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Abstract
High ammonium-nitrogen (NH4-N) concentration in solution may adversely affect greenhouse tomato (Lycopersicon esculentum Mill.) yield, but it has been reported that small NH4-N fractions improve yield and may increase vegetative growth and nutrient element uptake. The effects of short- or long-term supply of NH4-N to tomato plants is not clear, and further information is required to determine how it can affect fruit yield. The objective of this study was to determine the tomato yield response to 0:100, 10:90, 20:80, 30:70, and 40:60 NH4-N:NO3-N ratios supplied at the vegetative, vegetative plus flowering, flowering plus fruiting, and fruiting stages, and over the entire plant life cycle. Two experiments under greenhouse conditions were conducted with ambient light in which light intensity was 2,667 and 5,030 W h−1 m− 2 for the winter (1996–1997) and the spring (1997) experiments, respectively. In both experiments, neither the length of NH4-N supply nor the NH4-N concentration in solution affected tomato yield. Longer NH4-N supply increased the amount of fruit with blossom-end rot (BER) in the winter (1996–1997) experiment, but BER incidence was unaffected in the spring (1997) experiment by duration of NH4-N supply. The number of fruit with BER was greatly increased by higher NH4-N concentrations in solution in the spring (1997) experiment. Plant height was not affected by NH4-N concentration in either the winter or spring experiments, and neither was fruit firmness measured for fruit at the mature green stage. Fresh and dry weights were unaffected by NH4-N concentration or length of supply, but in the spring (1997) experiment, fresh weight of leaves, as well as their proportion to the weight of the aerial parts, were affected by both NH4-N concentration and length of supply. High concentrations of NH4-N and long periods of NH4-N supply increased calcium (Ca) concentration in leaf tissue, but only for the spring (1997) experiment was there a significant relationship between Ca concentration in leaves and BER incidence.
ACKNOWLEDGMENTS
First author is grateful to the Mexican National Council for Science and Technology (CONACYT) and Colegio de Postgraduados en Ciencias Agrícolas, México for financial support.