Effects of nitrogen fertilizers on growth and yield of potato solanum tuberosum l. ilam hardy onion allium cepa l. pukekohe longkeeper garlic allium sativum l. y strain and hybrid squash cucurbita maxima l. delica

Buwalda, J.G.; Freeman, R.E.

Scientia Horticulturae 32(3-4): 161-174


ISSN/ISBN: 0304-4238
Accession: 005316477

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The effect of 5 levels of nitrogen on the growth, tissue composition and yields of potato, onion, garlic and hybrid squash were examined under field conditions at Pukekohe, New Zealand. The growth of all crops correlated closely with temperature, and was described using low-order polynomial regressions with growing degree days as a base. These regressions suggested that the largest effects of fertiliser nitrogen on the relative growth rates occurred during very early growth for potato and onion, but were sustained for garlic and hybrid squash. The effects of fertiliser nitrogen on marketable yields followed closely the effects on growth. The maximum effects of fertiliser nitrogen on tissue N contents coincided with the time when effects on relative growth rates were also greatest. This stage of crop development appeared to be the most sensitive for assessing the nitrogen status of the crop. Nitrate-nitrogen in the youngest fully expanded leaf was more sensitive as an index of crop nitrogen status than total nitrogen in all leaves or in the youngest fully expanded leaf, or mineral nitrogen in the soil. A second experiment examined the effects of applying various proportions of a similar total nitrogen dressing at different stages of crop growth for potato, garlic and hybrid squash. For all crops, the treatment giving highest yields was that where nitrogen was provided when the relative growth rate of the crop was also highest. At least some of the total nitrogen dressing could be applied as late as 2, 4 or 8 weeks after emergence for hybrid squash, potato and garlic, respectively, without a significant loss of yield. These results suggest that early assessments of the crop nitrogen status may be made, and corrective nitrogen additions applied if necessary.