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ThesisItem Open Access Dynamics of soil phosphorus in relation to carbon under different cropping systems(Punjab Agricultural University, Ludhiana, 2016) Dhram Prakash; Benbi, D.K.Dynamics of phosphorus in soils were studied in relation to nutrient management and land-use practices. The nutrient management practices evaluated included source (rock phosphate and single superphosphate) and rates of P application in rice-wheat system; and integrated nutrient management (INM) and organic farming practices in basmati-wheat system in field experiments conducted at the research farm of Punjab Agricultural University, Ludhiana. The land-uses studied included ricewheat, maize-wheat, cotton-wheat and poplar based agroforestry systems at farmers’ fields in different districts of Punjab. After seven cycles of rice-wheat cropping, farmyard manure (FYM) and rock phosphate (RP) application increased available P and soil organic carbon (SOC) by 72% and 98%, respectively over control. Inorganic P constituted the largest proportion (88-92%) of total P in soil and relative abundance of different inorganic P fractions in soils followed the order Ca-Al associated > Fe associated > humic bound > water soluble P. In basmati-wheat system, application of recommended rates of NPK and adoption of INM improved available P in soil over unamended control by 75 and 100%, respectively. The comparison of three organic sources revealed that available P was the highest in soil receiving 400 kg N ha-1 through FYM followed by rice straw compost and the lowest in vermicompost-amended plots. Application of FYM significantly increased inorganic, organic and total P, SOC and labile C pools compared to INM treatments. The INM increased inorganic, organic and total P by 77, 82 and 78%, respectively over NPK. Humic-bound organic P constituted major proportion (39.5-49.5%) and water soluble organic P comprised the smallest proportion (0.83-2.5%) of organic P in soils under basmati-wheat system. Beneficial effects of different treatments on soil properties were higher in surface soil (0-7.5 cm), which decreased with soil depth. Generally, soil P fractions were positively correlated with soil C pools. Cumulative P released in 96 hours of equilibration increased with manure and fertilizer application either alone or in combination. Phosphorus release kinetics were best described by Elovich and power function equations (R2≥0.98). Results of land-use studies showed that agroforestry systems had relatively higher proportion of organic P (27%) compared to sole cropping (6-7.7%). Soil organic C was the highest (0.58%) under agroforestry and was significantly correlated with soil P fractions under sole cropping systems. Soil properties viz. clay, organic C, CaCO3 and available P content significantly influenced soil P sorption and release kinetics. Phosphorus release decreased with increase in clay and CaCO3 content. On the contrary, P release increased with increase in available P and organic C. The results suggested that P availability will be higher in coarse-textured, non-calcareous soils having higher levels of organic C and available P. Therefore, for efficient P management it is important to take into account soil texture, the existing soil P level, organic C content and calcareousness of soil. Practices that increase SOC content and ameliorate CaCO3 could lead to improved P use efficiency.