Wind and Plants

WIND   Wind has a major effect on agricultural and horticultural production in NZ.   The prevailing winds are the most common winds in an area.   NZ has a westerly wind pattern due to the earth’s spin. This is changed in some areas by local features and topography.   The ranges to the north and the mountains to the sough turn the westerlies blowing towards Wellington into northerlies as they flow through Cook Strait.   Strong moist northerly winds are common in Wellington in spring, these damage blossom and new plant growth.

Wind   Wind can be measured using the Beaufort scale.

Effects of wind on plant productivity Structural damage  Lodging – flattening of cereal crops  Cuticle damage on leaves – increases water loss  Broken branches  Loss of petals on flowers  Soil displacement causing soil erosion

Physiological damage  Removal of the layer of humid air around the leaves which forms a protective environment  This causes:

Physiological damage  Removal of the layer of humid air around the leaves which forms a protective environment  This causes: High winds remove humidity Increase in transpiration Water stress Loss of productivity Guard cell close CO 2 cannot get inLess photosynthesis

  Increased erosion and removal of topsoil as dust. _ For each of the following problems, make notes on why it is not good. Wind can cause many problems including:

  Lodging of plants (when leaves become entangled), making them difficult to harvest

  Spreading weed seeds, meaning more costs of removal, or lower income due to contamination of seed crops.   Reduced or damaged plant growth. Damaged leaves do not carry out as much photosynthesis. Flowers can be damaged or blown off the plant. Wind- damaged fruit does not store as well and is less marketable. Cuticle damage to leaves causes an increase in water loss.

Upsetting insect movement. May bring salt spray or cause spray drift

Positive effects of the wind:   Reduced likelihood of frost   Providing air movement that will dry the outer leaves of a plant and therefore prevent the growth of fungal diseases   Assisting with the pollination of wind pollinated plants   Aid the drying of hay or grains before harvest.

Activity on wind page 45

Correct order  NZ is a fairly windy place  Wind is caused by  An anticyclone  Near the Earth’s  Over elevated

Activity page 46

Answers for pg 46 Defoliation – stripped of leaves Increased transpiration – leaf scorching Abrasion – sand particles Root damage – plant rocking in ground Branches rub – scarring on branches Plant distortion – plant leaning away Lodging – the flattening of cereal crops Reduction in pollination – loss of petals

Fruit loss – apple windfalls Fruit loss, knocked off tree – pears downgraded Water loss – wilting of plant Interference with insect movement – bees cannot fly Crop maturation – harvesting time later Spraying – drifts from your property to another

Lessens humidity – perfect disease free crop Reduces chance of frost – Large open areas Increase in wind pollination – grass pollen Guard cells – the stomata changes shape

Techniques to modify wind   Artificial Shelter   Artificial windbreaks are expensive to set up and are often used for high value or short term crops.   The strongest likely wind has to be considered along with the soil type to prevent the support posts blowing over.

Advantages  a crop has instant shelter  usually low maintenance  takes up little space  does not use up soil water and nutrients  Does not have many of the disadvantages of live shelter

Disadvantages   require replacing after several years due to damage from light and wind   not biodegradable creating disposal problems   expensive   Does not have many of the advantages of live shelter

Wind Break Design  1. Permeable windbreaks are more effective at reducing the force of wind than a solid barrier.  Live shelter should be triangular in vertical cross section – this shape will reduce turbulence on the leeward side and cast less shadow.  If the windbreak is impermeable, turbulence is a  possibility on the leeward side.  This is because the wind goes up and over the impermeable object.

  2. Areas with heavy snow drifts are protected by thicker shelter belts in the form of a small woodlot.   3. Distance between windbreaks should be no more than 20 times the height of the windbreak to prevent the build up of unsheltered windspeed.   Large shelter is often planted around perimeters of blocks and subdivided with artificial shelter.

  4. Planting in double rows to allow:   reduction of draughts below taller shelter.   replacement trees for older shelter belt.   5. In frost areas, where shelter is planted across valleys to prevent wind tunnelling, either deciduous shelter or gaps are used to allow cold air to drain away.

 6. Plant shelter across valleys to prevent wind tunnelling

  7. Run windbreaks north –south where possible to reduce shading

Student activities  Page

Answers to student activity 1. 14% at 8m 2. Air temp – 16% at 1m, soil evap - -40% at 3m, relative humidity – 8% at 1m, soil moisture – 20% at 1m, wind speed -60% at 4m 3. Air temp 2%, soil evap -25%, relat. Humid -0%, soil moisture 3% and wind speed -45%

4.