Marcus,
My opinion for what it’s worth is I would not apply lime without trying to correct it in another way. No doubt you likely know as much about it as I do. It’s logical to add lime since it’s PH is higher but the problem is it’s never just calcium rather 50% calcium and most of the remainder is magnesium. Here is a summary of the problem Dolomite Lime: More Harm Than Good | Organica: Garden Supply & Hydroponics. Humus has a CEC several times that of the clay soil I have Cation-exchange capacity - Wikipedia. “Clay and humus have electrostatic surface charges that attract and hold ions”. This breaks it down a step further http://nutrients.ifas.ufl.edu/\nutrient_pages\BSFpages\CatExchange.htm. The idea is I lower my PH via organic materials such as aged cow manure and aged wood chips aka humus Humus - Wikipedia in most situations to release soil nutrients for my pears to use. Anions go where water carries them which is good and bad but more about that in a minute. “CEC soils have fewer negative charges, cations will move more quickly through low CEC (sandy-based) soils than they will through high CEC (loamy and silt/clay-based) soils.” This sentence is quoted from this link http://msue.anr.msu.edu/news/anions_and_cations_in_plants_oh_my_but_why_do_we_care . Now with that said my soil is High CEC and yours I’m assuming is low CEC. My soil has many nutrients locked up by the clay. In my case Boron is mobile in the soil which means my soil problems start making a lot of since. In the south you get a lot of rain and have a low ph soil. In the same article look at this sentence “Over application of most (+) charged elements on a low CEC soil can move that element through the system since there are not enough (-) charges on the soil particle surface to bind to the cation.” What that means is in my opinion you need to increase humus in your soil rather than calcium. The humus will then hold on to more nutrients http://organicsoiltechnology.com/cation-exchange-capacity-of-humus.html. From the link “The 5 most important cations in soils are calcium (Ca++ ), magnesium (Mg++), potassium (K+), sodium (Na+) and aluminium (Al+++).” The reason my soil is good even though the nutrients are locked up by clay is they can become usable. “The higher the CEC value, the more effective it can be for improving plant growth, vigor and health. All very small particles, not just humus and clay, carry electrical charges. The part of the nutrient that carries the electrical charge are called ions. Ions with a positive charge are called cations and ions carrying a negatively charged are called anions.” “The element having the highest CEC would be humus.” “Some important positively charged nutrients include, Ca++, Mg++ and K+. You may note that a very important nutrient, Nitrate NO3-, is not listed. This is because it carries a negative charge. Humus has not only negatively charged ions ready for retaining positively charged minerals, some have positively charged ions as well which can hold on to negatively charged minerals such as our precious nitrates and nitrites.”"The surface areas of a plant root hairs contain their own electrical charges. Any time a plant’s root hair penetrates the substrate, it may exchange its own cations for those mounted on humus or clay debris and then absorb the cation nutrient for intake as nourishment. Plant roots use a hydrogen cation (H+) for the exchange. They eject one hydrogen cation for every cation nutrient adsorbed. This keeps a charge balance. This is the way plant life eats. " I apologize for the long winded answer. So another words apply wood chips made from small banches, leaves and things like that to your trees instead of lime in my opinion http://compostguide.com/using-leaves-for-composting/. Leaves are very high in trace minerals. Oaks leaves particularly are high in calcium. Here is another great article on leaves http://www.the-compost-gardener.com/composting-leaves.html. I like to put wood chips on the top around my trees and let the earth worms do the rest. Lime when added to your soil has a calcium to magnesium ratio of 2:1 but in your soil it’s supposed to be 7:1 Dolomite Lime: More Harm Than Good | Organica: Garden Supply & Hydroponics. It would correct one imbalance but create another. When it comes to soil science think of nutrients like magnets a - and a + are attracted to each other. By adding the humus we create a situation where the plants can thrive. Many trees are starving for nutrients because of lack of organic matter in the soil but all around them there is food they can’t get to. By the way here are some great pictures of harrow pears Pear Photo Gallery.
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