Abstract

                                Phosphorus (P) is one of the least available of all essential nutrients in the soil and its concentration is generally below that of many other macronutrients. An experiment was conducted to study the phosphorus use efficiency (PUE) of the sorghum and blackgram in soils of varying calcium carbonate content using radiotracer phosphorus (32 P). The pot culture experiment was conducted during 2017-2018 at Radioisotope (Tracer) Laboratory, Department of Soil Science and Agricultural Chemistry, Tamil Nadu Agricultural University, Coimbatore. The treatment structure of the pot culture experiment comprised of four types of soils and two levels of phosphorous (control and recommended level of phosphorus as phosphoric acid) with sorghum and blackgram as test crop. The results of the pot culture experiment showed that the grain yield of sorghum and blackgram decreased with increasing calcareousness of the soil. Lowest grain yield recorded was 14.14 g pl-1 for sorghum and 2.20 g pl-1 for blackgram in strongly calcareous soil (S4). In both sorghum and blackgram non calcareous soil (S1) was recorded the highest total P uptake (101.24 mg pl-1),(37.07 mg pl1)respectively. Among crops, blackgram recorded the highest per cent Pdff (69.71%) than the sorghum (24.31 %). The highest sorghum per cent Pdfs (100 %) was observed with control (T1) which differed significantly from P application (75.70%), in blackgram the highest per cent Pdfs in blackgram (67.35 %) was recorded in slightly calcareous soil (S2) and the lowest % Pdfs (60.04 %) was registered in strongly calcareous soil (S4). Mean Phosphorus Use Efficiency (PUE) showed significant difference in non-calcareous soil (27.13 %) followed by slightly calcareous soil (23.81%). The mean lowest efficiency was observed in strongly calcareous soil (19.41%). Blackgram recorded higher PUE than sorghum in all the soils.

Key words : Phosphorus Use Efficiency, P uptake, Per cent Pdff, Per cent Pdfs, Calcareous soils,Sorghum, Blackgram.