Foliar Application of Different Phosphorus Sources for Transplanted Irrigated Pigeonpea [Cajanus cajan (L.)] in North Western Zone of Tamil Nadu 

Pigeonpea [Cajanus cajan (L.)] is one of the major grain legume crops of the tropics and subtropics, endowed with several unique characteristics. It finds an important place in the cropping system adopted by small farmer in a number of developing countries. India occupies 90 per cent of world redgram area and accounts for 80 per cent of world production of redgram. According to fourth advanced estimates of 2010-11 released redgram occupies an area of 4.42 million hectares and production of about 2.89 million tones, having an average yield of 655 kg per ha. Phosphorus deficiency is usually the key factor for seed yield of pulse crops on all soil types.

Soil application of phosphate fertilizers undergoes many undesirable changes like fixation, leaching, soil acidity, alkalinity and water logging. Phosphorus is a key element involved in various functions in growth and metabolism of pulses. It is frequently a major limiting nutrient for plant growth in most Indian soils. Only a part of the phosphorus supplemented through fertilizer is utilized by the plants and a large portion of it is converted into insoluble fixed forms, the recovery efficiency of phosphorus in crops is generally 10-30% (Swarup, 2002). To overcome this problem, foliar application of nutrients is essential at crop stage. Foliar applied nitrogen and phosphorus applied have been effectively absorbed and tanslocated to the pods resulting in more number of pods per plant (Solaiappan et al., 2002). Presently, 2% DAP is recommended for foliar spray in pulses to prevent flower drop and better seed set. At present, inspite of several demonstrations on effect of 2% DAP spray on boosting yield in redgram, farmers are failing to adopt this technology as dissolving of DAP is time consuming, filtering of supernatants requiring skills. During spray, sometimes it causes severe phytotoxicity effects due to accumulation of solid form at the time of spraying as it settles after some time. The major benefit to the farming community is foliar nutrition reduces the cost of cultivation so that this practice leads to economizing crop production. Thangaraj (2000) indicated that foliar application of nutrient for pulses save time to fixation and immobilization in soil. The foliar application of superphosphate and DAP was found effective when compared to soil application in crops (Chandrasekar and Bangunasamy, 2003). Foliar application of nutrient and growth regulator at pre flowering and flowering stage reduced the flower drop percentage in green gram (Ganapathy et al., 2008). Foliar application of NAA @ 40 ppm at pre flowering stage in blackgram increased the plant height, number of branches and leaf area index (Jayakumar et al., 2008).

Application of macro and micronutrients as foliar spray at critical stages of the crop absorbed and translocated effectively to the developing pods in soybean and produced more number of filled pods (Jayabal et al., 1999). The foliar spray of 0.5 per cent zinc sulphate at flower initiation stage in pigeon increased the yield (400 kg ha^-1) by Masood Ali and Mishra (2001). Thiyageshwari and Ranganathan (1999) stated the effect of foliar application of nutrients with the recommended dose of fertilizer in soybean  shown the highest seed yield of 1832 kg ha^-1 compared to the recommended NPK (1225 kg ha^-1). The foliar spray of micronutrients proved to be economical in pulses (Savithri et al., (2001). Pandian et al., (2001) reported that basal dose of fertilizer with foliar spray of 2 per cent DAP at twice shown the higher plant height (73.5 cm) and net return in greengram. Phosphorus deficiency is usually the key factor for seed yield of pulses crops on all soil types. Singh and Singh (2000) sated that that foliar spray of NAA @ 30 ppm has increased the number of leaves and branches in pulses. Application of P to pulse crops must be one of the most important strategies to increase productivity of pulses in India (Ganeshamurthy et al., 2003). Hence, the present investigations were carriedout to study the foliar application of different sources of phosphorus on yield and economics of transplanted redgram.

To overcome insolubility of DAP, the present investigation was carried out to study the effect of foliar application of different sources of phosphorus on yield of transplanted red gram (Cajanus cajan) under irrigated conditions at Regional Research Station, Tamil Nadu Agricultural University, Paiyur, Tamil Nadu, in June (Kharif) 2014 to 2015 and 2015 to 2016, respectively in randomized block design with three replications. The treatments were foliar spraying of 0.5%, 1.0%,1.5% and 2.0 % mono ammonium phosphate (MAP) and 1.0%,1.5% and 2.0% 19:19:19, 1.0%  pulse wonder spray, 2% DAP along with water spray (Control). Foliar spraying was done on flowering and15 days after first spray. For planting in main field, pits were formed with size of 0.15m×0.15m×0.15 m at spacing of 150 × 60 cm by using hand hoe and transplanting of redgram was done on 20.07.2014 and 25.07.2015 respectively. Planting was done with 25 days old seedlings. Irrigation was given in 7 days interval with surface irrigation methods. Foliar application of MAP (0.5, 1.0, 1.5 and 2.0%), 19:19:19 (1.0, 1.5 and 2.0%), DAP (2%) and pulse wonder (1%) were applied during flower initiation and 15 after first spraying as per the treatment schedule. The variety of LRG 41 was used for the study and its duration was 180-200 days. The observation on growth parameters was recorded in the following treatments imposed on red gram at flowering phase.

Growth characters
 
Plant height was recorded at 30, 60, 90,120,150 and 180DAS. There was no significant variation in plant height among the treatments upto 120 DAS (Table 1). Among the different foliar sprays, application of 0.5% mono ammonium phosphate (MAP) on flowering (105 days) and 15 days after first spray (T3) recorded taller plants of 268.1 and 262.1 cm and  274.8 and 273.6 cm at 150 and 180 DAS during 2014 and 2015, respectively. Control (water spray) (T₁) recorded shorter plants of 235.1and 245.9 cm and 244.0 and 245.2 cm at 150 and 180 DAS during 2014 and 2015, respectively. Regarding no. of branches, spraying of 0.5% Mono Ammonium Phosphate (MAP) on flowering (105 days) and 15 days after first spray (T₃) recorded higher no. of branches of 19.7 and 21.9 during 2014 and 2015, respectively.  Control (water spray) (T₁) recoded lower no. of branches of 15.1 and 17.3 during 2014 and 2015, respectively. Foliar spraying after 120 DAS recorded higher plant height during 150 and DAS due to better accumulation of source due to energy transfer. The growth parameters of green gram was increased due to foliar spraying of 0.5% MAP (Sivakumar et al., 2019).
 

 
Yield parameters
 
Among the different foliar spray, application of 0.5% mono ammonium phosphate (MAP) on flowering(105 days) and 15 days after first spray (T₃) recorded higher yield parameters like number of pods/plant of 1210, no. of seeds/pod of 5.1, stem girth of 11.2 and 100 seed weight of 12.7 g at harvesting stage. This was followed by application of 1.0% mono ammonium phosphate (MAP) on flowering(105 days) and 15 days after first spray (T₄) and recorded yield parameters like number of pods/plant of 1116, no. of seeds/pod of 5.0, stem girth of 10.9 and 100 seed weight of 12.4 g at harvesting stage. Control (water spray) (T₁) recorded lower number of pods/plant of 987, no. of seeds/pod of 5.0, stem girth of 9.0 cm and 100 seed weight of 11.6 g. (Table 2). The higher values of yield and yield attributes may be as cribbed to the effect of P on root development, energy transformation and metabolic processes of the plant, which in term resulted in greater translocation of photosynthates towards the sink development (Singh and Ahlawat, 2007), (Manivannan et al., 2002) and (Prakash et al.,2003).
 

 
Pooled analysis
 
Pooled analysis was done for grain yield and stalk yield (Table 3). Regarding yield, application of 0.5% mono ammonium phosphate (MAP) on flowering (105 days) and 15 days after first spray (T₃) recorded grain and stalk yield of 2512 and 8228 kg ha^-1 respectively. Control (water spray) (T₁) recoded lower number grain and stalk yield of 1760 and 6056 kg ha^-1 respectively. Application of 0.5% mono ammonium phosphate (MAP) on flowering(105 days) and 15 days after first spray (T₃) recorded 4% higher over application of 1.0% mono ammonium phosphate (MAP) on flowering (105 days) and 15 days after first spray (T₄) and 29% higher yield over Control (water spray). (T₁). Phosphorus application had increased the yield of redgram (Malarmathi and Thomas Abraham, 2003).Foliar application of  1% DAP + 0.5% urea recorded higher number of pods/plant in irrigated blackgram (Subramani et al., 2002).
 

 
With regard to economics, application of 0.5% mono ammonium phosphate (MAP) on flowering (105 days) and 15 days after first spray recorded higher net income and B:C ratio of Rs.95215/- and 2.97, respectively. The economics was increased due to application of 0.5% MAP (Sivakumar et al., 2019).

This was followed by application of 1.0% mono ammonium phosphate (MAP) on flowering (105 days) and 15 days after first spray (T₄), which recorded a net income and B:C ratio of  Rs. 88383/- and 2.80, respectively. Control (water spray) (T₁) recoded lower net income and B:C ratio of Rs. 54053/- and 2.14, respectively.

Application of 0.5% mono ammonium phosphate (MAP) on flowering (105 days) and 15 days after first spray (T₃) recorded higher growth and yield parameters viz., number of branches per plant per plant, no. of pods per plant, no. of seeds per pod and 100 seed weight resulting in higher grain yield of 2512 kg ha^-1, net income of Rs. 95215/- and B:C ratio of 2.97. Thus, application of 0.5% mono ammonium phosphate (MAP) on flowering (105 days) and 15 days after first spray (T₃) recorded 4%  higher over application of 1.0% mono ammonium phosphate (MAP) on flowering (105 days)  and 15 days after first spray (T₄) and 29%  higher yield over control (water spray) (T₁).