Nitrogen Management for No-tillage Zucchini Squash

Although fertility management in no-tillage (NT) systems is important to maximize productivity, little information is available on fertilizer recommendations [especially nitrogen (N)] for vegetable crops grown in this type of production system.  A field study was conducted at a grower location in southern Illinois to determine the effect of N application rates in NT zucchini squash production following the herbicide burn-down of a wheat cover crop in early spring.  The amount of available N in soil was 86 kg/ha following burn-down; and, soon thereafter, a maintenance preplant fertilizer mix (18 kg N + 10 kg P₂O₅ + 132 kg K₂O/ha) was applied prior to transplanting squash into the residue.  When plants had 8 to 12 true-leaves, N was sidedress applied [1:3 blend of NH₄NO₃ and Ca(NO₃)₂] at 6 rates: 0, 17, 34, 67, and 134, and 201 kg/ha.  Results indicated that the maximum total squash fruit yield was achieved at 34 and 67 kg N/ha sidedress rates.  Although plant growth was maximized at 134 and 201 kg N/ha, the overall total yield was less compared to the 34 and 67 kg N/ha rates.  It appears that if excess nitrogen is available, squash plants will use N for plant foliar growth rather than for fruit production.  Therefore, the N rate needed to maintain adequate plant growth and provide maximum yields over a growing season was between 138 and 171 kg N per hectare. Many vegetables are inefficient users of nutrients and high fertilizer rates are often used by growers that exceed crop demand to insure high yields.  However excess amounts of applied fertilizers will not only increase grower input costs and cause potential N runoff problems, but this research indicates that too much N can lead to reduced crop yields.