Fertigation of Bell Pepper (Capsicum annuum L.) in a soil-less greenhouse system : effects of fertiliser formulation and irrigation frequency

Abstract

Increasing costs and more limited availability of water and fertiliser, coupled with mounting concern over nutrient leaching damaging the environment has led to greater interest in improved methods of managing these inputs. Greenhouse horticulture could, until recently, be characterised by large fertiliser inputs and low fertiliser use efficiency. Adoption of fertigation (application of fertilisers through irrigation water) within greenhouse production systems brings the potential for close control of both water and fertiliser applications. It is claimed that timing, amounts and ratios of fertilisers applied are easily controlled leading to optimisation of yield and product quality. However efficient operation of fertigation systems is hampered by lack of data on optimum consumption rates of essential nutrients by important crops as functions of time. The biological, chemical and physical database on fertigation is still very limited and simple extrapolation of the data to different climatic and substrate conditions may lead to operational errors. The aim of this research study was to evaluate the effects of varying fertiliser concentration and irrigation frequency on growth and yield of greenhouse bell pepper (Capsicum annuum L.) grown in rockwool using a fertigation system. A study on responses to varying nitrogen and potassium concentrations at different growth stages showed that increasing N from 126mg l-1 to 265mg l-1 and 385mg l-1 and increasing K from 106 mg l-1 to 214mg l-1 and 321mg l-1 increased fruit yield significantly over the control. Higher yield was associated with higher leaf area and total dry matter production, better quality fruits and better nutrient uptake. Indications were that recommended doses of nutrients in soil-less culture should change according to the growth stage of the crop with the fertigation program being adjusted during the growing season to suit plant development. In another experiment, effects of varying nitrogen and potassium rates and ratios on growth, yield, and the incidence of blossom - end rot (BER), leaf chlorophyll content, Fertigation of bell pepper (Capsicum annuum L.) in a soil-less greenhouse system photosynthetic aspects and NPK uptake was investigated. Phosphorus concentration (55mg l-1) was kept constant whilst N:K ratio varied. Increasing the NPK concentration from low concentration (44-55-71 mg l-1) to high concentration (126-55-106 mg l-1) significantly increased growth and yield with no further increases up to 500-55-625 mg l-1. Plants subjected to high NPK concentration in the second and third stage had more fruits with BER. The implications are that nutrient management must avoid too low and too high fertiliser concentrations and carefully manage electrical conductivity (EC) of nutrient solution in order to achieve high yield and quality whilst reducing nutrient leaching to the environment. The ability of fertigation systems to increase irrigation frequency affords a major advantage to crop production. As no research had examined effects of irrigation frequency at different growth stages an experiment was made to quantify the potential benefits of more frequent irrigation. With 20 irrigation events day-1 throughout the season, yield increased significantly by 22% over the control (5 irrigation events day-1 throughout the season). Higher yield was associated with taller and thicker plants, higher leaf area, greater total dry matter production, bigger fruits and better NPK uptake. The difference in growth and yield over the control could be attributed to differences in leaf phosphorus concentration, indicating the main effect of fertigation frequency was related to improved phosphorus mobilisation and uptake. Increasing the daily fertigation frequency from five to twenty irrigation events day-1 significantly reduced BER incidence. A final experiment examined effects of defoliation (removal of older, lower leaves) which may influence nutrient use efficiency and dry matter production and partitioning. There were four treatments: two irrigation schedules (5 and 10 irrigation events per day) and two defoliation strategies (0% defoliation and 20% of lower leaves removed). Defoliated plants reduced yield compared to non-defoliated plants irrespective of fertigation frequency because of less leaf area, lower total dry matter production and lower NPK uptake. Clearly, defoliation caused by leaf eating insects, disease or deliberate removal by the grower should be avoided or yield is likely to suffer.