Water and nitrogen use efficiencies of cucumber under negatively pressurized fertigation

Objectives This study aimed to search suitable combination of irrigation and fertilizer through the distribution of nitrate nitrogen and water and nitrogen use efficiencies of cucumber.

Methods A complete two factor pot experiment was conducted. Irrigation included five levels: 0, –5, –10, –15 kPa and conventional irrigation, recorded as W1, W2, W3, W4 and CK in turn; N input rates of 0 (N0) and 0.3 g /kg soil(N1) were included in each water treatment. Soil water and nitrate nitrogen contents were investigated in different depth and different growing stages, the water and nitrogen use efficiencies of cucumber were calculated.

Results Water supply was highly significant and positively correlated with the water consumption of cucumber in all the treatments (y = 0.96x + 3.4,R² = 0.99,P < 0.01), so the water supply in the negatively pressurized irrigation system was dominated by the crop water consumption, and in this way the system was able to keep a balance between water consumption and water supply. The average soil water content was significantly affected by water supply pressure. The soil water contents under irrigation pressure of 0, –5, –10 and –10 kPa were respectively 28.7%, 22.7%, 20.0% and 15.6%, and the soil water contents were stable with the coefficient of variation less than 0.1 during cucumbers growth period. The negatively pressurized fertigation system could extremely increase distribution uniformity of soil water and nitrogen within 0–25 cm soil layer. The average coefficient of variation (CV) of the vertical distribution of soil nitrate was decreased by 58.6%–71.2% compared with CK. Compared with the N0 treatment, the plant dry weight, yield and water use efficiency under N1 treatment were respectively increased by 4.6%–256.1%, 12.6%–196.6% and 7.76%–86.27% at the same water supply pressure of the fertigation system. Under treatment of W2 (–5 kPa), the average plant dry weight and yield were all the highest, which were 153 and 1406 g/pot respectively, and the water and nitrogen use efficiencies were increased by 136.8% and 52.32% respectively.

Conclusions The negatively pressurized fertigation system shows advantages in steady and timely water supply, and even nitrate distribution in 0–20 cm soil layer during the whole growing season of cucumber than conventional irrigation system. The optimal water supply pressure was the negative pressure of –5 kPa for cucumber.