Soil and associated plant potassium status of sunflower in lower sindh (PAKISTAN)

Increasing present level of Potassium (K/sup +/) in calcareous soils improve sunflower yield. Soil and plant K/sup +/ status as yield-limiting factor for sunflower crop in calcareous soils was investigated through a survey study in the areas of lower Sindh (Sujawal, Badin and Hyderabad). Soil and crop productivity data from thirty sunflower farms were surveyed to assess soil-plant K/sup +/ status, some basic physicochemical properties, seed yield, and to get information on common crop husbandry practices. Composite samples of soil and sunflower leaf tissue were gathered from randomly chosen locations and analyzed for K/sup +/ content. Besides, the soil samples (0–20 cm depth) were also analyzed for some basic physicochemical properties. Furthermore, information about seed yield and common fertilization practices for each farm was also collected. The seed yield of sunflower in the study farms ranged from 1.63 to 1.86 tonnes ha-1 with an average of 1.73 tonnes ha-1. It was found that soils had a marginal to adequate K/sup +/ content (105–247 mg kg-1) with 47 % having marginal K/sup +/ content (100–150 mg kg-1) and 53% having sufficient K/sup +/ content (>150 mg kg-1). Most of the soils were found clayey in texture, moderately to strongly alkaline (pH1:5 7.7–8.8) in reaction, non-saline (EC1:5 0.12–0.24), moderately to strongly calcareous (CaCO/sub 3/ 8.45–17.65 %) in nature, and low to adequate (0.38–1.82%) in organic matter content. Exchangeable Ca/sup 2+/ remained as the dominant cation, followed by Mg/sup 2+/, K/sup +/, and Na/sup +/ Due to the high clay content, the CEC of the soils ranged between 15.34 and 33.48 cmolc kg/sup -1/. The leaf tissue K/sup +/ concentration varied between 1.38 and 3.41%, with a mean of 2.43. Around 60% of leaf samples were below a critical value (2.6%), 37% were above critical, and only 3% were found adequate. In sampling farms, soil K/sup +/ contents indicated a significant, positive, and linear relationship with the leaf tissue K/sup +/ concentration. Similarly, Soil K/sup +/ activity ratio had a significant, positive, and linear relationship with the K/sup +/ concentration in sunflower leaf tissue and seed yield. Appropriate field studies maybe planned and conducted in the future to formulate general K+ recommendations for sunflower farming in the region. (author)