8. theoretical applications in soil fertility soil 5813 soil-plant nutrient cycling and...

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  • 8. Theoretical Applications in Soil FertilitySOIL 5813Soil-Plant Nutrient Cycling and Environmental QualityDepartment of Plant and Soil SciencesOklahoma State UniversityStillwater, OK 74078email: wrr@mail.pss.okstate.edu Tel: (405) 744-6414

  • Liebig's law of the minimum Bray's Nutrient Mobility Concept Sufficiency (SLAN) Mitscherlich Bray modified Mitscherlich Base Cation Saturation Ratio

    Liebig's law of the minimum (Justus von Liebig 1803-1873)He stated that the nutrient present in least relative amount is the limiting nutrient. soil contained enough N to produce 50 bu/acsoil contained enough K to produce 70 bu/acsoil contained enough P to produce 60 bu/acN would be the limiting nutrient.Crop used up all of the deficient nutrient in the soil making the yield directly proportional to the amount of the deficient nutrient present and the crop content of the nutrient.Brief History

  • From Tisdale, Nelson, Beaton (1985)Justus von Liebig (1803-1873), a German chemist, very effectively deposed the humus myth. The presentation of his paper at a prominent scientific meeting jarred the conservative thinkers of the day to such an extent that only a few scientists since that time have dared to suggest that the carbon contained in plants comes from any source other than carbon dioxide. Liebig made the following statements: 1 .Most of the carbon in plants comes from the carbon dioxide of the atmosphere. 2. Hydrogen and oxygen come from water. 3. The alkaline metals are needed for the neutralization of acids formed by plants as a result of their metabolic activities. 4. Phosphates are necessary for seed formation. 5. Plants absorb everything indiscriminately from the soil but excrete from their roots those materials that are nonessential. Not all of Liebig's ideas, of course, were correct. He thought that acetic acid was excreted by the roots. He also believed that the NH4+ form of nitrogen was the one absorbed and that plants might obtain this compound from soil, manure, or air. Liebig firmly believed that by analyzing the plant and studying the elements it contained, one could formulate a set of fertilizer recommendations based on these analyses. It was also his opinion that the growth of plants was proportional to the amount of mineral substances available in the fertilizer. The law of the minimum stated by Liebig in 1862 is a simple but logical guide for predicting crop response to fertilization. This law states that every field contains a maximum of one or more and a minimum of one or more nutrients. With this minimum, be it lime, potash, nitrogen, phosphoric acid, magnesia or any other nutrient, the yields stand in direct relation. It is the factor that governs and controls ... yields. Should this minimum be lime... yield ... will remain the same and be no greater even though the amount of potash, silica, phosphoric acid, etc.... be increased a hundred fold. Liebig's law of the minimum dominated the thinking of agricultural workers for a long time thereafter and it has been of universal importance in soil fertility management. Liebig manufactured a fertilizer based on his ideas of plant nutrition. The formulation of the mixture was perfectly sound, but he made the mistake of fusing the phosphate and potash salts with lime. As a result, the fertilizer was a complete failure. Nonetheless, the contributions that Liebig made to the advancement of agriculture were monumental, and he is perhaps quite rightly recognized as the father of agricultural chemistry. Following on the heels of Liebig's now famous paper was the establishment in 1843 of an agricultural experiment station at Rothamsted, England. The founders of this institution were J. B. Lawes and J. H. Gilbert.

  • Sufficiency: SLAN (Sufficiency Levels of Available Nutrients)Range of nutrient (insufficient to sufficient)Amount extracted from the soil is inversely proportional to yield increases from added nutrients.Calibrations exist for the changing levels of available nutrients with fertilizer additions and yield response.Concept assumes little if any effect of the level of availability of one ion on that of another.Recognizes that an addition of the most limiting element may cause more efficient utilization of a less limiting element.

  • Mathematical expression of the law of diminishing returns where increases in yield of a crop per unit of available nutrient decreases as the level of available nutrient approaches sufficiency.The concept is based on Mitscherlich's equation:dy/dx = (A-y)cYield increases (dy) per unit of available nutrient (dx) decrease as the current yield (y) approaches a maximum yield (A) with c being a proportionality constant.The derivative was developed for studying tangent lines and rate of change. The first derivative is the slope of the tangent line at xod/dx xn = nxn-1Quadratic: Y = bo + b1x - b2x20 = b1-2b2x2b2x = b1x=b1/-2b2xyY = bo - b1x + b2x2

  • Plant Response to Soil Fertility as Described by the Percent Sufficiency and the Mobility ConceptPlants respond to the total amount of mobile nutrients presentPlants respond to the concentration of immobile nutrients presentYield is proportional to the total amount of mobile nutrient present in the soil. Yield response to immobile nutrients is not related to the total amount of the available form present in the soil, but instead is a function of the concentration of available form at, or very near, the root surface. Response of crops to mobile nutrients should be linear because mobile nutrients (like water) are not decreased in availability by reaction with the soil. The linear response to mobile nutrients continues with each added increment of nutrient until yield potential for that growing environment has been reached, after which it is zero (see figure below)

  • Reaction of mobile nutrients with soil is minimal. rules of thumb have been developed to guide the use of mobile nutrients like nitrogen, such as it takes 2 lbs N/bushel of wheat. 2 lbs is calculated from the protein or N content (on average) of a bushel of wheat, with the added assumption that measured soil nitrate-N and added fertilizer N will be only 70% utilized. 13.28% protein / 5.7 = 2.33%N * 60 lbs/bu = 1.4 lb N/bu 1.4/0.70 = 2.0 lb N/buBrays mobility concept: If available N is limited to level below maximum yield potential then a yield plateau will occur at that point. Exampleenough N to produce 20 bumidway through the season better than average weather conditions result in increasing the yield potential to 30 bumobility concept implies the yield will be limited to 20 bu. because the total supply of nutrient will be used up to produce 20 buadditional yield can only be obtained if more of the nutrient is added (reason for topdressing wheat midway through the season).In-SEASON use of the mobility CONCEPT (sensors-NDVI?)

  • For immobile nutrients, like P, plants can only extract the nutrient from soil close to the root surfaceVery little of the nutrient is moved to the root by water in the transpiration stream because soil solution concentrations are small (< 0.05 ppm for phosphate compared to as high as 100 ppm for nitrate-N). As a plant grows and roots extend out into the soil, roots come in contact with new soil from which they can extract phosphate. The amount extracted is limited by the concentration at (or very near) the root-soil interface. If the concentration of phosphate available to the plant at the root -soil interface is inadequate to meet the needs of the plant, then the plant will be deficient in P throughout its development. contact exchange mass flow diffusionThe deficiency will always be present, and plant growth and crop yield will be limited by the degree to which the immobile nutrient is deficient. Another, perhaps more common way of expressing this nutrient limitation is to state that yield will be obtained according to the sufficiency of the nutrient supply

  • Nutrient Mobility Concept

  • Brays Mobility Concept ? Perkins, Feekes 4, 1997

  • When the nutrient limitation is expressed as a percentage of the potential yield then the term percent sufficiency may be applied. When percent sufficiency
  • MobileImmobileConceptyield goalsufficiencyEnvironmentdependentindependentSorption Zoneroot systemroot surfaceInfluence of crop uptake on total availablelargesmallSoil test is an indicator of the total availableyesnoSoil solution concentrations0-100 ug/g
  • Example:Wheat (4081 kg/ha = 60 bu/ac)2.5%N in the grain =102.03 kg N(4081 kg/ha = 60 bu/ac)0.36%P in the grain =14.69 kg PSoil 0.1% N*10000=1000 ug/g * 1.47 * 1.524 = 2240 kg N/ha 0-15 cmNO3-N: 10 ug/g * 1.47 * 1.524 = 22.40 kg NO3-N/ha 0-15 cmNO3-N soil test is the actual N available at time XNO3-N soil test is valid for one point in time (1 crop or year)Some states predict N mineralization0.1% P*10000=1000 ug/g * 1.47 * 1.524 = 2240 kg P/ha 0-15 cmP soil test is an index (sufficiency) of availabilityP soil test is valid for up to 5 years or more**10 ug/g P, Mehlich III is not equal to 22.40 kg P/haWe cannot predict P mineralization(102.03/2240)*100 = 4.5%(14.69/2240)*100 = 0.65%

  • Steps for Using the Sufficiency Concept:1. Selection or determination of the sufficiency levela. estimated from results of studies with a crop on similar soils2. Computation of fertilizer required for sufficiencya. amount of soluble P required to raise the available P from the initial level to the sufficiency level.3. Method of supplying the fertilizers (and/or lime)a. soil build-up plus crop needs (BUILD-UP) long-termb. crop needs (MAINTENANCE) short-term

  • Mitscherlich-Baule percent sufficiency concept:When more than one nutrient was deficient, the final percent sufficiency is the product of the individual sufficiencies._____________________________________________________


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