Soil Application of Different Nutrient Levels with Soil Amendment Charred Rice Husk and Seed Treatment of Arbuscular mycorrhizae: Effects on Crop Productivity and Nutrient Uptake on Groundnut (Arachis hypogaea L.)

Groundnut (Arachis hypogaea L.), belongs to the legume family (Fabaceae). Peanuts are often referred as poor man’s protein. They are widely cultivated in India, Africa, USA, China and other countries. India occupies the first position in terms of area and second position in terms of production with a cultivated area of 5.34 million hectares and production of 7.46 million tons with average productivity of 1398 kg ha^-1 (DES, 2018-19) Availability of nutrients is the main factor which determines the productivity of the groundnut, especially during the critical stage (Balasubramanian et al., 2020).
               
The annual rice husk available in India is around 24 million tons (Shwetha et al., 2014). Charred rice husk is a unique adsorbent material with 20 to 30% pore space. Normally arbuscular mycorrhiza is a mutualistic relationship between host plants and can provide nutrients to the host plant in exchange for carbohydrates provided by the host plant for the fungi and seeds inoculated with arbuscular mycorrhiza are generally more efficient in the utilization of nutrients and lead to improved plant growth (Osseni et al., 2010). The present study was carried out on the influence of different levels of nutrient management practices with soil amendment of charred rice husk along seed treatment of arbuscular mycorrhiza on productivity and nutrients use on groundnut crop during summer, kharif and rabi seasons respectively.

Field experiments were conducted summer, kharif and rabi seasons of 2016-17 and 2017-2018 at AC and RI, TNAU, Madurai. The experimental field was sandy loam in texture and belongs to vylogam series. The structural morphology of charred rice husk was studied by using a scanning electron microscope at low and high resolutions and diameter varied from 3-4μm. The soil was low in available nitrogen (151.50, 158.75 and 156.00 kg ha^-1), medium in available phosphorus (21.20, 24.00 and 23.00 kg ha^-1) and high in available potassium (191.50, 199.50 and 197.00 kg ha^-1). The experiment was laid out in a split plot design with three replications. The main plots consisted of three levels of irrigation scheduling viz.,  I₁- 0.8 IW/CPE, I₂- 0.6 IW/CPE and I₃- 0.6 IW/CPE ratio and sub plot comprised of four level of nutrient management practices viz., N₁- 75% of recommended dose of fertilizer with 5t of charred rice husk, N₂- 50% of recommended dose of fertilizer with 5t of charred rice husk, N₃- 75% of recommended dose of fertilizer with 5t of charred rice husk along with seed treatment of Arbuscular mycorrhiza and N₄- 50% of recommended dose of fertilizer with 5t of charred rice husk along with seed treatment arbuscular mycorrhiza. The bunch variety VRI-2 (100-110 days) with a seed rate of 125 kg kernel ha^-1 was used. The seeds were treated with arbuscular mycorrhiza culture at 10 g ha^-1 of seeds. Spacing of 30 cm between rows and 10 cm between plants was adopted. Soil amendment i.e., charred rice husk was applied at 5t (moisture-free) and incorporated well in the field before sowing of crop. The entire quantity of nutrients (N,P,K) i.e., 25:50:75 kg ha^-1 was applied as basal before sowing and no top dressing was done. Growth parameters, plant height, leaf area index dry matter production, pod and haulm yield and nutrient uptake were recorded and the experimental data collected were statistical analysis by Gomez and Gomez (1984).

Growth attributes
 
Plant height and dry matter production of groundnut were influenced by different levels of nutrient management practices (Table 1 and 2). The tallest plant heights of 48.25, 49.26 and 46.32 cm and dry matter production of 4998, 5030 and 4805 kg ha^-1 were observed with 75% of recommended dose of fertilizer adding with 5t of charred rice husk along with seed treatment of arbuscular mycorrhiza at harvest stage during summer, kharif and rabi seasons respectively. Application of nutrients along with soil amendment of charred rice husk which has supplied adequate moisture might have increased the microbial activity, presence of adequate carbon in the soil and provide a good microclimatic environment in the rhizosphere region of the crop (Balasubramanian et al., 2020). Further, conjugation of arbuscular mycorrhiza could have paved way for increased availability of nutrients resulting in enhanced root growth. It also creates a more adsorptive surface for the uptake of nutrients by the crop. The earlier works of Hogan (2011) and Zhang et al., (2014) corroborates the above findings.
 

 

 
Physiological parameters
 
Physiological parameters were significantly influenced by the application of 75% of recommended dose of fertilizer conjugated with 5t of charred rice husk along with seed treatment with arbuscular mycorrhiza (Table 3). Higher leaf area index with respect value of 3.89, 3.93 and 3.86 at harvest stage and leaf single photon avalanche diode (Table 4) with a value of 54.25, 55.34 and at 75DAS during summer, kharif and rabi seasons respectively. It might be due to higher chlorophyll content by application of sufficient amount of nutrients along with charred rice husk, leading to the higher photosynthetic efficiency by higher uptake and utilization of nutrients by the crop. This corroborates with the findings of Panwar (1991).
 

 

 
Yield
 
Concerning nutrient management practices, application of 75% of recommended dose of fertilizer in combination with 5t of charred rice husk along with seed treatment of arbuscular mycorrhiza recorded the higher pod yield (1783, 1935 and 1854 kg ha^-1) and haulm yield (4401, 4272 and 4950 kg ha^-1 during summer, kharif and rabi) and the data are furnished in Table 5a, 5b and 5c. The presence of growth-promoting substances due to the colonization of arbuscular mycorrhiza promoted plant growth and could have increased chlorophyll production by boosting the photosynthetic process and stimulating vegetative growth. Thus, an overall plant performance would have enhanced accordingly and finally reflecting through increased production of haulm (Gouda et al., 2018). Moreover, basal application of soil amendment of charred rice husk along with seed treatment of arbuscular mycorrhiza might have had a positive effect on the soil physical properties such as bulk density and pore space, which could have increased the water retention capacity. Enriched charred rice husk 1983 and haulm 5115 kg/ha. With respect to economics, among the organic manure treatments, the charred rice husk recorded the gross return of Rs.60300/ha., maximum net return of Rs.37457/ha and benefit cost ratio of 2.64 due to the cheaper material cost (Balasubramanian and Chinnamuthu., 2020).
 

 

 

 
Nutrient uptake
 
The uptake of nutrients (N,P,K) in 75% of recommended dose of fertilizer with 5t of charred rice husk and seed treatment with arbuscular mycorrhiza recorded the highest nitrogen, phosphorus and potassium uptake with the value of 106.02, 32.43 and 66.20 kg ha^-1 during summer, 106.37, 65.03 and 122.31 kg ha^-1 during kharif and 106.56, 30.03 and 59.14 kg ha^-1 during rabi seasons at 75 DAS and the data are furnished in Table 6, 7 and 8. Normally, charred rice husk being highly porous with the high specific surface area was attributed to the release of more nutrients in to soil and act as mulching on soil microflora. This could be explained due to the regulation of soil temperature, conservation of moisture and improvement in the humic acid content of the soil that are important factors in increasing the zymogenic soil microflora. In legume plants, the importance of arbuscular mycorrhiza symbiosis has been attributed to high phosphorus requirements on the nodulation and nitrogen fixation process. In this present study, seed treatment with Arbuscular mycorrhiza enhanced the growth of plants and also enhanced the uptake of phosphorus. Further, Arbuscular mycorrhiza has a specialized intracellular structure and highly ramified hyphae with very fine terminal tips, resulting in a surface to volume ratio that is greater and the cells that are inhabited by arbuscular develop elaborate machinery for active nutrient transfer (Steiner et al., 2011).
 

 

 

 
Soil enzyme activity
 
The experimental data revealed that the activity of the arylsulphatase, phosphatase and dehydrogenase enzyme were largely varied by different levels of nutrient management practices and the data are furnished in Table 9, 10 and 11. Application of 75% of recommended dose of fertilizer with 5t charred rice husk and seed treatment with arbuscular mycorrhiza recorded higher arylsulphatase, phosphatase and dehydrogenase enzyme activity of 78,88 and 84 µg g^-1 h^-1 during summer 72, 92 and 78 µg g^-1 h^-1 during kharif’ 76, 94 and 81 µg g^-1 h^-1 during rabi at 75DAS in the soil. The addition of soil amendment as rice husk served as a carbon source which enhanced the microbial biomass in the soil with the advancement of crop growth stages (Yao et al., 2006). Cohn et al., (1998) reported that an adequate supply of nutrients could enhance the nitrogen transforming microorganisms which could have increased the nutrient availability in the soil. Thus, it could have resulted in increased uptake of nutrients resulting in higher yield.