soil fertility. fertility and forest soil n forest managers generally take a passive rather than an...

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  • Soil Fertility

  • Fertility and Forest SoilForest managers generally take a passive rather than an active approach to managing forest soil fertilityIn other words, unlike agriculture, forest managers do not generally amend (ie fertilize) forest landsThis does not mean that soil fertility is not of great importance however

  • Fertility and Forest SoilFor most forestry operations the management of soil fertility involves:recognizing the differences between sites in terms of fertility, and especially nutrient holding capacitymaintaining fertility through the use of appropriate forest harvesting and silvicultural treatments

  • Fertility and Forest SoilIn intensive forest management operations the management of soil fertility may involves:creating optimal growing media for the production of greenhouse container stockmeasuring and amending the fertility of forest sites for uses such as bareroot nurseries, and seed orchardsdesigning specific treatments to enhance fertility (ie peatland drainage)

  • Soil Macro and Micro Nutrients

    Soils require various elements in order to conduct the processes of food manufacturing (photosynthesis), growth and differentiation of cells, cellular respirationMacro-Nutrients are the elements that are required in the greatest amount by plantsMicro-Nutrients are essential but are required in smaller amounts

  • Macro Nutrients MACRO NUTRIENTS (primary) OFTEN LIMITING FOR PLANT GROWTHNitrogen (N)Phosphorous (P)Potassium (K)MACRO NUTRIENTS (secondary) USUALLY NOT LIMITING FOR PLANT GROWTHCalciumMagnesium (Mg)Sulfur

  • Micro-NutrientsMicro-Nutrients occasionally limiting for forest growthCopper, Iron, Manganese, Boron, Zinc

    Micro-Nutrients with no reported deficiencies for forest growthChlorine, Cobalt, Silicon, Sodium, Vanadium

  • Roles of Macro-NutrientsNitrogenbuilding proteinscritical to photosynthesispromotes lush vegetative growthAvailable to the plants in cation form as NH4+ or as an anion as NO3-Nitrogen FertilizersAmmonium Nitrate (NH4NO3), 34-0-0Ammonium Sulphate (NH4)2SO4), 21-0-0-24SUrea (CO(NH2)2), 46-0-0 Organic manure

  • Roles of Macro-NutrientsPhosphorouscritical to cellular respiration and energy transferpromotes rootingAvailable to plants as a soluable anion PO43- Fertilizers are derived from rock phosphate treated with acidCalled superphospate, triple super phosphate etc. (Chem analysis is P2O5)Manure is also phosphate rich

  • Roles of Macro-NutrientsPotassiumActs as a catalyst in cellular respirationAvailable to plants as a soluable cation K+Original source is mineral potashMost common form of fertilizer is Muriate of Potash or KClWood ash is an organic form of pottasium fertilizer

  • Critical Limits and Luxury ConsumptionAt a certain point the availability of a single nutrient element may be criticalIn other words there is simply not enough available to permit plant survival and growthIn certain soils an abundance of certain nutrient elements exist in a state of luxury of consumption where far more nutrient is available that the plant can ever utilize

  • Concept of Optimal LevelsBetween the critical limit and the point of luxury consumption exists a range in which plants will survive and growA theoretical optimal level of a specific element can be calculated (experimentally) for a specific plant (crop)

  • Concept of the Limiting FactorThe ability of a plant to benefit from increased supply of a certain nutrient element or other factor (ie light, moisture, warmth) is based on the interaction of the supply of all other elements and factorsThe factor which is in shortest supply is deemed to be the Limiting Factor

  • Concept of Limiting FactorAnalogy;man needs food, water, shelter to live; if you are on the desert, with a tent but there is no water; you are going to suffer and die even if someone builds you a house or gives you more food.

  • Concept of Limiting FactorPlants growth, and vigor will be adversely affected by the element/factor that has lowest availability vs demand; additions of other elements beyond the optimal level will not improve the growth or vigor of the plants.

  • Nutrient Cycling

    Sources of Nutrient Elementsatmospheric content (nitrogen, oxygen, hydrogen, carbon)geological content (phosphorous, calcium, potassium and other nutrients except Nitrogen)organic content; decomposition, throughfall

  • Nutrient CyclingAvailable NutrientsOnly nutrients in solution or capable of moving into solution are available to plantsElemental Nitrogen is the source of all nitrogen for plant growth but is unusable by most plantsCertain plants, (legumes), bacteria, are able to to convert nitrogen to usable nitrate or ammoniumAlso lightning changes atmospheric nitrogen into a soluable form which reach the earth through precipitationChemical fixation; production of fertilizers

  • Nutrient CyclingNutrient storageIn ClaysThe nutrient holding capacity of a mineral soil is directly proportional to the amount of clay in the sampleClay is formed of layers of oxygen and silicon atoms (silicates); various cations (positively charged elements) can adhere to negatively charged sites on the broken edges of clay particles

  • Nutrient CyclingNutrient storageIn Organic MaterialOrganic Material is important for its role in releasing nutrients back into the nutrient cyclestoring nutrient cations holding moistureThe combined capacity of clay and organic combines to store cations (positively charged nutrient elements) is termed the soils cation exchange capacity

  • Nutrient CyclingNutrient storageLots of nutrients are stored in the living plants in an ecosystemThe relative amount, compared to other storehouses, is important when considering the impact of forest harvesting.

  • Nutrient CyclingNutrient LossesCrop Removals (tree harvesting)deep leaching and surface runoffvolatilization (forest fire)

  • Nutrient CyclingNitrogen Cycle (example)Original source is atmospheric nitrogenAtmospheric nitrogen is converted into soluable nitrates through electrical stormsN2 is converted to NH4 (fixation) and then to NO3 (nitrification), which is the plant soluble form, primarily by the action of bacteria (also some plants i.e. legumes)Nitrogen is taken up and stored in plant structures and then released back to the ecosystem; nitrogen can also be lost back to the atmosphere through volatilization

  • Carbon/Nitrogen RatioNitrogen is extremely important to the survival and growth of plantsCarbon is a basic building block of plants but it is brought in from the atmosphere However In order for Nitrogen to be available for the uptake of plants there is a critical balance in the soil known as the carbon/nitrogen ration

  • Carbon/Nitrogen RatioThe bacteria which breakdown organic matter also consume nitrogenCertain organic matter has a high C/N ratio (ie sawdust is 500:1) other matter (vegetable waste) is low (approx 10:1)When the C/N ratio in the soil exceeds 30:1 then the efficiency of the bacteria is decreased and the amount of available nitrogen in the soil decreases and therefore plants suffer from nitrogen deficiency

  • Soil AcidityMeasured by Soil pHNormal ranges from 4 to 7.5 (normally 4-6.5)Generally conifer ecosystems perpetuate a more acidic condition than do hardwoodsStrongly acid soils have slower nutrient cycling and may render some elements such as phosphorous unavailable for plant growth

  • Soil Aciditysome nutrient elements (micro nutrients) such as boron, copper, iron, and manganese are more available when soil is more acidic.Generally more acidic soils (ie lower pH) have lower cation exchange capacity

  • Soil AciditySoil pH in land can be adjusted through the addition of lime (raised) or lowered through the addition of Aluminum or Sulfur.Wood ash naturally increases the pH of soils thereby making nutrients more available immediately following forest fire

  • Forest Operations and FertilityHarvestingSite Disturbancerutting, compaction, erosionNutrient RemovalsThe impact of harvesting depends on the size of the nutrient reserves on the site, the rates of nutrient cycling, the amount of nutrient removed, and the amount of time between subsequent entries

  • Forest Operations and FertilitySite PreparationCreation of Micro-sitesSite preparation or site damagePrescribed burning

    Species Selection


  • Fertilization and Soil AmendmentIt is customary in agriculture to amend soils annually to replace nutrients removed with a harvested cropIn forestry the period between harvests is sufficiently long that in most cases natural processes of nutrient cycling, soil weathering replace the nutrients that are removed with the crop

  • Fertilization and Soil AmendmentFor certain specialized forestry operations such as the management of seed orchards or the production of nursery stock, direct fertilization may be requiredIn order to fertilize affectively the manager must first know the current levels of various nutrients in the soil

  • Fertilization and Soil AmendmentBased on fertility trials, experience and published results, the manager will establish fertility targets for the site and the crop being grown.The manager will amend the plow layer with fertilizer to move the soil towards the desired fertility target.This may involve one or more amendments