ALBERT

Description: Zero tillage increases stratification of immobile nutrients such as P. However, it is unclear whether near-surface stratification of soil P eases or hampers P uptake by maize (Zea mays L.) which needs an optimum P supply at/before six–leaf–stage to achieve potential grain yield. The aim of the three-year study was to determine whether P stratification, under zero tillage, impaired yield of maize and which P placement methods could improve P uptake on an Aeric Albaquept soil subgroup. Phosphorus fertilizer was placed by: (a) broadcasting before final tillage and sowing of seeds; (b) surface banding beside the row; and (c) deep banding beside the row (both the band placements were done at three–four leaf stage) Phosphorus treatments were repeated for 3 years along with three tillage practices viz.: (a) zero tillage (ZT); (b) conventional tillage (12 cm; CT); and (c) deep tillage (25 cm; DT). In the third year, all the tillage practices gave similar yield of Bangladesh Agricultural Research Institute (BARI) hybrid maize–5, but the highest grain yield was obtained by surface band P placement. After three years of tillage and P placements, the root mass density (RMD) at 0–6 cm depth increased significantly from 1.40 mg cm−3 in DT under deep band placement to 1.98 mg cm−3 in ZT under surface band placement, but not at the other depths. The combination of ZT practices, with broadcast or surface band placement methods, produced the highest available, and total P, content in soil at 0–6 cm depth after harvesting of maize. Accordingly, a significant increase in P uptake by maize was also found with surface banding of P alone and also in combination with ZT. Organic carbon, and total N, also increased significantly at depths of 0–6 cm after three years in ZT treatments with P placed in bands. By contrast, CT and DT practices, under all placement methods, resulted in an even distribution of P up to 24 cm depth. Phosphorus application, by surface banding at the three–four leaf stage, led to increased P uptake at early growth and silking stages, which resulted in highest yield regardless of tillage type through increased extractable P in the soil. Even though ZT increased P stratification near the soil surface, and it increased plant available water content (PAWC) and RMD in the 0–6 cm depth, as did surface banding, it did not improve maize grain yield. Further research is needed to understanding the contrasting maize grain yield responses to P stratification.