Abstract

Mollisols of the Pampean region in Argentina are considered to have among the richest potassium content of soils in the world. Enriched K bearing minerals such as illites and smectites are an important part of the clay fraction in these soils. This results in a very high level of exchangeable potassium, with typical levels ranging from 0.8-to 2.5 cmolc kg-1.

It is widely accepted among research in the country that the parent material is demonstrating a changes in the Intensity / Quantity relationship (Q/I) with cultivation, yet, potassium application is excluded from fertilization programs. Approximately 80% of the cropped area of wheat (6 Millions ha), receiving regularly only N and P fertilizers, and more recently, sulfur.

Former results in the Pampean region showed responses to KCl to be in the order of a 5 to 10% increase in grain yield. Since the K and Cl were not applied separately, it is not clear whether the positive effect derives from K or Cl.  

The effect of chloride application has been demonstrated in the Mollisols of North America, showing positive responses when applied to wheat. Chloride may be responsible for enhancing leaf disease resistance, which results in larger effective leaf area during critical periods of grain filling. Positive response to potassium application was largely demonstrated even in soils with high levels of soil K, thus achieving a better photosynthesis and water balance relationship, which resulted in better water use efficiency and translocation of photosynthates to filling grains.

Two field experiments in wheat were carried out during 1999 and 2000 at 5 and 3 locations, respectively, across Typic Argiudolls of Buenos Aires and Santa Fe provinces in the Pampean region.

In 1999, two sources of K were compared using KCl and K-Mg-S (Sulpomag). Four levels of K (0, 20, 40 and 60 kg K₂O /ha) and S (0, 20, 40 and 60 kg S /ha) were compared. Each treatment had increasing rates of chloride (9, 18 and 27 kg Cl/ha) or magnesium (2, 4 and 6 kg Mg/ha).

In year 2000, two sources of chloride were compared, using KCl and NH₄Cl₂. A split plot design was applied: Main plots included a) No fungicide control and b) Optimum fungicide control. Secondary plots comprised of three levels of Cl (0, 20 and 40 kg Cl/ha), three levels of K (0, 25 and 50 kg K₂O/ha) and three levels of both nutrients combined (K and Cl), with the addition of control with no Cl or K. All treatments received 100 kg/ha of N and 46 kg of P₂O₅/ha. 

Results obtained from both experiments indicate differences in wheat grain yield levels at seven of the eight sites. Although the combined analysis did not show differences among sources of K, some sites showed clear responses to the potassium source, indicating response to Cl and S. Foliar analysis for chloride indicated low levels, close to critical values as published by North American studies. Some sites exhibited severe visual symptoms of leaf diseases, which negatively affected yields. Increased Cl application was correlated with grain yield.

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Biblioteca

(*) Ingeniero Agrónomo, Ph. D en Ciencias del Suelo. Efectuó su trabajo doctoral en la Universidad de Carolina del Norte (EE.UU). Se desempeñó como Coordinador del Sub-Programa de ámbito Nacional de Manejo de suelos para Zonas Húmedas, con sede en la Estación Experimental Pergamino.

Desde 1996, es Coordinador del Proyecto Fertilizar y editor de la Revista Fertilizar, publicada por el proyecto. En su actividad profesional ha publicado más de 50 artículos en revistas científicas y más de 100 de divulgación técnica en el área de suelos y fertilización de cultivos.