Location: Horticultural Crops Production and Genetic Improvement Research Unit
Project Number: 2072-21000-055-044-S
Project Type: Non-Assistance Cooperative Agreement
Start Date: May 1, 2023
End Date: Oct 31, 2025
Objective:
Evaluate different fertilizer methods for increasing fruit calcium (Ca) and assess their effect on yield and fruit quality of blueberry, raspberry, and blackberry.
Approach:
On-farm trials will be established in commercial raspberry and blueberry fields in Lynden and Prosser, Washington and in commercial blueberry and blackberry fields in Salem, Oregon. One or two cultivars will be used for each crop, including ‘Duke’ and ‘Draper’ or ‘Aurora’ for blueberry, ‘WakeField’ or ‘Meeker’ for raspberry, and ‘Black Diamond’ or ‘Columbia Star’ for blackberry. In each case, treatments will be arranged in a randomized complete block design and include: 1) soil applications of lime or gypsum (selection will depend on soil pH at the site); 2) foliar applications of calcium chloride or a comparable certified organic formula; 3) fertigation with calcium thiosulfate, calcium ammonium nitrate, and/or hydrolyzed lime or gypsum; and 4) an untreated control. Each treatment will be applied to 60-foot-long plots and replicated five times. Fertilizers will be applied for two years according to label instructions, with calcium (Ca) rate held constant across the treatments. Soil applications of lime or gypsum will be applied in early spring each year to give it time to react and infiltrate the root zone prior to the growing season. Surfactants will be used with the foliar treatments to enhance penetration of the Ca fertilizer into the fruit and leaves. Fertigation treatments will be applied using positive displacement injectors installed in the drip irrigation system. Soil solution will be collected weekly from each treatment plot using soil moisture samplers and analyzed for availability of Ca and other nutrients using an inductively coupled plasma spectrometer. Samplers will be located beneath the drip emitters, where most roots are located, as well as between emitters, where mobile nutrients such as Ca tend to concentrate. Soil cores will be collected in September each year and sent to a commercial laboratory for complete soil analysis. Each core will be taken at the same location as the soil solutions and divided into 4-inch depth increments from 0 to 12 inches. Fruit will be hand- or machine-harvested, depending on the crop, and weighed to determine yield in each plot. Subsamples of fruit will also be weighed to determine average berry weight and then oven-dried for nutrient analysis. Additional samples will be analyzed for fruit quality, including Brix, firmness, and titratable acidity. Leaves will be sampled and analyzed for nutrients in early August each year. Finally, the drip system will be tested in each treatment to determine whether there is any plugging in the emitters. Input costs (labor, equipment, and product) will be recorded for all activities required to fertilize the plants and harvest the fruit. Cash cost and return budgets will be constructed for each treatment to compare net returns. Data will be analyzed by analysis of variance using a mixed model and repeated measures when appropriate. Fixed effects will include fertilizer treatment, year, and their interactions, and random effects will include block and interactions between block and fertilizer treatment. Regression analysis will be used to identify any relationships between soil conditions and yield, fruit quality, and fruit and leaf nutrients.
