Soil test crop response based integrated plant nutrition system for hybrid castor on an Alfisol

Castor (Ricinus communis L.) is the most important non edible industrial oilseed crop grown across the world in tropical, sub-tropical and warm temperate region. Castor oil has multifarious applications in production of wide industrial products ranging from medicines, aviation fuels, fuel additives, biopolymers and bio-diesel (Prasad, 2012). India is known as the world leader in castor seed and oil production and leads the international castor oil trade. Castor oil production in this country usually fluctuates between 250,000 and 350,000 tons per year. Approximately 86% of castor seed production in India is concentrated in Gujarat, followed by Andhra Pradesh and Rajasthan. Specifically, the regions of Mehsana, Banaskantha and Saurashtra/Kutch in Gujarat and the districts of Nalgonda and Mahboobnagar of Andhra Pradesh are the major areas of castor oil production in India (Shrirame et al., 2011).
       
India is the world’s largest producer of castor contributing to around 85 per cent of world’s total production.  In India, castor is cultivated in area of about 7.5 lakhs hectare with production of 1.19 million tonne in the year 2018- 2019. Average yield of castor in India is about 1594 kg hac^-1 (www.indiastat.com). Also it meets more than 80 per cent of the demand of castor oil, thereby enjoying a dominant position in the world castor scenario.
       
In Tamil Nadu, castor was grown as a low input dry land crop in an area of 15,000 ha. Mostly used as a border or inter crops, where its drought - hardy nature helps to provide as cash for farming community and castor leaves provided for excellent green fodder for small ruminants. Castor growing areas in Tamil Nadu 1500 ha was mostly under rainfed condition and irrigated condition. Major limitation other than irrigation is varietal preferences. As farmers were growing different local varieties in intercrop, border crop and some parts as pure crop under rainfed condition and obtained very poor yield and less farm income. Hence, the study was undertaken with the objectives to formulate fertilizer prescription question for  the high yielding castor hybrids as pure crop in terms of yield, acceptability and adoption potential for the local condition (Murugan and Akila, 2020).
       
Soil is an important part of successful agriculture, most precious natural resources and also the main basis for crop production activity. Imbalance in use of fertilizers not only deteriorates the soil quality but also affect the nutrient use efficiency. So to meet the increasing demand of agriculture, there is need to promote the balanced use of chemical fertilizers.
              
At this juncture, the prescription procedure outlined by Truog (1960) and modified by Ramamoorthy et al. (1967) as “Inductive cum Targeted yield model” provides a scientific basis for balanced fertilisation and balance between applied nutrients and soil available nutrients. Based on this concept, Soil Test Crop Response correlation studies under Integrated Plant Nutrition System (STCR-IPNS) were undertaken in different parts of India (Dey and Das, 2014) and Tamil Nadu (Santhi et al., 2017) and fertiliser prescriptions have been derived for desired yield targets of various major field and horticultural crops on different soil types. STCR-IPNS takes into account the nutrient requirement of crops, contribution of nutrients from soil, fertiliser and organic manures in deriving fertiliser prescriptions ensuring balanced nutrition to crops with sustained soil fertility. These prescriptions are of practical importance for efficient and judicious use of fertilisers in increasing crop production and in addition prescription for desired yield target of crops could be made based on resource availability of farmers (Dey and Santhi, 2014). Studies on Soil Test Crop Response based Integrated Plant Nutrition System (STCR-IPNS) have not yet been carried out for Hybrid castor in Tamil Nadu. Keeping the above facts in view, the present investigation on STCR-IPNS for Hybrid castor has been undertaken on Alfisol soil order in North Western Agro- climatic Zone of Tamil Nadu.
 

Study area

The study site is located at the Tapioca and Castor Research Station, Yethapur Salem district, Tamil  Nadu, India (11°35'N Latitude, 78°29'E Longitudes) at an altitude of 282 meters above mean sea level). In this study, the data from 72 plots were studied. Each plot size of about 25 m² and all are sown with the same hybrid YRCH^-1 castor. The growing period for castor in our study was from June to November 2021.
   
Experimental soil (0-15 cm deep) was red in colour, sandy loam in texture, almost  neutral (pH = 7.52), non-saline (EC 0.32  dS m^-1), with cation exchange capacity of 22.7 cmol (p+) kg^-1 and non-calcareous in nature. The initial experimental soil had 0.61% of organic carbon, 210 kg ha^-1 available alkaline potassium permanganate (KMnO₄) oxidizable nitrogen (N), 16.3 kg ha^-1 Olsen phosphorus (P) and 245 kg ha^-1 neutral normal ammonium acetate (NH₄OAc) exchangeable potassium (K), respectively. The DTPA extractable micronutrients status (i.e) zinc (Zn), iron (Fe), copper (Cu) and manganese (Mn) of experimental soil were in the sufficiency ranges. 
    
In this study initially, fertility gradient was artificially created by applying three graded levels of fertilizers i.e., level 1(N0P0K0), level 2 (N1P1K1) and level 3 (N2P2K2) and an exhaustive crop of dual-purpose sorghum (var. CO 30) was sown to improve the soil fertility and harvested at pre-flowering stage as fodder by adopting the inductive methodology developed by Ramamoorthy et al. (1967). The level of N was based on the recommendation of gradient crop. Based on the P and K fixing capacity of the experimental soils the levels of P and K were 100 and 80 kg ha^-1, respectively.
       
Pre-sowing and post-harvest soil samples were collected from each strip of gradient crop and analyzed for available nitrogen, available phosphorus and available potassium. Each strips were divided into 24 plots after the development of fertility gradient and soil samples were collected from all the seventy-two plots prior to castor sowing and analyzed for alkaline KMnO₄-N (Subbaiah, 1956), Olsen P (Olsen, 1954) and NH₄OAc-K (Stanford and English, 1949).
       
The experimental treatment structure was laid out in a fractional factorial design with three factors and four levels in each i.e, Nitrogen (0, 45, 90 and 135 kg ha^-1), Phosphorus (P₂O₅) (0, 20, 40 and 60 kg ha”1) and Potassium (K₂O) (0, 20, 40 and 60 kg ha^-1) comprising twenty-four treatments (Table 1). Three levels of Farmyard manure (FYM) (no fym, fym @ 6.25 t ha^-1, fym @ 12.5 t ha^-1) were superimposed across the strips. 24 treatments were present in all the strips and treatments were randomized in such a way that consisted of 21 fertilizer treatments and three controls in either direction. The treatment structure is given in Table 1. FYM and phosphorus fertilizers were applied basally while nitrogenous and potassium fertilizer was applied in three splits (i.e., 50% @ basal and 25% @ 30 DAS and 60 DAS). The crop was grown along with all the management practices. Castor capsules are harvested @ 90, 120 and 150 DAS and the capsules were sun-dried and seeds were dehulled. The samples from 120 DAS were processed and analyzed for Plant N (Humphries, 1956), P and K (Jackson, 1973) and the total uptake of NPandK was computed by multiplying the mineral content with the dry-matter yield.


       
The basic parameters viz., i) Nutrient requirement (NR).
ii) Nutrient contribution from soils (Cs). iii) Nutrient contribution from fertilizers (Cf) were computed utilizing formula described and outlined by Ramamoorthyet al. (1967). iv) Nutrient contribution from farmyard manure (Co) were accounted using formula outlined by Santhi et al. (1999).
 
(i) Nutrient requirement for hybrid castor (kg q^-1)
   
(ii) Percentage contribution of nutrient from soil to total uptake (Cs)
   
(iii) Percentage contribution of nutrient from fertilizer to total uptake (Cf)
 

The post-harvest soil available nutrient values revealed that the mean available soil nitrogen were 174 kg  ha^-1 in strip 1,  202 kg ha^-1 in strip 2 and 221 kg ha^-1 in strip 3. The mean available soil phosphorus were 10.8, 17.9 and 24.1 kg ha^-1 in strip 1, strip 2 and strip 3 respectively. For available potassium, the mean values were 211, 242 and 256 kg ha^-1 respectively (Table 2).  The mean seed yield of hybrid castor YRCH-1 were 1860, 2134 and 2257 kg ha^-1. The nutrient uptake ranged from 42.9 to 90.0 kg  ha^-1 for nitrogen, phosphorus ranged from 5.8 to 15.8 kg ha^-1 and potassium uptake ranged from 40.4 to 85.3 kg ha^-1 in strip 1- 3.


       
In the current study, the difference in hybrid castor seed yield and NPK uptake was due to the presence of  variation on soil available nutrient status of  N, P and K. The variation is the prerequisite for developing the fertilizer prescription equations using basic parameters for desired yield target. Sherene et al., (2016) and Santhi et al. (2011) reported similar existence of an operational range of available N, P and K for cotton under vertisol and beetroot on Alfisol.
 
Basic parameters
 
Basic parameters were calculated using the data on castor seed yield, NPK uptake, initial available soil nutrients and the fertilizers applied.
 
Nutrient requirement (NR)
 
The data revealed that the hybrid castor requires 3.20 kg of nitrogen, 1.23 kg of phosphorus (P₂O₅) and 3.28 kg of potassium (K₂O) for producing a 100 kg of hybrid castor seed (Table 3). Nutrient requirement trends were potassium > Nitrogen > phosphorus for the castor seed production. A similar trend of requirement was reported by Ahmed et al., (2001) in castor, Smitha John (2004) for cabbage and Agila et al., (2021) for tomato respectively.


 
Contributions percentage of nutrients from fertilizers (Cf), farmyard manure (Co) and  soil (Cs) to total uptake
 
The soil nutrient contribution to the total uptake was computed using the above given formula in absolute control plot in each strip. The study revealed that soil nutrient contribution (Table 3) was high in case of available phosphorus (41.87%), followed by available nitrogen (21.56%) and soil available potassium recorded 19.12% contribution respectively towards P, N and K  nutrient uptake by hybrid castor. A similar sort of soil contribution towards the plant uptake was reported by Mahajan et al. (2013) in rice in alluvial soil. In the case of fertilizer nutrients contribution, NPK fertilizer applied plots of all the strips were used to compute and results showed that fertilizer contribution towards nutrient uptake was in the trend K₂O > N > P₂O₅. The calculated Cf revealed that potassium fertilizer (52.12%) magnitude was 1.69 times more than the fertilizer nitrogen (30.83%) and 1.95 times more than the phosphorus fertilizer (26.67%). Comparing the contribution from soil vs fertilizer, greater contribution was recorded from the fertilizer than from the soil. Above results coincide with the report on fertilizer contribution towards aggregatum onion by (Sugumari et al., 2021) and (Katharine et al., 2013) on cotton.
       
From farmyard manure alone applied plots of all strips, the nutrient contribution from farmyard manure (Co) towards total uptake was computed. The results revealed that FYM contribution was 21.40% of N, 10.35% of P₂O₅ and 26.06% of K₂O respectively towards total nutrient uptake by hybrid castor following the trend K₂O> N > P₂O₅. Similar nutrient contribution from farmyard manure (Co) was reported by Madhavi et al., (2020) in sesame in Alfisol soil type. Similar trends for Cs, Cf and Co were reported by Madhavi et al. (2020) in sesame and Ahmed et al. (2001) in castor under Alfisol soil type.
 
Fertilizer prescription equations
 
The targeted yield model of hybrid castor was formulated using the basic parameters.
 
Inorganic fertilizer alone
  Inorganic fertilizer with FYM
  Where:
FN, FP₂O₅ and FK₂O = Fertilizer Nitrogen, Phosphorus and Potassium in kg ha^-1, respectively.
T = Desired yield target in q ha^-1; SN, SP and SK are soil available nutrients in kg ha^-1.

ON, OP and OK = The quantities of nitrogen, phosphorus and potassium supplied through farmyard manure in kg ha^-1. Ahmed et al., (2001) documented the formulation of fertilizer prescription equations for castor crop under rainfed conditions at Palem, Mahbubnagar district of Andhra Pradesh. Santhi and her co-worker developed fertilizer prescription equations and documented for various crops like rice (Santhi et al., 1999), beetroot (Santhi et al., 2011), aggregatum onion (Santhi et al., 2005) and sunflower (Santhi et al., 2004) in different parts Tamil Nadu.

Fertilizer prescriptions for desired yield target of hybrid castor under inorganic alone and IPNS based fertilization
 
A fertilizer prescription table was outlined for a yield targets of 25 and 27.5 q ha^-1  based on the above given equations for a certain range of soil test values (Table 4). The table data exposed that the mineral nutrient requirement decreases with an increase in soil test value. i.e., In case of Nitrogen and Potassium for every increase in 10 kg of soil available nutrient, there was an 8 kg and 4 kg decrease in fertilizer N and K₂O requirement respectively. Incase of phosphatic fertilizer there was a reduction of 14 kg of fertilizer for every 4 kg increase in soil available phosphorus. Table data also revealed that for every 250 kg increase in the target level of castor seed yield, an additional 28 kg, 11.54 kg and 15.5 kg of fertilizer nitrogen, phosphorus and potassium are required respectively for the same initial soil nutrient status.

In the present investigation, Fertilizer prescription equations (FPEs) were developed for both inorganic nutrition alone and under the Integrated Plant Nutrition System (IPNS) for the desired yield target for Alfisol of Tamil Nadu. The findings of the above study indicate that in STCR-IPNS technology, the fertilizer doses are tailored to the requirements of specific yield targets of hybrid castor taking into account the contribution from soil, fertilizers and organic manure. Hence, there will be a balanced supply of nutrients coupled with recycling of organic wastes avoiding either under-or over-usage of fertilizer inputs. Fertilizer recommendations based on this concept are more precise, quantitative and meaningful and farmers can also choose the desired yield target for hybrid castor according to their availability of resources and management conditions. Above equations should be used for the same or allied soil type and the maximum yield target should be based on the genetic characteristic of the hybrid which can be attained for that crop in that region. FPEs must be utilized in confined range of experimental soil test values and cannot be generalized.
 

The help and cooperation of scientists at All India Co-ordination Research Programme on Soil Test Crop-Response (AICRP-STCR), TNAU, Coimbatore, India in taking up the field experiment and analyzing field data are gratefully acknowledged.