Saturday, January 29, 2011

Natural Fertilizers and Biodiversity

To learn which fertilizers were most effective, in 1843 John Bennet Lawes began a series of test plots still going today, which makes Rothamsted Research both the world's oldest agricultural station and the site of the world's longest continual field experiments. Lawes and John Henry Gilbert, a chemist, began by plating 2 fields: one with white turnips, the other with wheat. They divided these into 24 strips, and applied a different treatment to each.

The combinations involved a lot, a little, or no nitrogen fertilizer; raw bonemeal, superphosphates, or no phosphates at all, minerals such as potash, magnesium, potassium, sulfur, sodium; and both raw and cooked farmyard manure. Some strips were dressed with local chalk, some not. In the following years, some plots were rotated with barley, beans, oats, red clover, and potatoes. Some strips were periodically fallowed, some continually planted with the same crop. Some served as controls, with nothing added to them at all.

By the 1850's,  it was clear that when both nitrogen and phosphate were applied, yields increased, and that trace minerals helped some crops and slowed others. They took samples and recorded results. They wanted to test any theory of what may help plants grow, even slathering crops with honey.

Rothamsted Manor


One experiment which is stll going today involved no crops, only grass. An ancient sheep pasture just below Rothamsted Manor was divided into strips and treated with various inorganic nitrogen compounds and minerals. Later, they added fish meal and farm manure from animals on different diets. In the 20th century, with increasing acid rain, the strips were divided again, with half receiving chalk to test growth under different pH levels.

From this pasture experiment, they saw that although inorganic nitrogen fertilizer makes hay grow wasit-high, biodiversity decreases. While 50 species of grass, weeds, legumes, and herbs may grow on unfertilized strips, adjacent plots dosed with nitrogen hold just 2 or 3 species. Since farmers don't want other seeds competing with the ones they've planted, they have no problem with this, but it causes problems with nature.

Laws said that any farmer who thought he could "grow as fine crops by the aid of a few pounds of some chemical substances as by the same number of tons of farmyard dung" was mistaken. He advised anyone planting vegetables and garden greens that he would "select a locality where I could obtain a large supply of yard manure at a cheap rate."

Tucked behind all the gleaming research facilities is a 300-year-old barn which is Rothamsted's archive, containing more than 160 years of research of human efforts to grow plants. The specimens, sealed in thousands of five-litre bottles, are of virtually everything. From each experimental strip, Gilbert and Lawes took samples of harvested grains, their stalks and leaves, and the soil where they grew. They saved each year's fertilizer, including manure.  The bottles, stacked chronologically on 16-foot metal shelves, date back to the first wheat field in 1843. During war years, when bottle supplies were low, samples were sealed in coffee, powdered milk or syrup tins.

Thousands of researchers have climbed the ladders to view the time-yellowed bottle labels-to extract, for example, soil collected in Rothamsted's Geesecroft Field at a depth of nine inches in April 1871. Many bottles have never been opened-along with organic matter, they preserve the very air of their era. This heritage will survive intact long into the future, even after humans are gone.  More than 300,000 samples are here, containing soil and preserved plant matter. They serve as a time-lapse record of a century and a half of human history.

The oldest jars contain relatively neutral soils that didn't stay that way for long as British industry redoubled. The pH drops farther into the acid end by the early 20th century, as the discovery of electricity led to coal-fired power stations, which spread pollution beyond factory cities to the countryside. There was steadily increasing nitrogen and sulfur dioxide until the early 1980s, when improved smokestack design lowered sulfur emissions so much that some of the soil samples were spiked with powdered sulfur, which farmers had to start adding as a fertilizer.

Traces of plutonium first appeared in Rothamsted's grassland plots in the early 1950s, a mineral that rarely occurs in nature, let alone in Hertfordshire. Like vintage wine reflecting annual weather conditions, the fallout from tests in the Nevada desert, and later in Russia, affected Rothamsted's distant soils with their radiation.

Alan Weisman, "The World Without Us".


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