Mitigating continuous cropping stress in greenhouse lettuce cultivation using organic and inorganic soil amendments

In greenhouse cultivation systems, repeated and intensive cropping often lead to soil problems such as salt accumulation, organic matter depletion, deterioration of soil physical properties, and increased pest and disease incidence, resulting in reduced crop growth and yield.This study was conducted to mitigate continuous cropping obstacles and improve soil conditions by applying various organic and inorganic soil amendments, including biochar (BC), rice husks (RH), rice straw (RS), and weathered granite soil (MS).The experiment was carried out in a greenhouse lettuce (Lactuca sativa L.) field in Bibong-myeon, Wanju-gun, Jeollabuk-do, Korea, where lettuce had been continuously cultivated for more than 10 years.Soil amendments were applied four weeks before transplanting at rates of 0.2, 2, and 2 ton 10a -1 for BC, RH, and RS, respectively, and 35 ton 10a -1 for MS.The effects of each amendment on soil physicochemical properties, crop growth, and disease incidence were evaluated.BC and RH treatments significantly reduced soil bulk density to 0.9 Mg m -3 compared with the control (1.3 Mg m -3 , p < 0.05), increased effective soil depth up to 27 cm, and decreased electrical conductivity from 5.3 to 1.4 dS m -1 .In terms of lettuce growth, the number of leaves per plant (12.5 and 12.3, respectively) and yields (5,037 and 5,061 kg 10a -1 , respectively) in BC and RH treatments were significantly higher than those of the control (1,941 kg 10a -1 ), representing approximately a 2.6-fold increase.In contrast, the MS treatment exhibited the highest bulk density (1.2 Mg m -3 ) and the lowest organic matter content (28.0 g kg -1 ), indicating minimal improvement in soil physical properties.Additionally, BC treatment effectively suppressed soil nematode density (31 individuals per 100 g soil) and reduced fusarium wilt incidence.While RH and RS treatments slightly increased nematode populations, they positively influenced root development (p < 0.05).These results suggest that biochar and rice husks are effective amendments for mitigating continuous cropping stress in greenhouse lettuce cultivation, and that long-term studies are required to establish optimal application strategies for sustainable soil management.