THE DRAIN BRAIN
From the ancient Romans to the modern Dutch, engineers have constantly risen to the challenge of land drainage. In problem areas, the need is obvious even though the solution may be difficult. Few crops, with the exception of rice, grow well with their roots in standing water, so that flooded land, land with a very high water table, land with impeded natural drainage, have to be attended to before regular production can be assured.
The transition to, and the translation of ideas into, the realm of more normal land areas is a more difficult mental process. Such land provides the great majority of potential food-producing soil and yet the need for drainage tends to be axiomatically assumed without, in all cases, a sufficient change of emphasis from that which is clearly appropriate to the problem areas.
The aim of drainage is to preclude the presence of excess water in the soil, to prevent the exclusion of oxygen and the possible inclusion of harmful concentrations of ethylene. In other words it is a means whereby the farmer provides good conditions for root growth, for without good roots no crop can be highly productive.
So far, so good, but two critical questions remain to be answered. Firstly, how often do such unfavourable conditions occur? Secondly, to what extent does drainage ameliorate such conditions?
The first problem is largely solvable by the agricultural meteorologist. It is not merely a problem of rainfall regime and the frequency of occurrence of heavy falls of rain over various periods of time;it is also a problem of soil moisture regime and so cannot be solved by pure climatology alone. The disposal of rain water falling on a fallow or crop-covered land can be quite different to that falling on an urban concrete covered area. A heavy fall of rain over land with a relatively large soil moisture deficit may be mainly beneficial; a similar fall over land already at field capacity is quite another state of affairs, and may only be beneficial to the water engineer who is trying to harvest the water.
Nevertheless, with modern knowledge of evaporation and transpiration, it is reasonably possible to quantify the risks of such adverse meteorological circumstances. If then the plant physiologists can interpret the effect of such conditions in terms of the check to production and growth, it is theoretically possible to express in economic terms the net result of the excess water. This being done, the dimensions of the problem will be known. In problem drainage areas, such dimensions are visibly large enough to make such meticulous calculations unnecessary. Elsewhere, the assessment of danger is nothing like so simple; the monster may not be a dragon, but only a lizard.