|Keywords (Extracted from title, table of contents and abstract of thesis)
sulphur status, pothwar soil, rapeseed, brassica napus, sulphur fertilizers, rainfed conditions, ustochrepts, balkassar, chakwal, therpal, kahuta, guliana, haplustalfs, qutbal, missa, rajar, ustorthents, qazian, torripsamment, satwal, chromusterts
A comprehensive study was carried out to evaluate sulphur (S) status of prominent soils of Pothwar, addition of S through rainfall to soils, the relationship of plant available S with important soil characteristics and to assess the response of rapeseed (Brassica napus) crop to different S fertilizers under agro-climatic conditions of Pothwar region. The study comprised of two parts, in the first part, fifteen important soils of Pothwar were selected. Among these Missa, Basal, Talagang, Rawalpindi, Rawal, Timaul soils belong to the Ustochrepts; Balkassar, Chakwal, Therpal, Kahuta and Guliana to Haplustalfs; Qutbal, Missa and Rajar to Ustorthents; Qazian to Torripsamment and Satwal to Chromusterts great groups. Soil samples at two depths i.e., 0-15 and 15-30 cm were collected and analyzed for plant available S (SO4-S) contents and related physico-chemical properties. The rainwater samples were collected from two different locations in the Pothwar throughout the year and analyzed for S contents. In the second part, the response of rapeseed (Brassica napus) to different sulphur fertilizers was evaluated. For this purpose field experiments were conducted at two S deficient soils i.e., Rawal (Sandy loam, Ustochrepts) and Therpal (Sandy loam, Haplustalf) in Pothwar region, during the years 2004-05 and 2005-06. The treatments include application of three sources of S i.e.; single super phosphate, ammonium sulphate and gypsum, each applied at five different (0, 10,20, 30 and 40 kg ha-1) S levels. The results revealed that sulphur contents in soils ranged from 5.0-21.3 µg g-1 at upper and 6.3-22.5 µg g-1 at lower depths, respectively. Maximum S contents of 21.3 µg g-1 at upper and 22.8 µg g-1 at lower depth were recorded in Satwal and Chakwal soils, respectively while lowest S contents of 5.0 µg g-1 at upper and of 6.3 µg g-1 at lower depth were recorded in Qazian soils. Sulphur deficiency was mostly observed in well drained soils of Rawalpindi and Attock areas, having high to medium rainfall, while satisfactory level of S was observed in soils of Chakwal area with medium to low rainfall. Total S added though rain was 15.8 kg ha-1 year-1 At Rawalpindi and 17.3 kg ha-1 yea-1 at Chakwal. The major part (40-50 %) of the total atmospheric S addition through rainwater occurred through heavy summer (monsoon) rains. Sulphur exhibited significant positive correlation with clay (r = 0.77**) ECe (r = 0.77), orgamc C (r = 0.82 ), total N (r = 0.88 ) and extractable P (r = 0.72 ) contents in soil. While the correlation coefficients (r) of S04-S with sand (r = -0.41), soil pH (r = -0.49) and CaCO3 (r = -0.60*) contents were negative. Multiple regression analysis depicted close association of S with clay, ECe, total organic C, total Nand extractable P content of soils. However, among the soil characteristics organic C and total N had most pronounced effects (R2= >65) on S availability in soil which emphasized the importance of organic matter to plant nutrients availability including S in the soils of Pothwar.
Field experiments clearly demonstrated that the yield and quality of oilseed rape was significantly increased through S fertilization. The sulphur application in both soils under study improved the yield and yield contribution parameters. Oil content were found to be at peak (44.6 %) at 30 kg S ha-1, followed (44.5 %) by 40 kg S ha-1 application rate. The application of ammonium sulphate (AS) at 30 kg ha-1 increased seed yield by 8.18 % and oil contents 13.0 % as compared to control. The highest S content (0.158 g 100g-1) in plant was observed with application of 40 kg S ha-1 but it was statistically at par with 30 kg S ha-1 rate. The highest mean S uptake of 17.0 kg ha-1 was recorded in soil fertilized with AS at 30 kg ha-1. The recovery of added S though S fertilizers by rapeseed crop was 6.5 to 29.2 %. The application of AS at 30 kg ha-1 resulted maximum S recovery, 32 % at Rawal and 26 % at Therpal soils. The economics analysis clearly suggested that S fertilization to rapeseed crop could bring more return to the farmers. The highest mean value cost ratio (VCR) values were obtained through AS, and lowest though gypsum applications. The application of AS at 30 kg ha-1 resulted highest VCR value of 5.9. Marginal rate of return (MRR) analysis pointed out that S application at 30 kg ha-1 was the most appropriate rate for maximum economic return and the application beyond this was not economical. Generally AS has proved as most favorable and economical S fertilizer. It increased the plant growth, yield and S-uptake as compared to other sources though its beneficial effects in most parameters were non-significant to those of SSP and gypsum, other sources used in the experiment. The successive addition of S during two year of study maintained the S contents of the soils in comparison to the control showing decline in S contents. This study concluded that the maintenance of the soil organic matter, utilization of subsurface inorganic S needed to maintain the S status of the soils in the future. While, the use of S containing fertilizers like AS and SSP should be preferred over non S bearing fertilizers as DAP and TSP for high S requiring crops like oilseed and legumes.