Crop rotation, cover crops and ecological weed management

Assist.Prof.Dr. Boonthida Kositsup

Department of BotanyFaculty of Science

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Definition of a weed• A weed is an undesired

plant out of place– Water hyacinth in a

aquatic garden: not a

weed– Water hyacinth clogging

canals: a weed

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What is a Weed?

• A plant that is growing where it is not wanted Roberts et al. 1982. Weed Control Handbook

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What is a Weed?

• A plant that is successful in colonizing disturb, and maintaining their abundance under conditions of repeated disturbances

MohlerC., 2001. Ecological Management of Agricultural Weeds

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Disturbance

• An event that disrupts ecosystem, community or population structure

• Changes resources, substrate availability or the physical environment

Pickett and White, 1985

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Why Do We Have Weeds?

BECAUSE WE CREATE THE ENVIROMENTS WHERE WEEDS THRIVE (go, develop or be successful)!

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What management practices contribute to weed problems?

• Poor soil management• Excessive use of manure• Poor crop rotations using crops with similar

seasonal growth patterns which have similar weed species associated with them.

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Weed Management

• GoalManage cropping systems (not just weeds!) so that the resources made available through disturbances are captured by crop and not by weeds

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What are some conventional treatments used to control weeds?

• Physical removal– The use of agricultural tools such as hoe to

physically remove weeds

• Chemical suppression– Herbicide application is not favored in ecological

farming

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What are some basic principles for ecological weed control?

• Create a diverse ecosystem. Use as many species and types of plants as possible

• Use a good crop rotation• Don’t over fertilize your soil with manure or

fertilizers as this will leave too much fertility on the soil for weeds

• Use clean seed (free of weeds)

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Crop Rotation

“Rotation of crops, when accompanied by care in the use of pure seed, is the most effective means yet devised for keeping land free of weeds.”

Leighty (1938)

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Crop rotation

• is the practice of growing a series of dissimilar types of crops in the same area in sequential seasons.

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Crop rotation: two considerations

1.Vary the seasonality of plantingVarying crop seasonality and management practices

prevent any one species from getting out of control

2.Vary crops allow you to vary management practices

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How does crop rotation help control weeds?

• Breaks weed multiplication cycles, as certain weeds are associated with certain crops.

• Maintain soils fertility which helps crop growth.

• Crops that have different season growth patterns compete for weed space on the field, as weeds have different growth cycles.

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Cover crops

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are crops whose main purpose is to benefit the soil, to manage soil fertility, but is not intended to be harvested for feed or sale.

What is a cover crop?

A crop whose main purpose is to benefit the soil or other crops in one or more ways, but is not intended to be harvested for feed or sale.

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Cover crops

• Plants that are grown for various ecological benefits other than as a cash crop (a crop that is grown mainly to be sold).

• They may be grown in rotations during periods when cash crops (main crops) are not grown.

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Advantages of cover crops

• Cover crops can also improve soil quality by increasing soil organic matter. Increased soil organic matter enhances soil structure, as well as the water and nutrient holding of soil.

• Weed suppression

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