The use of portable chlorophyll meter for the management of N fertilization in cantaloupe (Cucumis melo L.) grown under transparent polyethylene low tunnels

One of the main goals of the research in horticultural production is the correct management of nitrogen (N), in order to reduce both environmental impact and production costs. In this study we report our results with the application of an optical diagnostic system (N-tester Yara) to guide N fertilization in Cantaloupe (Cucumis melo L.) grown in protected environment in a private farm. Plants were sown in a nursery and transplanted on soil 30 DAS. A transparent PE film (0.05 mm thick) was used for mulching and a transparent PVC film (0.08 mm) was used to cover plants with a low-tunnel structure (1 m wide and 0.60 m height). We considered four fertigation managements, and the experimental design was a randomized blocks with three replications. Considered treatments were as follows: a) Control, traditional fertigation regime adopted by the grower in the farm; b) NRC, fertigation regime based upon the nitrogen requirement curves reported in literature; c) N30, application of nitrogen fertilization when N-tester values were at least 30 points below the control treatment; d) N60, application of nitrogen fertilization when N-tester values were at least 60 points below the control treatment. Consistently, N application were of 120, 70, 80 and 60 kg N ha-1, respectively for Control, NRC, N30 and N60 treatments. During cultivation plant growth and both leaf N and chlorophyll contents were monitored, and measurement with N-tester were conducted every 2-3 days. At harvest biometric determination were conducted on fresh fruits and yield was subdivided in marketable and losses (fruits broken, rotten, burned and underweight) and marketable yield was classified for fruit size and according to quality parameters (main colorimetric indexes and total soluble solids, TSS). Little differences in total yield were recorded between control and NRC treatments, while fruit quality was dramatically enhanced through the use of N-tester. Particularly in N30, we observed an enhancement of marketable yield, reduction of the losses, and increased fruits size.