Nonleguminous Cover Crops To Reduce Nitrate Leaching
In Vegetable Cropping Systems
Louise Jackson1, Bill Chaney, Steve Koike, Richard
Smith, Lisa Wyland
Department of Vegetable Crops, University of California, Davis,
CA 95616
Our work with cover crops focuses on using non-leguminous cover crops to decrease nitrate leaching during the winter rainy period in vegetable production systems of the Central Coast region. This is a region of high agricultural non-point source contamination of nitrate in groundwater. In previous work, we have shown that nitrate tends to accumulate in these soils in fall and winter, as a result of high nitrogen mineralization potential in this mild winter climate. Merced rye (Secale cereale) and phacelia (Phacelia tanacetifolia) are two species which take up approximately 100 kg N/ha in a short winter growth period (34 months). Our research has determined that to reduce the time and energy for cover cropping, these cover crops are seeded into shaped beds in the fall, then incorporated directly into the beds in the spring, using minimum-tillage equipment. The vegetable crop is planted into the same beds about one month later.
During the past year, our projects have involved two main topics
that concern the benefits of cover cropping in cool-season vegetable
production systems in the Salinas Valley. In one project, the
Erosion Productivity Impact Calculator model (EPIC) is being calibrated
for a Merced rye cover crop and broccoli. Field data on N pools,
plant biomass, and nitrate leached (as determined with ion exchange
resin bags) are being used. The objective is to predict how several
management options for cover crops affect nitrate leaching and
the yield of the subsequent broccoli crop. In a second project,
phacelia was isotopically labelled with 15N, (a stable isotope
of nitrogen), and the fate of the labelled material in plant biomass,
soil microbial biomass, and soil N pools is being monitored.
Intensive measurements were made during the first month after
incorporation in order that decomposition processes be described
in detail. Both projects will provide information on the ability
of the cover crops to decrease nitrate leaching, and on the potential
for reducing fertilizer inputs as a result of mineralization of
N from cover crop residues.
Cover Crop Research and Education Summaries