Effect of Zinc Sources on Nutrient Content and Uptake in Soybean [Glycine max (L.) Merril] under the Acidic Soil Conditions of Nagaland

Soybean is an important oilseed crop grown on a wide range of soil and agro-climatic conditions. Among the oilseed crops, soybean contain the highest protein 40% and oil 20%. It contents essential amino acids such as glycine, tryptophan and lysine which is similar to cow’s milk (Raghuwanshi et al., 2017). Zinc is an important micronutrient required in small amount in plants for activation of various enzymes, reproductive development and fertilization in plants. It plays an important role for production of hormone auxin (Ganeshamurthy et al., 2018).
       
Its deficiency in plants causes poor growth, yield, quality and affects the water uptake and transport in plants (Hafeez et al., 2013 and Pandey et al., 2018). Its deficiency is increasing worldwide. Low crop production in the North East region of India is seen mainly due to 60% of zinc deficiency (Kumar et al., 2016). Shukla et al., (2018) reported 4.62% of zinc deficiency in Nagaland. Zinc deficiency in this region may be due to slash and burn cultivation practices in the hills, leaching due to intense rainfall and runoff which declines the top soil fertility and causes zinc deficiency (Bandyopadhyay et al., 2018). Zinc deficiency can also be induced by leaching in acid soils where available zinc is low in plants (Sutradhar et al., 2016). Lack of restoring the soil fertility along with rapid removal of nutrient by the crop may also lead to zinc deficiency (Chen et al., 2002). It is thus required to be supplied in adequate amount for optimum growth in plants. However limited research has been done in micronutrient in this region. Therefore the present research was conducted to assessed the “Effect of zinc sources on nutrient content and uptake in soybean [Glycine max (L.) Merril] under the acidic soil conditions of Nagaland”.

The present investigation was conducted at the Experimental Research Farm, School of Agricultural Science and Rural Development (SASRD), Medziphema campus, Nagaland University, 2019 in the first year and at the State Horticulture Nursery, Green Park, Dimapur, 2020 in the second year. The soil parameters analysed initially are shown in Table 1. Datas on parameters such as NPK and Zn content and uptake in seed and stover were recorded during the first, second year and pooled. The experiment was conducted in randomised blocked design using the soybean crop variety JS 97-52. It consisted of 16 treatments and 3 replications. The zinc sources used were zinc 21% (ZnSO₄ 7H₂O) @1, 2.5, 5 kg ha^-1, Zinc 33% (ZnSO₄ H₂O) @ 1, 2.5, 5 kg ha^-1, Zn-EDTA 12% @1, 2.5, 5 kg ha^-1, Liquid ZnO @ 300, 600, 900 ml ha^-1. RDF was applied @ 20: 60: 40: 30: 1.5 (N:P:K: S:B) kg ha^-1 in all the plots irrespective of the treatment viz. T₁- 0 (Control), T₂- RDF + 1 Kg ZnSO₄ 7H₂O, T₃- RDF + 1 Kg ZnSO₄ H₂O, T₄- RDF + 1 Kg Zn-EDTA, T₅- RDF + 2.5 Kg ZnSO₄ 7H₂O ha^-1, T₆- RDF + 2.5 Kg ZnSO₄ H₂O ha^-1, T₇- RDF+2.5 Kg Zn-EDTA ha^-1, T₈- RDF + 5 Kg ZnSO₄ 7H₂O ha^-1, T₉- RDF + 5 Kg ZnSO₄ H₂O ha^-1, T₁₀- RDF+5 Kg Zn-EDTA ha^-1, T₁₁- 300 ml ha^-1 liquid ZnO, T₁₂- 600 ml ha^-1 liquid ZnO and T₁₃- 900 ml ha^-1 liquid ZnO. Lime was added @ 1/10 of LR before 20 days of sowing. The datas recorded were statistically analysed using the F-test (Gomez and Gomez, 1984).
 

Nutrient content
 
The N, K and Zn content in seed were observed to be significantly increased at T₉ in first and second years and pooled (Table 2). The highest N, K and Zn content in seed recorded were 6.30, 6.19 and 6.25% N, 1.69, 1.63 and 1.66% K and 53.69, 63.65 and 58.67 ppm Zn (Table 2), this was followed by  T₈ and T₁₀ in both the years and pooled. The lowest nutrient content in seed was recorded in control. However the P content in seed was not increased significantly and the highest P content was recorded in control plot i.e. 0.22, 0.21 and 0.21% P during both the years and pooled.
 

       
In Stover, the N, K and Zn content was significantly increased at T₉ followed by T₈ and T₁₀ among the other zinc sources during the consecutive years and pooled. The P content was not significantly increased except it was increased in the control i.e. 0.20, 0.18 and 0.19% P. The highest nutrient content in stover were 1.71, 1.69 and 1.70% N, 2.62, 2.42 and 2.52% K and 28.33, 28.65 and 28.49 ppm Zn (Table 3). The lowest was recorded at control.
 

 
Nutrient uptake
 
The NPK and Zn uptake in seed of Soybean were significantly increased at T₉ which was followed by T₈ and T₁₀ in 2019, 2020 and pooled. The highest N, K and Zn uptake in seed recorded during the first, second year and pooled were 114.31, 113.77 and 114.04 N kg ha^-1, 30.67, 29.96 and 30.32 K kg ha^-1 and 97.42, 116.98 and 107.20 g ha^-1 Zn (Table 4). However for P uptake, T₉ showed increased in P uptake as compared to the rest of the zinc sources but it failed to produce significant result. Similarly, in stover, the N, K and Zn uptake was significantly increased at T₉. The highest N, P and Zn recorded were 39.07, 38.12, 38.60 N kg ha^-1, 57.59, 53.88, 55.74 K kg ha^-1 and 62.27, 63.78, 63.03 Zn g ha^-1 in both the years and pooled respectively (Table 5) which was closely followed by T₈ and T₁₀. The lowest being recorded at control in both the seed and stover. The P uptake failed to produce significant result in stover and the highest was recorded in control (3.58, 2.99 and 3.29 kg ha^-1).
 

 

       
The significant increased in the nitrogen content and uptake in seed and stover of green gram @ 5.0 kg ha^-1 was also reported by Solanki et al., (2017). This increased in nitrogen content and uptake in seed and stover might be due to synthesis of protein, fat and carbohydrates due to stimulation by zinc application on the proteinase, dehydrogenease and peptidase enzyme (Balai et al., 2017). The application of zinc significantly decreased the phosphorus content in seed of black gram as compared to control (Meena et al., 2021). Yadav et al., (2021) reported significant increased in N, K and Zn content and uptake with the application of 6.0 and 4.0 kg Zn ha^-1 over control in pearlmillet. Keram et al., (2012) observed that nutrient uptake of N, K and Zn except total P increased significantly with the application of recommended NPK+Zn @ 20 kg ha^-1 in wheat. This reduction in P content and uptake may be due to the increased in the concentration of zinc which hinders the P absorption and translocation from the roots to the plants due the antagonistic effect between Zn and P (Singh et al., 2012). Choudhary et al., (2016) reported significant increased in K content and uptake in chickpea @ 5 kg Zn ha^-1 which might be due to its higher availability in the soil leading to more absorption by the crop. The increased in the Zn content and uptake might be due to positive response to zinc application in the soil which increases its availability in the soil leading to higher Zn uptake by the crops (Raghuwanshi et al., 2017).

From the experiment conducted, it was observed that the application of 5 kg ZnSO₄ H₂O ha^-1 + RDF (T₉) significantly increased the nutrient content and uptake of N, K and Zn which was followed by T₈ and T₁₀ among all the other zinc sources in soybean under the acidic foothill condition of Nagaland.