Effect of Phosphorus and Zinc Interaction on Performance of Green Gram [Vigna radiata (L.) Wilczek]

Green gram is an important pulse crop that can be grown twice a year. Its seed is more palatable, nutritive, digestible and non-flatulent than other pulses grown in country. It contains about 25% protein, which is almost three times that of cereals. At the national level, it is grown on 3.10 m ha land area and produces nearly 0.94 MT with an average productivity of 304 kg ha^-1  (Bairwa et al., 2014).
    
  There are estimates that more than 30% of agricultural soils globally are zinc deficient (Alloway, 2008) and 48% soils in India are zinc deficient (Singh, 2009). Phosphorus and zinc are essential nutrients required for normal plant growth. Green gram responds well to phosphorus nutrition since phosphorus is involved in energy transformation and cell division. It is required for flowering and fruiting including seed development. It also helps for better root growth to extract nutrients and moisture more efficiently from deeper soil layer under residual moisture condition leading to better growth and development of plants (Sarkar, 1992). Zinc is involved in auxin metabolism like, tryptophane synthesis, tryptamine metabolism, protein synthesis, formation of nucleic acid and helps in utilization of nitrogen as well as phosphorus by plants. Zinc also stimulates resistance for dry and hot weather, bacterial and fungal diseases and ribosomal fraction in the plants. It also promotes nodulation and nitrogen fixation in leguminous crops (Demeterio et al., 1972). Phosphorus and zinc deficiencies can cause reduction in yield of many crops because of their mutual antagonistic behavior on each other, resulting in phosphorus and zinc deficiency. Mutual application of dosages of phosphorus and zinc reveals significant effect on yield and yield attributes of green gram (Nissa et al., 2019 and Lokhande et al., 2018).
       
Under Jammu, condition only scanty work has been done on phosphorus and zinc in mung bean. A little or no information is available on phosphorus and zinc interaction under Jammu conditions in green gram. Keeping in view the above facts, the present study was carried out to investigate the effects of phosphorus and zinc interaction on yield and yield attributes of green gram in subtropical zone of Jammu.

A field experiment was conducted to study the effects of phosphorus and zinc interaction on yield and yield attributes of green gram [Vigna radiata (L.) Wilczek cv]. SML-668 at Research Farm of the Division of Soil Science and Agricultural Chemistry, SKUAST-J, Main Campus, Chatha during summer of 2015-16. The experiment comprising of four levels of phosphorus, i.e., 0, 20, 40 and 60 kg ha^-1 and four levels of zinc, i.e., 0, 5, 10 and 15 kg ha^-1, was conducted at Research Farm of the Division of Soil Science and Agricultural Chemistry, SKUAST-J, Main Campus, Chatha during summer of 2015-16. The treatments were laid in randomized block design (factorial) with three replications. Geographically, the experimental site was located at 32^o-40^o’ North latitude and 74-58^o’ East longitude with an altitude of 332 meters above mean sea level in the Shiwalik foothills of North-Western Himalayas. The experimental site was mainly sub-tropical in nature endowed with hot and dry early summers followed by hot and humid monsoon seasons. The initial physico-chemical properties of the soil were determined according to standard methods (Page, 1982; Bingham et al., 1982). The soil texture was sandy clay loam, low in organic carbon, nitrogen, sulphur and zinc and medium in phosphorus and potash, slightly alkaline in reaction with pH 7.93 and EC 0.15 dSm^-1. The seed of green gram cv. SML-668 were planted @ 20 kg ha^-1 in a plot size of 3×2 m², maintaining line spacing 30 cm. All the recommended package and practices were followed for raising a healthy crop. The data recorded on plant height(cm), number of pods plant^-1, 1000 seed weight (g), seed and stover yield (kg ha^-1) were subjected to statistical analysis by using the method of Steel and Torrie (1980).
 
Observations recorded
 
Yield and yield attributing parameters
 
Plant height (cm)
 
Plant height of five tagged plants was measured with the help of meter scale rod from the ground surface to the tip of the upper most fully opened leaf from net plot area of each plot. The observations were averaged to work out the mean plant height per plot.
 
Number of pods per plant
 
Number of pods from five tagged plants were counted separately from net plot area of each plot.
 
1000 seed weight (gm)
 
One thousand seeds were randomly taken from the bulk produce of each net plot and were counted and weighed.
 
Seed yield (kg ha^-1)
 
The threshed seeds of green gram obtained from each net plot were weighed separately and finally converted into kg ha-1 by multiplying with conversion factor given below:
                                     
 
Stover yield (kg ha^-1)
 
The total biological yield (Seed + Stover) from the net plot was recorded and stover yield was worked out by subtracting the seed yield from the biological yield and expressed in kg ha^-1 by multiplying the same conversion factor employed for seed yield of green gram.

Effect of phosphorus and zinc application on plant height (cm) of green gram (Table 1)
 

 
Plant height of green gram significantly increased with the successive levels of phosphorous, was highest (42.51 cm) at 60 kg ha^-1 and found to increase with time interval. The increase in plant height with the successive application of phosphorous might be due to the medium levels of available phosphorous in the experimental field and the adequate amount of phosphorous in the soil favoured rapid plant growth. The results obtained were in accordance with the results of Phogat et al., (2018) and Ram and Dixit (2001). The plant height was also significantly influenced by different levels of zinc and was highest (32.07 cm) at zinc 10 kg ha^-1 thereafter, it was found to decrease and the per cent increase in plant height at maturity was 11.26% and 15.02% with the application of zinc 5 and 10 kg ha^-1 and found to decrease with further application of zinc beyond 10 kg ha^-1. The increase in plant height with the addition of zinc was due to the response of green gram to zinc application in zinc deficient soil and also its involvement in synthesis of auxin which enhance the elongation process of plant development. The result was in accordance with (Kumar and Bohra, 2014) who reported highest plant height with the application of 10 kg zinc ha^-1 in cowpea.
       
A significant interaction was found between phosphorus and zinc with respect to plant height. The highest (48.70 cm) plant height was obtained at the combined application of phosphorous 60 kg ha^-1 and zinc 10 kg ha^-1 and found to decrease beyond this level. The decrease in plant height beyond zinc10 kg ha^-1 may be due to the antagonistic effect of zinc with the phosphorous and it was reported that the high levels of phosphorous may decrease the availability of zinc in soil (Mousavi et al., 2012).
 
Effect of phosphorus and zinc application on number of pods plant-1 and 1000 seed weight (g) of green gram (Table 2 and 3)
 

 

 
Application of different doses of phosphorous (0, 20, 40 and 60 kg ha^-1) to green gram significantly enhanced the number of pods per plant and 1000 seed weight (g). The maximum number of pods per plant (26.22) and 1000 seed weight (31.85 g) was recorded with phosphorous 60 kg ha^-1 over other treatments and the minimum number of pods per plant (19.99) and 1000 seed weight (24.98g) was recorded in control. The per cent mean increase in number of pods per plant and 1000 seed weight (g) with the application of phosphorous (0, 20, 40 and 60 kg ha^-1) was 15.66%, 22.36%, 31.17%, 9.53%, 17.09% and 27.50%, respectively. The increase in number of pods per plant and 1000 seed weight (g) with these levels might be due to various enzymatic activities related to phosphorus which controlled flowering and pod formation. Similar finding was also reported by Khan et al., (1999) in green gram and Phogat et al., (2018) in black gram.
       
Effect of zinc fertilization on number of pods per plants and 1000 seed weight (g) was significant up to zinc 10 kg ha^-1 and decrease with higher levels of zinc over 10 kg ha^-1. The maximum number of pods per plant (24.53) and 1000 seed weight (29.45 g) was recorded with zinc 10 kg ha^-1 over other treatments and the minimum number of pods per plant (21.85) and 1000 seed weight (27 g) was recorded in control. Zinc application up to certain levels effectively increased the number of pods plant^-1 which may be due to its direct influence on auxin synthesis but further increase in zinc levels found to have antagonistic effect on number of pods per plant. The results were in agreement with Ram and Katiyar, (2013) and Ram et al., (2004).
       
The interaction effect of phosphorus and zinc on number of pods per plant and 1000 seed weight (g) was observed significant and the maximum number of pods per plant (27.15) and 1000 seed weight (32.7 g) was with the combine application of phosphorous 60 kg ha^-1and zinc 10 kg ha^-1. It was reported that zinc application in combination with phosphorous resulted in significant increase in number of pods plant^-1 and 1000 seed weight (g) than the control up to certain levels, there after found to decrease due to negative interaction between phosphorous and zinc and such negative interaction may be due to reduction in zinc translocation through the endodermis and epidermis of roots that cause a reduction in its absorption by plant (Benvindo et al., 2014).
 
Effect of phosphorus and zinc application on seed and stover yield (kg ha^-1) of green gram (Table 4 and 5)
 

 

 
The data pertaining to the effect of phosphorous and zinc on seed and stover yield of green gram revealed that the seed and stover yield of green gram was significantly increasing with the successive levels of phosphorous (0, 20, 40 and 60 kg ha^-1). The highest seed (884.26kg ha^-1) and stover yield (2220.04 kg ha^-1) of green gram was observed with the application of phosphorous 60 kg ha^-1. The per cent increase in mean seed and stover yield of green gram with the successive application of phosphorous were 29.82%, 50.23%, 75.45%, 29.97%, 49.41% and 73.74%, respectively. The highest seed and stover yield of green gram with the application of phosphorous 60 kg ha^-1 may be due to response of green gram to applied phosphorus. Phogat et al., (2018), Bairwa et al., (2014)and Nandal et al., (1987) reported that phosphorous stimulates early root development, leaf size, tillering, flowering and grain yield.
       
The effect of zinc fertilization on seed and stover yield of green gram was significant and was found to increase with zinc fertilization up to 10 kg ha^-1 and further reported to decrease with increase in zinc levels. The per cent increases in mean of seed and stover yield of green gram were 14.27%, 26.39%, 13.91% and 26.74%, respectively with the application of zinc 5 and 10 kg ha^-1 and decrease with further increase in zinc i.e., 15 kg ha^-1. The interaction effect of phosphorous  and zinc on seed and stover yield of green gram was also highly significant and was maximum with the combined application of phosphorous  60 kg ha^-1 and zinc 10 kg ha^-1 (957.25 and 2398.30 kg ha^-1 respectively) and further reported to decrease with increase in zinc levels. Such decrease in the yield due to combined application of phosphorous and zinc might be explained as the antagonistic effect between these two elements. Ram and Katiyar (2012) and Teotia et al., (2000) reported the same result in green gram. It has been reported that the interaction between phosphorous and zinc occurred in soil because added phosphorous decreased the available zinc content in plants. The increase in seed and stover yield might be due to its role in biosynthesis of IAA especially due to its role in initiation of primordial for reproductive parts and partitioning of photosynthates towards them which resulted in better flowering and fruiting.

Based on the results, it is concluded that the optimum seed and stover yield (955.50 and 2398.30 kg ha^-1 respectively) of green gram were recorded with combined application of phosphorous 60 kg ha^-1 and zinc 10 kg ha^-1 and further decreased with increase in zinc levels clearly indicating antagonistic effect of phosphorous and zinc on each other as both the nutrients were mutually antagonistic. The other growth and yield attributing parameters of green gram like plant height (cm), number of pods plant^-1 and 1000 seed weight (g) were also showed same trend as that of seed and stover yield. Hence, it can be recommended to the farmers that to improve the productivity of green gram and sustainability of soil in the sub-tropical zone of Jammu division of J and K, the combined application of phosphorous 60 kg ha^-1 and zinc 10 kg ha^-1 is the best option.

Authors are highly thankful to the Division of Soil Science and Agricultural Chemistry, SKUAST-Jammu for providing all necessary facilities to conduct this study.