Effects of Sustainable Intensification Practices on Herbicide Stewardship in Dairy Cropping Systems

Commodities

• Agronomic: corn
• Animal Products: dairy

Practices

• Crop Production: double cropping
• Pest Management: chemical control, integrated pest management

Many Pennsylvania dairy farmers have adopted double cropping
annual forages as a sustainable intensification practice. This
system has potential soil health and environmental benefits, but
effects on weed management have not been studied. Studies suggest
that repeated use of atrazine, an important corn herbicide, can
result in enhanced microbial degradation. This would decrease the
potential weed control benefits of using atrazine, although it
may also reduce the environmental risks of atrazine run-off and
non-target effects. In this project, we will test how different
crop management practices affect atrazine persistence in soils
from dairy cropping systems. We will also quantify microbial
activity in these soils to determine the extent to which this
effect is microbially mediated. We hope to identify if these
sustainable intensification practices are reducing the
persistence of an important corn herbicide, and which in-season
manure management practices influence persistence. We propose to
conduct soil sampling on dairy farms in Pennsylvania and use
laboratory assays to assess atrazine persistence. Results will be
shared with farmers, Extension agents, and researchers through
presentations and publications to inform herbicide stewardship in
these systems.

Our overall objective is to understand how crop management legacy
and in-season management practices affect the persistence, and
thus efficacy, of atrazine in fields with atrazine history.

Specifically, we will:

Objective 1: Quantify the effects of crop management
legacy on soil persistence of atrazine in fields with atrazine
history.

Hypothesis 1: Soils from annual double cropping
(ryelage/corn silage) systems will have lower degradation rates
of atrazine compared to soils from a corn-soy rotation with no
cover crops. We expect carbon inputs within annual double
cropping systems that result from additional manure inputs and
continuous living cover will provide an alternative food source
for microorganisms, reducing their degradation of atrazine.

Objective 2: Test how in-season management practices of
different manure sources affect atrazine degradation in soils
from different crop management histories.

Hypothesis 2a: Addition of manure prior to the
application of atrazine will reduce atrazine degradation rates in
both management legacies but will reduce atrazine degradation
rates more in the corn/soy rotation. We expect reduced
degradation in both types of soils because microbes will use
manure as a nitrogen source over atrazine. The effect size will
be bigger in corn-soy rotation soils with lower soil organic
matter.

Hypothesis 2b: Addition of digestate before atrazine
application will reduce atrazine degradation rate compared to no
manure addition, but increase it compared to adding regular
manure because of a larger microbial population.

Objective 3: Determine the relationship between atrazine
degradation rate in different treatments and microbial activity
and diversity.

Hypothesis 3: Microbial activity and diversity will be
higher in the annual double cropping treatments, and manure
addition will further increase microbial activity. In response to
atrazine application, there will be a larger increase in
microbial activity in the corn-soy plots than in the annual
double cropping treatments.