Late March 2017
All nutrients are important in the growth of healthy, vibrant plants, fruit and vegetables, but some nutrients are more often used in gardening and agriculture than others. While I do have a science degree, my approach to market gardening has been that of the layman, simply expanding ‘old fashioned’ (low-tech) home gardening up to the largest scale that I, myself, could manage. Most of the garden literature I had read referred to calcium largely in association with lime (calcium carbonate) and its ability to make an acid soil more alkaline (aiming for a pH of around 7.2), and therefore increasing the availability of soil minerals to plant roots. Then I read the old adage “lime and more lime makes for rich fathers and poor sons”, and I wondered about that. Upon researching some of the more progressive agricultural science books, I learned that calcium does far more than merely altering soil pH.
My understanding of calcium in general is that plants use more of it by weight and volume than any other mineral, and that calcium is the ‘background mineral’ that other minerals react with to release the nutrient energy required for optimal plant growth and health. So, in the old adage, the father gets rich by using lime to mobilize the minerals inherent in the soil for good crops, but will deplete these minerals if they aren’t replaced by, say, a multi-mineral rock dust/fish & seaweed fertiliser, for example, in addition to lime.
As calcium is used in the building of cell walls, a good indication of sufficient soil calcium levels is vegetable plants with thick, strong leaves. Of course, one can always have too much of a good thing, and this includes soil calcium. I have never had my soil tested in a lab for content of various minerals (which I may do in the future), instead I have taken a holistic, observational & intuitive approach to adding calcium based on my 20+ years of gardening experience. And I will add that a few decades of gardening is to me only a starting point in the amazingly complex job of growing nutrient-rich food. Within the terms ‘agriculture’ and ‘horticulture’, the term ‘culture’ refers to the body of knowledge traditionally passed on from generation to generation within the practise of food production. Much of this knowledge and ability has been lost in the modern industrial, chemical and genetically engineered agricultural methods.
Another old adage that caught my attention goes something like this: “manure and more manure without lime drives you bust in half the time.” Likewise, I wondered what that meant, and researched accordingly. My understanding is that this is due to the relatively low pH (acidity) inherent in organic matter, including animal manure. Regularly applying manure to soil over time without balancing it with the alkaline nature of calcium carbonate can lower the pH to levels in which minerals are less available to plants because the beneficial soil life helps to make minerals available to plants cannot thrive in an acidic pH.
Over the years, my soil, being a volcanic silt loam with 60 or so trailer loads of organic matter added to it (compost, manured sawdust, green mulch), has responded well to fairly heavy dustings of lime 2 -3 times yearly on average. In New Zealand, lime is readily available and inexpensive. Initially I used 20 kg bags of fine lime (lime flour) because of its fast activation, but in recent years I have purchased 1 ton bags of regular lime, which works in the soil over longer time periods, and is many times more cost efficient in bulk.