Soil Test and Yield Target Based Balanced Fertilizer Prescription Model for Green Gram on Alfisols of Tamil Nadu

In agriculture, fertilizer is one of the costliest inputs, hence use of right quantity of fertilizer is basic for farm profitability and environmental protection (Kimetu et al., 2004) Application of fertilizers in the farmers fields without the knowledge on soil fertility status and nutrient requirement by crop leads to adverse effects on soil and crop (Ray et al.,  2000). Soil testing is highly essential for optimal fertilizer use where general fertilizer recommendation leads to over use or suboptimal level of fertilizers doses for crops leads to wide variations in growth and yield of crops. Balanced supply of nutrients is not only provides adequate amount of nutrients at required ratios but also fulfilling the requirement of nutrients to achieve the yield target of the crops. Among the various soil fertility evaluation methods, an inductive methodology known as Soil Test Crop Response approach provides a holistic way to manage soil fertility with aimed yield target of crops. Soil Test Crop Response (STCR) approach based site-specific fertiliser prescription is essential for achieving higher crop productivity besides maintaining the soil health. Integrated plant nutrition system (IPNS) provides the scientific way of nutrient budgeting under combined use of fertilizers and manures. An annual net negative balance of about 8-10 million tonnes of nutrients is reported in India (Tandon, 2007).
       
Fertilizer prescription based on soil testing and combined use of mineral and natural manures can avoid deterioration in soil health due to indiscriminate use of chemical fertilisers. India is the second largest consumer of fertilisers in the world, after China with a consumption of  306.42 lakh tonnes (www.indiastat.com). India accounts for 20.21 million MT and 7.92 million MT of consumption of N and P₂O₅ during 2022-23 and registered an increase of 4% and 1.2%, respectively, over 2021-22. However, consumption of K₂O at 1.72 million MT witnessed a sharp decline of 32.2% during the period (Fertiliser Association of India, 2023).  By adopting soil test based fertiliser prescription, use efficiency, economic return and quality of crops can be improved.
       
Green gram (Vigna radiata L.), is an important pulse crop in India. Green gram grown in an area of 51.9 lakh ha with a production of 31.02 lakh tonnes in India (www.indiastat.com). Madhya Pradesh, Maharashtra, Rajasthan, Uttar Pradesh, Karnataka, Telangana and Andhra Pradesh are the major pulse-producing states in India.
       
Considering the inadequate adoption of production technologies that led to low productivity of pulses, various alternatives were considered over the conventional cultivation practices (Sowmya et al., 2023). In the recent times, targeted yield concept found to be useful which considers available nutrient status in the soil and also the crop requirements that facilitates balanced fertilization. Targeted yield approach was first developed by Troug (1960). A theoretical basis and experimental technique was established by Ramamoorthy et al., (1967) to suit the same to Indian conditions. This target yield model is considered as a soil and fertilizer based precision farming technique to meet nutrient demands for a specified yield target of crops (Balasubramanian, 1999). Fertiliser prescription equations has been developed for Glory Lily  (Sellamuthu et al., 2015a) under IPNS based concept.  The STCR equations  have been developed for green gram with optimum use of fertilizers (Saren et al., 2017).
       
To harvest the maximum benefit, better nutrient use efficiency and reduced nutrient losses, mineral fertilizers must be applied in the right quantity and proportion, from the right sources at the right time using the right methods. In the present context, it is essential to develop fertiliser prescription equations for getting maximum yield and sustaining soil fertility. Hence, the present study was undertaken to validate the STCR-IPNS based fertilizer prescription equations developed for maximising the productivity of green gram on Typic Rhodustalf (Palaviduthi soil series) in Tamil Nadu.

FN = 9.75 T - 0.29 SN -0.70 ON
 
 FP₂O₅ = 12.12 T - 2.83 SP-0.79 OP
 
FK₂O = 8.65 T - 0.14 SK-0.62 OK

FN, FP₂O₅ and FK₂O = Fertiliser N, P₂O₅ and K₂O in kg ha^-1, respectively.

       

 

Growth parameters
 
Plant height,  number of pods per plant,  number of seeds per pod and 100 seed weight  were recorded in all the four experiments. Mean values of  four experiments indicated that the highest plant height was recorded in the treatment receiving STCR-IPNS-12 q ha^-1 (50.3 cm) followed by STCR-IPNS -10 q ha^-1(48.6 cm) and STCR-NPK -12 q ha^-1 (48.6 cm).  The STCR-IPNS treatments recorded relatively higher plant height over STCR -NPK alone treatments (Table 3).  Blanket recorded markedly lower plant height than STCR-IPNS treatments.  Arulmani et al., (2024) reported the highest plant height in beet root due to the STCR-IPNS based fertilization.  The soil test based balanced fertilization might have boosted photosynthetic activity, chlorophyll content, nitrogen and auxin metabolism in plants, resulting in a notable increase in plant height (Kirad et al., 2010 and Yanthan et al., 2012).
       
The mean highest number of pods per plant was recorded in the treatment receiving STCR-IPNS-12 q ha^-1  (36.4) followed by STCR-NPK alone -12 q ha^-1 (35.4 ).  When compared to STCR-NPK treatments, STCR-IPNS treatments recorded relatively higher number of pods per plant (Table 3).                               

Farmers practice and blanket recorded lesser pods per plant than STCR-IPNS treatments. Absolute control recorded the lowest pods per plant. The number of seeds per pod indicated that the highest value in the treatment receiving STCR-IPNS-12 q ha^-1 (12.60) followed by STCR-IPNS -10 q ha^-1 (11.53).  Relatively higher number of seeds per pod was noted in the STCR-IPNS treatments over other treatments (Table 3).


       
The highest 100 seed weight was recorded in the treatment receiving STCR-IPNS-12 q ha^-1  (4.23 g) followed by STCR-IPNS -10 q ha^-1 (4.18 g) indicating that the STCR -IPNS treatments recorded relatively higher number of 100 seed weight over other treatments (Table 3). Kanchana et al., (2020) observed the highest yield attributes in pearl millet under STCR-IPNS.
 
Grain yield of green gram
 
The pooled mean grain yield of four locations revealed that the highest mean grain yield was recorded in the treatment STCR-IPNS-12 q ha^-1  (11.51 q ha^-1) followed by STCR-NPK alone -12 q ha^-1 (11.23 q ha-1) indicating that the STCR-IPNS treatments recorded relatively higher yield over STCR-NPK alone treatments (Table 3 and Fig 1). STCR-IPNS-12 q ha^-1 recorded an yield increase of 34.1 per cent over blanket recommendation (8.59 q ha^-1) and followed by STCR -NPK-12 q ha^-1 (30.84 per cent). Also STCR-IPNS-12 q ha^-1 and  STCR-INPK-12 q ha^-1 recorded yield increase of 58.08 and 54.24 per cent respectively, over  Farmers Practice. 


       
Higher yield of green gram is possible with integrated use of inorganic  and organic sources (Kumar et al., 2024).  During the organic residue decomposition, intermediate acids produced and they solubilise fixed forms of nitrogen and phosphorus in soil leading to increased available nitrogen and phosphorus (Henri et al., 2008) which leads to overall enhanced productivity of green gram. Similar findings indicated that application of inorganic fertilizers along with organic manures recorded higher grain and straw yield (Sellamuthu et al., 2015b and Sellamuthu et al., 2016) and ultimately due to higher uptake (Sathish et al., 2011) and increased use efficiency of nutrients (Sahu et al., 2017). Similar results were also recorded by Bagavathi Ammal  et al. (2019) in rice-rice sequence where saving of fertilizers were with combining organic and inorganic fertilizers based on STCR approach. The conjoint application of mineral fertilizers and organic manures have beneficial impact on both root nodules and grain yield (Krithika et al., 2023) by enhancing the use efficiency of phosphorus in black gram. 
 
Per cent achievement, response ratio and cost benefit ratio
 
The highest per cent achievement of the yield target was recorded with STCR-IPNS-8 q ha^-1 (98.75) followed by STCR-IPNS-10 q ha^-1 (98.18) (Table 3). Yield targeting with IPNS recorded relatively higher per cent achievement than that aimed under their respective NPK alone treatments.  The per cent achievement of the targeted yield among the four verification trials, was within ±10 per cent variation. STCR-IPNS technology ensures sustainable crop production with economical use of fertilizer inputs (Mahajan et al., 2013).
       
The mean RR recorded for various treatments ranged from 2.09 kg kg^-1 in Farmers practice to 3.84 kg kg-1 in STCR-IPNS-12 q ha^-1 (Table 3).  Among the STCR treatments, IPNS   recorded relatively higher RR than NPK alone due to the better use efficiency of applied fertilizers under IPNS. The results are confirmed with the findings of Muralidharudu et al., (2011). STCR-IPNS-12 q ha^-1 was found to record the highest B:C ratio of 2.26 (Table 3) which was in close conformity with the findings reported by Sellamuthu et al., (2015b) and Sellamuthu et al., (2016).
 
Post harvest soil fertility
 
Soil available N ranged from 199 to 236 kg ha^-1 at Kallipatti, 181 to 214 kg ha^-1 at Viralipatti, 195 to 232 kg ha-1 at Kunjanampatti and 192 to 223 kg ha^-1 at Theppakulathupatti (Table 4). In all the locations, the higher available N was recorded in STCR-IPNS treatments followed by STCR-NPK alone. When compared with the initial soil fertility,  control, farmers practice and blanket, recorded reduction in available N but the degree of reduction was less in blanket.


       
Soil available P ranged from 19.3 to 26.2 kg ha^-1 at Kallipatti, 21.1 to 28.9 kg ha^-1 at Viralipatti, 17.2 to 24.3 kg ha^-1 at Kunjanampatti and 14.7 to 19.9 kg ha^-1 at Theppakulathupatti (Table 4). In available phosphorus also, STCR-IPNS treatments recorded higher available P in all the locations followed by STCR-NPK alone treatments and blanket while control and farmers practice recorded lower available P.
       
Soil available K ranged from 278 to 329 kg ha^-1 at Kallipatti, 317 to 385 kg ha^-1 at Viralipatti,  302 to 358 kg ha^-1 at Kunjanampatti and 278 to 329 kg ha^-1 at Theppakulathupatti (Table 4). Higher available K was recorded in STCR-IPNS treatments in all the four locations followed by STCR-NPK alone treatments while control and farmers practice recorded lower available K. The degree of reduction was higher in control and farmers practice when compared to the initial soil fertility while in blanket reduction in available K was less.Similar results were recorded by Sellamuthu et al., (2016).
       
Post harvest soil fertility values of KMnO₄-N, Olsen-P and NH₄OAc-K highlighted the build up and maintenance of soil fertility owing to soil test based fertilizer prescription under IPNS, despite higher uptake of nutrients by green gram, the soil fertility status was maintained in STCR-IPNS as compared to STCR-NPK alone (Table 4). Application of organic manures in conjunction with mineral fertilizers not only enhances the productivity but also improve the soil fertility (Jaga and Upadhyay, 2013).  A notable reduction in fertilizer requirement was observed with application of inorganic fertilizer along with FYM due to the nutrient supplement through FYM (Selvam et al., 2022).

The present study was supported by ICAR - All India Coordinated Research Project on Soil Test Crop Response and Tamil Nadu Agricultural University, Coimbatore.
 
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.
 
Informed consent
 
All animal procedures for experiments were approved by the Committee of Experimental Animal care and handling techniques were approved by the University of Animal Care Committee.