[Effects of nitrogen forms on the growth, yield and fruit quality of tomato under controlled alternate partial root...

The effects of nitrogen (N) forms (ammonium-N and nitrate-N) on the growth, yield and fruit quality of tomato plants (cv. Zhongyan 988) under controlled alternate partial root zone irrigation (APRI) were examined in a split-root experiment. Under the same irrigation mode and/or controlled soil water limitation treatment, ammonium-N promoted plant growth at the early stage, while nitrate-N improved plant growth and development at the later stage leading to higher biomass accumulation and fruit yield at harvest. Under APRI and the same soil water conditions, plants of the nitrate-N treatment improved the content of vitamin C and the ratio of soluble sugar to organic acid and thus facilitated fruit quality when compared with those of the ammonium-N treatment. Plant height and leaf area under APRI treatment were lower compared with conventional irrigation (CK) under the same N form, but the stem diameter under APRI treatment with 60% theta(f) (field water capacity, theta(f)) soil moisture showed a slight increase at the late growth stage. Under the same N form, fruit yield was significantly lower in APRI treatment than that of the CK. Compared with the CK, fruit yield decreased by 22.4%-26.3% under the APRI treatment with 40% theta(f) soil moisture. Under 60% theta(f) soil moisture, the APRI treatment significantly improved fruit quality and water-use efficiency compared with the CK regardless small reduction (5.3%-5.4%) in fruit yield. The experimental results suggested that the APRI treatment with the lower limitation of soil moisture controlled at 60% theta(f), and nitrate-N supply would be the optimal option in terms of sustainable use of water resource and fertilizer.