Water and Plant Growth

1. Water and Plant Growth • All water used for irrigation contains some dissolved materials. Some water has none dissolved materials • Salt has the biggest effect. • Weed seeds

2. As a user • One should know the effects that your water quality & irrigation practices used have on: • Salt content (salinity) of the soil. • Sodium status (sodicity) of the soil. • Rate of water infiltration. • Toxic elements content of the soil. • Soil nutrient status and groundwater quality. • Plugging of micro irrigation system.

3. Irrigation • We irrigate to replenish the water that is lost due to: • Evaporation. • Used by growing plants. • Transpiration. • Drainage passed the root zone.

4. Irrigation method used. • Application method depends on: • Type of crop being grown. • Soil texture & depth. • Water cost. • Topography. • Water cost. • Water quality.

5. Irrigation Frequency • Once again, one must consider several factors. • Type of crop being grown. • Soils water holding capacity. • Leaching requirements. • Climatic considerations. To assist you, you can go to this web site. www.cimis.water.ca.gov

6. How does water enter the soil? • through pores in the soil • sandy soils have the largest pores, but are often filled with other material • medium textured soils (loamy) have good water entry properties • clays, pores swell shut when they get wet

7. What is Adhesion? • it is the attraction of two different molecules (water to soil)

8. What is Cohesion? • it is the attraction of two similar molecules (water to water)

9. What is the importance of adhesion and cohesion in soils? • water molecules are strongly attracted to soil minerals and organic materials due to adhesion • water molecules are also strongly attracted to each other due to cohesion • soil holds a thin layer of water, that layer holds a thin layer of water etc., the farther away from the soil particle you get, the looser the water is held

10. What is the importance of adhesion and cohesion in soils? • -water then tends to move from wetter places to drier places. Roots remove water, then water is drawn from surrounding areas • in dry conditions, water moves slowly and only fractions of an inch, thus roots must be well distributed

11. How is soil water classified? 1) Hygroscopic Water is held so strongly by the soil particles (adhesion), that it is not available to the plants 2) Capillary Water is held by cohesive forces greater than gravity and is available to plants 3) Gravitational Water is that water which cannot be held against gravity • as water is pulled down through the soil, nutrients are"leached" out of the soil (nitrogen)

12. Saturation Percentage • Immediately following an irrigation, the film of water is thick, and smaller pores are full of water. The soil particles can not hold the water. It is easily lost to the plant. • 1/10 Atmosphere (Near Saturation)

13. What is Field Capacity? • when the soil contains the maximum amount of available water, the greatest amount of water it can hold against gravity. • 1/3 Atmosphere • ½ saturation %

14. What is Permanent Wilting Point? • the soil has so little water, that plants can no longer recover from wilting. • roots can no longer take in water. • 15 Atmospheres. • ¼ Saturation %

15. What is Available Water? • the amount of water between field capacity and wilting point

16. What is Water Table? • the level beneath the soil which the soil is saturated with water • marshes develop where the water table is just below the ground surface • if the water table is not too low, dryness tends to correct itself through capillary movement

17. What affect does soil particle size have on its water holding ability? • the smaller the individual particles are, the more surface area there is, thus it will hold more water • consider a book compared to all of its pages

18. What factors determine the amount of soil moisture? • amount of snow, rain, irrigation • rate which soil permits water entry • water storage capacity of soil • evaporation rate • height of water table • rate which water can move within the soil • amount and type of vegetation

19. How is soil moisture measured? • soil is weighed dry, then wet (expressed as a percent of dry wt) • electrical conductivity

20. When to irrigate • 1. Tensiometer – measures in atmosphere • 2. Electrical Resistance Blocks (gypsum blocks) electrical resistance • 3. Neutron probe – neutrons collide with hydrogen atoms soil (water in soil) • 4. Thermal dissipation sensor – measures dissipation of heat • 5. Time domain reflector – high speed microwave pulse

21. How can we increase the amount of available water to the plant? • Precipitation: better utilize snow and rain by keeping the water on the soil surface. • windbreaks • keep snow in place (cover) • strip cropping • contour strips • grassland farming • Irrigation: may not be practical • Water entry: reduce cultivation, green manures, correct alkaline soils

22. How can we increase the amount of available water to the plant? • Storage capacity: increase O.M. (manures) • -Evaporation: conservation tillage, shelter belts, strip cropping • -Water movement in soil: O.M. • -Vegetative covering: holds water

23. Water Analysis Terminology • Dissolved salts = ions • Cations = positively charged ions • Anions = negatively charged ions • pH = expresses the acidity or alkalinity • Total Salt Content = electrical conductivity (EC) also reported as decisiemens per meter (dS/m)1 • Total Dissolved solids (TDS) = total salt content

24. Water Analysis Terminology • Parts per million (ppm) = 1 part of salt to 1 million parts of water. • Milliequivalents per liter (meq/L) = is a meacurement of charge concentration per liter. • Most meaningful method of reporting chemical components of water. It takes the atomic weights divided by the valence.

25. Cations – determine the physical as well as chemical properties of soil. • Calcium Ca++ • Magnesium Mg++ • Sodium Na+ • Potassium K+

26. Anions – indirectly affect the physical properties of soil by altering the ratio of Ca and Na attached to the clays. • Bicarbonate HCO3- • Carbonate CO3= • Chloride Cl- • Sulfate SO4= • Nitrate NO3- • Boron B

27. Evaluating Irrigation Water • Saline soil – contains soluble salts in such quantities that they interfere with plant growth. • Sodic Soil – contains enough sodium adsorded on a clay particle to interfere with plant growth.

28. Evaluating Irrigation Water • Salinity hazard – irrigating can lead to a build up of soluble salts in the root zone. • Sodium or permeability hazards – results in reduced rates of water penetration. • Applying gypsum, reduce pH & bicarbonate of water by adding sulfuric acid, and incorporating sulfur into problem soil if adequate free lime is present.

29. Toxic Constituents • Boron Hazard • Chloride Hazard • Sodium Toxicity

30. Salt movement in soil.

31. Salt movement in soil.

32. What do we do with our tail water? What is the problem with tail water? Drainage

33. Water for sprinkler Benefits : • Less loss of water. • Deep percolation of water may be less. • Problems: • Not for every crop. • More loss of water.

34. Water for low volume Benefits : • Tail water runoff can be completely eliminated. • Evaporation may be reduced. • Total volume of soil wetted is usually less • Deep percolation of water may be less • Problems: • Plugging caused by insoluble calcium carbonate, algal growth, suspended solids, & reactions to injected fertilizers.