Use of Humic Products for Production of Berry Crops.

Many berry growers in the United States and elsewhere are incorporating humic acid products into their fertilizer programs. Proclaimed benefits of these substances include improved soil properties and structure, greater bioavailability of soil nutrients, increased microbial populations, and plant hormone-like effects. Recently, we discovered that application of humic acids increased plant growth during the first two years after planting in northern highbush blueberry. The effect of humic acids on root growth were particularly apparent and resulted in 46% to 75% greater root dry weights than conventional fertigation, granular fertilizers, slow-release fertilizers, or a control treatment that lacked humic acids but contained exactly the same nutrients as the humic acid treatment. We also observed more root and primocane growth with humic acids in a new planting of summer-bearing red raspberry. Humic acids are clearly beneficial during establishment of these crops. However, there is limited evidence to date on whether humic products are beneficial in mature, fully-productive plantings of berry crops. After 2 years of application, mature blueberry plants tended to produce more roots when grown with than without liquid humus, while mature raspberry plants had numerical higher concentration of N, P, and K in the leaves relative to a conventionally fertilized control when humic acids were used in conjunction with brassica seed meal. We did not find in either trial any effect of these products on fruit production. Apparently, response to humic products may be lacking or delayed in mature plants due to large amounts of carbohydrate and nutrient reserves in the woody tissues from the previous growing seasons.