Growth and Fruit Yield Response of Khatoni Melon to Nitrogen Application Rates

Melons are vegetable crops belonging to the family Cucurbitaceae, which consists of about 118 genera and 825 species. Persian melon is one of the most important melons with high economical and nutritional values and widely cultivated in Khorasan Razavi province. Nitrogen is the main plant nutrient resources with a structural and functional roles that affect growth and yield of melon production. Regarding to the importance of melon production in Khorasan Razavi province, this study aimed to determine the required amount of nitrogen fertilizer to reach maximum melon yield and to reduce excessive nitrogen application by farmers.

A field experiment was conducted at Torbat-e Jam in 2019. The effect of five levels of nitrogen fertilizer (0, 70, 140, 210 and 280 kg ha-1) was evaluated in a randomized complete block design with three replications. The size of each individual plot was 6 by 8 m and the melon row spacing was 2 m. Melon seedlings at three-leaf stage were planted about 75 cm apart in rows, on 23 June 2019. The studied traits in the experiment included leaf chlorophyll and leaf area at fruiting stage, number of fruits per plant, average fruit weight per plant, fruit yield, percentage of soluble solids and total dry matter.

Analysis of variance showed that nitrogen fertilizer application had a significant effect on all measured traits, except soluble solids of fruits. The results also showed that nitrogen fertilizer application increased leaf area index and leaf chlorophyll content by 37 and 22%, respectively. The highest leaf chlorophyll content and leaf area index was obtained from 210 and 140 kg nitrogen fertilizer application, respectively; and more nitrogen application was not a significant increase in leaf area and chlorophyll content. The melon dry matter production increased by 42% with nitrogen fertilizer application compared to non-nitrogen fertilizer application. The highest dry matter production was obtained from 210 kg N ha-1, and more nitrogen application was not a significant increase in dry matter production. The highest amount of the produced fruit per plant and fruit weight was obtained from 280 kg N ha-1. Fruit yield increased by 41% with nitrogen application compared with no N application. Fruit yield of melon at 70, 140, 210 and 280 kg N ha-1 increased by 39, 57, 41 and 28%, respectively. The highest fruit yield (33 ton ha-1) obtained at 140 kg N ha-1, and the more nitrogen application significantly reduced melon yield.

Nitrogen application improved growth and fruit yield of melon plants. The highest quality and quantity of melon yield was achieved with application rate of 140 kg N ha-1, and application of excess nitrogen would reduce fruit yield. Nitrogen agronomic efficiency showed that fruit yield increased by 87 kg ha-1 for each unite of N application rate under the optimum nitrogen fertilizer treatment. The study of the net economic income from the use of nitrogen fertilizer showed that the growers can experience up to 50% more economic profit with the optimal application of nitrogen fertilizer.