Source: Clark, M.S., W.R. Horwath, C. Shennan, and K.M. Scow. 1998. Changes in soil chemical properties resulting from organic and low-input farming practices. Agron. J. 90:662-671.

This study by a team at UC Davis seeks to analyze the differences in the chemical properties of soils where different farming practices have been utilized. Because soil fertility is directly related to the soils' chemical properties, this information is vital in order to farm with organic methods safely and productively. By understanding how organic farming influences the soil, we attempt to strike a sustainable balance between mimicking nature and feeding a growing human population. In this 8-year study, a plot of land, previously devoted to conventional farming practices was divided into subplots of four different farming techniques. These were as follows (1) A four-year rotation of tomato, safflower, corn, and a biculture of oats and vetch followed by bean in the fourth year managed according to the regulations of California Certified Organic Farmers (CCOF). This included application of animal manure, grass and legume cover crops, and mechanical cultivation. (2) A four-year rotation of tomato, safflower, corn, and wheat and bean under conventional management. This management philosophy included application of urea, NH₄NO₃, (NH₄)₂SO₂, superphosphate, and mixtures of nitrogen, potassium, and phosphorus. Application of pesticides was done according to University of California Integrated Pest Management (IPM) guidelines. (3) A two-year rotation of tomato and wheat managed using the same practices as the four-year rotation under conventional management. (4) A four-year rotation of the same crops cultivated in the organically managed plots, using a "low-input" technique. In the low input plots, application of the synthetic fertilizers and pesticides used in the conventional plots was reduced by also planting grass and legume cover crops. Manure was also applied to the low input plots for the first three years of the experiment. Soil samples were taken for analysis every four years. The following variables were tested: percent organic carbon, pH, electrical conductivity, and amounts of soluble phosphorus, exchangeable potassium, soluble calcium, and soluble magnesium. In all of the plots, the soil's pH increased over the experiment's duration. The increase was highest in the organic plots and lowest in the conventional ones. In general, the values for organic C, soluble P, exchangeable K, soluble Ca, and soluble Mg were all higher in the organically managed plots. These results coincided with previous findings that farming organically increases the organic matter and inorganic nutrients found in the soil. The authors conclude that these general and gradual changes can have long lasting effects on the productivity of the soil.

Abstract author: Sean Pilger, 15 November 1998.

SUSAG Abstracts: Go back to the SUSAG Abstracts search page.