Effect of spent tea waste, compost and biochar on some growth parameters and concentration of nitrogen, phosphorus and potassium in spinach (Spinacia oleracea L.) under salinity stress

Salinity is a major environmental problem that adversely affects plant growth by increasing soil osmotic pressure and disrupting plant nutrition. Using organic amendments is a viable tool for reducing physiological and morphological effects of excessive soil salinity on plants. To show the impacts of tea waste, compost and biochar on nutrient status and growth parameters of spinach (Spinacia oleracea L.) raised in salinity conditions, this study has employed factorial CRD with two treatments involving soil salinity (2.5 and 8 dS m(-1)) and organic materials (spent tea waste (STW), spent tea waste compost (STWC) and spent tea waste biochar (STWB)) at 0 and 3% w/w in three replications. As soil salinity increased from 2.5 to 8 dS m-1, fresh weight and dry matter production decreased by 31.5% and 30.4%, respectively. Phosphorous and potassium concentrations in plant tissue also decreased significantly due to the increase in salinity. Organic amendments (except STW) due to their physicochemical properties increased the nutrients uptake and growth parameters of the plant. Compared to other amendments, biochar reduced salinity effects on plant growth more effectively, which is possibly due to its high nutrient adsorbing and water holding capacity. In saline conditions, the highest potassium to sodium ratio belonged to the biochar treatment, which was 3.22 and 2.78 times greater than spent tea waste and compost, respectively. Therefore, it was preferred to change the spent tea waste into biochar before being used as soil amendment.