1. College of Resources and Environment, Southwest University, Chongqing 400716, China 2. The National Monitoring Base for Purple Soil Fertility and Fertilizer Efficiency, Chongqing 400716, China
Abstract：In order to investigate the effect of long-term (1991—2013) K fertilizer deficiency and surplus on potassium-bearing mineral and K nutrition of purple soil-soil primary, clay mineral composition and potassium (K) nutrition were determined on the long-term experiment of fertility and fertilizer efficiency in neutral purple soil by using X-ray diffraction (XRD) analysis technique. Five soil samples were selected from soil samples library for soil mineral analysis, including original soil, which preserved in 1991 before the experiment carrying out; K deficient treatment for 12 years and 22 years, which means no K fertilizer was applied during 1991—2003 and 1991—2013, respectively; and K surplus treatment for 12 years and 22 years, which means excess K fertilizer was applied during 1991—2003 and 1991—2013, separately. The result showed that, soil potassium-bearing primary mineral, such as mica, potassium feldspar, had apparently weathered and slaked for the K deficient treatment and the weathered extent gradually aggravated following fertilization ages, demonstrating fertilization for 22 years<12years<original soil. However, for K surplus treatment, the content of mica and potassium feldspar only had a little decline. As similar with primary mineral, for soil clay potassium mineral, the content of illite and mica was also seriously reduced for K deficient treatment and a slightly declined for K surplus treatment, representing the disintegration of soil potassium mineral under rice-wheat rotation system, and the deficient input of K fertilizer would obviously accelerate this weathering process. The two treatments all represented raising of vermiculite with the increasing of fertilization ages, and it’s much higher on K surplus treatment than K deficient treatment. In addition, we found that the silica-sequioxide ration of soil clay, which indicated the degree of soil weathering, decreased as the fertilization ages increasing, and after 22 years K deficient input soil clay had the lowest silica-sequioxide ration, showing the greatest weathering extent of soil clay silicate minerals. To further research the changing of soil K nutrition, we analyzed the content of soil available K, slowly available K and total K. The result indicated that, for K deficient treatment, soil available K and slowly available K content all gradually declined with the increasing of fertilization ages, about 62.0% and 37.4% down from 1991 to 2013, respectively. While there had a gain trend of soil available K content after long-term K surplus input, versus slightly dropping of slowly available K content. However, we found that long-term fertilization had no obvious effect on soil total K content. Therefore, long-term K deficiency could have negative effect on soil K, exhausting soil K resource and accelerating soil mineral weathering. It seems to be difficult maintaining soil slowly available K and potassium-bearing mineral content, even excess applied K fertilizer.
Key words：X-ray diffraction spectroscopy;Clay mineral;Long-term fertilization;Potassium deficiency and surplus
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