Magnesium Supplementation Concerning Soil Chemical Properties and Cowpea Yield in Ultisol of Kerala, India

Ultisol of Kerala faces high magnesium deficiency due to poor retention of magnesium to soil exchange surfaces under high rainfall conditions. Hence magnesium nutrition management is an important aspect of fertility improvement in these soils. We conducted a pot culture study to determine the influence of varying magnesium levels on soil chemical properties and yield of cowpea in Ultisols of Kerala. We used a completely randomized design. The study was carried out in the Radiotracer Laboratory, College of Agriculture, Vellanikkara, Kerala Agricultural University, in January-April 2019. Magnesium carbonate at levels 5 to 80 mg.kg-1 was provided along with recommended doses of fertilizers for cowpea maintained in pots. Rhizosphere samples were analyzed during flowering and at harvest of the crop following standard procedures. Yield and yield attributes are recorded at the time of harvest. Graded doses of magnesium introduced significant (P< 0.05) variations in the soil available nutrients and yield of cowpea. Soil pH and available magnesium in rhizosphere soil during flowering and post-harvest increased with the increasing levels of magnesium carbonate, and using 80 mg kg-1 of magnesium recorded the highest pH, available phosphorus, potassium, and magnesium. In contrast, the gradation of magnesium could not produce significant variation in yield. The highest yield was recorded in treatment supplied with 10 mg kg-1 of magnesium and was on par with those of higher levels of magnesium supplement. Graded doses of magnesium introduced variation in available nutrients but a better yield response in cowpea was obtained from magnesium at 10 mg.kg-1.