DYNAMICS OF SOIL PHOSPHORUS IN RELATION TO CARBON UNDER DIFFERENT CROPPING SYSTEMS
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Date
2016
Authors
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Punajb Agricultural University
Abstract
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 (R
2
≥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 CaCO
3 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 CaCO
3 could lead to improved P use efficiency.
Description
Keywords
Fertilizer P, Farmyard manure, Cropping system, Agroforestry, Available P, Soil phosphorus pools, Soil carbon pools, Calcium carbonate, ##Unable to generate tags dhram prakash ph.d. thesis with papers.pdf, ##Unable to generate tags dhram prakash ph.d. thesis with papers.pdf