Growth chamber study of phosphorus applied as drilled granules or as seed coatings to wheat sown in soils differing in P-sorption capacity

Abstract

The effect of seed coatings or drilled granules containing phosphorus (P) on the early growth of wheat was evaluated in a pot trial in two soils differing in P-sorption capacity. P as monocalcium phosphate (MCP) was applied in seed coatings (C) at rates of 0 (inert coating of diatomaceous earth), 5 and 10 kg P ha⁻¹ whereas drilled rates (D) of P were applied at 0, 5, 10, 20 and 40 kg P ha⁻¹ to wheat sown at the equivalent of 60 kg ha⁻¹. The soils used were an aquic haplustalf with low (LS) and a gibbsiorthox with high (HS) P-sorption capacities respectively. Both soils were deficient in P, having 7.3 and 13.1 ppm available P in the LS and HS soils respectively. Emergence was recorded and plant height was measured at regular intervals. Shoot and root dry weights and P contents were determined in the final harvest at 27 days after sowing.

Emergence was significantly delayed only by C10. Cumulative plant height per pot of C5 was significantly greater than that of C0, C10, D0, D5 or D10 from day 17 onwards. The only drilled treatments to produce a significant increase in plant height over D0 were D20 and D40. Dry weights increased in the LS soil up to 20 kg P ha⁻¹ and up to 40 kg P ha⁻¹ in the HS soil. Whilst C10 suffered some injury during emergence which also reduced the early growth of that treatment, seed coating at 5 kg P ha⁻¹ resulted in more effective use of P than an equivalent drilled rate in both soil types, particularly with respect to plant height and root weight.