Effect of Phosphorus on Yield, Nutrient Acquisition and Use Efficiency of Groundnut in West Bengal, India

Groundnut (Arachis hypogaea L.) is world’s thirteenth most important food crop and originated from Mato Grosso do Sul region of Brazil (Gregory et  al., 1980) a self-pollinating legume. The herbaceous legume is fourth key source of edible oil and third chief source of vegetable protein (Taru  et al., 2008). It has a tremendous potential to mitigating the protein nutrition in poverty ridden countries of the world. It can fix atmospheric nitrogen in soils through root nodule bacteria and improves soil fertility. Groundnut seed contains 47-53% oil, 26% protein and 11% starch along with vitamin B and vitamin E (Das, 1997). It is an efficient cover crop for the land susceptible to soil erosion hazards.
       
Groundnut provides sustainability to the cereal-based cropping systems and ensures good economic return (Halder and Panda, 2014). Judicious application of fertilizer may raise groundnut production. Indian soils are poor in available P (Rokade and Patil, 1992). The ability of consumption of P is very low (20-25%) due to chemical fixation in soil. Further there is buildup of insoluble phosphates in soil where P fertilizers have been applied over long periods. The P deficiency is more acute in India as the country has to mainly dependent on imported raw materials (Guar, 1990). A wide discrepancy in response of groundnut to phosphorus fertilizer application is observed and the definite indications on balanced nutrition of groundnut are still inadequate and fragmentary in coverage. Therefore it is necessary to work out nutrient management strategy precisely for each agro-climatic region to increase the production level. On this background, present study aims to investigate the impact of various P fertilizer rates on groundnut pod yield, nutrient acquisition and the relation between pod yield and P-use efficiency (PUE).

The field experiment was carried out at the Instructional farm, Uttar Banga Krishi Viswavidyalaya, Cooch Behar, West Bengal, India (26°19`86² N latitude, 89°23`53² E longitude and altitude 43 meters above mean sea level), during summer seasons of 2016 and 2017. The soil is sandy loam and further classified as inceptisol (Chakraborty et al., 2019). The soil pH (4.3), organic carbon (1.8%), sand (50.4%), silt (19.3%), clay (30.3%) and available P (0.0049%) content were estimated by the methods as described by Jackson (1973), Walkley and Black (1934), Nelson and Sommers (1982), Deuis and Freitas (1984)  and Bray and Kurtz (1945)  respectively.

The experimental site classified under sub-humid climate zone with annual rainfall 3000 mm. During summer temperature is ranging from 21°C to 31°C. Meteorological observations were collected through automated weather station (AWS) installed at instructional farm of the institute. During experimentation temperature ranged between 5-35°C and received 144 mm and 245.4 mm precipitation for 2016 and 2017 respectively.
       
 
Three predominant and popular groundnut varieties,‘JL-24’ (early maturity), ‘Gangapuri’ (early maturity) and ‘TAG-24’ (medium maturity) were sown at a spacing of 30 cm × 15 cm (inter and intra row) during second fortnight of January in both the years. Four levels of P: 0 (P₀), 40 (P₄₀), 60 (P₆₀) and 80 (P₈₀) kg P₂O₅ ha^-1 in the form of Single Superphosphate (16% P₂O₅) were investigated. Experiment was laid out in a split-plot design and replicated thrice. Varieties were assigned in main plots and level of P in subplots. The plot size was 20 m². Effects of P fertilizer were studied after satisfying basic requirements of plants for nitrogen (20 kg ha^-1) and potassium (40 kg ha^-1). P fertilizer was applied as per treatment at the time of final land preparation. Hand weeding twice at 20 and 40 days after sowing (DAS) and earthing up was done at 40 DAS. Both the year crop was harvested during first week of May.
 
Observations recorded
 
During harvesting, replication wise plant samples were collected from 1 m² area for each treatment. The dry matter was calculated by oven drying the samples at 85±5°C (Halder and Panda, 2014). Yield data was recorded from net plot area. Groundnut shelling percentage was calculated as described by Halder and Panda (2014). Nutrient uptake values were worked out by multiplying its concentration with corresponding dry matter production at harvest. Additionally, agronomic efficiency (AE), agro-physiological efficiency (APE), physiological efficiency (PE), P partial factor productivity (PPFP), recovery efficiency (RE) and utilization efficiency (UE) were computed by using the following formulae (Eq. 1-6) to explore the PUE (Zhu et al., 2012).

                                                                               
                                                                                                                               

                                                                           
                    
 
 

 
 

 
                                                                                                                                                                                                                 

Protein content was estimated using the Kjeldahl method (Jones, 1931). Oil content in kernel was determined following the standard procedure as described by AOAC (1990).
 
Statistical analysis
 
Statistical analysis was done using GenStat version 11.0 software. The comparisons of treatment means were based on Duncan’s test at the p<0.05 probability level (p<0.05). Analysis of variance (ANOVA) was done for plant dry matter, number of pods per plant, kernels per pod, 100 kernels weight, pod yield, shelling percentage and PUE.

Plant dry matter
 
Dry biomass of the three selected varieties increased with  P rate (Table 1). Dry matter of ‘TAG-24’was higher (1027.4 gm^-2) compare to‘JL-24’ (939.9 g m^-2) and ‘Gangapuri’ (985.9 g m^-2). Application of P (P₄₀-P₈₀) recorded significantly (P£0.05) higher dry matter production than that of P₀ (0kg ha^-1). Dry matter accumulation for P₄₀-P₈₀ (40, 60, 80 kg ha^-1) was 5.5%, 7.7% and 10.9% higher than P₀ (Table 1). P is second major nutrient (Gervey, 1987) and its effect on root development well established. Sharma and Yadav (1997) reported that, P had a significant role in legume growth with extensive root development and ensuring good yield. Nitrogen and P together improved the supply of other nutrients to the plants, resulting in an increased photosynthetic area and hence more dry matter accumulation (Prihar and Tripathi, 1989). P application increases in plant height, leaf area index (LAI), number of branches, nodulation and seed yield (Sharma and Yadav, 1997; Balasubramanian et al., 1980) which increases dry matter production.


 
Yield attributes and yield
 
Advancement in P rates significantly increased yield attributes (pods per plant and 100-kernel weight) and pod yield. Whereas, P rates had failed to significantly affect the kernels per pod. Number of pods were significantly (P£0.05) influenced by groundnut varieties. Maximum number of pods per plant was recorded in variety ‘Gangapuri’ (50.6) than ‘TAG-24’ (41.9) and ‘JL-24’ (45.8) as shown in Table 1. Maximum number of pods (51.3) (Table 1) was observed with P₈₀ (80 kg ha^-1) which was 34% higher than P₀ (0 kg ha^-1). Highest 100-kernel weight (38.9 g) and pod yield (1.80 t ha^-1) recorded with the variety ‘Gangapuri’. Pod yield for P₄₀-P₈₀ rates were 15.4%, 27.3% and 39.9% higher than P₀. Shelling percentage also increased with advancement of P rate (Table 1). These results are in confirmation with studies carried out on influence of P on legumes as well as other non-legume (Shiyam, 2010; Kamara et al., 2011; Tran and Tu, 2011; Rezaul et al., 2013). Photosynthetic rate stimulated by P and increase in dry matter accumulation, which was particularly important for pod yield. Pod yield increased with P rate might be due to balanced fertilizer application, which resulted in higher number pod per plant and kernel weight. Pod yield, kernel yield and shelling percentage were significantly influenced by phosphorus (Halder and Panda, 2014).
 
Nutrient acquisition
 
Nutrient uptake increased gradually with the increase in P rate (P₄₀-P₈₀). Significant difference was found among varieties also. Advanced pod and haulm yield with increased nutrient content were responsible for higher nutrient uptake by groundnut. Application of nutrient  may be a possible reason for increase in nutrient uptake (Daft and El-Giahmi, 1975). P₈₀ among the P applied rate was observed significantly higher N, P and K uptake (Table 2 ). P is important for effective production, growth, development, nitrogen fixation as well as nodule formation of groundnut (Hayman, 1986; Ranjit et al., 2007). Balasubramanian et al., (1980) reported that the uptake of P significantly increased with fertilizer levels.


 
Phosphorus use efficiency
 
Different varieties and P rates had distinct effects on P use efficiency. The PPFP, APE and PE increased upto P₄₀ level of P application and declined thereafter. Whereas, AE, RE and UE were increased with applied P (Fig 1, 2, 3). The relationship between applied P rate and PUE defined perfectly with a quadratic equation (y=ax²+bx+c). Maximum values of PPFP were recorded with P₄₀ and APE and PE had exhibited same trends (Fig 1, 2). AE was increased with rate of P applied and had a supreme value for P₈₀ (Fig 1). Enhanced AE and PPFP might be due to higher uptake and use of P by the plant. AE had an accompanying association with pod yield. A balance should be maintained between AE and PPFP to achieve higher pod yield and economic return. AE would be a better descriptor for PUE (Zhu et al., 2012). Disparity in PUE of P applied indicated that P rate is a factor to influence PUE. Availability of nutrients, affected by soil and fertilizer doses was a chief source of deviation in yield, nutrient uptake and UE of oilseed crops (Sadras, 2006). Havlin et al., (2005) reported that with increase in P rate, RE will also be increased.






 
Protein and oil content
 
Protein content increased with rate of P (P₄₀-P₈₀) by 4.7%, 9.1% and 12.9% compare to P₀. Variety ‘Gangapuri’ recorded highest protein content of 24.27% (Fig 4). These findings are corroborated with the findings of Elshiekh and Mohamedzein (1998). Oil content ranged from 43% to 47%, whereas, groundnut seeds contain 40-50% oil (Okello et al., 2010). Oil content did not reach to the level of significance with the variation in variety and P rate. ‘Gangapuri’ variety showed maximum oil content (45.41%) than ‘JL-24’(44.77%) and ‘TAG-24’ (44.14%), whereas, oil content increase gradually with increase in P rate during the experiment (Fig 4). Seed quality was influenced by nutrient availability and a positive impact of P on pod yield, seed oil and protein content. To increase in yield and enhancement in nutritional quality of oilseed, addition of P is crucial to achieve high protein and oil yield (John and William, 1999). For root development, legumes require more P than others. P boosts the symbiotic N fixation in legume crops and N content increases (Nelson and Cox, 2017). Nitrogen is a key component of amino acids and amino acids are the building blocks of all proteins (Singh et  al., 2000). Therefore, increase in P level favor to increase protein content in groundnut.

The study indicates, P fertilization with increased rate affects the crop biomass, pod yield, nutrient uptake and P-use efficiency. P application of 80 kg ha^-1 is favourable for enhancing groundnut production and P-use efficiency  in sandy clay loam soil of eastern India. Simultaneously, increase in P rates favors in increasing protein and oil percentage in groundnut. Early maturing bunch type variety ‘Gangapuri’ may be recommended for the farmers of eastern India.