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elements K (2.1%) 8 90 elements are naturally occurring on planet Earth > 99% of the Earth’s crust Elemental concentrations in soil vs. earth’s crust 0.001% 0.01% 0.1% 1% 10% 100% Plant essential elements are green Light green elements are exceptionally enriched in soil relative to crust soil crust Adapted from Essington (2003) These are not the only elements found in plants! ~ 18 elements have been identified as essential for the growth of all plants Soil C OH air & water N K Ca Mg P S Cl Fe Mn Zn B Cu Mo macronutrients micronutrients 0.1% V Co Ni Needed by some plants Na Si Essential element criteria Organisms cannot complete their life cycles without EE EE are not replaceable by other elements and/or EE are proven to be necessary for specific physiological functions Essential elements are all relatively light elements 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 minerals Soil solids Where are the contain in nutrients nutrients soil ? organic matter Soil water contains nutrients H 20 K+ H 20 Ca+2 Mg+2 H20 - --Humus -- H 20 H20 exchangeable ions H 20 Clay H20 SO4 Al+3 -2 ++ H 20 -- + Ca+2 H 20 H 20 H20 soil solution H20 H20 - Na K+ H20 H20 What’s in the soil soup ?? Fe+3 DOM Ca+2 NO3- Ca+2 +2 NO3- Mg +2 H PO 2 4 Ca Cu+2 DOM - K+ K+ NO3 +2 Ca+2 Mg Zn+2 DOM Mg+2 Fe+3 NO3- DOM Ca+2 SO4-2 Adapted from Brady and Weil (2002) crop removal Amount of nutrient in the soil Re-seasoning the soup Modified from Havlin et al. (1999) Which forms of nutrients are available to plants ? “active” OM humus exchangeable weatherable minerals solution Clay mineral Fe Fe - - Fe Fe O O - P O O Inner sphere HPO4-2 anion Outer sphere Ca+2 cation Diffuse ions Adapted from Brady and Weil (2002) Inorganic nutrient forms taken up by plants Co2+ 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 Micronutrient deficiencies frequently occur when naturally acid soils are over-limed http://www.fftc.agnet.org/library/image/bc51002p7.html Avoid over-liming !! Understanding nutrient uptake H 20 Root growth N, S, P Root exudates activate soil microbes NO3- Transpirational stream H 20 Ca+2 + Diffusion K+ H2PO4- Both strategies important ! Feed the soil vs.are Feed the crop Healthy roots available inefficiently… nutrients ! Unhealthy rootsneed use nutrients Acute root disease Chronic root malfunction Small increases in OM can improve macro-aggregation Superior air/water relationships Healthier root growth and function Aluminum toxicity Aluminum toxicity Classic concept of yield response to nutrient availability …… Crop yield Micronutrients Macronutrients tend to have a tend to have narrow a broad sufficiency range sufficiency range Deficiency Symptoms Nutrient availability 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) http://www.ipm.iastate.edu/ipm/icm/2003/11-17-2003/mehlich3.gif moisture temperature microbial activity Extractable nutrient levels are not directly related to most of the factors controlling nutrient availability during a growing season. rooting depth root health http://www.extension.umn.edu/distribution/horticulture/components/M1190fig1.htm Relatively immobile nutrients Relatively mobile nutrients So what about Nitrogen? Nitrogen is an integral component of many essential plant compounds Amino acids Proteins enzymes Nucleic acids Chlorophyl 2.5 - 4% 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 too high 96% of the time 1.2 : 1 line 1 : 1 line 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 !! Well-fertilized crops often obtain more Where does the N Nfrom come from than half of their SOM ? Why more soil N? Magdoff and Weil SOM (2003) More productive soils normally supply more N from Weather often regulates crop productivity more than nutrient input rates in high productivity systems http://www.fertilizer.org/ifa/publicat/PDF/2005_ag_frankfurt_lammel_slides.pdf The on-going process of N shifting from one form to another is collectively called the N cycle Soil Plant 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 O2 is not present Denitrification NO3- NO2- NO N2O N2 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 water Justus von Liebig discovered, through the analysis of hundreds of samples of plant ash, that Law of plants contain the elements Minimumpotassium, such as sodium, 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 (1803 -1873) Slide from a recent student presentation in my upper level nutrient management class. 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.