90 elements are naturally occurring on planet Earth Al (8.3%) Fe (5.6%) Ca (4.2%) Na (2.4%) Mg (2.3%) K (2.1%) 8 elements > 99% of the Earth’s crust

100%1%0.1%0.01%10%0.001% Elemental concentrations in soil vs. earth’s crust soil crust Adapted from Essington (2003) Plant essential elements are green Light green elements are exceptionally enriched in soil relative to crust

N K Ca Mg P S macronutrients micronutrients air & water Soil ~ 18 elements have been identified as essential for the growth of all plants C O H Cl Fe Mn Zn B Cu Mo Na Co Si VNi Needed by some plants 0.1% These are not the only elements found in plants!

Essential element criteria Organisms cannot complete their life cycles without EE EE are not replaceable by other elements EE are proven to be necessary for specific physiological functions Essential elements are all relatively light elements and/or

Some elements (e.g. Se, I, As, Cr) have been identified as essential for animals but not for plants. Boron is the only element that has been identified as essential for plants but not for animals

Micronutrients are important components of enzymes What is an enzyme? Enzymes are biomolecules that lower the activation energy required for biochemical reactions

Soil solids contain nutrients minerals organic matter Where are the nutrients in soil ?

exchangeable ions soil solution Humus Clay Na + Ca +2 Al +3 K+K+ Ca +2 Mg +2 K+K+ H20H20 H20H20 H20H20 H20H20 H20H20 H20H20 H20H20 H20H20 H20H20 H20H20 H20H20 H20H20 H20H20 H20H20 H20H20 Soil water contains nutrients + SO

What’s in the soil soup ?? Adapted from Brady and Weil (2002) Ca +2 NO 3 - Ca +2 K+K+ K+K+ Mg +2 Ca +2 Mg +2 Ca +2 Mg +2 Ca +2 NO 3 - SO 4 -2 NO 3 - H 2 PO 4 - DOM Fe +3 Cu +2 Fe +3 Zn +2

Re-seasoning the soup Modified from Havlin et al. (1999) Poorly buffered Highly buffered Highly buffered soils have a large reserve of nutrients that can resupply the soil water Amount of nutrient in the soil crop removal

Which forms of nutrients are available to plants ? solution exchangeable “active” OM humus weatherable minerals inner sphere

Outer sphere Ca +2 cation Inner sphere HPO 4 -2 anion Diffuse ions Adapted from Brady and Weil (2002) Fe --- O O O O P Clay mineral

Co 2+ Inorganic nutrient forms taken up by plants

Plants take up mostly inorganic forms of nutrients when inorganic forms of nutrients are readily available In some natural ecosystems (e.g., tundra), organic forms of nutrients are very important

Nutrient availability varies with pH

Avoid over-liming !! Micronutrient deficiencies frequently occur when naturally acid soils are over-limed

Understanding nutrient uptake Transpirational stream H20H20 H20H20 Root exudates activate soil microbes Root growth N, S, P + Diffusion NO 3 - Ca +2 K+K+ H 2 PO 4 -

Acute root disease Feed the soil vs. Feed the crop Both strategies are important ! Healthy roots need available nutrients ! Unhealthy roots use nutrients inefficiently… Chronic root malfunction

Small increases in OM can improve macro-aggregation Superior air/water relationships Healthier root growth and function

Aluminum toxicity

…… Nutrient availability Crop yield Deficiency Symptoms Classic concept of yield response to nutrient availability Macronutrients tend to have a broad sufficiency range Micronutrients tend to have a narrow sufficiency range How can we assess the availability of nutrients in soil?

Goals of routine soil testing Rapid Cheap Predictive Widely applicable Very different from research analysis of soil

By themselves, extractable nutrient levels are not informative. Extractable nutrient levels provide an index of nutrient availability that can be interpreted using results from field experiments.

Illinois Agronomy Handbook

Crop response to soil test P in IL Critical level for corn and soybeans

Build and maintenance approach

On average, 9 lbs of fertilizer P2O5 are needed to raise soil test P levels by 1 lb/acre On average, 4 lbs of fertilizer K2O are needed to raise soil test K levels by 1 lb/acre

Meaningful interpretation of soil test results requires field calibration 100 % yield 50 % yield Soil test P concentration (ppm)

Extractable nutrient levels are not directly related to most of the factors controlling nutrient availability during a growing season. moisture temperature microbial activity rooting depth root health

Relatively mobile nutrients Relatively immobile nutrients

So what about Nitrogen? Nitrogen is an integral component of many essential plant compounds Amino acids Proteins Nucleic acids Chlorophyl enzymes % of plant dry matter

Relationship between optimal N rate and optimal corn yield in IL (72 site years) Only 13 out of 72 site-years in IL required more than 1 lb of N per bushel 1 : 1 line 1.2 : 1 line too high 96% of the time too high 82% of the time BOTTOM LINE There is no line that fits this data well Yield is a poor predictor of optimal N rate !!

Where does the N come from ? Magdoff and Weil (2003) Well-fertilized crops often obtain more than half of their N from SOM Why more soil N? More productive soils normally supply more N from SOM

Weather often regulates crop productivity more than nutrient input rates in high productivity systems

The on-going process of N shifting from one form to another is collectively called the N cycle Plant biomass Plant uptake Soil Microbial biomass

Why is nitrate such a slippery character ? Nitrate is an anion Nitrate compounds are very soluble Nitrate is next in line as an electron acceptor when O 2 is not present

NO 3 - NO 2 - NO N 2 O N 2 Denitrification Warm, anaerobic conditions + OM promote rapid denitrification

GreenSeeker Technology

Some day soon soil testing may consist of on-the-fly “sensing” of soil hundreds to thousands of times per acre like a yield monitor

Justus von Liebig discovered, through the analysis of hundreds of samples of plant ash, that plants contain elements such as sodium, potassium, calcium, and phosphorus. He concluded that the minerals contained in plants must come from the soil and that without fertilization, the mineral content of soils could become exhausted, rendering the land unproductive for agricultural purposes. Justus von Liebig ( ) Law of the Minimum water

 Soil sampling is the only manual step left in the process. With the implementation of robotic samplers, the number of samples will increase and the cost per sample will decline, thereby enhancing the economic return and the advancement of soil testing knowledge.  The are at least a dozen primary factors which impact crop yield potential. A study a number of years ago ranked soil fertility as #9!  Development of new technologies will eventually lead to new knowledge systems for managing crop production. Slide from a recent student presentation in my upper level nutrient management class.