STOCKS OF CARBON AND SOIL FERTILITY IN ORGANIC AND MINERAL SYSTEMS OF FERTILIZATION FOR VEGETABLES, IN EIGHT YEARS OF CROP ROTATION

Abstract

The accurate fertilization and nutrient cycling strategies are very important in organic production systems. This experiment was implemented from 1991 to 1999 and had as objective evaluating three systems of organic and mineral fertilization and a control (no fertilization), in a randomized complete block design with three replications tracks formed by permanent 25 m long and 4 m wide (100 m2). The treatments were: T1. Organic compost - CO (15 t.ha-1, dry weight); T2. Organic compost - CO (15 t.ha-1, dry weight) + mineral fertilizers - MF (according to analysis); T3. Mineral fertilizers - MF (according to analysis); and T4. Control (no fertilization). In systems with organic fertilizer, a fraction of added carbon has accumulated in soil over time. The isolated mineral fertilization system and without fertilization revealed high emissions of soil carbon stocks. In 8 years, the stock of carbon in the system with organic fertilizer increased by 20.5%, from 38.5 t.ha-1 in 1991 to 46.4 t.ha-1 COT in 1999, while the system with mineral fertilizer decreased by 38.2%, from 33.0 t.ha-1 to 20.4 t.ha -1. The data show that systems submitted to organic fertilizers are more resilient as the carbon losses. The accumulation of carbon in eight years showed that there was a gain of approximately 7.9 t.ha-1 of COT with organic fertilizer, which corresponds to a sequestration or avoided emissions of 29.0 t.ha-1 of CO2-equivalent. The loss of 12.6 t.ha-1 COT system with mineral fertilizer corresponded to an emission of 46.6 t.ha-1 CO2-equivalent. Organic fertilizer, isolated or associated with mineral fertilizer, helped to correct acidity and phosphorus in elevation and soil base. Yields of potatoes and corn were similar in the three fertilizers, which had higher yields than the system without fertilization. For growing cabbage, organic fertilization showed average yields similar to mineral fertilization. The highest yields were obtained with combined use of organic manure with minerals.