Influences of Nitrogen and Potassium Fertigation on Nutrient Uptake, Production, and Quality of Pepper Irrigated with Disinfected Urban Wastewater

Abstract

The use of regenerated water (RW) for irrigation of horticultural crops in the Mediterranean area could contribute to reduce fertilizer inputs, water consumption, and contamination of the environment. The nutrient content of RW and nutrient demand by crops needs to be match to achieve these benefits. This work studies the influence of different levels of nitrogen (N)– potassium (K) fertigation with purified wastewater obtained from Almería city, Spain, on yield, fruit quality, and macronutrient uptake of pepper plants. The experiment was conducted in a polyethylene greenhouse with pepper cv. Aifos, grown on a sand-mulched sandy loam soil using trickle irrigation. The experimental design was randomized blocks with four replicates. Six treatments were applied: two unfertilized controls (RW and ground water, GW) and four NK levels with regenerated water, RW (N₁K₁, N₁K_1.5, N_1.5K₁, and N_1.5K_1.5). N₁K₁ is the recommended rate under local conditions, and 125 kg N ha⁻¹ and 193 kg K ha⁻¹ respectively are average nutrient concentrations in fertigation of 9.8 mM N (NO₃ ⁻ + NH₄ ⁺) and 5.4 mM K. The results showed that production parameters were equal in unfertilized RW irrigated plants compared to those irrigated with GW water, both resulting in low commercial production. Fertigation with N₁K₁ produced yields similar to the RW control. Significant increases in marketable yields, number, and weight of fruit were recorded with N_1.5K_1.5, N₁K_1.5, and N_1.5K₁ rates compared to RW control. The NK level had no effect on fruit quality attributes (pH, fruit firmness, total soluble solids, and titratable acidity of fruit). Nutrient uptake of plants followed the same order in all treatments: K > N > calcium (Ca) > magnesium (Mg) > phosphorus (P). The treatment N_1.5K_1.5 showed the greatest uptake of N and P, and K uptake was similar to N₁K_1.5 and N_1.5K₁ treatments.

Keywords:

• Calcium
• fruit firmness
• magnesium
• nitrogen
• NK rates
• pH
• phosphorus
• potassium
• sand mulch
• titratable acidity
• total soluble solids
• uptake

Acknowledgments

The work has been funded by the Ministry of Education and Science (Project INIA RTA2006-00032-00-00), European funds FEDER, and the Institute of Agricultural Research and Training and Fisheries (IFAPA), Department of Agriculture and Fisheries (Junta of Andalusia).