Climate & Agriculture

Agricultural has evolved into a highly technical field.Dramatic changes occurred in the 20th century: genetics, improved fertilizers, increased

disease resistance, and the substantial input of energy into farming methods has dramatically increased on productivity. However

The prevailing climate of a region still places distinct limitations on what crops can be grown and, in part, determining the hazards to which the crops are exposed.

Example: bananas will not grow in Wisconsin; Deciduous fruit trees will not fruit in tropics; Climate has impact on quality (protein content) of wheat. Highest protein content wheat is in wheat belts of North America and black-steppe area of the former U.S.S. R. (mid-lat grassland biomes of the world); But hazards for wheat are still problems: hailstones. Example: a single storm in Nebraska destroyed 3 million bushels of standing wheat.

Energy input: sunlight, fuel for tractors, food for the farm workersMonoculture:Pro: maximize the benefits of this energy supplant and obtain highest yield for all input.Con: it contrasts to climax ecosystem, where diversity is a key to the maintenance of the

systemExample: Boll Weevil problem in the cotton belt of southern USPotato famine of Ireland and Europe, 1840s (potato blight led to 2 million death).

Due to the weather-related risks in agricultural practices, some adaptations have been made to ease the vulnerability:

1. Risk spreading though insurance schemes and cooperative farming schemes

2. Environmental manipulation (irrigation and fertilization)

3. Managed diversification (crop rotation and dual-purpose livestock)

4. Modified farming system (modified crop calendar and improved storage)

Relocation of plants based on climate conditions

Banana is native to SE Asia, now spread into tropical America

Potato originated in America, now in EuropeSugar cane from SE Asia, now in tropical AmericaRubber trees from equatorial rainforest in Amazon basin,

now are in plantations in SE Asia.Relocation results in better yields:1. Native place, they are integral part of the environment,

thus susceptible to pests and the competition of other plants of that origin. Through transportation natural limiting factors are removed

2. Due to purpose of production, they are treated with special care and afforded much attention.

Extending climate limits

1. Frost protectionRadiation frost occursat local area; Advectionfrost is caused by cold airflowing into region and covers

a wider areas (cP air from North)

a. Plant way from cold valley (above inversion)

b. Heater to mix air c. Sprinkling and flooding

to increase thermal conductivity, reduce excessive cooling, supply latent heat

d. Brushing: cover up plants to reduce nighttime radiation loss

2. irrigation: water required by a plant to function at its maximum capacity (PE) design irrigation system using water budget.

Three areas need augmentation of precipitation:a. Perpetual drought (desert)b. Seasonally water deficitc. Periodic drought

Thornthwaite and Mather’s Water Budget Calculation

Rules:1. When P is larger than PE, excess water will go to

recharge soil moisture until it reaches the field capacity, then leftover will be runoff

2. When PE is larger than P, plants draw moisture from soil and the soil storage falls below capacity

3. Actual evapotranspiration (AE): If P>PE, AE=PEIf P<PE, AE=P+ absolute value of storage change4. Deficit occurs when AE<PE5. After deficit period, (when P becomes >PE), excessive

water will recharge soil to capacity before surplus (or runoff) occurs

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

T (°C) 0.5 0.7 5.5 11.3 17.1 21.8 24.2 23.4 20.0 13.8 7.5 1.7

PE 0 0 15 43 89 128 150 135 94 52 20 2

P (mm) 87 80 96 91 92 98 119 128 93 78 82 86

P-PE 87 80 81 48 3 -30 -31 -7 -1 26 62 84

Storage 150 150 150 150 150 122 99 94 93 119 150 150

Storage change

0 0 0 0 0 -28 -23 -5 -1 26 31 0

AE

Surplus

0

87

0

80

15

81

43

48

89

3

126

0

142

0

133

0

94

0

52

0

20

31

2

84

Deficit 0 0 0 0 0 2 8 2 0 0 0 0

Climatic water budget for Wilmington, DE (using handout soil moisture table)

Climate and Crop Yield: light, heat and moisture condition are the most important factors

Light(1)Photosynthesis: carbon+water+solar energy=hexose

sugar+oxygen (sun light determine the rate of photosynthsis)

(2) Photoperiodism: plants response to the length of the daylight hours

Long-day plants: flower only when daylight is greater than 14hours

Short-day plants: flower only when daylight is less than 14hours

Day-neutral plants: bud under any period of illuminationIntermediate plants: flower with 12 to 14 hours of daylight

but not outside these limits

(2) TemperatureTropical plants: 20-30C(68-86F)Mid-latitude plants: 15 to 20C (59-68F)Growing degree days (GDD): degrees accumulated above

a certain baseline (depending on plants)Sunflower and potatoes: 45F; corn and soybeans 50F;Agriclimatology