Limitations of the K:N ratio in the nutrient feed of drip-irrigated greenhouse tomatoes as a crop-management tool

Abstract

Greenhouse tomato cultivars were grown over three spring (1987, 1988 and 1989) and two fall (1987 and 1988) seasons in soil to assess the yield and fruit-quality effects of the potassium (K):nitrogen (N) concentration ratio in the fertigation solution. In the spring, the K:N ratio was varied over the first 11 wk following planting to provide a high, medium or low K:N ratio in the fertigation solution. The K:N ratio in the fertigation solution varied from 14:1 (week 1) to 2:1 (week 11) or from 8:1 (week 1) to 2:1 (week 11) or remained steady at 2:1 (weeks 1–11) for the high-, medium- and low-K:N treatments, respectively. In the fall the K:N ratio varied from 3:1 (week 3) to 9:1 (week 10), or from 2.3:1 (week 3) to 6:1 (week 10), or from 1.5:1 (week 3) to 3:1 (week 10) for the high-, medium- and low-K:N treatments, respectively. The marketable yields harvested averaged around 7.5 kg plant−1 in the spring and 2.5 kg plant−1 in the fall. The K:N ratio in the fertigation solution had no significant effect on early, or final, total or marketable yield. Similarly, there were no significant effects on fruit quality. It was concluded that provided a recommended overall osmotic effect (measured as electrical conductivity) of the nutrient solution is maintained, fertilizers can be selected and used on the basis of cost, or other important criteria, without concern for yield loss due to undesirable K:N ratio effect. Key words: Lycopersicon esculentum, marketable yield