Effects of irrigation water type and nitrogen on growth, yield and nutrient partitioning of tomato. (Lycopersicon lycopersicum (L.) Karstern

Abstract

A field experiment was conducted at the Botswana College of Agriculture (BCA) to evaluate the effects of irrigation water type and nitrogen on growth, yield and nutrient partitioning of tomato (Lycopersicon lycopersicum (L.) Kartcn). The treatments were irrigation water types (treated secondary sewage effluent and potable water) and nitrogen levels at 0, 25, 50, 75, 100 and 125 kg N/ha. The results showed that treated sewage secondary effluent (TSSE) without or with nitrogen supplementation significantly (P < 0.05) increased tomato vegetative growth compared to plants irrigated with potable water (PW) under the same fertilizer regime. Similarly tomato plants irrigated with TSSE significantly (P < 0.05) produced higher fruit yield per hectare and larger fruit size (fruit diameter) than plants irrigated with PW. Plants irrigated with TSSE without or with nitrogen had significantly (P < 0.05) higher root, stem leaf and fruit water content but lower dry matter than plants irrigated with PW. Plants irrigated with TSSE without or with nitrogen had significantly (P < 0.05) higher fruit nitrogen content and increased the uptake and partitioning of phosphorus (P), potassium (K), calcium (Ca), sodium (Na) and magnesium (Mg) in various tomato plant parts compared to those irrigated with PW. Nitrogen increased vegetative growth, fruit size, yield, uptake and partitioning of N, P, K, Ca, Mg and Na to various plant parts and organs, irrespective of irrigation water type. An adequate N supply is critical for tomato production. Too much N favours excessive vegetative growth over fruit development and too little N when demand is high would decrease yields and plant vigour, which increases tomato plant susceptibility to stress. Basing on the quality of TSSE, fruit yield and yield components, absence of faecal coliforms, Salmonella spp, Escherichia coli, and heavy metals in the tomato fruit, it was concluded that the TSSE can be used for irrigation and fertigation of horticultural crops such as tomatoes as it contains a cheap source of available plant nutrients both macro- and micro-nutrients. It was also concluded that if TSSE is used as irrigation water, farmers should apply 75 kg N/ha to determinate tomatoes in order to maximize genetic potential and yield. In order to avoid contamination of the fruit and human health hazard, drip irrigation and not sprinkler should be used, and at least 2 weeks of irrigation withdrawal should be done to ensure safety of the tomato fruits from microorganisms. However, the government of Botswana should come up with policies and regulations that would control the use of TSSE for irrigation in order to reduce health hazards associated with the use of TSSE.