September 28, 2005

By Peter J Lester 

Many facets of plant growth and animal performance are checked by low temperatures, as are they with elevated temperatures. It may be an opportune time to visit these. We could begin with seed germination. Whatever any plant does throughout its course of growth cycle depends on; A: its hereditary background and B: the environment under which it is grown. 

The availability of elements to plants is tied in with biological activity, which is also tied to temperature – physics – and moisture. The type of vegetative cover on a given soil affects the nature of the soil that forms, and thus its nitrogen content. Nitrification, as the process is termed, is the conversion Ammonia (NH3+) to Ammonium (NH4+) and by the addition of oxygen, to form first Nitrite (NO2-) and ultimately Nitrate (NO3-) in which form it becomes the preferred plant form of N. 

The first two steps in the formation of Ammonia and Ammonium do not require oxygen (O) and can therefore take place in cold acid soils, and soils that are too wet to sustain most plant growth, except for some weeds. Weeds can therefore indicate the presence of ammonia and ammonium compounds in a soil. When soils are too wet, denitrification occurs. Soil organisms that live in soils devoid of free oxygen cause denitrification by taking the oxygen from nitrates. If the soil is too cold, nitrification will not proceed normally, and the plant will reveal all the signs of nitrogen deficiency. To apply N under these circumstances, the plant may take up the applied N but be short of all the other elements necessary for the formation of protein compounds. As the conversion of ammonia and ammonium to nitrate is a biological process, temperature plays a major role in this conversion. 

When soil temperature falls below 10ºC most plant growth ceases. Even at 13ºC growth is slow. The ground temperature at the lab today, 15/10/02 at 12.05 pm was 10.3ºC All elements required for plants are affected by temperature, and it is not wise to try to stimulate growth by the application of N or any other means, outside the ability of the soil to sustain that growth. This means, every condition that serves to create an environment that is conducive to plant growth must be present and operating. The temperature levels of biologically active soils are on average 3-5 degrees higher that those same soils with low biological activity. REF: Soil Biology. Burges Raw. 

ANIMAL PERFORMANCE:

Animal performance is adversely affected under extremes in temperature change. It takes energy to keep warm and energy to keep cool. This energy normally comes form the sun and via the sun through plant life. In times when the energy in the feed falls below the energy demand of the animal and its environment, the animal metabolism will be checked, and the production it can perform will be limited. The critical temperature, is that temperature at which the heat created by digestion and body metabolism equals that by which the animal dissipates by convection, evaporation, radiation and conduction. It is the temperature at which the animal can perform with little or no discomfort. 

At temperatures below the comfort zone, additional nutrients need to be converted to heat to keep the animal warm; and any temperature above this comfort zone requires nutrients to keep the animal cool.