Objective The seasonal utilization rate of phosphate fertilizer is generally low. Active functional groups in humic acid can complex ions related to soil-fixed phosphorus, alleviate phosphorus fixation, activate soil sparingly soluble phosphorus, and improve phosphate-fertilizer use efficiency, so as to enhance soil phosphorus availability.
Methods A field experiment was carried out on artificial Leymus chinensis grassland in gray-desert soil of Xinjiang. Six treatments were set, including CK, HA, 100%P, 90%P+HA, 80%P+HA and 70%P+HA. Soil samples were collected at the regreening, jointing, heading, full-bloom and harvest stages of Leymus chinensis. Changes in soil phosphorus fractions at different growth stages were analyzed to explore the appropriate phosphate-fertilizer input rate under phosphorus-reduction combined with humic-acid application.
Results The contents of soil inorganic-phosphorus fractions and their proportions in total phosphorus varied obviously across all growth stages of Leymus chinensis. Combined application of phosphate fertilizer and humic acid altered the distribution of soil inorganic-phosphorus fractions and increased soil available-phosphorus content. The treatment with 20% phosphorus reduction plus humic acid exhibited higher soil phosphorus availability compared with conventional fertilization. Correlation analysis and multiple stepwise regression analysis indicated that Ca2-P exerted a positive effect on soil available phosphorus under phosphorus-reduction combined with humic-acid application. Its content was significantly correlated with soil available-phosphorus content, and it could serve as one of the major phosphorus pools governing soil phosphorus availability.
Conclusion Compared with conventional fertilization, the treatment of 20% phosphorus reduction combined with humic-acid application can cut phosphate-fertilizer input, raise the contents of soil inorganic-phosphorus fractions and improve soil available-phosphorus availability.
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