06916nam a2200361 a 450000100080000000500110000800800410001902000150006010000160007524501610009126000380025230000100029050000760030052058960037665000110627265000120628365000150629565000170631065000250632765000100635265000200636265000220638265000240640465000090642865000190643765000160645665000160647265000110648865000130649965300130651265300110652565300180653615588242007-09-28       1998    bl uuuu      00u1 u    #d  a38971235091 aKATO, O. R.  aFire-free land preparation as an alternative to slash-and-burn agriculture in the Bragantina region, Eastern Amazonbcrop performance and nitrogen dynamics.  aGottingen: Cuvillier Verlagc1998  a132p.  aDoctoral dissertation apresentada a Gorge-August University, Gottingen.  aIn the Amazon region, shifting cultivation with slash burning is practiced by at least 500, 000 small farmes, has been considered one of the main activities responsible for deforestation. To considerably reduce deforestion rates the level of sustainability of the shifting cultivation systems, has to be increased and technologies permitting an increase in the period used cultivation of an area to three or more years need to be employed. Thus, the present study had following objectives: 1) to evaluate the effects of fire-free land preparation on crop performance and nitrogen dynamics; 2) to evaluate the importance of chemical fertilizer use in use in systems without the use of fire and 3) to select rice, maize, cowpea and cassava cultivars suitable for mulch systems. The studies were conducted in the community of Comaru in the municipality of Igarape Acu (Para, Brazil) on two neighboring sites with 4-year-old (FV4y) and 10-year-old fallow vegetation (FV10y). There treatments for preparation were tested with and without fertilizer. The treatments were: 1) burning + NPK fertilization; 2) mulching + NPK fertilization; 3) incorporation of the fallow vegetation biomass into the soil + NPK fertilization. Rice was planted followed by cowpea and cassava in two consecutive cropping periods. Yield characteristics of the crops as well as the nitrogen dynamics in the soil and the nitrogen uptake by the were evaluated. Furthermore, screening experiments were set up to evaluate the yield characteristics of a total of 8 rice, 18 maize, 21 cowpea and 5 cassava cultivars under mulch conditions with and without fertilizer application. The land preparation experiment revealed that without fertilization, burning significatly increased the grain yilds of rice in the ferts cropping period compared to cropping without burning. This result was most likely due to the slow release of nutrients from the mulch or the incorporated plant material, possibly exacerbated by nutrient immobilization. In the second cropping period, no differences in rice yield were detected in the FV10y due to increasedyilds in the not burned and not fertilized treatment. In the second cropping period rice grain yields with burning showed an overall reduction of 7 and 30% in FV4y and FV10y, respectively, compared to the first period. The inverse trend is observed in systems without the use of fire. In the second cropping period an increase in yilds compared to the first cropping period of 117 and 233%, respectively. The yield increases in the second cropping period may be realted to the liberation of nutrients through the decomposition of mulch. Use of fertilizers significantly increased the rice grain yields in the two cropping periods in both areas and erased the land preparation effect seen without the use of fertilizers. The cowpea yields without fertilizer were around 0.3 t ha in the burned treatments. When the field was not burned the yilds were around 0.20 t ha in FV4y but cowpea did not produce at all in FV10y. With fertilization, cowpea grain yields were around 1.5 t ha, irrespective of the lenght of the fallow period and land preparation. In the second cropping period the greatest response in grain yield in relation to the first period were in the plants with much (with and without fertilizer). In the first cropping period cassava tuber yields were not influenced by land preparation, but residual fertilizer of the previously fertilized rice and cowpea crop doubled the yields. In the second cycle, without residual fertilizer, tuber yields decresed in the burned plots by 30% and 34% in FV4y and FV10Y, respectively. With residual fertilizer such a reduction was observed only in FV4y. In the treatments where fire not applied tuber yields were higher in FV4y than in FV10y. After burning, the topsoil pH increased approximately 1.5 units in both sites studies, whereas the plots no treated with fire shouwed only small pH variations over time. Eighteen months after planting, diffrences in pH between the burned plots and the unburned plots could no longer be detected. total nitrogen conyen of the soils of the two sites shouwed similar values. Approximatey 10 monyths after land preparation the soil reached the total N levels found prior to land preparation, regardless of the land preparation methods. NH4-N represented an average of 71% of the mineralized N (Nmin). During the rice crop phase (January to May) the Nmin values in the burned plot of FV10y decreased. The opposite effect occurred in the plots where fire was not applied. Low concentration (&lt0.2 mg) of NH4-N were found in the soil solution taken at a depth of 40cm. NO3-N concentration, lowever, were high in the beginning of the cropping period, the highest levels could be detected in the treatment with burning (15.1mg-1). But, during the rice crop phase these concentration reached values below 1 mg 1 in a 1-1in all treatments. An improved cultivar (CNA 7706) was found which achieved economic yields without fertilization and yielded 39% more than the locally mos-widespread cultivar. The maize and cowpea cultivars currestly available in the Amazon region seem poorly suited to soils of low fertility and thus require fertilization under mulch conditions. The tuber yields of all cassava cultivars were satisfactory under slash-and-mulch conditions, with and without fertilization, and showed a great capacity to take advantage of residual nutrients from previous croppings. As the last crop in the slash-and-burn system cassava escapes the negative effects of mulch decomposition so that no specific breeding targets are needed for this crop. The nitrogen available in the soil for the plants was overall not very influenced by land preparation or fertilizer application, suggesting that nutrients others than nitrogen the production in the slsh-and-much system when fertilizers are not used.  aBrazil  aburning  acrop yield  afire ecology  ashifting cultivation  aslash  asoil management  aCobertura do Solo  aCultivo Migratório  aFogo  aManejo do Solo  aNitrogênio  aPerformance  aPlanta  aQueimada  aAmazonas  aBrasil  aLand clearing