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Nematode Community and Plant Growth Response to Root Leachate Treatments on Fruiting Vegetables in Low Desert of California

Agronomy & Pest Management

Philip Waisen
UCCE Riverside
Palm Desert


Tons of vegetable crop residues are generated every cropping season in California’s ‘Winter Salad Bowl’. Soil-dwelling microbes decompose and release nutrients that are held in organic form to plant-available form for subsequent crops. An ideal soil contains 5% of soil organic matter (SOM), where microbes are accommodated to perform ecosystem services like decomposition. In southern desert valleys of California, however, SOM content is below 1% attributed to scorching summer temperatures burning to negligible levels. This is low that microbial activity and overall soil health can be compromised. One way to stimulate microbial activity would be to condition the soil with root leachate pre-plant treatments. Root leachate contains sugars that can recruit and nourish beneficial microbes, serves as a source of microbes by inoculating planting beds to jumpstart microbial activity, and can break dormancy of weed seeds or survival structures of soilborne pathogens to be controlled by pre-plant chemigation. Two field trials were conducted to examine the effects of root leachates on cantaloupe and pepper in Coachella Valley. In Trial I, 6-week-old cantaloupe transplants were planted on 70 m × 1 m raised beds. Treatments included with or without tomato root leachate treatment and replicated 4 times in a randomized complete block design. The root leachate was prepared by running 19 L of water through 4 potted tomato plants and water collected was applied through drip one week after planting. In Trial II, tomato and pepper root leachates were used on pepper crop. In Trial I, tomato root leachate increased cantaloupe canopy and nitrate-N in the soil (P≤0.05), and numerically increased beneficial nematodes including bacterial feeders, omnivores, and total nematodes. In Trial II, pepper root leachate significantly increased chlorophyll content (P≤0.05), and numerically increased leaf nitrogen content and bacterial-feeding nematodes. These results suggest that root leachate treatment is stimulating microbial activity in SOM-deficient soil as reflected by increased beneficial nematodes. An increase in microbial activity increased nitrate-N in the soil and subsequently increased plant growth. More research is needed to dissect and understand the mechanisms, but these findings point to a potential organic management option for the growers in the desert.

Authors: Philip Waisen
  1. Philip Waisen Dr., University of California Cooperative Extension, California, 92211