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20132
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Subject: Soil Science × End date: 2013 × Start date: 2013 ×
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    ThesisItemOpen Access
    TEMPERATURE DEPENDENCE OF CARBON MINERALIZATION FROM ACTIVE, SLOW AND PASSIVE POOLS OF SOIL ORGANIC MATTER
    (Punjab Agricultural University, Ludhiana, 2013) Boparai, Arpandeep Kaur
    The present investigation was conducted to study the effect of temperature on C mineralization from active, slow and passive pools of soil organic matter (SOM) in comparison to bulk soil. Laboratory incubation experiments were conducted at 15, 25, 35 and 450C temperature and field capacity moisture to study C mineralization from three isolated SOM fractions viz. >250 μm, 53-250 μm and <53 μm that respectively represent active, slow and passive pools of SOM. During 54 days of incubation at different temperatures, the highest amount of C (1196-13104 mg C kg-1) was mineralized from >250 μm SOM fraction, followed by 53-250 μm fraction (305-1955 mg C kg-1) and the lowest from <53 μm fraction (258-1263 mg C kg-1). The amount of C mineralized from bulk soil ranged between 249 and 1047 mg C kg-1 at different temperatures. For a given SOM fraction and bulk soil C mineralization rate was highest at 450C and lowest at 150C. The C mineralization rates (mg C kg-1 d-1) at different temperatures ranged between 72 and 375 for >250 μm fraction, 26-149 for 53-250 μm fraction, 9-105 for <53 μm fraction and 7-91 for bulk soil. Of the total organic C, 66 percent of C was mineralized in >250 μm fraction, 60 percent of C in 53-250 μm fraction, 10 percent of C <53 μm fraction and 14 percent from bulk soil. First order single compartment kinetic model provided good fit to all the data sets and yielded high coefficient of determination (R2=0.864 to 0.999). Different SOM fractions differed significantly with respect to temperature sensitivity of decomposition. The Q10 values for decomposition of different SOM fractions ranged between 1.8 - 2.0 for >250 μm fraction, 1.6-1.8 for 53-250 μm fraction and 1.4-1.6 for <53 μm fraction. Bulk soil showed temperature sensitivity similar to <53 μm fraction with Q10 values ranging between 1.4 and 1.5 for different treatments. The higher Q10 values for SOM fraction >250 μm suggested that decomposition of labile fraction was affected to a greater extent by increase in temperature as compared to other stable fractions. Since the labile pool of SOM (>250 μm fraction) constituted only about 4-5 percent of the bulk soil organic matter, the results suggest that the effect of global warming on soil organic C content will probably be small.
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    Simulating the yield, water and nitrogen productivity in wheat as affected by sowing date, cultivar, irrigation regimes and nitrogen levels”
    (2013) Jaswinder Kumar
    ABSTRACT In view of shrinking water resources and the anticipated effects of climate change on water availability, management interventions need to be refined in respect of planting time, cultivar, irrigation and fertilizer N regimes. This study includes the evaluation and application of DSSAT-Wheat model. In order to evaluate DSSAT-Wheat model, database was generated on two experiments. In the first experiment, sowing dates, cultivars and irrigation regime effects were evaluated on growth and yield of wheat; while in second experiment, interactive effect of irrigation and nitrogen level on crop yields, water and nitrogen uptake was studied. Field experiments were conducted on a sandy loam soil during 2011-12 growing season at research farm of Punjab Agricultural University, Ludhiana (30o54'N, 75o48'E, 247 m above sea level), Punjab, India. The treatments include a combination of three planting dates (D1 25 October, D2 8 November and D3 20 November), two cultivars PBW-621 (V1) and PBW-550 (V2).and two irrigation regimes (IS stage based and I0.9 IW/PAN-E 0.9) for experiment one and wheat (cv. PBW 550) was planted on 20 November under four irrigation regimes (I0.6 IW/PAN-E 0.6, I0.8 IW/PAN-E 0.8, I1.0 IW/PAN-E 1.0, and I1.2 IW/PAN-E 1.2) and four fertilizer N levels (0 (N0), 60 (N60), 120 (N120) and 180 (N180) kg N/ha) for experiment two. This evaluation analysis has demonstrated that simulation of crop phenology and harvest time biomass or grain yield was reasonable with normalized RMSD of 10 - 20 % between measured or simulated values, while simulation seasonal water use was fair (normalized RMSD of 20–30 %).Simulated total N uptake had normalized RMSD of 25-35% for measured values of the two sets of data, while grain N uptake had greater variance. Scenario analysis based on 20 years of weather data showed that potential grain yield of V1 had a tendency to increase with shift in planting from Oct 25 to Nov 10 and Nov 25. Interaction effects of irrigation and nitrogen demonstrated that N response of yield was greater under full than under limited irrigation. Water productivity increased with N rates and decreased with increase in irrigation; while NUE had reverse trends.