2018 ASHS Annual Conference

Citrus growers in the foothills of Northern California are challenged by poor soils with low organic matter and fertility, limited water, and high production costs. Many foothill growers use non-traditional practices such as mulching to mitigate these issues. We have been conducting field research in five commercial mandarin orchards to determine the impacts of mulching on tree health, water use, fruit yields and quality.

The research questions are to determine if mulching can reduce herbicide, fertilizer, and water use while maintaining or improving soil and tree health and orchard productivity. Mulch is applied annually in the spring, and comprised of 50% composted horse manure and 50% wood chips, placed along the tree row under the canopy. Data collected includes soil moisture status, organic matter, microbial activity, and overall soil health; mulch composition and microbial activity; ambient temperature and relative humidity; tree growth, nutrient status, fruit yields, and fruit quality.

This paper will present results of the mulching trials to date. We have observed significantly higher available soil moisture with concomitant impacts on reduction of tree stress in periods of high heat or dry winds. We developed specific mulching methods to prevent the growth of troublesome weeds under the canopy and root sprouts on Cleopatra rootstock. We have also learned key lessons on optimal soil conditions and timing of mulch applications.