NITROGEN FERTILIZATION IN SOYBEAN UNDER LOW LATITUDE AND LOW NATURAL SOIL FERTILITY

In soybean, some studies have shown yield increase when nitrogen is provided through symbiotic fixation along with nitrogen fertilization. Thus, this study aimed to evaluate the effect of nitrogen fertilization on soybean cultivated at a low natural fertility area. Two experiments (field and pot) were conducted. A randomized block design was adopted, with 24 treatments and 3 replications. The treatments were arranged in a 2x12 factorial scheme, represented by two cultivars (TMG 1288RRTM and CD 251RRTM) and 12 combinations of nitrogen supply (CNS). The CNS used were: without inoculant and nitrogen; only inoculant; 20; 40 and 60 kg ha-1 of N + inoculant; 50; 100; 150; 200; 250; 300 and 350 kg ha-1 of N. The doses of N were divided into three applications: 20% applied at planting, 40% at early flowering and 40% at grain-filling. The nitrogen fertilization associated with seed inoculation did not result in significant gains for crop yield. The mineral nitrogen supply affected negatively the number and mass of nodules, and positively the root mass.En el cultivo de la soja, algunos estudios han demostrado un aumento en la productividad cuando se suministra el nitrógeno a través de la fijación simbiotica junto con la fertilización nitrogenada. Así, el presente trabajo se realizó con el objetivo de evaluar el efecto de la fertilización con nitrógeno en soya cultivada en un área de baja fertilidad. Se realizaron dos experimentos, uno en campo y el otro en macetas. El diseño experimental utilizado fue en delineamiento bloques al azar, con 24 tratamientos y tres repeticiones. Los tratamientos se dispusieron en un esquema factorial de 2x12, siendo dos variedades (TMG 1288 RR y CD 251RR) y 12 combinaciones de suministro de nitrógeno (CSN).  Los CSN utilizados fueron: sin nitrógeno y sin inoculante; sólo inoculante; 20, 40 y 60 kg ha-1 de N + inoculante; 50, 100, 150, 200, 250, 300 y 350 kg ha-1 de N. Las dosis de N se dividieron en tres aplicaciones, siendo el 20% aplicado en la siembra, el 40% al inicio de la floración y el 40% durante el llenado del grano. La fertilización nitrogenada asociada a la inoculación de las semillas no dio lugar a un aumento significativo de la productividad del cultivo. El suministro de N mineral afectó negativamente al número y peso de los nódulos y positivamente al peso de las raíces.Na cultura da soja, alguns estudos têm revelado aumento de produtividade quando o nitrogênio é fornecido através da fixação simbiótica juntamente com a adubação nitrogenada. Assim, o presente trabalho foi realizado com o objetivo de avaliar o efeito da adubação nitrogenada em soja cultivada em área de baixa fertilidade natural. Foram conduzidos dois experimentos, sendo um em campo e outro em vasos. Os experimentos foram em delineamento de blocos ao acaso com 24 tratamentos e três repetições. Os tratamentos foram dispostos em um esquema fatorial 2x12, representado por dois cultivares (TMG 1288 RR e CD 251RR) e 12 combinações de fornecimento de nitrogênio (CFN). As CFN utilizadas foram: sem inoculante e sem nitrogênio, apenas inoculante, 20, 40 e 60 kg ha-1 de N + inoculante, 50, 100, 150, 200, 250, 300 e 350 kg ha-1 de N. As doses de N foram divididas em três aplicações, sendo 20% aplicada no plantio, 40% no início do florescimento e 40% no enchimento de grãos. A adubação nitrogenada em associação com a inoculação das sementes não resultou em ganhos significativos na produtividade da cultura. O fornecimento de N mineral afetou negativamente o número e peso dos nódulos e positivamente o peso das raízes

Fungal Community Structure as an Indicator of Soil Agricultural Management Effects in the Cerrado

<div><p>ABSTRACT Forest-to-agriculture conversion and soil management practices for soybean cropping are frequently performed in the Cerrado (Brazilian tropical savanna). However, the effects of these practices on the soil microbial communities are still unknown. We evaluated and compared the fungal community structure in soil from soybean cropland with soil under native Cerrado vegetation at different times of the year in the Tocantins State. Soil samples were collected in two periods after planting (December) and in two periods during the soybean reproductive growth stage (February). Concomitantly, soil samples were collected from an area under native Cerrado vegetation surrounding the agricultural area. The soil DNA was analyzed using a fingerprinting method termed Automated Ribosomal Intergenic Space Analysis (ARISA) to assess the fungal community structure in the soil. Differences in the fungal community structure in the soil were found when comparing soybean cropland with the native vegetation (R = 0.932 for sampling 1 and R = 0.641 for sampling 2). Changes in the fungal community structure after management practices for soybean planting in Cerrado areas were related to changes in soil properties, mainly in copper, calcium, and iron contents, cation exchange capacity, base saturation, and calcium to magnesium ratio. These results show the changes in the fungal community structure in the soil as an effect of agricultural soil management in Cerrado vegetation in the state of Tocantins.</p></div