EFFECT OF NITROGEN ON THE YIELD AND QUALITY OF VEGETABLES
For most vegetable species, the N level producing the highest yield produced the best quality edible plant part. For tomato, high N levels produced the firmest fruit with the highest total soluble solids and dry matter content. For zucchini, medium N levels produced fruit with the highest dry matter content. For cabbage and lettuce, the crispness of heads (inversely related to dry matter content) was reduced at low and high N levels. Doubling the optimum N level for potato yield increased the dry matter % and specific gravity of potato tubers. Further increases in N level reduced dry matter % and specific gravity.
Tomato and zucchini fruit accumulated negligible nitrate whereas N increased the nitrate-N concentration in potato tubers and in cabbage and lettuce leaves. At the highest N application levels, the nitrate-N concentration in potato tubers and in the petiole sap of the wrapper leaf of cabbage and lettuce (fresh weight basis) were respectively 180, 2 700 and 2 300 μg/g.