Although promoted as an alternative to secure rain-fed agriculture, supplementary irrigation cannot ensure sustainable food production, regardless of the rational and optimal use of organic matter. Therefore, an experiment was set up in a sandy loam soil (bulk density =1.55 g/cm3; field capacity =18%; wilting point=1.4%) to determine the optimal combination of irrigation depth and compost rate. The experimental design was a split plot with four replications. The main factor was the irrigation water depths, which represented 50%, 75%, and 100% of the tomato crop’s water requirement (2800 m3/ha/Irrigation). The second factor consisted of two compost rates: 5 t/ha (C5) and 10 t/ha (C10). Six combinations were tested: C10 + 100%, C10 + 75%, C10 + 50%, C5 + 100%, C5 + 75%, and C5 + 50%. Fertilizers (NPK 14-23-14 and Urea 46%) were applied at the recommended rates of 250 kg/ha and 150 kg/ha, respectively, at 15 and 35 days after transplanting. The adopted irrigation interval was 2 days. After transplanting, a constant water depth (DI 100%) was applied, and water treatments were initiated 15 days after transplanting. Water application was postponed to the next irrigation if rain occurred.
The results showed that, in general under supplementary irrigation, the addition of compost increase growth parameters, yield and water use productivity. However, when water requirement is reduced by half this increase is not consistent. Indeed, the higher yield was induced by C5 + 75% treatment. The combination of C10 + 50% improved water productivity by 70%. Therefore, the combination of C10 + 50% should be recommended for the sustainable management of land and water resources.

Supplementary irrigation, land management, water productivity, tomato