The fall cover crop mix planted in early November at both locations has had excellent germination and growth. This mix included daikon radish, coker, Wrens grain rye, and dove millet. Sunnhemp, alyce clover, sesbania, dixie crimson clover, and yellow sweet blossom clover were included in the mixes for the nitrogen-fixation treatments (1/2 of the rows). Germination counts and biomass samples have been collected, and are currently being analyzed.
Measurements of the abundance of specific N-cycling genes has begun for soil samples collected at the last annual collection. After one year of cover crops, the abundance of nitrification genes (ammonia-oxidizing archaea and bacteria) significantly increased in treatments with cover crops when compared to the grower standard control, suggesting an increase in soil nitrogen availability. Measurements are in progress to determine the abundance of nitrogen-fixing genes (important with legumes since they are related to changes in the content of ammonium in soils) and denitrification genes (often linked to changes in soil organic carbon, organic matter, and nitrogen losses from the soils). Multivariate statistical analyses are also in progress to evaluate the influence of abiotic (soil properties) on biotic (microbial gene abundance) variables in treatments with and without cover crops.
Dataloggers and soil moisture probes continue to record soil moisture every hour. Root growth measurements using the mini-rhizotron tubes installed in both groves were performed in March and July 2019 and Feb 2020. Data on these measurements are currently being analyzed and will continue in Fall 2020. Initial analysis of yield, trunk area and canopy volume found no significant differences after 1 year of cover crops for one location. However, preliminary data indicates a greater canopy volume and trunk area at the second field site in treatments with the cover crop + legume mixture compared to other treatments. There were no significant differences in soil phosphorous, potassium, or magnesium concentrations between treatments at either location after 1 year of cover crops. Additional nutrient measurements are still in progress.
Weed density measurements from both study locations were collected in Aug 2019 and Jan 2020. Preliminary analysis of weed density data suggests that cover crops significantly reduced (up to 84%) weed pressure in treated row-middles when compared to non-treated controls. Moreover, cover crops improved the biodiversity in the treated row middles. Annual biomass data collection was also performed in both study locations in Jan 2020. Cover crop and weed biomass was harvested from the plots and bagged. In the lab they were sorted and weighed out to gather information on total weed/cover crop biomass from the treatment/control plots.
The first harvest since cover crops have been planted will occur in Spring 2020 (likely end of March). A project meeting with the grove managers will be held after harvest to discuss the next planting of cover crops. Some root rizhotrons and data loggers were damaged at one of the sites by hogs and some heavy equipment. These problems will be rectified in the next quarter to ensure continuity of of measurements in some treatments.