Fall cover crop nitrogen uptake drives reductions in winter-spring leaching

Area of Science:

• Agricultural Science
• Environmental Science
• Soil Science

Background:

• Cover crops are implemented to reduce nitrate leaching, but their effectiveness on water quality in the Chesapeake Bay watershed is limited.
• Typical cover crop planting times in Maryland may be too late for sufficient nitrate uptake before winter drainage.

Purpose of the Study:

• To investigate the impact of cover crop planting dates on biomass production, nitrogen accumulation, and nitrate leaching.
• To compare the effectiveness of a radish-crimson clover-triticale mixture with pure rye and radish, and a no-cover control.

Main Methods:

• Compared various planting dates for a cover crop mixture over four site-years on sandy and silty soils.
• Measured cover crop biomass, N content, and deep soil porewater nitrate concentrations using tension lysimeters.
• Calculated cumulative nitrate leaching based on porewater concentrations and drainage estimates.

Main Results:

• Earlier planting dates resulted in significantly higher cover crop biomass and nitrogen accumulation.
• Mean porewater nitrate-N concentrations decreased with earlier planting, from 17.1 mg L⁻¹ (late planting) to 2.71 mg L⁻¹ (earliest planting).
• A three-species mixture performed comparably or better than monocultures of rye or radish in early planting trials.

Conclusions:

• Early cover crop planting is crucial for maximizing biomass and nitrogen uptake, thereby reducing nitrate leaching.
• Optimizing planting dates can significantly improve the efficacy of cover crops in protecting water quality from agricultural runoff.
• The findings support the hypothesis that delayed planting hinders cover crop effectiveness in mitigating nitrate loss.