Effect of salicylic acid on productivity and nutrient uptake of Brassica species under different planting durations

A field experiment was conducted at Udaipur during the Rabi season of 2011 to 2012 to evaluate the effect of planting duration and salicylic acid (SA) application on yield, quality and nutrient uptake of Brassica species. The results revealed that crops sown during SMW (Standard Meteorological Week) 41 recorded significantly (p < 0.05) higher seed, stover and oil yields, N and P uptake in seed and stover than SMW 43 and SMW 45 sown crops. Amongst Brassica species, B. juncea var. Bio-902 proved superiority over Brassica juncea var. RGN-73 and Brassica campestris var. BSH-1 in terms of seed, stover and biological yield, and N and P uptake in seed and stover. The foliar spray of salicylic acid produced significantly (p < 0.05) higher seed yield and oil content compared to water spray.


INTRODUCTION
Production potentiality of mustard can be fully exploited with suitable agronomic practices and the selection of genotypes.Among the different agronomic practices, optimum sowing time plays an important role to fully exploit the genetic potentiality of a variety as it provides optimum growth conditions such as temperature, light and humidity.The growth phase of the crop should synchronize with optimum environmental conditions for better expression of growth and yield.It is a fact that specified genotypes does not exhibit the same phenotypic characteristics in all environmental conditions.The different genotypes, growth response vary in different environments and their relative ranking usually differ and this ultimately decides the selection of genotypes for a particular or different sowing dates in other to stabilize higher yields.Out of the various abiotic stresses, high temperature is the most important stress, which can strike a crop at any time and imposed many limitations on growth and development.Developing crop plants with improved thermo tolerance can mitigate the adverse effect of heat stress.
Brassica is an important oil seed crop and its early sowing implies many important advantages such as escape from aphids infestation, while late sown crop encounters high temperature stress at seed development stage, which causes a great yield reduction (Abolfazl et *Corresponding author. E-mail: solanki.narayan@rediffmail.com al., 2009).The application of plant growth regulators is known to play an important role in plant response to stress (Chakrabarti and Mukherjee, 2003).Salicylic acid (SA) has recently been recognized as a plant growth hormone and plays diverse physiological roles in plants including thermogenesis generate a wide range of metabolic and physiological responses thereby affecting their growth and development (Hayat et al., 2010).SA has been found to be involved in both basal and acquired thermo-tolerance in plants (Dat et al., 1998a(Dat et al., , b, 2000;;Lopez-Delgado et al., 1998).In the context of the above views, the present study was undertaken to test the hypothesis that SA will mitigate the adverse effects of temperature stress in Brassica.

Plant materials and growth conditions
The field experiment was conducted during Rabi season of 2011 to 2012 at Instructional Farm, Rajasthan College of Agriculture, Udaipur situated at Southern part of Rajasthan at an altitude of 582.0 m above mean sea level, at 24º34' N latitude and 73°42' E longitude.The region falls under agro-climatic zone IV A "Subhumid Southern Plain and Aravali Hills" of Rajasthan and agro climatic zone VIII (Central plateau and hills) of India.The soils of experimental field was clay loam in texture and slightly alkaline in reaction (pH 7.9) and calcareous in nature.The experiment consisted of 18 treatment combinations under three planting duration (Standard Meteorological Week (SMW) 41, SMW 43 and SMW 45) and three Brassica species (B.juncea var.Bio-902, B. juncea var.RGN-73 and B. campestris BSH-1).The experiment was laid out in split plot design with three replications.The crop was sown during SMW 41(12 th October), SMW 43 (27 th October) and SMW 45 (11 th November) with a seed rate of 5 kg/ ha and with 30 cm row to row and 10 cm plant to plant spacing.The crop was fertilized with 60 kg N and 40 kg P 2 O 5 ha -1 . One half of nitrogen and full dose of phosphorus were given as basal application.The remaining dose of nitrogen was top dressed at first irrigation 30 days after sowing (DAS).The foliar spray of SA 100 ppm was applied at 60 DAS and 75 DAS.The spray solution of 100 ppm SA was prepared by dissolving 100 mg of SA in one litre of water.

Nutrient estimation
Nitrogen content in stover and seed was determined by using Nesseler's reagent colorimetric method (Linder, 1944) and phosphorus by Vandomolybdo phosphoric acid yellow colour method (Jackson, 1967).Nitrogen and phosphorus uptake by plant at harvest was calculated by using following formula: 100 Nutrient uptake by seed/stover (kg ha -1 ) = Nutrient content in seed/stover (%) Seed/stover yield (kg ha -1 ) × The total nutrient uptake by the crop was estimated through summing up nitrogen and phosphorus uptake by seed and stover.

Yield components
Biological yield was recorded by weighing sun-dried plants of net plot along with siliquae and expressed in kg ha -1 for biological yield.The stover yield was obtained by subtracting seed yield from biological yield.Harvest index was worked out by the formula of Singh and Stoskopf (1971).

Statistical analysis of data
In order to test the significance of variation in experimental data obtained for various treatment effects, data were statistically analyzed as described by Panse and Sukhatme (1989).The critical difference was calculated to assess the significance of treatment mean wherever the 'F' test was found significant at 5% level.To estimate inter-relationship between various characters, correlation coefficients were computed.

Planting duration
Data on seed, stover and biological yields and harvest index presented in Table 1 shows that the highest seed yield of 1971.11kg ha -1 was obtained under SMW 41 sown crop which was significantly (p < 0.05) superior over SMW 43 and SMW 45 sown crop by 7.8 and 34.1%, respectively.Further, it was noted that the crop sown on SMW 43 gave significantly (p < 0.05) higher seed yield (1827.83 kg ha -1 ) by 24.3% over SMW 45 sown crop (1470.26kg ha -1 ).Similarly, SMW 41 sown crop recorded the highest stover (4877.99kg ha -1 ) and biological yields (6849.10kgha -1 ), which was significantly (p < 0.05) higher over SMW 43 by 10.3 and 9.6% and SMW 45 sown crop by 14.8 and 19.7%, respectively.Furthermore, the crop during SMW 43 recorded the maximum harvest index (29.4%)which was significantly (p < 0.05) superior over SMW 41 and SMW 45 sown crops by 2.4 and 13.1%, respectively.Similarly, SMW 41 sown crop recorded significantly (p < 0.05) higher harvest index over SMW 45 sown crop by 10.4%.Higher temperature prevailed during later phase of the crop growth which caused shortening of crop period and forced maturity resulting into reduced unit weight of seed and ultimately low seed yield under delayed sowings.The seed yield was negatively correlated with maximum, minimum and mean temperatures during 90 to 105 DAS (r = -0.654,-0.612, -0.639).In the present investigation, it was observed that an increase in mean temperature by 1°C during 90 to 105 DAS caused reduction in seed yield of about 250 kg ha -1 (Figure 1).
Interactive effects between planting duration and foliar spray on seed yield (Table 2) shows that the maximum seed yield of 1974.15kg ha -1 was obtained under SMW 41 sown crop with 100 ppm SA which was at par with treatment combinations viz.SMW 43+100 ppm SA, SMW 41+water spray and SMW43+water spray.Under SMW 41 and SMW 43, foliar spray of 100 ppm SA was at par with water spray.However, under SMW 45, foliar spray of SA produced significantly higher seed yield over water spray by 14.7%.Foliar spray of SA might reverse the effect of heat stress under SMW 45 sown crop resulting in significantly (p < 0.05) higher seed yield.It has been reported that exogenous application of SA enhanced photosynthesis efficiency, metabolism and growth of mustard plant under elevated temperatures (He et al., 2005;Kaur et al., 2009;Chhabra et al., 2013).Data pertaining to oil yield (Table 3) revealed that the crop sown on SMW 41 kept maximum oil content (38.10%) followed by SMW 43 (37.60%) and SMW 45 (36.48%).The crop sown on SMW 41 produced maximum oil yield (753.21 kg ha -1 ) followed by SMW 43 (689.74kg ha -1 ) and SMW 45 (538.25 kg ha -1 ).
Planting duration did not influence N and P content in seed and stover (Table 3).However, the crop sown on SMW 41 recorded maximum N uptake (63.02 kg ha -1 ) which was significantly (p < 0.05) superior over SMW 43 (57.63 kg ha -1 ) and SMW 45 (46.00 kg ha -1 ).Similar trends were noted with respect to P uptake (Table 4).The crop sown on SMW 41 recorded maximum total N and P uptake (105.26 and 19.69 kg ha -1 ) which was significantly ) and SMW 45 (82.05 and 15.95 kg ha -1 ).
The maximum net returns of 54469 ha -1 were obtained under SMW 41 sown crop which was significantly higher over SMW 43 and SMW 45 sown crops by 4943 and 17279 ha -1 , respectively.Further, SMW 43 planting duration gave significantly (p < 0.05) higher net return over SMW 45 by 12336 ha -1 (Table 4).

Brassica species
The highest seed yield of 1945.59 kg ha -1 was recorded in B. juncea var.Bio-902 which was significantly (p < 0.05) superior over B. campestris var.BSH-1 by 34.3% (Table 1).Further, it was noted that B. juncea var.RGN-73 gave significantly (p < 0.05) higher seed yield (1875.40 kg ha -1 ) over B. campestris var.BSH-1 by 29.5%.However, B. juncea var.Bio-902 was at par with B. juncea var.RGN-73 in respect to seed yield.Similar trends were recorded in stover and biological yields.However, Brassica species did not influence harvest index.The superiority of B. juncea var.Bio-902 seems to be on account of efficient translocation of metabolites towards sink.The B. juncea var.Bio-902 recorded significantly higher biological yield of 6901.11kg ha -1 and was 33.7% higher compared to varieties B. campestris var.BSH-1.This was attributed to significantly (p < 0.05)

Salicylic acid
Data on yield presented in Table 1 indicate that foliar spray of 100 ppm SA produced significantly higher seed yield (1799.12 kg ha -1 ) by 5.0% as compared to water spray (1713.68kg ha -1 ).Foliar spray of 100 ppm SA produced significantly higher stover and biological yields by 4.1 and 4.3%, respectively as compared to water spray.Increase in seed yield with foliar spray of SA could be ascribed to the fact that crop yield is not an abstract entity but it is an outcome of positive interaction between vegetative and reproductive growth of the crop.Significant improvement in yield components of wheat crop under the influence of SA was also reported by Hassanein et al. (2012).
Foliar spray of 100 ppm SA registered significantly higher oil content and oil yield by 3.1 and 8.0%, respectively as compared to water spray (Table 3).However, N and P content in seed and stover were not affected due to foliar application of SA.Foliar spray of 100 ppm SA significantly influenced N and P uptake by seed and stover as well as total uptake of N and P. Total N uptake by was higher under 100 ppm SA by 6.1% over water spray (91.28 kg ha -1 ).While total P uptake was 4.2% higher over water spray (17.34 kg ha -1 ) under the 100 ppm SA.The positive impact of nutrient uptake in seed and stover seems to be on account of better development of canopy which might have maintained adequate supply of metabolites for better growth.Thus better developed root system might have facilitated in more extraction of nutrients from soil and translocation to plant parts.Higher concentration of nutrients in seed along with higher seed yield under foliar spray of SA resulted in higher uptake of nutrients (Nafees et al., 2010).
Foliar spray of 100 ppm SA recorded significantly higher net returns of 48453 ha -1 over water spray by 2783 ha -1 (Table 4).

Conclusion
It can be concluded from the present study that Brassica juncea var.Bio-902 sown during SMW 41 gave maximum yield and foliar spray of 100 ppm SA enhanced seed yield in delayed sowing of Brassica.

Table 1 .
Effect of planting duration and salicylic acid (SA) on yields and harvest index of Brassica species.
Figure 1.Effect of mean temperature during 90 -105 DAS on seed yield of Brassica.

Table 2 .
Interaction effect of planting duration and foliar spray on seed yield (kg ha -1 ).

Table 3 .
Effect of planting duration and Brassica species on quality and nutrient content.

Table 4 .
Effect of planting duration, Brassica species and salicylic acid on nutrient uptake and economics.