Two years ago, UCCE Placer/Nevada embarked on a study to evaluate pruning and mulching in five local mandarin orchards. In a blog posted in June 2017, I discussed the beginnings of the study, the specific treatments and what the study was hoping to accomplish in the coming years. As the study enters the third year and data analysis begins, there are some observations that we should share.
The environment in our orchards is changing. We are experiencing unpredictable temperature swings and extreme periods of rainfall. Soil moisture levels this past winter and spring reached saturation levels for a prolonged period.
Roots need both water and oxygen. In saturated soils, oxygen in the soil pore spaces is displaced by water. This year, tree stress increased as the roots struggled to breathe. When root cells can't get oxygen, they die. Without them, the rest of the tree starts to die too. Many of us suffered tree loss due to the suffocation of root systems.
As orchards and fields began to dry, temperatures began to swing from high to low in unpredictable patterns. Stress was further introduced into the system. In the past few weeks, recorded temperatures in the five orchards have gone from lows in the 40's to recorded highs of 105 in the first few weeks of June. Citrus has a tendency to drop fruit that the tree cannot support and increased tree stress can increase fruit drop.
Field observations over the past few weeks show that drop is occurring at a much higher rate and volume in treatments that haven't been mulched. The picture on the left is from underneath the canopy of a tree without mulch (Control) and to the right is a mulched tree. These two trees are in the same orchard, approximately 18 feet apart.
Soil moisture levels are being monitored under both of these trees. Moisture levels under the mulched tree are consistent with what one would expect. The soil profile is able to retain moisture with minimal depletion at a 6-12” depth. Most moisture depletion is occurring in the top 6” of soil and is minimal compared to the Control. Moisture levels in the Control deplete at a more rapid rate throughout the soil to a depth of 12”. Once again, tree stress is on the rise. The soil moisture in the Control profile becomes much harder to replenish, resulting in longer irrigation cycles.
Soil temperature at a depth of 9” is also being monitored. Data from the Control show rather significant increases and decreases in temperatures in short periods of time. Data from the mulched tree reflect more temperature stability with the highs lower than those in the Control soil. Again, it seems that the Control may be under more stress due to the rapid temperature swings that the root mass is encountering.
It would certainly seem that a cursory examination of the data with field observations shows that mulching is a beneficial production practice in an orchard. However, there are some considerations to be had before one just charges ahead with this practice.
First, as we learned, timing is everything. Mulch should only be applied when the moisture in the soil profile is at capacity. Experience has taught us that applying the mulch when soil moisture is low results in playing catch up. I have observed orchards that were never able to replenish the full soil moisture content during the irrigation season.
Second, monitoring soil moisture is important. Mulching will change your irrigation timing and frequency. In our study, the period between irrigation cycles in mulched orchards has increased. Maturation appeared to be slowed in orchards that chose to stay with their old programs and not effectively monitor the soil moisture. Mulch reduces moisture loss from the soil, so if irrigation was not adjusted, the soil under the mulch stayed too wet. While less dramatic than the saturated soil situation this spring, stress was induced by the tree roots struggling to obtain oxygen and maturation slowed.
Certainly, mulching requires a little more effort on the grower's part. But is the not the reduction or control of the stress induced in the growing system beneficial to the entire orchard system? As a grower, I know that adding a little bit of stress into my trees at the right time and conditions is good for the fruit. Adding that stress at a time when it will not damage the tree or cause crop loss is key. Mulching certainly seems to mitigate stress in the growing system when stress is detrimental to the crop and system. Further data analysis will also provide us with more insight into the benefits that the mulch provides to the soil biology and composition. We will share those insights as they become available.
- Author: Hannah Meyer
I usually enjoy life and growing things as a farmer, however I was excited in the recent weeks to see the remains of something most definitely dead; owl pellets under an artificial nesting site. After a couple barn owl boxes were installed last year, I have eagerly awaited their occupation. Did you know that a family of barn owls will eat about 1,000 rodents in a single nesting season?
The recent owl pellet observation sparked my interest in researching the benefits of barn owls in agriculture. I found lots of information but focused on a particularly good peer-reviewed article called Agriculture land use, barn owl diet, and vertebrate pest control implications. (Kross, 2016). I will share with you the highlights, but you are welcome to read the research report yourself.
Research of owl presence at 25 California nesting boxes located mainly on row crops and perennial crops and forage, identified 1044 prey species. Pocket gophers, mice, and voles are generally the most important parts of the barn owl diet. Gopher numbers were highest in owl pellets found near perennial cropping systems but still a significant part of pellets found in annual cropping systems. Although mice are often considered less important as pests than gophers, they can carry pathogens that are a food-safety risk. 99.5% of prey items studied were agriculture pests, therefore owls are likely to provide valuable pest control services for farmers in our area if owl populations are fostered. Barn owls can persist if nesting sites and prey are available. Farmers seem to help provide the rodents, but let's not forget the nesting sites!
Alternative methods for rodent control such as trapping and poisoning can be expensive, labor intensive, and impact non-target species. Installation of nesting boxes to attract barn owls is not a proven method for sustained rodent control in agriculture systems by itself, rather it is best included as a component in an integrated pest management plan. Availability of nests sites appears to be the limiting factor of barn owl population growth in habitats that interface with humans (i.e. Farms and Ranches). Barn owls in the studied area occupied over half of the artificial nesting sites available to them, so installing nest boxes on farms may increase the natural barn owl rodent control.
Farmers and ranchers who wish to utilize the low-cost natural predation of rodent pests by barn owls in their agriculture systems or simply attract owls should:
- Provide abundant nest sites, including nest boxes. Funding and plans may be found through contacting your local resource conservation district.
- Increase crop type diversity in proximity to nest sites to include both perennial and annual systems to increase owl hunting efficiency.
- Install nest boxes now for this spring nesting season for best chance of owl occupation in the next 6 months.
Read the research article discussed above:
Kross S., Bourbour R., & Mertinico B. 2016. Agriculture land use, barn owl diet, and vertebrate pest control implications. Agriculture Ecosystems and Environment. 223, 167-174. http://sarakross.weebly.com/uploads/8/6/7/7/8677631/kross_bourbour___martinico_2016.pdf
NRCS Barn Owl Information Sheet and Owl box plans https://www.nrcs.usda.gov/Internet/FSE_DOCUMENTS/nrcs144p2_063925.pdf
UC Master Gardener Gopher Blog post, ideas for gopher management with great photos https://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=29485
UCANR Songbird, Bat, and Owl Houses https://anrcatalog.ucanr.edu/Details.aspx?itemNo=21636
This handy guide explores the benefits of the biodiversity and aesthetics of songbirds, bats, and owls. While written with vineyard managers in mind, anyone interested in learning about nest boxes will find this guide useful. Purchase this booklet at the link above for $15.