Growth , productivity and quality of soybean [ Glycine max ( l ) Merrill ) under different levels and sources of phosphorus and plant growth regulators in sub humid Rajasthan

In India, soybean is the third largest oilseed crop but its productivity is lower and that can mainly be related to low fertilizer phosphorus usage, poor phosphorus use efficiency and flower and bud drop. In this backdrop, to achieve sustained higher soybean productivity, twenty seven treatments [three doses: 20, 30 and 40 kg P2O5 ha; three sources: single super phosphate (SSP), phosphorus rich organic manure (PROM) and di-ammonium phosphate (DAP) and three plant growth regulators (PGRs): water spray, benzyl adenine 50 ppm and naphthalene acetic acid (NAA) 100 ppm] were evaluated in a split plot design having three replications on medium clay loam soils of Udaipur (India) during rainy seasons of 2009 and 2010. Results conclude that 40 kg P2O5 ha, SSP and NAA recorded significantly higher pooled plant height (51.65, 50.82 and 51.17 cm), branches plant (4.56, 4.43 and 4.48), oil content (21.40, 20.91 and 21.20%), oil yield (558.89, 528.75 and 521.79 kg ha), seed protein yield (1111.56, 1039.96 and 1045.60 kg ha), grain yield (25.95, 25.12 and 24.23 q ha) and stover yield (37.37, 36.23 and 35.73 q ha) over their corresponding treatments. Use of NAA and benzyl adenine were statistically indifferent, however, they recorded significantly early setting of 50% flowering and substantially extended the crop maturity period over water spray. However, various levels and sources of phosphorus were indifferent in periods of 50% flowering and maturity. Use of 40 kg P2O5 ha and NAA recorded significantly higher pooled seed protein content over their corresponding counterparts but phosphorus sources were indifferent.


INTRODUCTION
Soybean is the third largest oilseed crop in India but its productivity is far below the global average and demonstrated yields in the country due to a cafeteria of production constraints mainly the poor input management larger concentration of oilseeds in less productive dry lands and rain-fed areas and associated agronomical, physiological and genetic constraints (inadequate phosphorus nutrition, flower and bud drop, lack of synchronous flowering and maturity, improper dry matter partition etc.).Inadequate phosphorus nutrition is the main and most common constraint behind poor soybean productivity.Also, Indian soils are beset with high variability in crop response to varying doses and sources of inorganic phosphatic fertilizers in different agroclimates due to wide variations in relative fixation of applied phosphatic material on accounts of variations in soil pH, organic matter and calcium status and a complex chain of processes and factors that govern the ultimate crop phosphorus availability viz.clay content, C:P and C:N:P ratio, microbial immobilization, triggering of organic phosphorus mineralization on depletion of inorganic soil phosphorus, composition and solubility of fertilizer material, method of fertilization etc.
Clay loam soils of Udaipur are medium in available phosphorus but they are characterized by high pH (>8.0), organic carbon (about 0.69%) and calcium (about 3.53%) contents (quite conducive conditions for phosphorus precipitation).Increase in organic phosphorus decreases microbial phosphorus mineralization but C:P ratio of <200 enhances this release.Application of inorganic P 2 O 5 fertilizers may bring C:P ratio below 200 and induce organic phosphorus release for variable periods depending upon rate of precipitation of applied phosphorus into Ca-P complexes or immobilization otherwise and release of organic phosphorus can sharply decline or even stop beyond C:P ratio of 200.Phosphorus rich organic manure (PROM), a cheap, ecofriendly and water soluble source, has microbial ingredients (phosphorus solubilising bacteria and Azotobactor) potent to release organic acids to enhance native soil phosphorus availability while single super phosphate (SSP) contains 10 to 12% sulphur that can be of worth in lowering the high soil pH in furrow slice that may lead to enhancement in available phosphorus on band placement beneath the crop seeds.However, both these phosphorus sources have yet not been evaluated in soybean crop under sub humid ecosystem of Udaipur.Enhancement in soybean productivity and quality in terms of oil and protein content at higher phosphorus levels ranging from 30 to 60 kg P 2 O 5 ha -1 have been reported by several workers including Kanojia and Sharma (2009), Jahangir et al. (2009), Thakur and Girothia (2010) and others.Similarly, superiority of SSP in performance of yield and quality of soybean over diammonium phosphate (DAP) and rock phosphate is reported by many workers including Chavan et al. (2008) quality of different crops (Howard et al., 2001;Meena et al., 2012) due to improved photosynthesis and source to.regulators (PGRs) sustainably enhance productivity and Simultaneous use of phosphorus and plant growth sink output, maintenance of optimum hormonal levels and protection against abiotic and biotic stress (Bajguz and Hayat, 2009).Applications of benzyl adenine (Kanojia and Sharma, 2008;Kanojia and Sharma, 2009) and naphthalene acetic acid (NAA) (Thakare et al., 2006;Deotale et al., 2011) also significantly improve the growth, yield, yield attributes and quality of soybean.However, benzyl adenine or NAA and their interaction with different levels and sources of phosphorus have yet not been evaluated in soybean crop under Udaipur conditions specifically from point of view of productivity and quality performance.Therefore, this study aiming to achieve not only the higher efficiency of applied phosphatic fertilizers but also to evaluate quality parameters in terms of oil and protein content and yield, was conducted through assessing the effects of different sources and levels of phosphorus and PGRs in soybean crop.

MATERIALS AND METHODS
A 2-year field experiment was conducted at Instructional Farm of Rajasthan College of Agriculture, Udaipur which falls in agroclimatic Zone IV (a Sub-Humid Southern Plains and Aravali Hills) during kharif seasons of 2009 and 2010.The study site is located at 24°35' N latitude and 72°42' E longitude at an elevation of 582.17 m above mean sea level.Twenty-seven treatments comprising of three levels (20, 30 and 40 kg P 2 O 5 ha -1 ) and three sources (SSP; PROM and DAP) of phosphorus in main plots and three PGRs (water spray, benzyl adenine 50 ppm and NAA 100 ppm) in sub plots were evaluated in a split plot design having three replications.Foliar spray of designate concentration of PGRs was made twice at 30 and 65 days after sowing (DAS).Soil of study site was clay loam in texture with a slightly alkali pH (7.6), bulk density of 138 Mg/m 3 , calcium content of about 3.53%, organic carbon content of 0.69%, available nitrogen of 301.19 kg ha -1 , available phosphorus of 23.17 kg P 2 O 5 ha -1 and available potassium of 341.41 kg K 2 O ha -1 .Soybean (cv.Pratap Soya 1) was sown 30 × 10 cm apart with the commencement of Southwest monsoon in last week of June to first week of July in a field that was under continuous cropping during both rabi and kharif seasons for last 5 years.Total rainfall received by soybean crop during kharif 2009 and 2010 was 425.20 and 758.0 mm, respectively.Soybean was raised applying recommended package of practces for the region.PROM contained 15.18% P 2 O 5 , 1.45% N, 1.12% K 2 O and 0.4% S besides other micro-nutrients (Zn: 90 ppm; Cu: 32 PPM; Fe: 7920 ppm).Phosphatic fertilizers were applied through band placement below the seed before sowing.Plant height (length from base to tip of main axis) and branches plant -1 were estimated on basis of five randomly selected plants from each experimental unit.Oil content in seed was estimated by rapid non-destructive pulse magnetic resonance (NMR) spectrophotometer in accordance with Tiwari et al. (1974).Protein content was worked out by multiplying nitrogen content in seed with a constant factor of 6.25.Data were Table 1.Effect of different phosphorus levels and sources and PGRs on branches plant -1 , final plant height and periods of 50% flowering and maturity in soybean crop at Udaipur.

Treatment
Branches plant

Growth, reproduction and maturity
Data (Table 1) revealed that each increment in phosphorus level recorded significantly higher plant height and branches plant -1 during both the years and on pooled basis.Application of 40 kg P 2 O 5 ha -1 recorded 6.36, 17.01% and 8.06, 32.58% higher pooled plant height and branches plant -1 over 30 and 20 kg P 2 O 5 ha -1 , respectively.Similarly, application of 30 kg P 2 O 5 ha -1 recorded significantly higher pooled plant height branches plant -1 over 20 kg P 2 O 5 ha -1 by registering an increase of 10.01 and 22.67%, respectively.However, days taken to 50% flowering and maturity were not influenced by different levels and sources of phosphorus.Use of SSP recorded 10.41, 6.97% and 14.47, 13.01%higher pooled plant height and branches plant -1 over DAP and PROM, respectively.However, plant height and branches plant -1 recorded under DAP and PROM were indifferent.Foliar spray of NAA significantly enhanced the maturity period of soybean over benzyl adenine and water spray during both the years and on pooled basis.Also, use of NAA led to early induction and completion of 50% flowering during both the years and on pooled basis.Application of NAA led to 5.53 and 14.47% higher pooled plant height; 9.54 and 22.74% more pooled branches plant -1 ; 1.37 and 6.57% early pooled 50% flowering and 1.56 and 5.88% increase in pooled maturity period of soybean crop over benzyl adenine and water spray, respectively.Similarly, use of benzyl adenine outperformed the water spray in pooled performance of plant height, branches plant -1 and

Oil and protein content and yield
Each increment in phosphorus level, SSP and NAA recorded significantly higher oil content, oil yield, protein content and protein yield over their corresponding treatments during both the years and on pooled basis excepting the phosphorus sources which were indifferent in protein content (Table 2).Use of 40 kg P 2 O 5 ha -1 recorded 7.27, 18.10% and 3.49, 9.01% higher pooled oil and protein content in soybean seed and an additional pooled oil yield of 110.6 and 219.62 kg ha -1 and protein yield of 188.23 and 384.13 kg ha -1 was observed over 30 and 20 kg P 2 O 5 ha -1 , respectively.Application of 30 kg P 2 O 5 ha -1 also significantly enhanced the pooled oil and protein content in soybean seed than 20 kg P 2 O 5 ha -1 that corresponded to 10.10 and 5.33%, respectively.Significant higher oil and protein yield to a tune of 109.20 and 195.90 kg ha -1 was also recorded on application of 30 kg P 2 O 5 ha -1 over its immediately lower level of 20 kg P 2 O 5 ha -1 , respectively.Use of SSP recorded 10.05, 6.90%; 32.45, 26.34% and 22.58, 18.99% higher pooled values of oil content, oil yield and protein yield than DAP and PROM, respectively.However, DAP and PROM were indifferent in oil and protein content and protein yield.Foliar application of NAA recorded 15.59, 6.37% and 9.51, 3.88% higher pooled oil and protein content over water spray and benzyl adenine, respectively.Significant enhancement in pooled oil yield to a tune of 148.69 and 70.23 kg ha -1 and protein yield to an extent of 254.33 and 120.15 kg ha -1 30 kg P 2 O 5 ha -1 was recorded under NAA over benzyl adenine and water spray, respectively.Benzyl adenine also outperformed water spray in pooled performance of oil content, oil yield, protein content and protein yield by registering an enhancement of 8.67, 5.42, 10.29 and 16.96%, respectively.

Yield performance
Each higher phosphorus level, SSP and NAA recorded significantly higher grain and stover yield of soybean than their corresponding treatments during both the years and on pooled basis (Table 3).Application of 40 kg P 2 O 5 ha -1 recorded 16.42 and 40.27% higher pooled grain yield and 11.76 and 34.22% higher pooled stover yield than 30 and 20 kg P 2 O 5 ha -1 , respectively.Use of 30 kg P 2 O 5 ha -1 also outperformed 20 kg P 2 O 5 ha -1 by registering an enhancement of 20.49 and 20.09% in pooled grain and stover yield, respectively.Use of SSP recorded significantly higher pooled grain and stover yield than DAP and PROM by recording an enhancement of 22.18, 19.33% and 17.37, 15.09%, respectively.However, difference in pooled grain (0.49 q ha -1 ) and stover (0.42 q ha -1 ) yield between DAP and PROM were not marked.Foliar application of NAA recorded significantly higher pooled grain and stover yield than benzyl adenine and water spray by registering an enhancement of 8.56, 20.37% and 8.21, 19.54%, respectively.Benzyl adenine also recorded significantly higher pooled grain and stover yield than water spray that corresponded to 2.19 and 3.19 qha -1 , respectively.

DISCUSSION
Different levels and sources of phosphorus as well as PGRs significantly influenced the plant height; branches plant -1 , completion of 50% flowering, maturity period, oil content and yield, protein content and yield and grain and stover yield of soybean crop during both the years and on pooled basis under sub humid climate of Udaipur on medium clay loam soils.However, days taken to 50% flowering under different levels and sources of phosphorus as well as protein content under various phosphorus sources were indifferent.Significantly higher growth, prolonged crop period and yield performance of soybean crop at each incremental phosphorus level and SSP can be ascribed to more soil phosphorus availability and resultant higher crop phosphorus mining under these treatments.In fact effect of phosphorus nutrition on growth and productivity performance of legume oilseeds is grave that ultimately links to key role of this nutrients in plants (photosynthesis regulations, root and shoot growth, nitrogen fixation, partitioning of photosynthates, constituent of plasma membrane, nucleic acids, many coenzymes, organic molecules like adenosine tri phosphate and other phosphorylated products; quality parameters etc.).Phosphorus is reported to enhance growth, biomass and ramification of root as well as biological nitrogen fixation through increasing number and dry weight of root nodules in soybean or other legumes (Adelson and Marcelo, 2000;Ramasamy et al., 2000;Singh et al., 2001).Results further confirm that phosphorus levels and sources did not influence the flowering response which is a phenomenon governed by periodicity of light or night interruption.Results on enhanced growth and yield of soybean crop at higher phosphorus levels well corroborate with the findings of Sharma et al. (2002), Chavan et al. (2008) and other workers.
More phosphorus availability on application of SSP in soybean crop can be attributed due to pH ameliorating effect of 10 to 12% sulphur traces contained in this fertilizer material which variably amended the high soil pH (>8.0) in furrow slice on band placement beneath the seed.Also, the independent beneficial effects of sulphur traces contained in SSP on growth and yield of soybean crop cannot be ignored in backdrop of wide role of this nutrient in plants.Sulphur is a structural component of amino acids (cysteine and metionine), iron sulfur clusters, polysaccharides, lipids, vitamins (glutathione and phytochelatins), cofactors (Co-A, S-adenosyl-Met), secondary products (allyl Cys sulfoxides and glucosinolates) etc. Besides, sulphur has diverse cellular roles viz.regulation of enzyme activities (e.g.proteolytic and nitrogenase), redox cycle, xenobiotic detoxificants etc.The superiority of SSP over DAP and other phosphorus containing materials including PROM in soybean and other oilseeds/pulses are well supported by other workers including Chavan et al. (2008).However, DAP and PROM are reported to be at par in productivity performance of soybean, oilseeds and legumes (Meena and Sharma, 2005;Kanojia, 2006).
Significant delay in maturity of soybean crop was recorded under PGRs which directly implies to prolonged crop period that enabled the crop plants to continue on photosynthesis for larger period which in principle relates to higher net assimilation and productivity.Prolonged growth and maturity period together with early onset of flowering can be ascribed to different physiological and metabolic roles of PGRs.Nevertheless, it is well clear that overall impact of cytokinin group benzyl adenine was less pronounced than the auxinic NAA so far as effect of PGRs on growth in terms of plant height and branches plant -1 , completion of 50% flowering, maturity period and grain and stover yield of soybean crop is concerned.Various research reports and literature including Pandey and Sinha (2011) confirm that cytokinin is involved in initiation of cell division, counteracting apical bud dominance, inducing flowering in short day plants, morphogenesis, nucleic acid metabolism, protein synthesis, induction of flowering in short day plants, improvement in morphological characters and total chlorophyll etc. Auxins on other hand have role in cell elongation and enlargement, cell wall biosynthesis, xylem differentiation, fundamental change in enzyme system of cytoplasm, mRNA synthesis, seed germination, root initiation and differential behavior of root and shoot growth, delay in abscission, improvement in leaf area, leaf area index and total chlorophyll etc.
Significant enhancement in grain and stover yield of soybean crop under 40 kg P 2 O 5 ha -1 and SSP than the corresponding treatments was linked with significantly growth in terms of plant height and branches plant -1 while significantly higher yield performance on use of NAA was also linked with significant enhancement in reproductive/maturity/photosynthetic period.For instance, an enhancement of 4.56 and 4.07 q ha -1 in pooled grain yield as well as 5.37 and 4.75 q ha -1 in pooled stover yield (Table 3) under SSP was linked significantly higher pooled plant height and branches plant -1 that corresponded to 6.36, 17.01; 10.41, 9.10 and 8.06, 32.56 and 11.19, 6.18% (Table 1) over DAP and PROM, respectively.NAA recorded 8.56 and 20.37% higher pooled grain and 8.21 and 19.78% higher pooled stover yield than benzyl adenine and water spray which was again linked with significantly higher growth, early completion of 50% flowering and delay in maturity (Table 1).These results on effect of PGRs on soybean/other legumes well corroborate with findings of Kanojia and Sharma (2009), Deotale et al. (2011) and Rahdari and Sharifzadeh (2012).
Significantly higher seed protein content at higher phosphorus levels can be ascribed to higher seed nitrogen content which is a direct function of plant nitrogen assimilation and its translocation to real sink, that is, seed; however phosphorus nutrition can be critical in governing the source to sink strength due to its key role in deciding the energy relations within the plants.Higher seed nitrogen content appears to be linked with higher nitrogen uptake/biological nitrogen fixation at increasing phosphorus levels and phosphorus level has clear role in governing the root nodules plant -1 , nodules weight plant -1 , root growth and ramification; mining of different mineral nutrients from soil and optimization of phosphorus linked physiological and metabolic processes.Results of this study also revealed improved oil and protein synthesis, bold seed size (test weight) and dry matter productivity at increasing phosphorus levels.There exists a similar disposition of more phosphorus availability to soybean crop on supplementing phosphorus through SSP on account of amelioration of high furrow slice pH.The results on higher oil and protein yield at increasing phosphorus levels and SSP well corroborate with findings of Chavan et al. (2008), Jahangir et al. (2009), Kanojia and Sharma (2009), Thakur and Girothia (2010) and others.Higher oil and protein content in soybean seeds under PGRs can be attributed due to their physiological and metabolic roles in plants which is also well supported by Kanojia and Sharma (2009) Deotale et al. (2011) and others.

Conclusion
The findings of this research revealed that 40 kg P 2 O 5 ha - 1 , SSP and foliar spray of 100 ppm NAA resulted in sustained higher soybean productivity on medium clay loam soils of sub humid Rajasthan due to enhancement in phosphorus use efficiency that resulted in significantly higher pooled plant height, branches plant -1 , oil content, oil yield, seed protein yield, grain yield and stover yield over their respective counter treatments.Use of PGRs resulted in significantly early setting of 50% flowering and prolonged crop maturity period besides significant improvement in performance of various growth parameters, dry matter productivity and quality parameters of soybean crop evaluated in this study.However, more studies to mobilize precipitated phosphorus particularly organically bound phosphorus as well as to prevent precipitation of fertilizer phosphorus on medium clay loam soils of sub humid Rajasthan having high pH and high organic matter and calcium content is needed to argument the future crop production, are needed.

Table 2 .
Effect of different phosphorus levels and sources and PGRs oil and protein content and yield of soybean crop under Udaipur conditions.

Table 3 .
Effect of different phosphorus levels and sources and PGRs on grain and stover yield of soybean under Udaipur conditions.