Intensive cropping systems based on mechanical movement of soil have induced land degradation in most agricultural areas due to soil erosion and soil fertility losses. Thus, farmers have been increasing fertilization rates to maintain an economically competitive crop yield. This practice has resulted in water quality degradation and lake eutrophication in many agricultural watersheds. Research was conducted in the Patzcuaro watershed in central Mexico to develop appropriate technology that prevents nonpoint source pollution from fertilizers. Organic matter (OM) and nitrogen (N) losses in runoff and nitrate (NO3‐N) percolation in Andisols with corn under conventional till (CT) and no‐till (NT) treatments using variable percentages of crop residue as soil cover were investigated for steep‐slope agriculture. USLE type runoff plots were used to collect water runoff, while suction tubes with porous caps at 30, 60, and 90 cm depth were used to sample soil water solutes for NO3‐N analyses. Results indicated a significant reduction of N and OM losses in runoff as residue cover increased in the NT treatments. Inorganic N in runoff was 25 kg/ha for NT without residue cover (NT‐0) and 6 kg/ha for the NT with 100 percent residue cover (NT‐100). Organic matter losses in runoff were 157 and 24 kg/ha for the NT‐0 and NT‐100 treatments, respectively. Nitrate‐N percolation was evident in CT and NT with 100 percent residue cover (NT‐100). However, NT‐100 had higher NO3‐N concentration at the root zone, suggesting the possibility of reducing fertilization rates with the use of NT treatments.

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En el presente estudio se parte de la necesidad de conocer la diferencia entre cuencas representativas y cuencas experimentales, ya que de aquí se desprenden los protocolos de investigación para la parametrización de las variables del ciclo hidrológico. La poca disponibilidad de instrumentación en cuencas experimentales hace necesario el uso de algoritmos para el análisis de la escasa información como fundamento para la instrumentación mínima necesaria para caracterizar cuencas experimentales de zonas áridas. De aquí que el objetivo del trabajo sea proveer los elementos teóricos esenciales para la adecuada caracterización de cuencas experimentales desproveídas de instrumentación como requisito esencial para la planeación en la conservación del suelo y agua en ecosistemas cuyo régimen pluvial es errático y escaso y bajo condiciones de poca disponibilidad de información. Se presentan métodos de análisis y de evaluación de obras de captación de escurrimientos.

Abstract. We documented that the mapping of the fractal dimension of the backscattered Ground Penetrating Radar traces (Fractal Dimension Mapping, FDM) accomplished over heterogeneous agricultural fields gives statistically sound combined information about the spatial distribution of Andosol' dielectric permittivity, volumetric and gravimetric water content, bulk density, and mechanical resistance under seven different management systems. The roughness of the recorded traces was measured in terms of a single number H , the Hurst exponent, which integrates the competitive effects of volumetric water content, pore topology and mechanical resistance in space and time. We showed the suitability to combine the GPR traces fractal analysis with routine geostatistics (kriging) in order to map the spatial variation of soil properties by nondestructive techniques and to quantify precisely the differences under contrasting tillage systems. Three experimental plots with zero tillage and 33, 66 and 100% of crop residues imprinted the highest roughness to GPR wiggle traces (mean H R/S =0.15), significantly different to Andosol under conventional tillage (H R/S =0.47).

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