Nutrient Management for Cucumber

The project tested the response of cucumber to Ca and Mg in combination with N, P and K rates within the well-managed vegetable production area near Penzhou city, Sichuan. The optimal rates for N and P were adjusted downward to 210 kg N/ha and 105 kg P₂O₅/ha, based on the responses of cucumber to different fertilizer treatments in 2013. The three K fertilizer application rates were as 0, 300, or 450 kg K₂O/ha; the two Ca rates were 350 and 750 kg Ca(OH)₂/ha; and the two Mg rates were 22 and 44 kg Mg/ha. The fertilizer sources were urea (N 46%), single superphosphate (P₂O₅ 12 %), potassium chloride (K₂O 60 %), Ca(OH)₂ (0, 350 and 750 kg/ha), and MgSO₄· 7H₂O (Mg 9.7%). All P, lime, and MgSO₄, and half of the N and K were applied basally at seedling transplanting. The rest of the N and K was topdressed at the flowering and fruit harvest stages.

Under the same rate of N and P, cucumber yield significantly increased (11 t/ha or 16.2%) with addition of 300 kg K₂O/ha compared to K omission. Only a minor increase was observed with the treatment providing additional K. Further addition of Ca and Mg significantly increased yield by 5.5 t/ha (7.0%). At the K rate of 450 kg K₂O/ha, however, cucumber yield responded to the largest amounts of Ca and Mg tested. Interestingly, the contents of vitamin C and amino acids followed the same trends as was observed in cucumber yields. Nitrate concentrations in cucumber were lowered by addition of K and were further lowered with addition of Ca and Mg.

The results imply that at a given K rate, secondary nutrients must be provided in balance to match cucumber nutrient demand. Compared to the K omission treatment, the net economic profit increased by US$1,636 (18%) upon addition of 300 kg K₂O/ha; or by US$2,446 (27%) with 300 kg K₂O/ha plus the low rate of Ca and Mg.