Cover Crops

Introduction

• Definitions:– Cover crop – a crop planted between main crops

to prevent erosion or to be plowed in to enrich the soil

– Green Manure – a growing crop that is plowed in to enrich the soil

• The backbone of a sustainable crop system

Legumes

• Able to “fix” nitrogen• Nitrogen in atmosphere unavailable for plant

use• Bacteria in nodules converts inert nitrogen to

nitrates• Extra nitrogen fertilizer is not required• Examples: peas, beans, alfalfa & clovers

The Industrial Model

• Crop planted in spring• Pesticides used to control insects and weeds• Crop harvested in fall• Land left fallow in winter• Land fertilized in late winter• Land sprayed with herbicides in early spring• Crop planted in spring

Benefits of Cover Crops

• Prevent Erosion• Improve soil quality• Suppress weeds• Reduce insects• Prevent nutrient leaching

Prevent Erosion

• Roots hold topsoil in place• Water & wind strip topsoil from land• Sediment clogs waterways– Major water pollution problem

• Tillage exposes soil to erosion– Use No-till techniques

Improve Soil quality

• Root depth– Deep rooted crops break through compacted

subsoils – biological plow

• Soil aggregates– Decomposed organic material (humus) binds

mineral portion of soil in stable aggregates

Soil quality

• Soil Organic Matter– Replaces organic materials lost in cultivation

• Soil Fertility– Roots of legumes returns fixed nitrogen to the soil

Suppress Weeds

• Cover crops shade soil– Blocks sun to low-growing weeds– Reduces weed seed germination

• Residue left after harvest acts as mulch– Prevents weed seed contact with soil

• Allelopathy – some plant roots secrete natural toxins that slow the growth of competitor plants– Small grains like ryegrass & sorghum

Reduce Insect Problems

• Provides habitat for diverse insect populations• Increases the population of “predator” bugs

Prevent nutrient leaching

• Stops phosphorus pollution from sediment• Absorbs excess nitrogen from fertilized crops

and returns it in more stable form

Cover crop models• Winter cover crop

• Summer green manure crop

• Living mulch

• Catch Crop

• Forage Crop

Cover Crop Model

• Winter cover crop– Planted in fall – prevents erosion over the winter– Legumes increase soil nitrogen for next summer’s

crop• Summer green manure crop– Plant in late winter - early spring and plow under – Increases soil organic matter– Legumes add nitrogen– Non-legumes smother weeds

Others

• Living mulch– Plant vegetables into clover beds– Strips of grasses in alley ways between perennial

crops

• Catch crop– Plant rye after corn to collect excess nitrogen

• Forage crop– Cover crop grown for grazing

Killing cover crops

• Need to kill the cover crop before you can plant the main crop– Pesticide• Glyphosate (Round-up) kills all plant material

– Mowing• Mowing at proper stage prevents regrowth

– Crimping• Stalks are bent down and cracked

– Winter kills• Annual cover crops are killed by frost

Buckwheat

• Legume• Roots very fibrous but not deep• Adds nitrogen to the soil• Plant in spring or fall• Used to fight weeds

Clovers• Legumes• Live about 2 years• Plant in spring or fall• Kill & turn under 4 weeks before planting

crop• Used to– Add nitrogen– Build soil– Resist erosion– Fight weeds

Cowpeas, soybeans or field peas

• Legumes• Annual• Used to:– control erosion– Build soil nitrogen

Sorghum/Sudan grass

• Very vigorous root growth

• Used to:– Build soil– Loosen subsoil– Fight pests

Winter rye, wheat or oats

• Winter rye & wheat – grow during the winter• Oats and regular wheat grow in spring and fall• Annuals (die every year)• Extensive root system• Grow rapidly in proper season• Build soil, fight weeds and pests

Root boxes

• Plant your cover crop• Measure weekly:– Vegetative height– Root depth

Wrap - up

• What difference do you expect in the soil nitrogen levels after the crop is turned under?

• What do you expect to change when we test the soil again in June?

• Which plant root structures will penetrate the deepest in the boxes?

• How can you protect your garden soil from erosion?