Impact of bio-organic fertilizer and reduced chemical fertilizer application on physical and hydraulic properties of cucumber continuous cropping soil

The continuous cultivation of the same crop on the same plot can result in problems such as soil compaction, deteriorating hydraulic properties, and decline in crop yields. This study investigated the effects of bio-organic fertilizer addition, with reduced application of chemical fertilizer, on physical and hydraulic properties of a soil under continuous cucumber cropping. Based on long-term fixed-site experiments in a greenhouse of the Yangtze River Delta region of China with high-intensity continuous planting of two-season cucumbers, experiments were conducted with 9 treatments (T1–T9), which comprised 3 groups (CK, Y1, and Y2). The CK group received 0 t hm⁻² of bio-organic fertilizer, Y1 group received 10 t hm⁻² of bio-organic fertilizer, and the Y2 group received 20 t hm⁻² of bio-organic fertilizer. Each group had three chemical fertilizer treatments: 1 t ha⁻¹ (standard practice, 0% reduction), 0.9 t ha⁻¹ (10% reduction), and 0.8 t ha⁻¹ (20% reduction). Each treatment was replicated 3 times. Soil (0–20 cm) and cucumber plant samples were collected from each treatment during cucumber maturity of each season, to determine the soil bulk density, soil total porosity, hydraulic properties, and cucumber yields. Compared with the CK treatment group, the soil bulk density of the Y1 and Y2 groups decreased by 0.08–0.13 g cm⁻³ and 0.15–0.22 g cm⁻³ respectively; the soil total porosity of the Y1 and Y2 groups increased by 3.02–4.90% and 5.66–8.30%. The content of water-stable aggregates and their mean weight diameter (MWD) showed increasing trends. A multivariate non-linear regression model fitted to the data (R² = 0.956) predicts that a 20 t ha⁻¹ bio-organic fertilizer application with 0.92 t ha⁻¹ chemical fertilizer will give the theoretical maximum cucumber yield of 23.45 t ha⁻¹. Use of bio-organic fertilizer with reduced chemical fertilizer application can improve the physical and hydraulic properties of cucumber continuous cropped soil. These results can provide a scientific basis for mitigating cucumber continuous cropping problems.