Balanced Nutrient Recommendations for Dry Chilli in an Inceptisol of Tamil Nadu based on a Targeted Yield Model

Chilli (Capsicum annuum L.) belongs to Solanaceae family and key member among the spices grown in India. As a result of the Portuguese introducing the crop in the 17^th century, it is now produced all across India, with Andhra Pradesh, Karnataka, Tamil Nadu and Maharashtra accounting for 3/4 of the total area, along with Madhya Pradesh, West Bengal, Punjab, Bihar and Rajasthan (Chandramohan et al., 2018). The common ingredients in curry paste of chilli fruit and powder of dried fruits are carbohydrates and vitamins A and C. All types of pickles, sauces and paste are made from fresh, ripe and green chilies. Capsanthin, a red pigment, is utilised in premium cosmetic products like lipstick. The food and beverage sectors employ the essential oil oleoresin. The active element “Capsaicin,” an alkaloid found in pericarp and placenta that is a digestive stimulant, an essential component of daily diet and a treatment for many rheumatic conditions, is what causes the pungency (Chandini Raj et al., 2016).
       
The global area under chilli cultivation is 1.776 million hectare with a production of 7.182 million tones. India’s area under chilli cultivation is 316.47 thousand hectare and total chilli production is 3633.99 thousand MT. India, the world’s biggest producer and consumer of red spice, exported 44.90 thousand MT. chilli, worth Rs. 22,074.05 lakhs during the year 2017-18 (Source - Horticulture Statistics-2018). India is the world’s top producer, although its average yield is quite low (1.11 t ha^-1 dried chilli), especially when compared to advanced nations like the USA, China, South Korea, Taiwan, etc., where it is between 3 and 4 t ha^-1.
       
Fertilizers are essential to improve agricultural output since they can significantly enhance crop yields when used in the right quantities. Existing practice by farmers is the application of general dose of fertilizers to chilli without consideration of soil type (nutrient status) and crop response. This needs to be given a new dimension. Fertilizer recommendations based on soil tests lead to effective fertiliser use and soil fertility management. At this point, the Truog (1960) and Ramamoorthyet al., (1967) modified prescription approach, known as the “Inductive-cum-Targeted yield model,” offers a scientific foundation for balanced fertilisation and balance between applied nutrients and soil-available nutrients. In accordance with this concept, soil test crop response correlation studies under the integrated plant nutrition system (STCR-IPNS) were carried out in various locations throughout India (Dey and Das, 2014) and Tamil Nadu (Santhi et al., 2017) and fertiliser recommendations were made for the desired yield targets of various major field and horticulture crops.
               
Based on this methodology, quantitative fertiliser requirements have been calculated for specific yield targets of crops like rice, beetroot and SRI rice (Sharma et al., 2015; Santhi et al., 2011; Maragatham et al., 2018). Due to the combined use of soil and plant analysis, recommendations based on soil test crop response correlation (STCR) idea are more quantitative, exact and relevant. It provides a true balance between the nutrients that are applied and those that are already present in the soil and are available. This study was done with the aforementioned parameters in mind as well as the lack of quantitative data on fertiliser doses with organic manures based on desired yield for chilli in Tamil Nadu in an inceptisol.

The study’s location was in Tamil Nadu, India in Farmers Holding, Palaniyur, Dindigul district (10.348^oN Latitude, 77.872^oE Longitudes), at a height of 282 metres above mean sea level. Experimental soil (0-15 cm deep) was black in colour, sandy clay loam in texture, moderately alkaline (pH = 8.35), non-saline (EC 0.13 dS m^-1), with cation exchange capacity of 23.2 Cmol (p⁺) kg^-1 and calcareous in nature. The soil belonged to Periyanaickenpalayam soil series of Inceptisol soil order taxonomically referred as Vertic Ustropept. The initial experimental soil had 5.2 g kg^-1 of organic carbon, 170 kg ha^-1 available alkaline potassium permanganate (KMnO₄) oxidizable nitrogen (N), 17 kg ha^-1 Olsen phosphorus (P) and 350 kg ha^-1 neutral normal ammonium acetate (NH₄OAc) exchangeable potassium (K), respectively. The DTPA extractable micronutrients status (i.e) zinc (Zn), copper (Cu), manganese (Mn) of experimental soil were in the sufficiency ranges and iron (Fe) was insufficient (Table 1).
 

       
During phase-I, gradient experiment was conducted with fodder sorghum (var. CO 30) as the sole crop, three strips of fertility gradients, low, medium and high (in terms of accessible nitrogen, phosphorus and potassium), were established. By dividing the field into three equal strips (S1, S2 and S3), which received an application of three graded levels of fertilizers i.e., Strip 1-N⁰P⁰K⁰ (control), strip 2- N₁P₁K₁ (N₁- Blanket recommendation of sorghum, P₁ and K₁- P and K fixing capacities of soil) and strip 3- N₂P₂K₂ (double the dose of strip-2), the fertility fluctuation was purposefully produced. At 60 DAS, fodder sorghum was harvested. In order to monitor the emergence of a fertility gradient in the same field, soil samples were taken during sorghum harvest in order to measure the fertility gradient developed and fodder yield was also calculated. By splitting each fertility strip into three FYM blocks across the strip and using different NPK combinations total of 21 NPK combination treatments and 3 controls (Table 2), resulting in a total of 72 plots from the three strips of the field. Initial soil samples (0–15 cm) were taken from each of these plots analyzed for alkaline KMnO₄-N (Subbaiah, 1956), Olsen P (Olsen, 1954) and NH₄OAc-K (Stanford and English, 1949).
       
As a test crop chilli, with four levels of N (0, 50, 100 and 150 kg ha^-1), P₂O₅ and K₂O (0, 30, 60 and 90 kg ha^-1), along with three levels of FYM (0, 6.25and 12.5 t ha^-1) treatments structure was formed as shown in Table 2. The crop was raised as per the standard TNAU CPG-2020. From all of the plots, ripened chilli fruits and biomass yield were recorded and expressed in kg ha^-1. Plant and fruit samples were tested for N, P and K contents in accordance with Jackson’s (1973) standard protocols for total nutrient uptake. Initial soil data, dry chilli yield, plant biomass yield and nutrient uptake by the chilli crop were used to calculate the four crucial basic parameters viz., nutrient required to produce a quintal of dry chilli yield (NR), per cent contribution of nutrients from soil (% Cs), per cent contribution of nutrients from fertilizers (% Cf) and per cent contribution of nutrients from organic matter (% Co) using following formulae. By using the Ramamoorthy et al., (1967) technique, these basic components were converted into simplified, practical fertiliser adjustment equations for computing precise yield targets based on soil test data.
 

 
Nutrient requirement (NR) kg q^-1
   
Per cent contribution of nutrients from soil to total nutrient uptake (Cs)
   
Per cent contribution of nutrients from fertilisers to total nutrient uptake (Cf)  
Per cent contribution of nutrients from organics to total nutrient uptake (Co)
   
Fertiliser prescription equations (FPEs)
 
Fertiliser nitrogen (FN) Fertiliser phosphorus (FP2O5)
   
Fertiliser potassium (FK2O)
   
Where,
FN, FP₂O₅ and FK₂O = Fertilizer N, P₂O₅ and K₂O (kg ha^-1) respectively.
NR = Nutrient requirement (kg q^-1).
Cs = Percentage contribution from the soil.
Cf = Percentage contribution from fertilizer.
SN, SP and SK = Soil test value for available N, P and K (kg ha^-1), respectively.
Co = Percentage contribution from FYM, ON, OP.
OK= Quantity of N, P₂O₅ and K₂O applied through FYM.

From information on the initial nutritional status is showed in Table 3. In strips I, II and III, respectively, the mean values of alkaline KMnO₄-N, Bray’s P and NH₄OAc-K were 157, 189 and 217 kg ha^-1 for N; 11.8, 23.8 and 32.2 kg ha^-1 for P₂O₅ and 335, 367 and 392 kg ha^-1 for K₂O. The gradient analysis showed that soil NPK levels increased as fertiliser doses increased, indicating the creation of a distinct fertility gradient by the application of graded fertiliser and FYM dosages. (Abhishek et al., 2022)) with hybrid castor in an Alfisol found similar levels of gradient build up.  
 

       
The range and mean values of dry chilli production and NPK uptake by the chilli crop showed that strip III had the highest output and nutrient uptake, followed by strip II and strip I had the lowest. The average dry chilli yield across all plots was 1564, 1964 and 2240 kg ha^-1 in strips I, II and III, respectively. With mean values of 65.8, 87.5 and 94.4 kg ha^-1, the N uptake in strips I, II and III ranged from 37.6 to 77.4, 51.6 to 110.9 and 54.3 to 120.1, respectively. In strips I, II and III, respectively, the P uptake varied from 8.1 to 16.9 kg ha^-1 with a mean of 13.3 kg ha^-1, 9.2 to 20.5 kg ha^-1 with a mean of 16.4 kg ha^-1 and 11.2 to 22.0 kg ha^-1 with a mean of 18.4 kg ha^-1 respectively. The K uptake ranged from 38.5 to 74.8, 46.8 to 102.5 and 49.1 to 116.3 kg ha^-1 respectively in strip I, II and III. Similar operational ranges of N, P and K were reported by Durga et al., (2017) for marigold grown in Inceptisol. The aforementioned findings demonstrated that there was substantial difference in the soil test results, grain production and nutrient uptake between the strips and treatments, which is necessary to calculate the fundamental parameters and calibrate the equations for fertiliser prescription. Using the basic parameters FPEs were worked and given in Table 4. By using the basic parameters fertilizer prescription equations (FPEs) were developed for inorganic fertilizer alone and inorganic fertilizer with FYM (Table 5).
 

 

       
To fully explore the genetic potential of the crop, which depends on the contribution of applied nutrients and the capacity of the native soil to deliver those nutrients, nutrient optimization is absolutely necessary (Durga et al., 2017). One quintal of dry chilli production was found to require 4.24 kg of nitrogen, 1.91 kg of phosphorus pentoxide and 4.80 kg of potassium (Table 4). This study showed that, in comparison to phosphorus, chilli requires 2.2 times more nitrogen and 2.5 times more potassium. The percentage of nutrients estimated from fertiliser that contributed towards the total amount of nutrients taken up by dry chilli was calculated to be 44.09, 39.29 and 76.91 per cent of N, P₂O₅ and K₂O, respectively.K₂O >N>P₂O₅ was seen as the order of the fertiliser nutrients per cent contributions to total nutrient uptake, which is closely in accordance with Udayakumar and Santhi. (2017). These findings show that fertiliser sources contributed more nutrients than soil sources. Santhi et al., (2005) reported that the contributions of nutrients from fertiliser sources were greater than those from soil sources and the amounts of fertiliser needed to achieve a desired onion yield target decreased as soil test values rose. The results are in accordance with Selvam et al., (2022), regarding higher contribution of N from organic matter (3.40%) and may be attributed to enough carbon from FYM for the building of bacterial population to boost N availability. A substantial contribution of NPK was needed through FYM to meet crop needs, which reduces the amount of nutrients that must be administered through costly fertilisers.
 
Fertilizer prescription for dry chilli crop
 
To achieve the intended production target of the dry chilli crop, soil test-based fertiliser prescription equations were created as above by correlating the fundamental parameters gathered from the main experiment (Table 5).  Based on the previously mentioned formulae for a certain range of soil test values, a fertiliser prescription table was created for yield targets of 27.5 (Table 6) and 25 q ha^-1 (Table 7). Table 6 data showed that when the soil test value rises, the amount of required nutrients decreases. i.e., in case of nitrogen for every 20 kg increase and incase of potassium for every 10 kg increase of soil available nutrient, there was an 11 kg and 2 kg decrease in fertilizer N and K requirement respectively . For every 2 kilogram increase in soil-available phosphorus, there was a 4 kg reduction in phosphatic fertiliser needed. Table 7 data also showed that for the same initial soil nutrient status, extra amounts of fertiliser nitrogen, phosphorus and potassium of 24 kg, 12 kg and 16 kg, respectively, are needed for every 250 kg rise in the desired yield level of chilli.
 

 

               
When no FYM was used, the amount of fertiliser N, P₂O₅ and K₂O needed to achieve a yield target of 27.5 q ha^-1 of dried chilli with soil test values of 210: 19: 355 kg ha^-1 of KMnO₄- N, Bray’s-P and NH₄OAc-K was 175, 108 and 118 kg ha^-1, respectively. Nevertheless, 135, 82 and 85 kg ha^-1 of fertiliser N, P₂O₅ and K₂O, respectively, were needed with 12.5 tonnes FYM ha^-1 for the same soil test values and yield target (Table 6). Similar to the above, the fertiliser NPK nutrients needed for the target production of 25 q ha^-1 are 155, 96 and 102 kg ha^-1 respectively. In case of FYM @ 12.5 t ha^-1 application along with fertilizer nutrients, the amount of fertiliser N, P₂O₅ and K₂O needed is 111, 70 and 69 kg ha^-1 respectively for the above mentioned soil test values (210:19:355 kg ha^-1). As a result, targeted yield equations produced by STCR-IPNS technology enable both the sustained crop output and the economical use of expensive fertiliser inputs. Due to nutrient availability being increased by FYM through mineralization, the required dose of fertiliser under the IPNS approach is low. According to Santhi et al., (2011), an integrated plant nutrient system reduces the amount of fertiliser needed to reach desired yield targets. Both Cheli Lalitha et al., (2022) and Ranu et al., (2016) reported similar outcomes. These findings unambiguously demonstrated that for the same degree of crop yield, the fertiliser needs changed depending on the soil test results. Soil testing is necessary to provide balanced fertilisation, which is necessary to boost crop output. One quintal (1 q ha^-1) of dried chilli production can be increased or decreased by applying different amounts of the nutrients 9.6 kg N, 3.2 kg P₂O₅ and 6.4 kg K₂O, depending on the quantities of the nutrients needed to achieve a particular yield target. Similar variability in nutrient dosages were seen for aggregatum onion and tomato with a projected yield of 17 and 80 t ha^-1 respectively (Parvathi Sugumari et al., 2021; Agila et al., 2021).

The outcomes of this investigation clearly indicated that Inceptisols in Tamil Nadu may successfully adopt fertiliser prescription equations developed by inorganics or under IPNS to achieve the specified targeted yield of dry chillies. The results of the aforementioned study showed that using STCR-IPNS technology, fertiliser doses are customised to meet the needs of certain chilli yield targets while taking into account the contributions of soil, fertilisers and organic manure. Hence, a balanced supply of nutrients will be present along with the recycling of organic waste, preventing the under-or overuse of fertiliser inputs. Farmers can also determine the desired yield objective for dry chilli according to their resource availability and management conditions.

The help and cooperation of scientists at All India Coordination Research Programme on Soil Test Crop Response (AICRP-STCR), TNAU, Coimbatore, India in the work are gratefully acknowledged.

None.