Date Published: July 5, 2017
Publisher: Public Library of Science
Author(s): Anderson Fernando Wamser, Arthur Bernardes Cecilio Filho, Rodrigo Hiyoshi Dalmazzo Nowaki, Juan Waldir Mendoza-Cortez, Miguel Urrestarazu, P. Pardha-Saradhi.
The interactive effects of N (6, 9, 12 and 15 mmol L-1) and K (3, 5, 7, and 9 mmol L-1) concentrations in nutrient solutions were evaluated on bell pepper grown in a coconut-coir substrate and fertilized without drainage. An additional treatment with drainage was evaluated using N and K concentrations of 12 and 7 mmol L-1, respectively. The hybrid Eppo cultivar of yellow bell pepper was cultivated for 252 days beginning 9 November 2012. Electrical conductivity (EC), the N and K concentrations in the substrate solution, marketable fruit yield, total dry weight and macronutrient concentrations in shoots were periodically evaluated. Fruit production was lower in the system without drainage, regardless of the N and K concentrations, compared to the recommended 10–20% drainage of the volume of nutrient solution applied. Higher K concentrations in the nutrient solution did not affect plant production in the system without drainage for the substrate with an initial K concentration of 331.3 mg L-1. Fruit yield was higher without drainage at a nutrient-solution N concentration of 10.7 mmol L-1. The upper EC limit of the substrate solution in the system without drainage was exceeded 181 days after planting. Either lower nutrient concentrations in the nutrient solution or a drainage system could thus control the EC in the substrate solution.
The management of plant nutrition in substrate cultivation is based on the application of a complete nutrient solution by fertigation at a specific percentage of drainage of the volume applied . Draining renews the substrate solution and prevents its salinization by leaching excess nutrients and other elements not absorbed by plants between each fertigation . The drained nutrient solution can be stored in the reservoir to be reused in a closed system or can be directly discarded into the soil in an open or free-drainage system. This latter system is more common in substrate cultivation in Brazil. Soil-less cultivation with free drainage, however, has been associated with losses of large volumes of water and nutrients and with the contamination of groundwater from the release of nitrates [3, 4]. Efforts have thus recently been applied to develop management practices that reduce the release of nutrients by drainage [4–7].
An experiment was conducted at the Julio de Mesquita Filho campus of the State University of São Paulo (UNESP), Jaboticabal, São Paulo (21°14’S, 48°17’W; 549 m a.s.l.) in a greenhouse with a low-density polyethylene cover 150 μm thick and side and front closure with black polypropylene mesh providing 50% shade. The greenhouse was 48 m long, 12.8 m wide and 3.3 m high and was oriented east-west. A thermo-reflective mesh with 50% shading was installed to control the temperature inside the greenhouse.
Potassium had little influence on pepper yield in a wide range of concentrations in the nutrient solution. Other studies have also reported no differences in bell-pepper yield at K concentrations ranging from 2.75 to 5.0 mmol L-1 , 3.0 to 6.0 mmol L-1  and 2.5 to 7.0 mmol L-1 . Concentrations of 1.5 mmol L-1  and 14 mmol L-1 , however, decreased yield. Moreover, our results contrasted with those by Johnson and Decoteau , who concluded that at least 6.0 mmol L-1 K in the nutrient solution were required for optimal production. This concentration is similar to the recommendation of 6.3 mmol L-1 for hydroponics  used as a reference in our study.
Bell-pepper cultivation in a fertigated substrate without drainage provided lower fruit production regardless of N and K concentrations compared to the recommended system with 10–20% drainage of the nutrient-solution volume. Higher nutrient-solution K concentrations did not affect plant production in the system without drainage for the coconut-coir substrate with an initial substrate K concentration of 331.3 mg L-1. Fruit yield increased at a nutrient-solution N concentration of 10.7 mmol L-1 in the system without drainage. However, concentrations of N in the nutrient solution of 13, 11 and 6 mmol L-1 would be more adequate during the early harvest, intermediate harvest and late harvest, respectively. The upper EC limit of the substrate solution was exceeded 181 days after planting in the system without drainage. In this situation, a decrease in the nutrient-solution nutrient concentrations or the use of drainage would be alternatives for controlling the substrate-solution EC.