Growing mandarins in the foothills often produces a tantalizing crop of fruit that delights even the pickiest of connoisseurs, however, it is not produced without difficulty. UCCE Placer/Nevada has collaborated with five local citrus growers to research the effects of pruning to thin canopy and mulching to conserve soil moisture and create a healthier root zone. To learn more about this project, read Citrus Grower Bob Bonk's blog post, Mandarin Growers Test New Practices on the Foothill Farming blog. Research began just over a year ago and here are some of the things we have learned so far.
Mulch under citrus trees helps maintain soil moisture, reduces soil temperatures, and can effectively manage weed growth.
Methods: Mulch is best applied when the soil is saturated. Typically mulch is applied in March/April in this region but can be applied later if soil is irrigated to saturation level. Mulching is most effective for weed suppression when either little to no weed emergence has occurred, weed whacking, or herbicide spray is implemented first. Mulch alone reduces weed growth. Mulch applied over builder's paper or 6-8 sheets of newspaper then saturated to conform to the ground is even more effective. Fertilizer is best applied before mulching.
Materials: A 50/50 wood chip and horse manure blend is used in the research trials but either one can be used on its own. Composted manure alone decomposes rapidly, a mix of manure with wood chips will last longer. Wood chips last longer than either the wood chip/manure mix or manure alone but will provide little to no nutrient value to the tree.
We have observed that often irrigation with overhead sprinklers does not penetrate dense tree canopies and may lead to water stress. Tensiometers, which measure soil moisture, were installed in citrus orchards in summer 2017. They showed that overhead irrigation water was not reaching the ground under dense canopies, causing water stress in hot weather. As a result of some of this research, several commercial citrus growers have modified irrigation practices or are changing irrigation systems to mitigate water stress.
Looking to the future:
Soil temperature can affect root activity so beginning this year soil temperature are also being monitored throughout the research project. Citrus growers are attending workshops, field meetings, and learning what the orchard trials are teaching us. Many are implementing new methods and practices in their citrus operations. Citrus trials will continue at least through 2019. Look for more information in future blogs.
Commercial growers are invited to participate in a Composting & Mulching Workshop on Thursday, May 31st, 9 AM to 12 noon, register at this link. http://ucanr.edu/survey/survey.cfm?surveynumber=24853