Phosphorus Management in Greengram-Safflower Sequence on Shrink-Swell Soils of Maharashtra

A study was conducted on phosphorus management in greengram-safflower sequence at Dr. Panjabrao Deshmukh

Phosphorus is one of the major essential element required by the crop and is the key nutrient for increasing productivity of pulses in general and legumes in particular. It plays an important role in uniform grain filling besides a constitutent of ADP and ATP energy bonds. In black cotton soils, phosphorus gets fixed as calcium and magnesium phosphate and become unavailable to crop. The requirement of P by legume crops is generally doubled than N and K. However, the utilization efficiency of P is very low compared to N and K. Phosphorus availability is a major nutritional constraint limiting crop production in the Vertisols of central India (Subba Rao et al., 1998).
Legume-safflower cropping sequence is recommended for the Vertisols region for realizing higher production and profit besides improving soil fertility (Hegde, 2000). Appropriate nutrient management is the key to enhance safflower productivity in such cropping sequence on sustainable basis. Because of nitrogen fixation, legumes are independent for their nitrogen nourishment and leave a sustainable amount of nitrogen residues to succeeding crop. Safflower is an important oilseed crop of the semi-arid tropics. N and P deficiencies in Vertisol in which safflower is grown are common (Hegde, 2003). The component crops grown in a sequence remove considerable amount of nutrients from the soil.
Greengram (Vigna radiata L.) is an excellent source of high quality protein and high nutritional *Corresponding author email: basonune@gmail.com value among pulses. It occupies a prominent place and is gaining increasing popularity by virtue of its high nutritional value, short growth period, low production cost and adaptability to off season. The productivity of greengram and safflower crops is low in central India compared to National average. The reasons for this low productivity is imbalanced fertilization particularly P in a low native P black soils. Therefore present investigation was planned to study the phosphorus management on crop productivity, economics and residual soil fertility in greengram-safflower sequence on shrink-swell soils under semi-arid conditions of central India.

Materials and Methods
The experiment was conducted on shrink-swell soil with twelve treatments with three replications laid out in a randomized block design using greengram (Kopergaon)-safflower (AKS-207) in cropping sequence as test crops at Dr. Panjabrao Deshmukh Krishi Vidyapeeth, Akola during 2006-7. The soil was low in available nitrogen (181 kg ha -1 ) and phosphorus (10.2 kg ha -1 ) and high in available potassium (348 kg ha -1 ).
Recommended doses of fertilizer (as per national recommendation) 20:40: 20 NPK kg ha -1 (greengram) and 25:25: 25 NPK kg ha -1 (safflower) and PSB 25 g kg -1 seed were applied. A common dose of recommended nitrogen and potassium was applied to all inorganic treatments. The farmyard manure was applied every year one month before sowing of the crop as per treatments. Soil samples (0-15 cm) from the experimental field were collected before sowing and after harvest of greengram and safflower in each treatment. These samples were analysed for organic carbon by rapid titration method (Walkley and Black, 1934), available N by alkaline permanganate method (Subbiah and Asija, 1956). Available P was estimated by Olsen's method (Olsen et al., 1954) and available K by ammonium acetate extraction method (Jackson, 1967).

Grain and straw yield of greengram
The grain yield (Table 1) was significantly higher i.e. (9.90 q ha -1 ) in treatment T2 receiving 100% P and it was found to be at par with most of the treatments except treatments receiving 50 per cent P (T3 and T4) and control (T1 and T6) treatments. The treatment T6 (control) recorded the lowest grain yield (7.83 q ha -1 ).
The highest straw yield (9.85 q ha -1 ) was recorded with the application of 100% P (T10) and it was found at par with the treatments T2, T9, T11, T5 and T12. The lowest straw yield ( 6.56 q ha -1 ) was observed in control. The higher grain and straw yields observed in the treatments T2 and T10 receiving 100 % P, might be due to phosphatic fertilizer (100%) which helps to increase the yield of legumes by mobilizing the unavailable P in soil and make it available to crop. The results are in conformity with Sarkar et al. (1993) and Singh and Pareek (2003).

Seed and straw yield of safflower
The data presented in Table 1 showed that the seed yield of safflower was significantly higher (13.35 q ha -1 ) in treatment T8 receiving 100% P and it was found to be at par with the treatments T7, T2, T5, T3, T12 and T6. The lowest seed yield (9.46 q ha -1 ) was recorded in treatment T1(control). The highest straw yield ( 44.64 q ha --1 ) was recorded in treatment T6 receiving 100% P and it was found at par with most of the treatments except treatments T4 and T11 receiving 50% P and 5 t FYM ha -1 and treatment T1 and T10 (control). While the lowest straw yield (33.89 q ha -1 and 39.53 q ha -1 ) was found in treatments T1 and T10 (control) respectively. The similar results were also reported by Kumpawat (2006).

Economics of various treatments in greengramsafflower sequence
The data in respect of gross monetary return (GMR), cost of cultivation (CC), net monetary return (NMR) and benefit cost ratio (B:C) as influenced by different treatments are presented in Table 2. The highest GMR (Rs. 50562) was obtained in treatment T2 receiving 100% P to both crops, followed by treatment T12 (Rs. 48521) which received 100% P to greengram and 5 t FYM with PSB to safflower. The lowest GMR (Rs. 39629) were obtained in control treatment (T1). Similarly, highest NMR (Rs. 37784) was obtained in treatment T2 followed by T9 (Rs. 35518), while lowest NMR (Rs.21164) was obtained in control.
The trend of various treatments in respect of B:C ratio was similar to that of GMR, NMR and productivity also. The highest B:C ratio (4.0) was obtained in treatment T2 and T10 receiving 100% P to both crops. The increase in B:C ratio was ascribed to significant increase in productivity of crops over other treatments. The results are in conformity with the findings of Tomar and Tiwari (1990) and Jadhao et al. (1994).
Higher crop productivity and maximum B:C ratio were obtained in treatments receiving 100 per cent recommended P followed by 50 per cent P + PSB to both crops.

Fertility status of soil at harvest of greengram
Organic carbon is an indication of organic fraction in soil formed due to the microbial decomposition of organic residue. The data (Table 3) pertaining to the organic carbon content of soil as influenced by different treatments was statistically non significant and it ranged from 4.6 to 5.2 g kg -1 indicating that the highest (5.2 g kg -1 ) organic carbon content was recorded in treatments T5 and T8 (50 per cent P + PSB and 5 t FYM ha -1 + PSB, respectively). This might be due to PSB inoculation. Malewar and Hasnabade (1995) also recorded maximum organic carbon in the treatments containing chemical feritlizers combined with biofetilizers.
The available N status of soil was significantly influenced by different treatments. The highest available N (215 kg ha -1 ) was observed in treatment T5 (50 % P + PSB) which was found at par with treatment T11, T12 and T2 while, lower values of available N (179 and 180 kg ha -1 ) were observed in control treatments T1 and T6 respectively. The higher values of available N over the initial value might be due to symbiotic nitrogen fixation, which improve the available nitrogen status in soil by growing leguminous crop like greengram. The residual effect of leguminous crops improves the total and available nitrogen status of soil (Sharma et al., 1986).
The available P status of soil at harvest of greengram was found superior (15.3 kg ha -1 ) in treatment of 50% P + PSB (T5) followed by treatment T12 (15 kg ha -1 ). This might be due to PSB, which enhances the availability of phosphorus, which favoured the root growth by development of phosphorus solubilizing microorganisms in root zone of crop. However, all 100% P (T2, T9, T10, T11 and T10) treatments were found to be at par with the treatment T5. Similar results were also given by Abraham and Lal (2003).
The highest available K (390 kg ha -1 ) in soil was observed in treatment T5 receiving 50% P + PSB and it was found to be at par with the treatments T2, T11, T9, T10 and T12, receiving 100% P. The treatment T1 recorded the lowest K content in soil (347 kg ha -1) . Similar trends were also reported by Abraham and Lal (2003).

Fertility status of soil at harvest of safflower
The inclusion of legumes in cropping system significantly improved the soil fertility. The data presented in Table 4 revealed that the fertility status of soil after harvest of safflower was significantly influenced due to incorporation of organic manures and inorganic fertilizers along with biofertilizer. The organic carbon content of experimental site at harvest of safflower responded significantly to integrated phosphorus management and ranged from 4.7 to 5.5 g kg -1 . The higher organic carbon content (5.5 g kg -1 ) was recorded in treatment T5 (50% P + PSB) and was found superior to all other treatments. The higher values of organic carbon content at harvest of safflower might be due to residual effect of greengram grown in kharif season. These results are in conformity with the results recorded by Thomas and Lal (2003).
The available N in soil at harvest of safflower varied from 178 to 228 kg ha -1 . The maximum available N (228 kg ha -1 ) was observed in treatment T5 (50% P + PSB) which was superior over all treatments. This might be due to synergistic effect of biofertilizers. The lowest available N (183 kg ha -1 ) was noticed in treatment T1. Similar trend increase in available N was reported by Sharma et al. (1986) and Singh et al. (1996).
The data indicated that the different treatments had significant effect on the available phosphorus status of soil which ranged between 9.8 to 14.3 kg ha -1 . The highest available phosphorus (14.3 kg ha -1 ) was observed in treatment T5 receiving 50% P + PSB. This might be due to beneficial effect of seed inoculation with PSB which improved the available P status in soil by increasing fertilizer use efficiency. However, treatments T7, T8 and T6 (100% P) were found to be at par with treatment T5. Similar results were also reported by Carrie and Lamb (2003).
The data on available potassium status of soil at harvest of safflower varied significantly from 351.28 to 410.08 kg ha -1 . The highest available K status (410 kg ha -1 ) was found in treatment T5 receiving 50% P + PSB and it was found statistically at par with treatment T11 (5 t FYM ha -1) . Meshram et al. (2004) also recorded similar results.
Hence, it can be concluded that the treatment receiving 50 per cent P (20 kg ha -1 to greengram and 12.5 kg ha -1 to safflower) + PSB along with recommended dose of nitrogen (20 kg ha -1 to greengram and 25 kg ha -1 to safflower) and potassium (20 kg ha -1 to greengram and 25 kg ha -1 to safflower) to greengram and safflower was found to be beneficial in improving the soil fertility status, and obtaining higher crop productivity and economic returns.