A talaj, trágya, növény kapcsolat elméleti kérdései = Theoretical issues of soil, fertilizer, plant relationships

Buzás, István (2025) A talaj, trágya, növény kapcsolat elméleti kérdései = Theoretical issues of soil, fertilizer, plant relationships. SCIENTIA ET SECURITAS, 6 (1-2). pp. 33-41. ISSN 3057-9759

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Abstract

A talaj tápelemformáinak változásait a valóságot jobban megközelítő módon, dinamikusan (kinetikusan) szemléljük. Minden egyes tápelem számtalan nem felvehető vegyület formájában és néhány felvehető ion formájában létezhet, de a nem felvehető formák és a felvehető formák folyamatosan átalakulnak egymásba. Kevés növény által felvehető ion ismert. A nem felvehető formák rendkívül sokfélék lehetnek, és összetételük részben ismeretlen. Ha nem bolygatjuk a talajt, a felvehetővé alakulásnak és a felvehetők nem felvehetővé alakulásának sebessége azonos lesz, vagyis úgynevezett kvázistacionárius egyensúly jön létre. A talajtápanyag-vizsgáló módszerek használhatóságának feltétele, hogy a velük kapott értékek ne függjenek jobban a talajparaméterektől, mint a vizsgált tápelem mennyiségétől. | The field of agrochemistry can be placed at the border of physics, chemistry, and biology, and as such, uses their basic laws. At the same time, what makes agrochemistry an independent science is that there are some basic concepts that occur only in agrochemistry. It is striking that agrochemists often hesitate to define these concepts unambigu- ously, although in their absence the knowledge accumulated in the agrochemical literature does not form a unified system. The author attempts to clarify some well-known agrochemical concepts. It would be a step forward if we made a clear distinction between the nutrient needs of plants and the fertilizer need. It is believed to be important to view the changes in soil nutrient forms in a more realistic, dynamic (kinetic) way. According to this, each nutrient exists in the soil in the form of countless compounds that cannot be absorbed by plants, but only a few in the form of ions that can be absorbed by plants, and the forms that cannot be absorbed and the forms that can be absorbed are constantly being transformed into each other. The few ions that can be taken up by plants are well known, while the non-absorbable forms can be extremely diverse, and their composition is largely unknown. If we do not disturb the soil, the rate of conversion to absorbable and the rate of conversion of absorbable to non-absorbable will be the same over time, i.e. a so-called quasi-stationary equilibrium is established. With the help of the above, the concept of soil nutrient supply can be clarified, the decrease in soil nutrient supply over time can be explained, the causes of nutrient deficiency can be explained, and a novel explanation can be given for the yield-increasing effect of fertilization. An important part of the thesis is the interpretation of soil nutrient tests performed by service laboratories. The purpose of tests performed in soil laboratories operating for non-research purposes is not to determine the nutrient content of the soil, but to provide data that can be used to estimate how much fertilizer needs to be applied to achieve a planned crop yield. At a basic level, our primary expectation of a soil testing method is that the amount of a nutrient released from different soils by the extraction agent correlates with the amount of the same nutrient available to the plant from those soils. However, as we have shown in the example of ammonium quantification, the usability of the method also requires that the values obtained with it are not influenced more by other soil parameters than by the amount of the tested nutrient. The dynamic approach makes it possible to prove that the dependence on the soil parameters is small if the quantity of nutrient extracted by the method can still be assumed to be proportional to the quantity of absorb- able forms in the soil. The development of soil testing methods in recent decades also shows that it is primarily the weak extraction agents that meet this requirement. The author points out that although the values obtained by soil nutrient testing methods performed in routine laboratories are given in mg.kg–1 units, the calibration protocols as well as the methods laid down in the “Blue Book” consider them only as indicator numbers, and neither of them actually takes into account the extracted nutrient quantities. Although strictly speaking, advice based on calibration experiments is the only method of fertilizer recom- mendation that can be considered scientific, calibration experiments are so expensive and time-consuming that it has only been carried out for a few soil testing methods and a few crops. In the so-called “Blue Book” methods, which form the basis of most fertilizer recommendations currently, the actual calibration was replaced by experts estimating, based on available literature and their own knowledge, the soil test results at which individual soil types can be con- sidered adequately supplied. The author aims for this discussion paper to serve as a teaching aid for the fundamentals of agrochemistry. He hopes it will spark professional discussions, offering opportunities to explore each topic in greater depth.

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