Targeted Yield Model-based Balanced Nutrient Recommendation for Barnyard Millet on Inceptisol of Tamil Nadu

Barnyard millet is one of the important crops among the small millets viz., foxtail millet, pearl millet, little millet, proso millet, finger millet, etc. It is a short duration crop that can grow in adverse environmental conditions and can withstand various biotic and abiotic  stresses. Barnyard millet grain is a good source of carbohydrate, fibre, protein, low glycemic index and most notably, contains more micronutrients (zinc and iron) compared to other major cereals. India is the biggest producer of barnyard millet, both in terms of area (0.146 mha^-1) and production (0.147 mt) with average productivity of 1034 kg ha^-1 during the last three years (IIMR, 2018).
       
Maintenance of soil health and improvement of crop productivity is essential to meet the increasing food demand which is a serious issue prevailing all over the world. The low level of productivity of crops is due to the supply of low level of input and imbalanced use of fertilizers by the farmers without knowing soil fertility status and nutrient requirement of the crop which causes adverse effects on soil and crop in terms of nutrient toxicity and the deficiency (Yousaf et al., 2017). The decision on fertilizer use requires knowledge of the expected crop yield, soil nutrient status and efficiency of fertiliser (Dobermann et al., 2013). To solve all these problems, one of the sustainable nutrient management techniques such as “Soil Test Crop Response based Integrated Plant Nutrition System (STCR-IPNS)” can be applied for sustained soil health and higher crop productivity (Subba Rao and Lenka, 2020).
       
The targeted yield approach-based application of the fertilizers concept by Truog (1960) and later refitted by Ramamoorthy et al., (1967). Velayutham (1979) stated that targeted yield-based fertilizer prescription is an exclusive method that not only suggests soil test-based fertilizer application but also yields target orient. This approach considers the soil nutrient deficiency and the nutrient sources are applied proportionally to the degree of nutrient deficiency in soil (Das et al., 2016). The soil test-based recommendation of fertilisers mingled with IPNS considers specific soil type, crop, variety and fertiliser management. The fertiliser prescription equations for inorganic fertilisers and integrated nutrient application under STCR-NPK alone and STCR-IPNS for various crops were developed by carrying out several field experiments and documented by Muralidharudu et al., (2011), Dey and Bhogal (2016) and Santhi et al., (2017). The fertiliser prescription equations were developed after establishing a significant relationship between soil test values and the added fertilizers.
       
The nutrient application by STCR-IPNS has been considered as a better approach when compared to the general blanket recommendation and also improves the fertilizer use efficiency and soil health. The fertilizer prescription equations for hybrid pearl millet (Udayakumar and Santhi, 2017) on Inceptisol and maize (Suresh and Santhi, 2018) were developed. However, there is a shortfall of information regarding the fertilizer prescription equations for small millets in Tamil Nadu. Therefore, the present research work was endeavoured to develop integrated fertiliser prescription equations for barnyard millet on Inceptisol of Tamil Nadu to achieve higher productivity as well as soil health sustainability.

Field experiment site
 
The present investigation was conducted at Eastern Block Farm, Tamil Nadu Agricultural University, Coimbatore, Tamil Nadu with fodder sorghum (var. CO 30) as gradient crop and barnyard millet (var. MDU 1) as test crop during 2019-2020. The experimental field soil comes under Inceptisol belonging to Periyanaickenpalayam soil series, taxonomically referred to as Vertic Ustropept, which is mixed black calcareous and sandy clay loam in texture. The soil characteristics stated that the soil was moderately alkaline (pH 8.30) and non-saline (EC 0.49 dSm^-1). Considering initial soil fertility status, the soil was low (172 kg ha^-1) in KMnO₄-N, medium (21.0 kg ha^-1) in Olsen-P and high (505 kg ha^-1) in NH₄OAc -K.
 
Fertility gradient experiment
 
The fertility gradient experiment should be conducted prior to the test crop experiment as per the inductive methodology proposed by Ramamoorthy et al., (1967). It was conducted by dividing the experimental field into three equal rectangular strips. The fertility gradients were created by applying graded doses of fertilizers of N, P₂O5 and K₂O on the strips. The strip - I was left unfertilized (control), Strip - II received the blanket recommendation of N while, P₂O₅ and K₂O were applied based on the fixing capacities of soil which were 100 and 80 kg ha^-1, respectively and strip III received double dose fertilisers as that of Strip-II. The exhaustive crop fodder sorghum was grown which renders the fertilizers to undergo a transformation in soil. The crop was harvested at the fodder stage in each fertility strip and green fodder yield was recorded.
 
Test crop experiment
 
After confirming the establishment gradient, the main experiment was conducted with barnyard millet (var. MDU 1) as a test crop. The experimental design used was fractional factorial randomized block design. In the experimental field, each strip was divided into three sub-strips to impose three levels of organic manures such as FYM at the rate of 0, 6.25 and 12.5 t ha^-1. The experimental field layout is given in Fig 1. The test crop was grown by superimposing 24 treatment combinations with N, P­₂O₅ and K₂O each at four different levels viz., N (0,20,40 and 60 kg ha^-1), P₂O₅ (0,10, 20 and 30 kg ha^-1) and K₂O (0, 20, 40 and 60 kg ha^-1). Among the 24 plots, all the 21 selected treatment combinations along with three controls were superimposed in each strip. The treatment structure is given in Table 1. The crop is grown to maturity. After harvesting the crop, the grain and straw yield of barnyard millet was recorded plot-wise under each treatment in all the three fertility strips. 
 

       
 
  
       
Soil samples were collected before sowing of the crop, prior to FYM and fertilizer application, which were processed and analysed for KMnO₄-N (Subbiah and Asija, 1956), Olsen-P (Olsen et al., 1954) and NH₄OAc-K (Hanway and Heidal, 1952). After harvesting the gradient crop(sorghum) and test crop (Barnyard millet), plant and grain samples were collected plot-wise, processed and digested to determine the nutrient uptake (Tandon, 2001). 
 
Computation of basic parameters
 
The grain yield of barnyard millet, soil test values, nutrient uptake and fertilizer N, P₂O₅ and K₂O and FYM were taken into consideration for computing basic parameters viz., the nutrient requirement (NR) in kg q^-1, the contribution from soil (Cs), the contribution from fertilizer (Cf) and contribution from FYM (Cfym), expressed in percentage. The calculation was done as recommended by Ramamoorthy et al., (1967) and the contribution from FYM (Cfym) was calculated as prescribed by Santhi et al., (1999).

Nutrient Requirement (NR)
Kg of Nor P₂O₅or K₂O required per quintal (100 kg) of grain yield production, expressed in (kgq^-1).

 
Per cent contribution of nutrients from soil to total nutrient uptake (Cs)

Per cent contribution of nutrients from fertilizer to total nutrient uptake (Cf)



Per cent contribution of nutrients from organics to total nutrient uptake (Co)
Per cent contribution from FYM (Cfym)

Fertilizer prescription equations
 
Making use of these parameters, the Fertilizer Prescription Equations (FPEs) were developed for barnyard millet as furnished below:
 
Fertilizer nitrogen (FN)
 
FN = [(NR/(Cf/100)) × T] - [(Cs/Cf) × SN] 
FN =        [(NR/(Cf/100) × T] - [(Cs/Cf) × SN] - [(Cfym/Cf) × ON]
 
Fertilizer phosphorus (FP₂O₅)
 
FP₂O₅  = [(NR/(Cf/100))× T] - [(Cs/Cf) × 2.29 SP]
FP₂O₅  = [(NR/(Cf/100) × T] - [(Cs/Cf) × 2.29 SP] - [(Cfym/ Cf) ×2.29 OP]
 
Fertiliser potassium (FK2O)
 
FK₂O = [(NR/(Cf/100) × T] - [(Cs/Cf) × 1.21 SK]
FK₂O = [(NR/(Cf/100) × T] - [(Cs/Cf) × 2.29 SK] - [(Cfym/ Cf) × 1.21OK]

Where,
N or P₂O₅ or K₂O are fertilizer N or P₂O₅ or K₂O in kg ha^-1 and ON, OP and OK are the quantities of N, P and K supplied through FYM in kg ha^-1, respectively.
       
The relationship between the soil test values, crop yield and fertilizer dosage were derived by standard regression procedure (Draper and Smith, 1998). The present research study considers the varying grain yield of barnyard millet by the application of different fertilizer dosages keeping out other factors of soil and crop management practices as constants.

Test crop experiment
 
The experimental soil test value, grain yield and nutrient uptake by barnyard millet under different strips are mentioned in Table 2 and 3. The soil available KMnO₄ - N was 161,195 and 221 kg ha^-1 from Strip I to Strip III. Similarly, Strip I, Strip II and Strip III soil test values for Olsen - P were 15.4, 28.9 and 39.1 kg ha^-1 and NH₄OAc- K were 472,514 and 533 kg ha^-1, respectively. The overall soil available KMnO₄- N, Olsen -P and NH₄OAc - K in NPK treated and control plots were 193,28 and 508 and 189,25 and 505 kg ha^-1, respectively.
 

 

       
The average barnyard millet yield was 2213 kg ha^-1 (mean of 72 plots) and 1914, 2297 and 2428 kg ha^-1 in Strip-I, Strip-II and Strip-III, respectively and overall control and NPK treated plots were 1390 and 2330 kg ha^-1. The higher fertility status led to higher grain yield as well as nutrient uptake. The N uptake values were 45.55,57.50 and 69.97 kg ha^-1 in Strip-I, Strip-II and Strip-III, respectively. Parallelly, Strip-I, Strip-II and Strip-III reported P and K uptake values as 9.70, 13.16 and 15.22 kg ha^-1 and 45.44, 53.25 and 59.03 kg ha^-1, respectively. The average values of N, P and K uptake in overall control and NPK treated plots were 48.0, 9.6 and 40.3 and 59.0, 13.1 and 54.3 kg ha^-1, respectively. These results agree with Singh et al., (2016), Udayakumar and Santhi (2017) and Kumar et al., (2018).
       
The variation in grain yield attributed to the application of different fertilizer dosages was evaluated by regression analysis by finding the relationship between grain yield and fertilizer with N, P₂O₅ and K₂O which was significant (P<0.01). Regression analysis between N, P₂O₅ and K₂O fertiliser and grain yield revealed that N was responsible for 65.1% of grain yield, P and K were responsible for 44.5% and 32.2% of grain yield, respectively (Fig 2). The plant assimilation of applied nitrogen fertilizer was better compared to P₂O₅ and K₂O; it may be due to the mobile nature of nitrogen which in turn accounted for higher grain yield of barnyard millet. The integrated application of organic manures along with inorganic fertilizers was comparatively found better in increasing the grain yield than the application of inorganic fertilizers alone.
 

 
 
Basic parameters
 
The amount of nutrient required to produce one unit quantity of yield is defined as nutrient requirement (NR). The amount of nutrients (N, P₂O₅ and K₂O) vital for producing hundred kg of grain yield was found as 2.58 kg of N, 1.31 kg of P₂O₅ and 2.80 kg of K₂O (Table 4). From the data, the order of nutrient requirement was K₂O>N>P₂O₅. Fig 3 shows a linear relationship between barnyard millet grain yield and N, P and K uptake. Similarly, the results were in accordance with the findings of Santhi et al., (2011) and Sellamuthu et al., (2015). The soil available nutrient contribution (Cs) was reported as 23.33% N, 32.61% P₂O₅ and 7.01% K₂O, respectively. Among the three nutrients, the soil contribution towards P₂O₅ is high, followed by N and K₂O. The per cent contribution of N, P₂O₅ and K₂O from fertilizers (Cf) was 32.69, 44.72 and 64.66 which follows the order of K₂O> P₂O₅>N. The organic manure (FYM) contribution (Cfym) was recorded as 22.32% for N, 15.72% for P2O5 and 30.21% for K₂O, respectively and it contributes more towards K₂O. The results also in line with the findings of Santhi et al., (2011) and Sellamuthu et al., (2015) who observed a similar trend of relatively higher nutrient contribution towards K₂O rather than N and P₂O₅ from both fertilizer and FYM. It revealed that the contribution of nutrient sources for grain yield was higher from fertilizer sources than from soil available nutrients. Similar results were reported by Ray et al., (2000) in jute, rice and wheat; Basavaraja et al., (2017) in finger millet and Saren et al. (2017) in blackgram. Based on initial soil test values, crop yield and nutrient uptake by barnyard millet, the basic parameters were computed. The fertilizer prescription equations were developed for barnyard millet on Inceptisol using these basic parameters to get precise yield target and are furnished in Table 4.
 

 

 
Ready reckoner
 
The ready reckoners were prepared (Table 5) based on the fertilizer prescription equations, may be at different soil test values for different yield targets of barnyard millet under the NPK alone and NPK-IPNS condition. Nomograms were formulated for desired yield targets 2.5 and 3.0 t of barnyard millet for a range of soil test values under NPK alone and IPNS (NPK plus FYM @ 12.5 t ha^-1). The results indicated that to produce 2.5 and 3.0 t ha^-1 of grain yield for a soil test value of 220:24:500 kg ha^-1 of KMnO4-N, Olsen-P and NH4OAc-K, the amount fertilizer N, P₂O₅ and K₂O doses required was 41, 33 and 30 and 66, 33 and 30 kg ha^-1, respectively. Whereas, the application of FYM (26 per cent moisture and 0.56, 0.23 and 0.47 per cent of N, P and K) @ 12.5 t ha^-1 along with NPK fertilizer, the amount of N, P₂O₅ and K₂O doses required was 22,16 and 19 kg ha^-1 and 46, 31 and 30 kg ha^-1 for the yield target of 2.5 and 3.0t ha^-1 under the same soil test values. Consequently, the application of FYM has contributed 35, 17 and 25 kg of fertiliser N, P₂O₅ and K₂O, respectively. Udayakumar and Santhi (2017) also reported that application of farmyard manure at 12.5 t ha^-1 together with chemical fertilizer resulted in a saving of 40, 24 and 28 kg ha^-1 N, P₂O₅ and K₂O respectively in pearl millet.
 

       
Ready reckoners exposed that increasing the yield target, increases the fertilizer dose for similar soil test value, whereas the increasing soil test value decreases the fertilizer doses. In comparison with the application of inorganic fertilizer along with FYM and application of inorganic fertilizer alone, there was a notable reduction in fertilizer amounts when applied along with FYM, due to the nutrient supplement through FYM. The per cent reduction of fertilizers were increasing when applied along with FYM and also increasing the soil test values. A similar inclination of results was reported by Singh et al., (2018).

The present experiment revealed that Soil Test Integrated Plant Nutrition System-based Fertilizer Prescription Equations developed improves the yield of barnyard millet. It has been elucidated that STCR-IPNS is a balanced way of supplying nutrients through contribution from the soil, fertilizer and farmyard manure for achieving specific yield target of barnyard millet. By the way, the farmers will be benefited from rationalised usage of fertilizers, increased fertilizer use efficiency and recycling the farm wastes. Also, farmers can utilize the fertilizer prescription equations for specific yield targets based on their financial condition on similar soil series existing in Tamil Nadu.