RESPONSE OF SILAGE MAIZE TO PLACEMENT OF CATTLE SLURRY

Placement of nitrogen (N) or phosphorus (P) fertilizers can improve th e efficiency of fertilizer use, reduce the input needed for maximum pr oduction, and better balance the nutrient put in with fertilizers and removed with crop products. From this perspective, the effect of the p lacement of cattle slurry on the dry matter (DM) yield of silage maize was studied in five experiments on sandy soils in 1993 and 1994. Slur ry was injected in spring at a rate of 30 m(3) ha(-1) in slots 25 cm a part ('standard injection') or in slots 75 cm apart ('banded injection '). Subsequently, maize was planted at a row spacing of 75 cm parallel to the slots, either al random lateral positions in the 'standard inj ection' treatment or 10 cm next to the injection slots of the 'banded injection' treatment. All treatments, including a control without slur ry, were combined with 0 and 20-31 kg ha(-1) subsurface banded P start er fertilizer. DM yields of silage maize were on average reduced by 8% when conventionally injected slurry ('standard injected') was not sup plemented with a P-starter. However, the yield reduction was limited t o 2% when slurry was banded ('banded injection'). Observations on the distribution of soil mineral N and roots in two of the experiments ind icated that during the first 5-7 weeks after planting, nutrients were predominantly supplied by the soil volume close to the plant row. This may explain the positive response of maize to placement which was str ongest and significant on P-responsive sites, indicating that placemen t mainly improved the availability of slurry P. Improvements in the av ailability of slurry N may have played a secondary role. Our results s uggest that slurry placement can minimize the risk of yield loss assoc iated with reduced fertilizer inputs and contribute to a better nutrie nt balance between fertilizer inputs and removal in crop products.