Exploration of Responses to Potassium in Western Uruguay

Several regions of Uruguay has recently shown K deficiencies and responses. This project looks to determine the different areas with K deficiency, evaluate responses in the main field crops, and provide information on K soil testing.

IPNI-2007-URY-2

22 Feb 2011

2010 Annual Report


Traditionally, the agriculture in Uruguay has been done on soils with medium to high natural levels of potassium (K) (Hernández 1997b, Hernández et al, 1988). The decisions of K fertilization in field crops has been based on critical levels exchangeable K, referenced for other regions: 0.20-0.25 meq/100 g for medium textured soils, and 0.30 to 0.35 meq/100 g for fine soil textures (Ammonium acetate extraction). No response to K fertilization is expected above those exchangeable K levels, similarly to those operated until 2003 under tillage systems of U.S. Corn Belt (90-130 mg kg-1: 0.23 to 0.33 meq/100 g). The small number of experiments and years of study had indicated little or no response to the addition of K in soils of different textures and levels of exchangeable K. This explains why in most crops, K fertilization is not recommended. Those studies were mostly in soybean, under conventional tillage, and in soils located in the eastern region of the country, with exchangeable K levels ranging from 0.11 to 0.77 meq/100 g (Docampo et al., 1981; Marella et al., 1981; Colombo and Collares, 1982; Pereira et al., 1983).

However, the recent intensification of agriculture, crop rotations of high yields, may have decreased K levels in soils. On the other hand, the increasing expansion of the agriculture has included soils with many restrictions, some of which had already shown some response to K fertilization (Moir and Reynaert, 1962; Castro, 1965). Nutritional surveys in corn in dairy farms (Morón and Baethgen, 1996) and Lotus corniculatus L. (Barbazán et al., 2007), including many types of soil, indicated that there would be evidence for K deficiencies attributed to low levels of exchangeable K. More recent studies in the Western, Northern and Center areas of the country (Almada, 2006; Cano et al., 2007; Cano et al., 2008; Bautes et al., 2009) reported in some cases response to K even with exchangeable K levels considered medium to high under no-tillage situations, where the nutrient dynamics differs from those in conventional tillage (Bordoli, 2001).

While the country has made great effort to understand the dynamics of nutrients such as P and N in different production situations, by far much less research has focused on understanding the dynamics of K. Therefore, the country needs to set a system of fertilizer K recommendation, given the extensive area occupied by agriculture, the different soil types and the current price of fertilizers. In addition, the area with evidence of more probable response to K, in the short or medium term, is estimated in about 20% of the productive area of the country.

In this context, we are conducting several studies to understand the dynamics of K in agricultural soils under conservation tillage and get rational guidelines for K fertilizer recommendations in Uruguay. These studies are:



1) Study of the reserves of potassium: K non-exchangeable and clay type.
2) Study of buffering capacity of K in soils of Uruguay.
3) Study of leaching of K from crop residues and temporary changes in soil exchangeable K.
4) Study of equivalent K fertilizer.

Additional Resources

Informe_2009_10_K_URUGUAY - FINAL.pdfSize: 0.57 MB