Effect of Nutrient Management Practices on Sustaining Soil Health and Quality of Soybean (Glycine max L.) under Rainfed System in Western Himalayas

Agricultural production and sustainability are significantly influenced by soil health, particularly in rainfed ecosystems where soil fertility and water availability are major limiting factors. Known for their rugged landscapes and fragile soils, the Western Himalayas pose significant challenges like erosion, nutrient depletion and declining organic matter, aggravated by unsustainable agricultural practices (Singh et al., 2021). In India soybean [Glycine max (L.) Merrill] is a significant pulse as well as oilseed crop. As a legume crop, plays an important role in mountain regions of Great Himalayan ranges contributing to soil fertility through biological nitrogen fixation and improving livelihoods of the farmer community (Patel et al., 2018). Glycine max L. is among the most cost-effective and nutrient rich crops, with high protein (36-40%) and oil (20%) content (Raghav et al., 2019), thus, it is used to augment the protein requirement of humans in their diets.
       
In 2022-23, Himachal Pradesh produced 6.09 metric tonnes of soybeans on 10.75 ha of land, with a productivity of 756 kg ha^-1 (Department of agriculture, HP, 2023), which is below the optimal productivity of 1600-2000 kg ha^-1 under rainfed condition (National Food Security Mission, 2018). Steep topography, development of multi nutritional deficiencies brought on by insufficient organic resource recycling and imbalance fertilizer application all contribute to low production (Chaturvedi et al., 2010). Keeping in view the land as a limiting factor, low productivity and importance of the crop, it is the need of the hour to find best nutrient management practices for sustaining soil health and crop yields.
       
Soybean, with its high protein and oil content, requires a large amount of nutrients (Sharma et al., 2019), therefore exploration of nutrient management options, which can maintain ample nutrient supply required for various metabolic and physiological processes in the plant system. Various researchers had established the fact that neither inorganic nor organic amendments alone can maintain adequate availability of nutrients and organic carbon in soil (Kumar et al., 2020). In assurance that the crop’s nutritional requirements are satisfied, soil testing as a part of nutrient management aid in recognition of any nutrient deficiencies in the soil, letting farmers to change their fertilizer additions accordingly. Hence, the present investigation entitled “Effect of nutrient management practices on sustaining soil health and quality of soybean (Glycine max L.) under rainfed system in Western Himalayas was conducted with the objective to find sustainable nutrient management practices for promoting soyabean production in the Lesser Himalayan ranges.

The field trial of the experiment was laid down at the experimental farm of CSK HPKV-Hill Agriculture Research and Extension Centre, Bajaura, H.P. (India) during Kharif 2023, to undertake soil and crop responses against different nutrient management practices. The study site was situated at 31^o50'26"N latitude and 77^o10'12"E longitude at an altitude of about 1090 m amsl. The site comes under mid hill sub-humid zone, with an average rainfall of 940-950 mm annually. Meteorological data sets related to the crop season are provided in Fig 1.


       
The research area soil had a silt clay loam texture and a neutral reaction of around 6.5. Soils have organic C content of 7.30 g kg^-1, medium in available N and K (252 and 159 kg ha^-1), while rich in available P (26.60 kg ha^-1) and micronutrients viz., Fe, Mn, Zn and Cu (14.60, 15.30, 2.30 and 0.78 mg kg^-1) (Table 1) were sufficient.


       
A randomized block design was used to set up the experiment, which included eight treatments (Table 2), replicated three times. Soybean (variety-palam soya) was taken as the test crop. The recommended dose for the test crop is 120 kg N, 60 kg P₂O₅ and 40 kg K₂O ha^-1. Following the soybean harvest, soil samples were taken from each plot at a depth of 0-0.15 m.


       
After being air dried and crushed using a wooden pestle and mortar, sieved (2 mm) and placed in plastic bags for examination. The pH and EC of the soil was determined in pH/EC meter using a (1:2) soil:water suspension (Richards 1954). Organic Carbon (OC) was calculated using the rapid titration (Walkley and Black 1934), available N was determined using alkaline permanganate method (Subbiah and Asija 1956), available P was determined using colorimetric method (Olsen et al., 1954), available K was determined using flame photometric method (Jackson, 1973), available Fe, Mn, Cu and Zn was determined using atomic absorption spectrophotometry (Jackson, 1973) (Table 3). Grain and stover samples were collected from each plot during harvest and oven-dried at 60±5^oC, sieved (1 mm) for analysis. For P and K estimation, samples were digested in a di-acid mixture (HNO₃:HClO₄, 4:1) following Piper (1966) procedures. Separate digestion for N estimation was performed using a digestion mixture (potassium sulfate, copper sulfate, mercuric oxide and selenium powder) as per Jackson (1973).


 
Protein (%)
 

        Protein content (%) = N content x 6.25   (Jones 1941)

 
Nutrient uptake analysis 
                                                                       

Nutrient uptake (kg ha^-1) = Nutrient content (%) × Yield (q ha^-1)

 

Total uptake = Seed uptake + Straw uptake

 
Statistical analysis
 
A statistical analysis was performed on the data attained from examination of the plant and soil characteristics. The data were interpreted using the randomized block design analysis of variance approach. Using Rstudio 4.4.2, the correlation coefficient was calculated to determine the relationship between soil characteristics and nutrient uptake in seed and straw. The usual approach outlined by Gomez and Gomez (1984) was used to perform statistical analysis.

Nutrient uptake
 
Significant variations in nutrient uptake characteristics were reported owing to nutrient management strategies used (Table 4 and 5). In 100% NPK + FYM treated plots, total N uptake rose significantly from 31.72 kg ha^-1 (control) to 92.58 kg ha^-1. The incorporation of similar treatment resulted in the highest total P and K uptake with 296.4 and 182% increase above control. Besides, NFP (T₃) and FYM + biofertilizers (T₈) treatments increased the plant P uptake by 82.90 and 114.8% and K uptake by 67.45 and 75.59%, respectively. As per the results it has been observed that N, P and K uptake showed increasing trend with raising fertilizer application along with FYM, synergy of inorganic and organic inputs fostered better root development, nutrient efficiency (Saket et al., 2014), as FYM improves soil porosity and structure (Sharma et al., 2016), enabling more efficient absorption of essential nutrients (Sawarkar et al., 2014). FYM + biofertilizers combination outperformed the NPF in N and P uptake owing to addition of Rhizobium and PSB which facilitates the nitrogen fixation in soyabean and solubilization of P (Girma et al., 2017).



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The findings of the study also revealed that the application of 100% NPK + FYM resulted in maximum uptake of micronutrients viz., iron, manganese, copper and zinc in seed and straw of soyabean. Grain’s Fe uptake varied between 28.93 g ha^-1 (T₁) to 31.39 g ha^-1 (T₇). In addition, T₇ had a significantly greater Fe uptake in straw than T₆, T₅, T₄ and T₈. The maximum total Mn uptake was also documented in T₇ (45.60 g ha^-1) followed by T6 (44.94 g ha^-1). Copper uptake in grain was also significantly higher in T7 (4.76 g ha^-1) which experienced an increase by 14.98 % over control and was statistically at par with T6 (4.55 g ha^-1) and T₅ (4.33 g ha^-1). Further, total Zn uptake ranged from 45.86 g ha^-1 (T₁) to 49.91 g ha^-1 (T₇) experiencing an increase of 8.83% over control. It is evident from the results that uptake of micronutrients (Fe, Mn, Cu and Zn) varies slightly under different practices but conjoint use of NPK and FYM significantly outclassed other treatments. The synergistic interaction between FYM and chemical fertilizers optimizes nutrient availability, FYM provides organic acids that enhance micronutrient availability by reducing fixation in soil colloids, (Singh and Gupta, 2015; Gupta et al., 2020) boosting crop micronutrient uptake and yield (Singh et al., 2013).
 
Soybean quality
 
The protein content was lowest under control (34.10%) and highest (37.40%) with 100% NPK + FYM, which was statistically comparable to T6 (36.50%) (Fig 2), showing decrease of 8.82% as compared to treatment T₇. In comparison to T₆ (19.58%), T₅ (19.32%) and T₄ (19.32%), T₇ (19.72%) had significantly higher oil content. In terms of soybean quality, protein and oil content were reported significantly higher under integrative supply of chemical fertilizers and FYM by ensuring adequate N, P and K supply. Moreover, the increased availability of N and P (resulted in better root formation) ultimately led to higher absorption of nitrogen by seeds (Shah et al., 2019). FYM + biofertilizers was higher over NFP, T₂ (FYM alone) and control, owing to that rhizobium and PSB, further enhance soil fertility by fixing atmospheric nitrogen and solubilizing bound phosphorus, ensuring a consistent nutrient supply throughout the growing season (Nagar et al., 2018). The upsurge in oil content with increasing fertilizer doses may be credited to sulfur (incorporated via SSP) as a decisive nutrient for oil (Triacylglycerol) content in seeds (Bhattacharjee et al., 2013; Shah et al., 2019).


 
Soil fertility
 
Soil pH, a key factor influencing nutrient availability in the soil, was observed to be nearly neutral in the experiment, varied from 6.45 (T₇) to 6.51 (T₁). None of the fertilizer management techniques had a significant effect on soil EC; values between 0.20 and 0.25 dS m^-1 showed safer limits (<0.8 dS m^-1) for plant growth and development (Kumar et al., 2020). Soil organic carbon (OC), a CO₂ sink and nutrient regulator, increased by 5.87% with 100% NPK + FYM compared to the control (Table 6). A slight pH decrease under treatments is likely due to soil acidification (Paliwal et al., 2021), from nitrogenous fertilizers, influenced by their type, rate and duration of use. Further, combination of inorganic fertilizers and FYM increases soil OC through increasing biomass production of soybean (Kumar and Meena, 2015), which decompose and contribute to build up of soil OC during crop growth (Thakur et al., 2011; Singh and Bandyopadhyay, 2012). The notable increase in available N under T₈ can be due to Rhizobium’s (applied as biofertilizer) capacity to fix atmospheric nitrogen enhancing the availability of N to plants and in soil (Saikia et al., 2018; Raklami et al., 2019). Application of 100% NPK + FYM recoded an increase in available P and K by 51.29 and 28.78% with respect to control. The rise in available P and K with inorganic fertilizers and FYM owing to straight nutrient addition and reduced fixation through humus-clay interactions, leading to more availability of nutrients in the soil (Thakur et al., 2011).  Correspondingly, available nutrient status rose vis-à-vis higher fertilizer dosages, results from suitable replenishment of nutrients through sources (Hekmat et al., 2019). Availability of iron and manganese in soil varied from 13.02 and 16.09 mg kg^-1 (T₁) to 14.32 and 17.85 mg kg^-1 T₃ (NFP). Although, combined application of FYM and NPK led to slight decrease in Fe and Mn compared to initial levels (Table 6). Application of Jeevamrit and Ghanjeevamrit in NFP increases the solubility of Fe and Mn by boosting the activity of chelating agents (organic acids) during decomposition, preventing their fixation into unavailable forms and making them more accessible for plant uptake, improving soil fertility and crop health (Maqueda et al., 2011; David et al., 2022). The combination of various nutrient management practices did not show any significant increases in Cu and Zn concentration.


 
Correlation studies
 
Comprehensive overview of the relationship between variables used in the study, shows that higher nitrogen absorption is strongly linked (r ≈ 0.96) to better protein content, indicating that nitrogen is an essential nutrient for protein synthesis in plants (Almaz et al., 2017). Positive correlations between nutrient uptake and protein/oil content underscore the need for nutrient-rich soils to improve crop superiority (Awasthi et al., 2020). Total P uptake is strongly positively correlated with Total N and K uptake (r»0.98 and r»0.99), indicates synergistic relation among N, P and K uptake (Mamia et al., 2018). SOC and nutrients uptake relation highlights that more OC build up support nutrients uptake, likely due to enhanced nutrient availability in organic matter rich soils (Ozlu et al., 2019).  pH is negatively correlated with Total N (r ≈ -0.96), P (r ≈ -0.94) and K uptake (r ≈ -0.93), suggesting that slightly acidic soils favor nutrient uptake, possibly due to increased nutrient solubility (Puli et al., 2016). The strong correlations between N, P and K uptake underscore the importance of balanced fertilization strategies are crucial for optimal crop growth (Chakraborty and Hazari, 2016). Strong correlations of SOC with soil macronutrients (N, P, K) and micronutrients (Fe, Mn, Cu, Zn) show that organic matter is a critical factor for nutrient availability (David et al., 2022) (Fig 3).

Results of the study had reported that application of balanced fertilizers (N, P, K) along with FYM had positive impacted on soil OC, nutrient availability, uptake proficiency and quality characteristics of soyabean. When recommended fertiliser dosages were applied in conjunction with FYM, the highest nutrient uptake, protein and oil content was recorded in soybean. This was equivalent to adding 75% inorganic nutrients and 25% FYM-based N. Crop quality is significantly influenced by different nutrient management practices, as seen by trends in oil and protein content. Similar trend was reported for nutrient availability, in contrast available Fe and Mn was significantly higher in natural farming practices. Thus, it can be concluded that application of 100% RDF + FYM and 75% RDF + 25% FYM was comparable with each other and superior over other combinations in term of improving soyabean quality and maintaining soil fertility, indicating possibility of compensating 25% chemical fertilizers by using organic amendments in the region concerning health safety.

Sincere thanks are extended by the authors to the Department of Soil Science, CoA, Chaudhary Sarwan Kumar Himachal Pradesh Krishi Vishvavidyalaya, Palampur for providing the facilities and assistance required to carry out this study.
 
Disclaimers
 
The views and conclusions expressed in this article are solely those of the authors and do not necessarily represent the views of their affiliated institutions. The authors are responsible for the accuracy and completeness of the information provided, but do not accept any liability for any direct or indirect losses resulting from the use of this content.
 
Funding
 
Funding was provided by Department of Soil Science, CSK HPKV, Palampur.

No, I declare that the authors have no competing interests (financial and/or non-financial interests) regarding the publication of this article. This manuscript had been finalized under the set guidelines and does not include any unethical matter.