A Look at Amazon Basin Seasonal Dynamics with the Biophysical ...

NUTRIENT USE EFFICIENCY IN ABANDONED PASTURE SOIL UNDERORGANIC AND CHEMICAL AMENDMENTSLucerina Trujillo; Flávio J. Luizão; Johannes Lehmann. INPA-Ecology and CornellUniversity. E-mail: lucerina@inpa.gov.brMost of the agricultural systems in Amazon do not take into account the organic matter useand recycling, which is the key for the functioning of the original forest ecosystem. In orderto compare the efficiency of nutrient use for plant growth and production under two typesof fertilizers added to the soil (organic or chemical), an experiment was established at theEMBRAPA/CPAA Experimental Station, near Manaus. Using a randomized block designwith five repetitions, 1-m 2 suspended plots, filled with Yellow Latosol from abandonedpastures, were planted with green pepper (Capsicum sp), used as test-plants. Fourtreatments were used: addition of organic fertilizer; chemical fertilizer; organic+chemicalfertilizer; and, control (without fertilizer). Lime was applied in all treatments. The plantbiomass, amounts of nutrients in the leaves, shafts and roots of test-plants, besides the fruitproduction, were measured. In the plants under organic amendment, were necessary 0.42 gof P; 4.5 g de K; 1.19 g of Ca and 0.04 g of Mg to produce 1 kg of fruits. In the chemicaltreatment, the amounts of nutrients necessary were much larger (except for Ca): 1.05 g ofP; 13.2 g de K; 1.19 g of Ca and 0.95 g of Mg. That means that the use of nutrients for fruitproduction in the treatment with organic fertilizer was more efficient than in the treatmentwith chemical fertilizer, possibly due to a better retention of water and nutrients in the soilorganic matter. One consequence of that was significantly lower leaching of nutrients underthe organic amendment: 17 kg /ha of N; 1.3 kg /ha of K; 3.3 kg /ha of Ca and 0.4 kg /ha ofMg. Under chemical amendment, leaching losses were: 94 kg/ha of N; 212 kg/ha of K; 36kg/ha of Ca and 7.4 kg/ha of Mg. Additionally, under organic amendment plants developedlarger biomass of leaves and roots which allow larger photosynthesis rates and largersurface for nutriente uptake. At a basin scale, the largest nutrient retention in the soil and inthe plants would represent a lower risk of pollution of water bodies by agriculturalplantations, when organic fertilizer is used instead of chemical treatments.