Wheat (Triticum aestivum L.) is one of the most impor-tant cereal crops in China, and K fertilizer applica-tions have played a major role in increasing wheat yield. However, wheat production sometimes is limited because farmers give little attention to K application. Due to the limited potash resources in China and increasing fertilizer cost, ef-fi cient application of K is very important. Understanding the yield responses, profi tability and K use effi ciency parameters of K application is essential for the further improvement of K use effi ciency for high yielding wheat production systems.To evaluate K responses on winter wheat in northcentral China, fi eld experiments were carried out for nine sites/years in farmer fi elds in Hebei, Shandong, and Shanxi provinces from 2006 to 2009. The trial soils were . uvo-aquic, brown, and calcic cinnamon soils for Hebei, Shandong, and Shanxi respectively. Prior to sowing, soil samples (0 to 20 cm) were collected and analyzed for nutrient status. Soil nutrients were determined with procedures applied by the National Labora-tory of Soil Testing and Fertilizer Recommendation using the method described by Portch and Hunter (2002). Winter wheat was sown at the beginning of October and harvested in mid-June of the next year. Each experiment was designed in a randomized complete block with three replications of two treatments: with K application, and without K. Urea, SSP, and KCl were selected as fertilizer sources. All other limiting nutrients in addition to K were applied using a rate suited to eliminate limitations on yield (Table 1).
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