Agronomic efficacy of indigenous and exotic rock phosphates in soybean (Glycine max) in an acid soil

A field experiment was conducted during 1995 and 1996 to study agronomic efficacy of rock phosphates, North Carolina rock phosphate (NCRP), Udaipur rock phosphate (URP), and Mussoorie rock phosphate (MRP) as phosphorus source in an acidic silty clay loam soil at Palampur, with 'Bragg' soybean [Glycine max (L.) Merr.] as test crop and single superphosphate as standard. Direct application of rock phosphate @ 60 kg P2O5/ha resulted significant increase in growth and yield attributes of soybean over the control. Combination of rock phosphate with FYM or single superphosphate (50:50) further enhanced the growth and yield and seed yield. The uptake of P and Ca as affected by different treatments followed the trend, similar to seed yield. Application of 60 kg P2O5/ha through NCRP, URP and MRP along with 5 tonnes FYM/ha recorded substantial increase in agronomic efficiency of rock phosphate. Comparing the relative agronomic effectiveness (RAE) of different sources, the exotic source NCRP was superior.