As the seasons shift, daylength decreases, cooler temperature become the norm and our rainy season arrives in earnest, I tend to start paying much closer attention to the weather. Unlike late spring through fall when forecast discussions typically center on the intensity and duration of our daily fog regime, California winter weather is subject to constant flux, resulting from variations in the jet stream, ocean temperatures and the development of storm patterns far out over the Pacific.

On the central coast, we typically receive one of two types of winter storm, either the warm and wet storms that come out of the South Pacific, or the colder and usually less water-laden ones that arrive from the Gulf of Alaska. Between these storms we will often have several days to sometimes even a week plus with blue skies and cold, frosty nights. We pay close attention to the weather because it is these times between storms when we can get projects done outside and sometimes even in the soil if we have a long enough dry-down to work the ground without causing clodding and compaction. 

Perhaps surprisingly, as our rainy season begins, I have been thinking a lot about water conservation and our responsibilities and obligations to protect and assure access to our water supply. While this is an issue particularly for ASCFG members growing west of the 100th meridian, I believe that it is increasingly an issue for people the world over.

The 100th meridian, you will recall is the north-south line bisecting North Dakota, South Dakota, Nebraska, Kansas, Texas and the western edge of the bulk of Oklahoma. It was here that in 1879 John Wesley Powell divided the country based on typical rainfall patterns. East of the 100th meridian, growers usually receive at least 20″ of rainfall annually. Stillwater and Tulsa, the sites of our outstanding 2010 national conference, average approximately 36″ inches of rain annually, thus reducing the absolute necessity for irrigation.

West of the 100th meridian most areas receive fewer than 20″ of rain per year, thus greatly increasing the need for reliable sources of irrigation water to successfully grow the vast majority of crops. While this is clearly not an absolute point of division and many areas west of the line actually receive much more than 20″ of rain, what is almost universal is that western growers will experience prolonged periods of drought each year. Where I live in the Santa Cruz Mountains, we actually get an average of 42″ of rain. However, all of this rain comes between the end of October and the beginning of May, not exactly prime time for the majority of field-grown cut flowers.

As climate patterns continue to shift and population pressures continue to grow, water conservation will increasingly become a necessity if we are to successfully meet the water demands of agriculture, industry, direct human consumption and the environment on which we all depend. In an effort to use this precious resource as wisely as possible, we will continue and expand our efforts with tried and true conservation strategies. Building soil organic matter, which diversifies soil microbiology, improves nutrient availability, soil tilth, aeration and drainage, also has the obvious effect of being a reservoir to hold soil moisture longer, thus reducing irrigation frequency.

Drip irrigation is another useful tool. Currently about 80% of our flower, fruit and vegetable crops are grown on drip. Not only does this help reduce water lost to evaporation, it is also an incredible tool in preventing the establishment and spread of many fungal diseases in the crop canopy, thus reducing the need for intervention, whether you use conventional or organic growing practices. Timing of delivery, either early or late in the day, can be another means to prevent water lost to evaporation.

We also try to encourage a measure of drought tolerance and the development of deep root systems by irrigating less and less frequently but to greater and greater depths as crops mature. This strategy is not appropriate for all crops, but for many it can have a strong impact on underground growth and our overall conservation portfolio. Augmenting plant density, within the limits of local pathogen pressures, is another simple cultural practice that can help with conservation and increase productivity per row foot, thus improving the bottom line. Finally, mulching with woodchips, straw or some similar material is a time tested way to retain moisture, indirectly build soil organic matter and protect the soil surface from the potentially erosive and soil aggregate-degrading effects of rainfall and overhead irrigation. Many mulches can also be marvelous habitat for mice, slugs, snails and earwigs, so proceed with caution. 

In the context of conservation, I have also been pondering the realm of how to maintain high crop quality and yields while at the same time supplying far less water. Maybe other ASCFG growers would be interested in a collaborative research project on the subject of water conservation, crop quality and productivity. Perhaps in the future I should put together a grower grant request. Narrowing down the many variables will be key to research design, but it could be as simple as exploring different irrigation regimes for the same crops grown under otherwise identical conditions. What is the least amount of water one needs to grow the best quality crops? Even if conservation is not a primary concern for some growers, irrigation is still another input that requires time, labor, energy and infrastructure to deliver to our crops and reducing all of these costs can positively impact our financial sustainability. 

Christof Bernau

UCSC Center for Agroecology

Christof Bernau UCSC Center for Agroecology Contact at [email protected]