Status of available phosphorus, forms and distribution of phosphorus in soil under major cropping systems of Nellore district, A.P

An investigation was undertaken during 2018-19 in Southern zone of A.P. to study the Status of available phosphorus and forms of Phosphorus in soil under major cropping systems of Nellore district. The Ca-P was observed to be the predominant P fraction under all major cropping systems could be attributed to high CaCO3 content. The highest mean values for saloid-P (16.67 mg kg-1), total-P (538.21 mg kg-1) and other forms of P (342.07 mg kg-1) were recorded in groundnut-paddy cropping system and Fe- P (68.77 mg kg-1) and Al-P (61.85 mg kg-1) were highest in paddy-paddy cropping system, whereas available P2O5 (166.82 kg ha-1) and Ca-P (173.15 mg kg-1) were highest in groundnut-paddy and fallow-bengalgram systems, respectively. pH showed positive and significant relation with total-P (r= 0.507**) and other forms of P (r= 0.573**) where as free CaCO3 showed positive and significant correlation with Ca-P (r= 0.432*) in calcareous soils of S.P.S.R. Nellore district. Available P2O5 showed positive and significant correlation with saloid-P (r= 0.456*), Al-P (r= 0.765**) and Fe-P (r= 0.559**), saloid-P showed significant and positive correlation with total-P (r= 0.477*) and other forms of P (r= 0.510**). Al-P showed positive and significant correlation with Fe-P (r= 0.885**). Similarly, Ca-P showed positive and significant relation with total-P (r= 0.418*).