e_moon60 (e_moon60) wrote,

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Agriculture and land management 101-a

Due to LJ's limitations on post length, I don't think I can get everything in one post.   But here we go...

Background: I grew up in a farming community based on alluvial soils in a semi-arid to arid climate: intensive farming required irrigation, and as the decades wore on, the use of fertilizers and pesticides to maximize yield.   Flood-control dams and levees were intended to protect towns and farms from floods, but disrupted normal drainage channels and prevented floodwater from restoring soil nutrients and adding soil.   Irrigation with high-mineral-content water and the use of these chemicals degraded the once-rich and productive soil; most of it is now covered with houses, shopping malls, and roads.  The degradation of previously very productive soils occurred between the time my grandfather moved there (1918) and the present--less than 100 years (in fact, soil productivity was dropping visibly during my childhood and by the 1960s farming was becoming less and less economically feasible, esp. for small farmers.)   My mother worked for someone who owned a lot of land, there and elsewhere, and I had the chance to visit some of these properties, and meet the farm and ranch managers, from whom I learned a lot.  My second degree is in biology; my graduate work was mostly related to land management, water resource management, wildlife management...applied ecology, in other words.  While taking my second degree and in grad school, we did intensive organic gardening in our back yard  (raising all our own fresh produce, for instance) which also taught me a lot.  I have continued to read and learn about these and related matters at both the science level (through major journals) and the local, practical, hands-on level--I now live in a community that was, when we moved here, primarily agricultural (mostly ranch, some farm) and I managed some land for wildlife productivity, as well as own a few cattle (pastured elsewhere as our land isn't capable of sustainable grazing by cattle.) 

Land varies widely in its ability to produce sustainably.   The natural vegetation of land tells you what it's got, what it is presently capable of producing (be that "weeds" or grass or forest or salt-marsh.  Often, land has been under human management before, so the natural vegetation is natural only to its current, human-influenced state.  As soil loses its nutrients during cultivation, the quality of vegetation it can support decreases.  Changes in management change what the soil can support--by changing both physical and chemical qualities of the soil. 

Factors limiting productivity include low nutrient levels (depleted by prior farming, or leaching by heavy rainfall as in some tropical soils, or naturally low because of little soil formation),  compaction (usually by traffic of people or animals), innate soil structure (both heavy clays and sand), water availability and water quality (brackish or salt water, water contaminated with toxic materials), minerals that inhibit growth or make the product toxic), and of course climate.  Climate affects soil and directly affects plant growth. 

Every piece of ground as big as a square meter has a unique soil, derived from its entire past history: it is what it is because of the rocks that gave it its mineral content, the wind and water that put it in that place, the plants that have grown on it, the animals that ate the plants that have grown on it,  the soil microbiota (bacteria and fungi and protozooans) that have lived and died in it, the people who have owned it and/or used it and the uses they put it to.  If you take down an old toolshed, the soil under it is different than the soil next to it.  If you rip up an old road, the soil under it is different.   There are broad areas of land that have similar soils...but they are not identical across any fence, on the other side of any creek.   The land I presently manage is roughly a half mile long by a quarter mile wide.  In that space, I  have found bare rock presently being converted to a thin limestone gravel by tiny plants and algae and lichens...a thin soil (less than two inches thick) a little downslope, on the same rock formation, which supports cactus, low grasses, some forbs, and one or two stunted native trees...a gravelly red clay, quite thin (though thicker on the terrace berms created by a long-ago farmer) that supports mid-grass native grasses and forbs, black clay ranging from six inches to four feet deep, with some rocks in it (rocks clearly related to the rock on the low hill--limestone and fossils in limestone), sandy loam deposited by floods, near the seasonal creek, yellow clay (originally a lower soil horizon) from which the darker more fertile clays were stripped by erosion (west end) supporting native grasses, forbs, and invasive juniper,  chalky yellow-white clay undergoing active and rapid erosion, poorly compacted gravel bed, subject to erosion (creek bank in one area),  weak and frangible bed of fossiliferous limestone (creek bottom, one stretch.) 

Native vegetation, prior to agriculture, was a mixed tallgrass/midgrass prairie with a strip of riparian woods along the creek and its tributary.   It supported a wide range of wildlife, including forming part of the buffalo range.  The seasonal seeps and sloughs offered additional, seasonal, aquatic habitat.  The creek was probably a permanent source of water then (we know that springs, seeps, and flow were all greater prior to the 1930s.)   A drought in the 1930s and another in the 1950s caused permanent loss of some historic springs and changed some permanent creeks to intermittent flow...drilling for wells is almost certainly one reason, as the lowered water table couldn't supply everything.
Tags: agriculture, land use

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