Dealing with excesses

Adding minerals which are deficient is relatively straightforward. If you have low pH soil, this is likely your situation. If you have high pH soil, as in an arid region, you have an excess of minerals. This is harder to deal with. First, avoid creating excesses. Measure your area carefully before applying minerals; be sure to add the appropriate quantity for your area.

If you do have excess minerals, the first thing that will happen is they will crowd out the hydrogen cations. The pH scale basically counts how many H+ ions are available for interchange, so the pH measurement is high where there are excess cations. Yes, I know this sounds backwards, and it is. pH goes up when the H+ count goes down.

The cation hierarchy is Ca>Mg>K>Na> H+. Losing those H+ ions means losing a lot of ion mobility. Ion mobility makes it easier for plants to feed —plants basically exchange ions and bring minerals through their cell walls when they eat. Anyway, when there are excess cations and they are out of balance, it is much harder for plants to access nutrients, even if they are present.

When minerals are out of balance, an excess of one can block access to another. This is well illustrated in Mulder’s chart:
Muldars chart

Here are some of the most common practical interactions in table form:

Our method is based on the idea that if the minerals are not in the soil they will not be in the plants. This is true. But, just because the minerals are in the soil does not mean they will necessarily be in the plants. Without good biological activity, plants may be unable to access the minerals in the soil. Soils with excesses can block plant’s access to minerals.

When there are excesses we can try to balance the soil. We use the hierarchy Ca>Mg>K>Na> H+. For instance, if there is excess K and low Ca, adding Ca will displace some of the K. It will also displace some of the H+, Na, and Mg. Then, you re-test and see what happened. You can see this can be a long slow process.

Meanwhile, one needs to grow a garden or a crop. So, one turns to other tools. If the crop is large or the garden is not doing well, a tissue test is in order to close the knowledge gap between what’s in the soil and what’s in the plant. Then, missing nutrients can be supplied by foliar feeding. Another technique is to run brix tests. Using a refractometer, measure the brix of your plants. Apply a foliar spray. Measure the brix at the same time the next day. If the brix went up, you have discovered a way to supply a missing nutrient. What doesn’t work so well is visual observation. You are much better off using a refractometer than just looking for a response. For instance, adding foliar nitrogen almost always makes the plants look better, but it can decrease the weight and nutrient density of the harvest.

While the Mehlich 3 test measures the loosely held minerals on clay and humus particles, the Morgan test and the saturated paste test measure the minerals in the soil solution. It’s much more work, but if the plant can’t access the minerals held on the clay and humus (let’s call it CEC feeding) because of mineral imbalances, one can feed their plants through the soil solution. This is how hydroponics and most of commercial farming work.

If the CEC feeding vector is closed, there is yet another path whereby plants can feed. If the biological activity in the soil is increased enough, plants will live and grow as part of a very active biological system.

next… All growing is local

2/13/14 Copyright Erica Reinheimer, Steve Solomon Rev 03a