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The Soil Environment Soil Acidity Part 3
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column discusses how soil acidity changes as producers have managed it for crop production since Kansas was settled. We will focus on were soil pH started, how converting the land to crop production changed pH, and the role of evolving cultural practices. It may be helpful to refer to the previous two columns.
• When this area of the state was settled, it was mixed-grass prairie, intermediate between the tall grass to the east (think the Flint Hills) and the short grass prairie to the west. This reflects the moisture patterns in Kansas with higher average precipitation to the east and much less to the west. Here annual precipitation trended higher (more like the eastern section) over some periods or much lower than average (like the western section) resulting in a mixture of tall and short prairie grasses.
• Soil pH values reflect the previous point. Except for Southeast Kanas, pH values after the natural establishment of prairie were neutral with most above neutral (pH higher than 7) and the pH increases more as you move towards the Colorado border. Even in the immediate area pH values tend towards higher as you move from say Ellinwood towards the Otis area today.
• Soils in the region were in dynamic equilibrium that is while not unchanging the soil environment was a closed systems with additions and losses essentially equaling each other. Nothing was being added or removed from the system but being recycled.
• When settlers first starting farming the prairie, the first task was to break open the sod through moldboard plowing. This upset the equilibrium and caused the breakdown of the layer of organic matter at the soil surface. This started decreasing the organic matter content and as it was broken down organic acids were released. Then as crops were produced and harvested, the amount of recycling of nutrients was reduced. As basic cations were removed, the pH was lowered a bit more. Soil pH didn’t plummet but soil was moving towards neutral and below (acid). Even today, well over a century later, and with increasing production levels soils, depending on their composition, may be well above neutral. This is especially true as you move towards the Colorado border.
• The next major change that applied downward pressure on pH was the introduction and increased use of high analysis fertilizers for nitrogen fertility in the production of grass crops (corn, wheat, grain sorghum, etc.). Nitrogen fertilizers commonly used in field crop production release hydrogen ions (acidity) in the soil. As their use increased, pH levels started to decrease more rapidly. Then came improved genetics and increasing yield levels (in the case of corn increasing from 50 bu/acre in the early 1950s to over 200 bu/acre for irrigated corn today) which increased the use of nitrogen fertilizers and further moved the needle towards the acid side until soil pH levels since settling in some areas had moved from near neutral to very acid. Again the effect tended to be less as you moved west. The effect was accentuated where soils were sandier and lower in organic matter.
Next week – What can we do about this.