Wednesday, October 29, 2014

Can one have too much of a good thing?

Can one have too much of a good thing?

When it comes to compost the answer is yes. This is because compost can be a very good supplier of potassium. Many people growing organic use compost for soil structure, fertilizer, Soil Organic Matter, etc. 
“Soil Organic Matter (SOM) consists of plant and animal remains, in various stages of decomposition, root and microbial exudates, and humus. SOM improves a number of soil physical, chemical, and biological properties. However, the optimal range of SOM content for vegetable production or soil health varies across soil types. Generally, lower levels of SOM are sufficient, and practical to achieve, in coarse textured, sandy soils as compared to finer soils with more clay content. For example, 2.5% SOM in a loamy sand soil might be considered ideal while 2.5% could be considered marginal in a silt loam soil where 3 to 5% is more common”.

“With this information in hand we began looking closely at gardens and market gardens that had high levels of compost applied over several years. We consistently found the same pattern: very high potassium, generally high levels of phosphorous and extremely low levels of available calcium. We then asked these same gardeners how their garden was doing. The answers were telling: A lot of bug pressure – It used to be much better – Really poor tasting food – Very low brix levels.

This research lead International Ag Labs to promulgate two new quality indicators based off our soil tests: the calcium-potassium ratio and the calcium-phosphorous ratio. Both should be around 18:1. I have found that if the calcium to potassium ratio is narrow, say at 3:1 or less it is a sure indicator that the garden will not be producing high brix foods until the ratio is widened. Gardens with narrow ratios can still produce abundantly but the food will not be nutrient-dense and the flavor will leave a lot to be desired. “

Any time you get your nutrients out of balance you can find deficiency in key nutrients.

Excessive potassium levels will reduce boron availability, needed for nitrogen conversion and the transfer of starch from the leaves to the fruit.  When excessive enough, potassium - whether combined with sodium or not - can block manganese uptake, another key nutrient for vine strength, fruit set, and skin quality of the grapes.

Excessive phosphate levels in the soil can result in poor water utilization. Too much compost or manure, or even soft rock phosphate, or 11-52-0 (MAP) or 18-48-0 (DAP), or any phosphate source that will sufficiently build P levels in the soil can cause this to happen. Zinc is necessary for moisture absorption by the plant.  Excessive phosphate ties up zinc.

Too much nitrogen can cause a copper deficiency.  Though copper is only needed in "trace" amounts, along with potassium and manganese it helps to increase vine resilience and skin quality in wine grapes. 
High levels of nitrogen can also lead to a lot of green growth and not as much tuber growth.

If the compost has a proper Carbon:Nitrogen ratio of approx. 10-12:1, it does not tie up nutrients. High carbon composts always tie up nitrogen and sulfur, and sometimes other nutrients when worked in to the soil.

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