Organic farmers sharpen fertilizer, IPM techniques

Strategies for successful integrated pest management programs and crop fertilization were outlined for growers and crop advisors attending an organic production seminar held recently in Tulare.

Organic growers walk a fine line in applying fertilizer to grow a productive crop and preventing nitrogen from leaching into groundwater. Since the University of California report on groundwater quality was released last spring, there has been additional attention focused on nitrogen fertilizer use. Both organic and conventional farming operations are coming under increased scrutiny.

Organic fertilizers do contribute to the presence of nitrate in groundwater, but not equally with synthetic fertilizers, said Tim Stemwedel of California Organic Fertilizers. Research has shown that infiltration rates are lower for organic fertilizers and depend on the form of fertilizer applied, he said. One study he cited showed substitution of organic fertilizer for synthetic products could reduce leaching by 50 percent.

Organic fertilizers also contain amino acids, proteins and humus that must degrade before plant uptake. Compost is least susceptible to leaching due to the high amount of organic matter. Microbial activity in compost also slows its breakdown and subsequent leaching. Uncomposted manure, used in dairy production areas, likely leaches at the rate of synthetic fertilizers, Stemwedel said.

Organic fertilizers have been blamed for nitrate leaching due to slow degradation rates and nutrients remaining in the soil after crops have been harvested. Stemwedel said organic growers might be applying more than necessary to make up for slow uptake.

He advised using less fertilizer on crops, testing soils and using trap crops to take up the nutrients left by the initial crop. Farmers should also apply less fertilizer pre-plant and come in later with side dress to fill in the peaks during high crop demand, he said.

Growers should review their fertilizer and irrigation programs and, if possible, perform on-site leaching tests to determine rates for particular soil types.

Integrated pest management is an important factor in the success of organic production, but entomologist Tim Quick of the organic input company Grow More pointed out that organic production must also be profitable. Management of both pests and production must use a multidisciplinary approach of compatible, ecologically sound practices with reliance on knowledge, experience and observation, he said.

Organic pest management is complicated but is possible, Quick said. It begins with avoidance of pest problems, including use of resistant plant varieties, pest host management and sustaining biological controls. Using a pyramid model, the next action would be effective and selective chemical use and resistance management. Finally, there is continuing monitoring for pests.

Organic growers have more tools now than they did 10 years ago. Quick said they include preventive cultural practices such as improving soil tilth, optimizing planting times and locations, monitoring and trapping with lures or sticky traps, and using biological control, such as developing populations of natural enemies of pests.

The tools have to be tied to economics, Quick said. Inserting "production" for "pest" in IPM, a profitable organic food business should recognize all inputs: soil, seeds, water, fertilizer, labor certification and marketing.

The good news, Quick concluded, is that the organic farming business has effective organic pesticides and knowledgeable IPM and pest control advisors.

(Cecilia Parsons is a reporter in Ducor. She may be contacted at ceciliaparsons8@gmail.com.)