It is -evident that for optimum crop productivity the soil nutrient status, i.e. the fertility of the soil should be maintained by appropriate and efficient nutrient management. However, in order to make the best decisions on what measures and when to take one, has to obtain actual information on soil nutrient status. Considering the significance of soil fertility information, which is more than simple technical data but has also great environmental and economic consequences, it is little wonder that scientists have developed a number of methods and systems to evaluate the fertility of soils.
Recently, several approaches are commonly used to assess the nutrient status of soils. First of all, biological tests are commonly used. In these tests, which could be either greenhouse or field tests/experiments, the supply of nutrients for plant growth is quantified. Another way is the method of chemical analysis, whose aim is to quantify crop nutrient requirements by soil and plant analysis. Besides the above-mentioned ones, there are several diagnostic approaches using tissue analysis and the visual diagnosis of deficiency symptoms.
Greenhouse Experiments
Greenhouse experiments are used for several studies under controlled conditions. Such experiments may serve several purposes. By carrying out greenhouse tests we can, for example, quantify the nutrient availability in soil.
They make it also possible for us to study the nutrient supplying capacity of soil. Good examples for such tests are the so-called exhaustion experiments. Another great advantage of greenhouse tests is that they also allow the study of the existing interactions between selected nutrients. A very practical aspect of greenhouse tests - with potentially far-reaching economic consequences - is that they facilitate the study of the efficiency of various nutrient/fertilizer additions. It, of course, also means the possibility of studying the responses that particular crops may give to increasing nutrient rates. Such responses may manifest themselves by, for instance, maximum biomass production and/or in the nutrient content etc. By performing greenhouse experiments we can make a wide range of comparisons, for example of selected soils, crop varieties, fertilizer sources etc. It goes without saying that such comparative analysis may be extremely important in making strategic decisions in farming.
Finally, we must not forget that greenhouse tests can also focus on the influences of residual nutrients on freshly applied fertilizers/nutrient elements (e.g. Phosphorus).
Greenhouse experiments may have many types and forms. They are usually carried out in pots of various sizes.
The following are the most common pot sizes.
Small pots are often used in the so-called CHAMINADE methodology. This type of test would involve, for example, 1 kg of soil, perennial ryegrass (Lolium perenne L.) as a test plant. 1,000 seeds would be typically used per pot (Chaminade, R. 1960).
Medium size pots are generally used for cereals according to the MITSCHERLICH methodology using 5-6 kg of soil in each pot (Mitscherlich, E.A. 1909).
Big size pots are normally for tall crops with up to 15-20 kg soil. Big pot tests may be carried out according to various methodologies.
Greenhouse experiments may employ different growing media, such as water, sand and soil.
The conditions in which these experiments are carries out can also vary. They are normally done either in a greenhouse (glasshouse) environment or in a so-called fitotrone, which is a fully automatized, completely controlled environment, such as a chamber or a room.
E. A. Mitscherlich (1909) developed a methodolgy of "Mitscherlich containers" having a double bottom, into which excess fertilizer flows
Greenhouse experiment (Spring barley L.)
Greenhouse experiment Corn (Zea mays L.)
Field Tests/Experiments
The other type of experiments used in soil fertility evaluation is that of field tests/experiments. These are mainly used for developing fertilizer recommendations, i.e. the calibration of yield levels. As opposed to greenhouse
Soil fertility evaluation
treatments are usually replicated four times. Then the results of the four tests are statistically evaluated.
However, experiments under natural conditions alone are not always satisfactory for some purposes. In such cases field experiments are often used in conjunction with greenhouse tests for the better reliability and calibration of results.
In connection with field tests two very IMPORTANT aspects should be highlighted. Firstly, as for their functions, it is essential to know that field experiments are crucial for the development of fertilizer recommendations. Secondly, we must not forget the importance of long-term field experiments, since they are the most valuable and most reliable.
Field experiments can be classified in several ways. Most commonly these experiments are classified according plot size:
Lysimeter experiments (using isotopes e.g. 15N) are especially valuable for measuring nitrate leaching, providing quantitative information on both nutrient losses from soils and environmental impacts on water resources.
According to the most accurate methodology crops are grown in a large soil tank, which allows the rainfall input and water lost through the soil to be easily calculated.
Another basis for classifying field experiments is their duration. According to this criterion we must mention short-term field experiments first. Although short-term experiments may prove to be very useful for some purposes, they cannot always deliver the necessary results due to temporal limitations. In such cases long-term field experiments need to be performed. Some countries where considerable experience has been accumulated in connection with long-term field experiments include the UK, the USA, Canada, Germany as well as Hungary.
The oldest long-term experiments are 160-years-old (established at Rothamsted in England by J. B. Lawes and J. H. Gilbert in 1843).
Field experiments can also be grouped according to the design and arrangement of the plots. Very often the test plots are arranged in the form of randomized blocks. However, the various blocks may also be arranged by factors (e.g. increasing rates of fertilizers and irrigation etc.).
Usual design and picture of a lysimeter
Typical field experiments are shown in the next two photos, demonstrating their design and the test plants selected for the experiment: sunflower and corn, respectively.
Field experiment Sunflower ( Helianthus annuus L.)
Field experiment Corn (Zea mays L.)