Increasing the Sustainability of Blueberry Production with Cover Crops

In October and November 2024, we met with cooperators to select the cover crops suitable for blueberry production. Nine cover crops were selected:  crimson clover, hairy vetch, clover strawberry, clover white Dutch, Kentucky 31, Wrens Abruzzi rye, Lolium multiflorum, Sudan grass, and black mustard. Soil samples were taken from three commercial farms for soil nutrient analysis and a germination rate experiment. On November 12^th, 2024, the germination test was established to test the germination rate of the nine cover crops selected using soil only from three farms located in Nahunta, Abbeville, and Pearson. The seeds were sown in a germination tray containing soil from each of the three farms ( Fig 1.). The germination trial was terminated on  March 5th, using natural termination (incorporating the cover crop into to soil). Soil was analyzed after cover crop incorporation for soil organic carbon, nitrogen, phosphorus, potassium, and cation exchange capacity (results are pending).  On February 24th, soil samples were re-taken to assess the soil pH at the farm located in Leesburg ( new blueberry farm). In addition, soil was used to establish a second greenhouse experiment on March 5th using soil from the same four farms (Fig. 2), to validate the germination rates using more replicates. 

We communicated with growers and visited each of the farms involved in the study to decide if the cover crops would be placed in the row middle or on the raised-bed; we designed the experimental layout map layout for each of the farms accordingly. In Nahunta and Pearson, the soil samples were taken from the row middle and the raised bed.

In addition, as part of the project, soil samples were taken to conduct nitrification analysis.

Soil samples were collected from six blueberry farms in south Georgia (Table 1) in September 2024. The same sites were resampled in the spring of 2025 (February). These locations represent the major blueberry growing locations across the southern part of the state, wherein cultivation has been ongoing for over five years. All sites were chosen based on the type of blueberry grown: southern highbush blueberry. Four of the sites had the cultivar, Farthing, while the other two had Optimus. Soil samples were collected from four consecutive beds and the inter-plant zone at each location. A hand-held shovel or a post digger was used for obtaining the top 30 cm of soil at each site. Soil from within each farm site was pooled and homogenized. Subsequently, the soil was sieved using a 4 mm sieve and stored at room temperature with regular aeration by hand mixing.

Analyses of soil samples

Field moisture content was determined by weighing a sub-sample of each soil, drying and re-weighing. Soil water holding capacity was determined following saturation with water, drainage, and weight measurements. For the September 2024 collection date, the soil samples were analyzed at the University of Georgia, AESL lab. The analyses included texture analyses, pH, lime buffering capacity, organic matter concentration, soil nutrient concentration, total C, and total N measurements. Similar analyses of Spring 2025 collection date samples in currently underway.

Nitrification capacity of the blueberry cultivation soils was determined. Samples were re-wet to 50% water holding capacity. Sub-samples (300 g dry soil) from each site were transferred into 960 mL glass jars and subjected to one of two treatments. A. Control: no addition of N; B. N fertilization as [NH₄)₂SO₄] at the rate of 6.35 mg/kg soil (n = 4). The samples were incubated at room temperature for around 100 d. Soil samples were collected from the jars at regular intervals by sampling 5 g of soil. The samples were extracted in 1M KCl by shaking for 30 min at room temperature. The KCl extractions were analyzed using the Timberline Ammonia Analyzer to determine NH₄⁺ (ammonium) and NO₃^- (nitrate) concentrations. Nitrate concentrations were analyzed following reduction using zinc as a catalyst. 

Table 1. Soil samples were collected from south Georgia Blueberry farms in September 2024.