RESPONSE OF Lolium perenne TO TWO PHOSPHATE ROCKS WITH THREE PARTICLE SIZES PLUS SULPHUR OR ZEOLITE IN AN ANDOSOL

Abstract

The use of phosphate rocks as phosphorus sources for a crop, is especially attractive due to their low cost; however, their agronomic efficiency is ussually lower than that of superphosphates but they are convenient in acid soils. With the purpose of improving their solubility, in the present study the phosphate rocks were subjected to a finer grinding and the addition of sulphur or zeolite were also tested. Rates of 0, 91, and 182 mg kg-1 of P as Baja California phosphate rock (BCPR) or North Carolina phosphate rock (NCPR), were evaluated under three particle sizes (PS): coarse (-35 +100), intermediate (-100+200), and fine (-200 mesh U.S. Standard), alone or mixed with elemental sulphur (S) or zeolite, using triple superphosphate (TSP) as the reference fertilizer, regarding their effect on dry matter yield (DM) and P extraction by a Lolium perenne crop, in an Andosol of Michoacán, México. Increments in DM yields and P extraction by the crop were observed up to the 91 mg kg-1 P rate as TSP. Both phosphate rocks produced similar cumulative DM yields, but P extraction from NCPR was higher than that from BCPR. The PS did not affect cumulative DM yields, but cumulative P extraction was different between PS, since the application of BCPR or NCPR of -100+200 mesh size was better than that of -35+100 mesh size. The effect of adding sulphur or zeolite to BCPR, on DM yield or P extraction by the crop, depended on PS. When coarse BCPR was mixed with sulphur at 10 %, DM yield was 33 % higher than that obtained with S-free BCPR. Similarly, the addition of zeolite (12.1 g kg-1 soil) to fine BCPR increased DM yield by 49 %, compared to zeolite-free BCPR. Coarse BCPR plus S was as effective as coarse NCPR on DM yields or P extraction; this result is advantageous for the Mexican rock (BCPR) due to its lower cost.