Effect of soil amendments and sawdust mulching on growth,yield and leaf nutrient content of highbush blueberry plants

The effects of soil amendments (elemental S, peat, crushed pine bark or crushed pine bark plus elemental S) mixed into the planting hole, with or without a sawdust mulch over the soil surface, on the early growth and yield of highbush blueberry bushes (Vaccinium corymbosum L., ‘Bluecrop’) grown in a mineral soil were investigated in a 3-year field study.Plant growth and yields were increased by additions of all amendments and generally followed the order: bark plus S > bark = peat = elemental S > control. The reasons for the positive growth responses probably differed among the treatments. In the control treatments, growth appeared to be limited by Mn and possibly Fe deficiency. For the S treatment, a decrease in the soil pH with a concomitant increase in levels of Mn and Fe probably stimulated the response. However, concentrations of both leaf Al and Mn were very high in the S treatment, and toxicities of these elements may have been limiting a further growth response. For the peat amendment, the growth response was probably related to both a decrease in soil pH and an improvement in soil physical conditions. For the bark amendment, the growth response is likely to have been pricipally related to improved physical conditions and also to the reasonably high Mn content of the bark itself. For the bark plus S treatment, the additional effect of reduced pH provided for an even greater response than that for bark alone. It was concluded that additions of organic matter and an acidifying agent to the planting hole can greatly increase early growth and yields of blueberries in mineral soil.