Effects of supplementary irrigation on chemical and physical soil properties in the rolling pampa region of Argentina

Cien. Inv. Agr. 34(3): 187-194. 2007 www.rcia.puc.cl ARTICULO DE INVESTIGACION Effects of supplementary irrigation on chemical and physical soil properties in the rolling pampa region of Argentina Rodolfo Mon1, Carlos Irurtia1, Guido Fernando Botta2, Oscar Pozzolo3, Fernando Bellora Melcón2, David Rivero4, and Miguel Bomben4 1 Instituto Nacional de Tecnología Agropecuaria (INTA), Instituto de Suelos Castelar, Provincia de Buenos Aires Argentina. 2Facultad de Agronomía de la Universidad de Buenos Aires, Av. San Martín, 44 53 C.P. 1417, Ciudad Autónoma de Buenos Aires, Argentina. 3 Instituto Nacional de Tecnología Agropecuaria (INTA) Concepción del Uruguay, Provincia de Entre Ríos Argentina. 4Facultad de Agronomía Universidad Nacional de La Pampa, C.P. 6300, La Pampa, Argentina. Abstract R. Mon, C. Irurtia, G. F. Botta, O. Pozzolo, F. Bellora Melcón, D. Rivero, and M. Bomben. 2007. Effects of supplementary irrigation on chemical and physical soil properties in the rolling pampa region of Argentina. Cien. Inv. Agr. 34(3):187-194. The effects of supplementary irrigation on soil chemical and physical properties were studied in 21 locations in the north of the rolling pampa region of Argentina. The chemical and physical variables were measured in top soil (0-100 mm) to compare irrigated and non-irrigated soils. Chemical variables were: electrical conductivity (EC), pH, exchangeable sodium percentage (ESP), and organic mater content. Physical variables included structural index (SI) and percolation index (PI) measured in the laboratory, as well as infiltration, runoff, and soil losses, measured in the field with a small portable rainfall simulator. Water quality was established according to its chemical composition and Riverside USA classification. In irrigated soils, chemical data shows, on average, a slight increase in ESP (from 2.56 to 5.52) and in pH (from 6.13 to 6.45). EC, SI, and PI show the same values in irrigated and non-irrigated soils. The application of a simulated rainfall of 30 mm in 30 min revealed a different soil behavior. Irrigated soils present lower values of water entry and infiltration rates, and higher values of runoff and soil losses. The variation in chemical and physical soil properties show that within 10 years of supplementary irrigation a slight process of sodication and alkalinization occurs. Water quality and soil chemical data suggest that the sodication process and the increased soil erosion risk must be controlled in order to achieve a sustainable high production system. Keywords: Erosion risk, infiltration, sodication, supplementary irrigation. Introduction In the last decade, farmers in the wet pampa region of Argentina, a region with longterm continuous agriculture, began using supplementary irrigation to avoid water stress during critical periods. Crop growth is usually affected during the summer by short periods of water deficit that significantly decrease crop yields. Received 25 June 2007. Accepted 24 September 2007. 1 Corresponding author: Supplementary irrigation is needed when natural precipitation is not adequate to secure grain and forage production (Abu-Awwad and Kharabsheh, 2000). Depending on the size of the farm and the type of irrigation system, application of water is often made possible by using modern power sources from deep well pumps and storage of large quantities of water in reservoirs, ponds, streams and rivers. City water is also often accessed directly by small farmers who use drip irrigation for their vegetable gardens. Soil and water losses by erosion and runoff must CIENCIA E INVESTIGACION AGRARIA 188 be controlled in order to allow for sustainable agriculture. In Georgia, on relatively sandy soil with low organic matter content, Truman and Rouland (2005) found high erosion risk when a supplementary irrigation system was used. Natural water has different salt concentrations and qualities, and contains principally salts of high solubility like sodium, calcium, magnesium and potassium chlorides and sulfates. Salinization and sodication could limit the soil’s productivity, leading to fertility reduction (AlZu’bi, 2007). If the level of Na+ in the soil is high, the colloidal fraction behavior will be affected. The level of Na+ in soil is usually quantified by the exchangeable sodium percentage (ESP) or by its estimator, the sodium adsorption ratio SAR. When SAR increases, then the rate of the soil sodication process also increases (Herrero and Perez Covetta, 2005). Suarez et al. (2006) found that a SAR increase caused by irrigation water had an adverse impact on water infiltration for two types of soil, clay and loam. For the clay soil, even an increase from SAR 2 to SAR 4 resulted in a significant increase in infiltration rate, while in loam soil the increase in infiltration time was significant. Sodic soils are associated with structural changes that principally affect soil’s permeability. With high ESP and low electrolyte concentration, clay, as well as organic matter, begins to swell and disperse, causing negative physical effects such as restricted aeration and permeability. Damage to physical properties soon appears at low salt concentrations. Clay and organic matter swelling and dispersion are unavoidable after irrigation with water of low quality (Kamphorst and Bolt, 1978). Boivin et al. (2002) found that Sampling sites N Santa Fe Córdoba Buenos Aires Arrecifes Arroyo Capitán Sarmiento Carmen de Areco Colón Cnel. Bogado Los moros Los indios Gahan Las Varillas Maggiolo Manfredi Pearson Sol de Mayo Uranga San Antonio de Areco Est. Rojo Santa Isabel Teodolina Venado Tuerto Cintra Figure 1. Soil and water control sites in the selected area under supplementary irrigation in the pampa Region of Argentina. Figura 1. Sitios de muestreo de agua y suelos en el área elegida bajo riego suplementario en la región de la pampa de Argentina. VOL 34 N˚3 SEPTIEMBRE - DICIEMBRE 2007 189 the increase in alkalinity and Mg concentration in arid vertisol soil was caused partly by the composition of the irrigation water, and partly by the reduction and dissolution of Fe oxides, and Fe2+ fixation on exchange sites of the clay minerals. water irrigation impact on soil properties after 10 years of supplementary irrigation in a large area dedicated to grain production in the rolling pampa region of Argentina. Hydraulic conductivity (k) reduction is irreversible, or very difficult to restore, because of soil matrix changes caused by swelling and dispersion of clay and organic matter. Chen and Banin (1975) used microscopic observation to show that fine particle reorganization arranges a continuous net of fine material that fills all the void spaces. This study was performed in one of the most important areas under supplementary irrigation in Argentina, located north of Buenos Aires (39º 15’ S, 59º 21’ W) and south of Córdoba (33º 10’ S, 63º 40’ W) and Santa Fe (32º 3’, 61º 17 W) provinces (Figure 1). This area is (...truncated)