تلخیص
Changes in soil bioavailable potassium (K) and mineral composition determines long-term sustainability of a cropping system. After 5-year fertilizer treatments to cotton-wheat rotation, changes in soil mineralogy and the Kavailability indices were investigated to help devise optimum fertilization plan. The soil contained mica, quartz, and feldspars in the sand and silt fractions; mica and kaolinite with small amount of quartz, smectite and vermiculite in the coarse clay; and mainly smectite and some vermiculite and mica in the fine clay fraction as determined by X-ray diffraction and total K and Ca/Mg and K/NH4 CEC properties. The sand and silt from AB (14-27 cm) horizon of NPK treatment had stronger mica peak than that of NP. Treatment effect on mica in Ap (0- 14 cm) and Bwk (27-43 cm) horizons was limited probably due to sedimentation of fresh minerals entering the field with canal irrigation and less root activity in Bwk horizon. Boiling HNO3-extractable K varied from 196 to 432 mg 100 g-1 sand and from 181 to 197 mg 100 g-1 silt from the fallow profile. The NPK treatment contained greater boiling HNO3-extractable K in the sand and silt fractions as well as the soil NH4OAc-extractable K than the NP. The soil NH4OAc-extractable K ranged from 75 to 124 mg kg-1 soil and K-fixation ranged from 27.0 to 42.5 mg 100 g-1 soil. There was no long-term fertilizer treatment effect on soil K-fixation. The study conclude only marginal changes in soil bio-available K and in the mineral composition due to K-less fertilization in the canal irrigated cotton-wheat system in Southern Pakistan (Sindh
K. Shaikh1, , K.S. Memon2, , M. Memon3, M.S. Akhtar4*. (2007) Changes in mineral composition and bioavailable potassium under long-term fertilizer use in cotton-wheat system , The Journal Soil & Environment , Volume 26, Issue 1.
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