Nitrogen requirement of wide-spaced row crops in the presence of starter fertilizer

There is a need to develop sustainable nitrogen(N) management systems that minimize environmental losses by maximizing the use efficiency of applied f ertilizers, particularly with wide-row annual crops that are often poor at utilizing N A key approach is to match nitrogen supply with crop demand usi ng improved methods of fertilizer application and timing. One technique is to target liquid 'starter' fertilizers close to the seed, or around the roo ts of transplants, and to omit or reduce conventional broadcast application s. This paper examines the effects of starter fertilizer combined with vari ous rates of seedbed and/or top-dressed N on the growth and yield of bulb o nion (Allium cepa L.), crisp lettuce (Lactuca sativa L), forage maize (Zea mays Bonaf) and sugarbeet (Beta vulgaris L.). Starter fertilizer improved e arly growth and, in combination with reduced rates of supplementary N, gave yields comparable with higher rates of base N with each crop, except sugar beet. The use of top-dressed N was as effective as base N in supplementing starter fertilizer and had the benefit that it allowed a top-dressing requi rement to be estimated accurately using a simple nitrogen balance equation. These results, taken with earlier work, show that starter fertilizers offe r clear opportunities for reducing N inputs, while maintaining yield and qu ality of these crops.