Effect of wastewater as irrigation strategy on nectarine tree growth and nutritional status

Wastewater may represent an alternative source for irrigation and mineral nutrients in intensive agriculture, offering potential agronomical and environmental advantages. This work investigates the effect of STW (secondary treated wastewater) used for irrigation, on the nutritional and physiological response of 3-year-old nectarine trees. To this end, trees ('Big Top'/'GF 677') were individually grown on 40-L pots filled with a sandy-loamy soil and drip irrigated with: a) Tap water (U) (unfertilized trees); b) Tap water (M) (mineral fertilized trees) and c) Secondary treated wastewater (W) (trees did not receive mineral fertilizers). Each treatment was applied to five individual trees. Regardless of the water source, trees received 360 L tree(-1) season(-1) and only M-trees received 14.2, 2.35, 8.96, and 0.72 g tree(-1) season(-1) of N, P, K and Mg, respectively, from commercial fertilizers throughout the season. Shoot length and photosynthetic daily assimilation rates were promoted by STW, compared to U trees, although M trees showed the highest values. This response is likely related to the amount of nutrients supplied to the trees along the season. Although STW provided a "fertigation-like" effect, results suggest that this strategy did not completely fulfill the tree nutrient demand. On the other hand, the STW recycling as irrigation water was not detrimental to plant growth. Treatments affected mainly leaf rather than fruit mineral concentration. Mineral concentration resulted mostly in the optimal range for all the treatments, except the U, which showed nutritional deficiencies. Heavy metal concentration both in leaves and fruit tissues was unaffected by treatments, with concentrations within international limits imposed for the human consumption. Results indicate how STW may be conveniently recycled as water source in the irrigation strategies of perennial species grown in temperate environments although this strategy may only contribute to partial fulfilment of plant nutrient requirements.