photosynthesis, consequently increased the drymatter production and yield attributes, which ultimately increased grain yield and straw yield of mungbean. Similar observations were also made by Yadav and Singh (2014) and Patel et al. (2016) in mungbean.



Effect of foliar potassium nutrition on growth and yield of mungbean
 
Growth parameter
 
The significantly higher values of growth parameters like plant height (56.0), LAI (3.55), No. of branches plant^-1 (4.65), Drymatter accumulation (12.7 g plant^-1) and no. of leaves plant^-1 (5.37) were recorded under foliar applied 1% K through KNO₃ at flowering and pod development stage (T₆) and remained on par with 1% K spray through KCl at flowering and pod development stage (T₅) and the lowest was recorded under control treatment (T₁) (Table 1). This might be due to the involvement of potassium in cell division and cell expansion as well as the positive influence of potassium on water and nutrient uptake, thus creating the cell turgor necessary for growth, resulting in higher plant height, LAI, no. of branches and leaves plant^-1 and higher drymatter accumulation. These results are in close conformity with those of Govind and Thirumurugan (2000) in mungbean, Goud et al., (2014) in chickpea and Sanjay (2015) in mungbean.
 
Yield and yield attributes
 
The higher values of yield attributes viz., namely number of pods plant^-1 (17.2), number of grains pod^-1 (8.3), test weight (33.7), grain yield plant^-1 (4.4), grain yield (1152 kg ha^-1) and straw yield (2544 kg ha^-1) were recorded with the foliar application of 1% K through KNO₃ at flowering and pod development stage (T₆) followed by 1% K by KCl sprayed at flowering and pod development stage (T₅) than the control (T₁) (Table 2). This increase in number of pods plant^-1 and number of grains pod^-1 might be due to the increase in the fruit setting, diversion of energy towards sink followed by efficient transfer of metabolites and subsequent accumulation of these metabolites in the grains, which results in increase in the size and weight of individual grain. The increase in number of pods plant^-1, grains pod-1 and test weight resulted into higher grain yield plant^-1. Increase in yield attributes finally resulted into higher grain and straw yields. These results are in close proximity with the findings of Govindan and Thirumurugan (2000) in mungbean, Beg et al., (2013) in black gram and Lakshmi et al., (2018) in urdbean.
 
Effect of irrigation regimes on economics, water use efficiency and water productivity of mungbean
 
Economics
 
The irrigation scheduled at 0.6 IW/CPE ratio (I1) fetched significantly higher gross returns (Rs 66163 ha^-1), net returns (Rs 41897 ha^-1) and B:C ratio (2.7) as compared to 0.4 IW/CPE ratio (I2) (Table 3). The higher values of these parameters under 0.6 IW/CPE ratio irrigation schedule were mainly due to higher grain yield and straw yield under 0.6 IW/CPE ratio and only marginal increase in cost of cultivation. Similar results were also reported by Patel et al., (2016) in mungbean and Deewan et al., (2017) in cluster bean.


 
Water use efficiency
 
Significantly higher value of water use efficiency (2.17 kg ha-mm^-1) was obtained under I1 (0.6 IW/CPE) irrigation schedule but significantly higher water productivity was obtained under 0.4 IW/CPE ratio (I2) (Table 3). Higher moisture availability, increased growth, yield attributes and yield that might be responsible for increased WUE in mungbean  under I1 irrigation schedule (0.6 IW/CPE ratio).
 
Effect of foliar potassium nutrition on economics, water use efficiency and water productivity of mungbean
 
Economics
 
The results revealed that the foliar application of 1% K through KNO³ at flowering and pod development stage (T₆) incurred higher gross returns (Rs 69,038 ha^-1), net returns (Rs 45,096 ha^-1) and B:C ratio (2.87) than control (T₁) (Table 3). The higher values of these parameters under T₆ treatment was mainly due to higher grain yield and straw yield and only marginal variation in cost of cultivation. Similar results were also reported by Goud et al., (2014) in chickpea.
 
Water use efficiency
 
Significantly higher WUE and water productivity were recorded under foliar application of 1% K through KNO₃ at flowering and pod development stage (T₆), followed by 1% K through KCl at flowering and pod development stage (T₅) than control. In general, potassium is considered to be a better osmoticum, which favors maintenance of internal water balance, cell turgidity, inducing drought tolerance and helping in transport of carbohydrates which might be the reason for higher WUE and water productivity (Lugg and Sinclair, 1979). Achitov (1961) suggested that K increased water uptake and improved water use efficiency.

From the obtained results, it may be concluded that foliar application of 1% K through KNO₃ or KCl at flowering and pod development stages under 0.6 IW/CPE ratio irrigation schedule gave best results in terms of growth parameters, yield attributes and yield, and also proved to be beneficial for summer mungbean in terms of gross returns, net returns and B:C ratio.