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The Moon and the Water Table


Successful horticulture depends on the availability and regularity of soil moisture. Over-irrigation can be as harmful as under irrigating, and this is as true for a large commercial farm as for a small back garden. Plants are part of the living earth. Tides rise and fall to steady pulses, and all dance to the same tune as the Moon. Tides ebb and flow, as do weather patterns; they are generated by ebbing and flowing forces like solar winds that begin life beyond our cosmos. Weather calculation is important because when various lunar phenomena are evenly distributed throughout the month there are even weather patterns. But when two or more of these rhythms come into phase with each other in a way that is more extreme, and the tides are bigger, plants undergo greater growth
surges. For instance if one is planting seeds at the highest chance of rainfall, then these seeds will be more likely to grow into high yielding substantial plants.

The Earth is not ‘upright’ in space in its orbit around the Sun, but on a 23deg tilt, so the path (the ecliptic) of Sun, Moon and planets is not around Earth’s equator. That is why viewed from the southern hemisphere the Sun transits our northern sky. Because Earth rotates beneath the Sun, Moon and planets once every 24 hours, the tilt of the earth dictates that viewed from anywhere on Earth the ecliptic appears to be on a daily wobble. The word planet literally means to wander.

The tilt causes our seasons, important to agriculture because they are the growing seasons. The tilt causes changes in tides which in turn cause air pressure changes which result in changing weather systems. Without changing tides, seasons and weather, life as we know it would be unsustainable, so it can be said that the tilt makes life on Earth possible. NASA astronomers do not seem to realise that in looking for Earth-like planets that may host life, they need to find another on a 23deg lean! The tilt varies between 21deg - 25deg and back again to 21deg over a 41,000 year cycle. We are about in the middle of that range right now and the tilt is decreasing. Because a smaller tilt favours ice ages, we are in a phase of gradual global cooling. The decline is infinitesimal and we will not notice anything in our lifetime. In about 8,000 years the earth should drop in temperature about 1degree due to the tilt, which is about the amount we have warmed over the past 8,000 years as we get further from the last Ice Age.

The declination cycle is the cycle whereby because of the tilt of the earth the Moon changes hemispheres every 13 days, making a round trip every 27.3 days. There is a finite amount of both air and water on the planet. By way of its gravitational pull, as the Moon changes hemispheres it causes relative changes in the volume of water in the oceans which result in the tides, and these change the distribution in the volumes of air which result in weather. Higher tides on your coast result when the Moon is over your hemisphere. Barometric pressures change with declination in a general way that correlates negatively to tides, but local factors mask general trends.

What mariners know, meteorologists do not – it is simply not their focus. The air and water are interconnected and interfaced over 75% of the surface of the globe. When tides are at monthly highest levels, lower air pressures can accompany them and vice versa. A highest tide day will be so in all countries, with lessened air pressure above. This varies depending on geography and topography. At times of perigee (Moon closest to Earth), all tides are exaggerated and magnified, whereas apogee tends to lessen. Monthly perigee brings the highest tides. In 2010 tides are highest in the month when perigee accompanies the full moon day between January and April and when perigee accompanies the new moon day between April and November. Those will be the days to watch, for chances of flooding in low-lying areas if heavy rain is about. The highest tidal-variation day in 2010 will be at or near March 2nd. It will be the highest tide since March 2002, and tides won't be as high again until February 2014. As would be expected, it is also a time of a close perigee /ascending / full moon. The lowest tidal variation for 2010 is October 16th, a time of apogee / first quarter / descending moon.

When the tide is high at the coast it is also high in the water table under the ground, something grazing stock seem to be aware of. It is not uncommon for farmers to use the grazing positions of cows to visually estimate the state of the water levels under the land surface, because more below-ground moisture makes for juicier grass which is presumably more appealing to the cow’s palate. An unusual number of cows mysteriously feeding in a little-frequented area can indicate a rapidly rising water table which can be a sign of imminent flooding. I was once told by a farmer that the last time he saw his cows grazing by his house (which they hardly ever did) was on 1986 just before a flood, so this time he moved them to higher ground just in case. It was just as well, because the floods returned. He saved his stock but lost the house.

This daily invisible tide is important too for the gardener, who should water more on days, e.g. March 9th-10th, on which the water table is relatively low. Conversely one would not harvest pumpkins when the watertable was high as they would be waterlogged and would rot more quickly. The ideal time to pick if preserving, is when the watertable is lower. There is also, as one would expect, a tide of varying height of the sap in trees, climbing vines and other plants that extend well above ground. Insects aware of this variation become more active accordingly. Birds are aware of where and when the insects are going to arrive. At the end of this chain are the plants, in constant need of pollination servicing by both insects and birds. On days of high tidal variations, when more bird and insect life is on the move, pollination activities increase through sheer weight of numbers of insects and bees seeking nectar, and of birds joining the fray. Grafting is better done at times of higher water table levels, when plants are not under thirsting stress and nature is more on the move. By keeping an eye on monthly tidal charts you can make better decisions on when to irrigate and when not

© Ken Ring 2010  

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