Lecture 13a Soil Fertility – N-P-K. The study of supplying plant nutrients from the soil. Understanding CEC is the single most important concept in understanding soil fertility. (However soil pH is the most important chemical property)
Reed Palm – N Def on left
Wheat with N response
U.S. Geological Survey, 1993; 26-38.
Randall et al., 1997
Phosphorus is low in total amount in the soil and low in solubility and is readily fixed by Fe and Al at low pH and Ca at high pH.
H2PO4- and HPO4-- forms taken up by plants
P Fertilizer is made from rock phosphate
Rock phosphate mines are in Florida & South Carolina
P deficient tomato
P deficiency reduces root growth
Solid P Phase Solution Phase Root Hair
K deficient corn
> 160 ppm = very high
K deficient soybeans
Magnesium deficiency on corn
Boron - B
Zinc - Zn
Copper - Cu
Molybdenum - Mo
Chlorine – Cl
Manganese - Mn
Reasons why use of micronutrients has increased in recent years:
Increased knowledge of their role in plant nutrition, deficiency symptoms in plants, and behavior in soil.
Higher crop yields which have increased micronutrient needs.
Improved analytical methods, resulting in more soil tests and improved fertilizer recommendations.
Improved sources of micronutrient fertilizers and methods of incorporation into other fertilizers.
Land-shaping practices, such as terracing or land leveling for irrigation, which remove topsoil containing organic matter, often associated with most of the available micronutrient supply.
(Reference: The Fertilizer Handbook / The Fertilizer Institute - pp 91-92)Micronutrients
grape leaf symptoms of boron deficiency; right: boron toxicity)
Fe Deficiency on rhododendron,
Fe deficiency on pin oak
Jubilees (oxygen-deficient waters) occur in coastal areas around the world, as a result of excessive nutrients (particularly nitrogen) flowing from rivers into oceans.
Greenhouse – a controlled environment with soil homogeneity.
Legume intercropped with maize in Wenchi, Ghana, Africa