Andre Luis Thomas

Rendimento de grãos de soja afetado pelo espaçamento entre linhas e fertilidade do solo

Two soybean experiments were performed at lhe Agronomic Experimental Farm of the Federal University of Rio Grande do Sul, in the county of Eldorado do Sul - RS. In the 1994/95 growing season the cultivars FT-Saray and OCEPAR 14 (both early maturity and determinate type) were used, in row spacings of 20 and 40cm, and the soils with very low and sufficient phosphorus leveis, and population of 40 plants m-2. In the 1996/97 growing season the cultivar FT-Saray was used, row spacings of 20 and 40cm, soils with three fertility leveis (actual fertility, recommended fertiliwtion and twice the recommendation), and populations of 30 and 40 plants m-2. When the soil fertility reached the crop requirements, according to the technical recommendations, the row spacing reduction from 40 to 20cm increased grain yield from 3554 to 4104kg ha-1 (+15%), in the first year, and from 4322 to 5420kg ha-1 (+ 25%) in the second. When the soil fertility was below the critical level, the same decrease in row spacing lowered yield from 1843 to 1520kg ha-1 (-17%).

Efeito de populações e espaçamentos sobre o potencial de rendimento da soja durante a ontogenia

The objective of this study was to evaluate the effects of the row spacing reduction, plant populations and soil fertility on soybean potential yield at three stages of development. The experiment was performed at the Estação Experimental Agronômica of Universidade Federal do Rio Grande do Sul, in Eldorado do Sul, Rio Grande do Sul State, Brazil, in the 1996/97 growing season, in a Rhodic Paleudult soil . The experimental design was a split split-plot randomized complete block, with four replicates. Treatments were tested at three soil fertility levels (without fertilization, the recommended fertilization and twice the recommended fertilization), two plant populations (30 and 40 plants m) and two row spacing (20 and 40 cm). The cultivar tested was FT-Saray (early), in notill. Mean potential yields were 15.007 kg ha in R2, 10.282 kg ha -1 in R5 and 5.330 kg ha -1 in R8 (maturity). Plant populations as well as row spacing affected the soybean potential yield. The population of 40 plants m was greater than the 30 plants m in R5 but this advantage was not observed at maturity, because at this stage there was no difference between populations. With 20 cm rows the potential yield was greater than with 40 cm in R5, resulting in higher yield in R8.

Development of the nodulated soybean plant after flooding of the root system with different sources of nitrogen

Flooding leads to hypoxia, a stress to which symbiotic N2 fixation is especially sensitive. The response of fully nodulated soybean plants to a 21-day period of flooding was studied by measurements of growth parameters and xylem transport of organic nitrogenous components to the shoot, in the presence and absence of NO3- and NH4+ in the medium. Flooding was found to seriously impair N2 fixation, irrespective of the N source, as indicated by strongly reduced xylem ureide levels. In the absence of a source of N, growth was strongly reduced during flooding while accumulation of N in the shoot was virtually abolished. Flooding in the presence of 5 mM NO3- or NH4+ led to the accumulation of total N in the shoot but only NO3- promoted increases in total dry matter, plant height and leaf area above that found in the absence of N. The accumulation of N, however, was lower than that of the non-flooded control for both NO3- and NH4+. The increases in total dry matter, plant height and leaf area with NO3- was as high as those of the non-flooded control. These data clearly show the beneficial effects of NO3- during a prolonged period of flooding of the nodulated root system of soybean.

Potencial de rendimento da soja em razão da disponibilidade de fósforo no solo e dos espaçamentos

The experiment was performed during the 1994/95 growing season at the EEA/UFRGS, in Eldorado do Sul, RS, Brazil, in a dark red Podzolic soil (Rhodic Paleudult). The objective was to evaluate the soybean potential yield at the growth stages R2 (flowering), R5 (beginning of pod filling) and R8 (maturity). The treatments were arranged in subplots in a randomized complete block design, and consisted of two soil P levels (3 and 15 ppm), and two row spacings (20 and 40 cm). The early, determinate cultivar OCEPAR 14 was used. On the average of the treatments, potential yield in R2 was of 18 t/ha and of 10 t/ha in R5, and the final yield, in R8 of 4.6 t/ha. The treatment of 15 ppm of P reached greater potential yield in the three growth stages, due to less flower and pod abortion. The row spacing of 20 cm showed greater potential yield at the growth stages evaluated, but the percentage of yield reduction due to flower and pod abortion were similar.

Amino acid and ureide transport in the xylem of symbiotic soybean plants during short-term flooding of the root system in the presence of different sources of nitrogen

The transport of organic N compounds to the shoot in the xylem sap of nodulated soybean plants was investigated in an attempt to better understand the changes in N metabolism under root hypoxia (first 5 days of flooding), with different sources of N in the medium. NO 3 - is beneficial for tolerance of plants to waterlogging, whereas other N sources such as NH 4 + and NH 4 NO 3, are not. Nevertheless, in the presence of NH 4 + high levels of amino acids were transported in the xylem, consistent with its assimilation. Some increase in the transport of amino acids was also seen with NO 3 - nutrition during waterlogging, but not with N-free medium. Ureide transport in the xylem was severely reduced during waterlogging, consistent with impaired N 2 fixation under these conditions. The relative proportions of some amino acids in the xylem showed dramatic changes during treatment. Alanine increased tremendously under root hypoxia, especially with NH 4 + as N source, where it reached near 70 % of the total amino acids present. Aspartic acid, on the other hand, dropped to very low levels and was inversely related to alanine levels, consistent with this amino acid being the immediate source of N for alanine synthesis. Glutamine levels also fell to a larger or lesser extent, depending on the N source present. The changes in asparagine, one of the prominent amino acids of the xylem sap, were most outstanding in the treatment with NO 3 - , where they showed a large increase, characteristic of plants switching from dependence on N 2 fixation to NO 3 - assimilation. The data indicate that the lesser effectiveness of NH 4 + during waterlogging, in contrast to NO 3 - , involves restricted amino acids metabolism, and may result from energy metabolism being directed towards NH 4 + detoxification.

Effect of population and spacing on soybean potential yield during ontogeny

The objective of this study was to evaluate the effects of the row spacing reduction, plant populations and soil fertility on soybean potential yield at three stages of development. The experiment was performed at the Estação Experimental Agronômica of Universidade Federal do Rio Grande do Sul, in Eldorado do Sul, Rio Grande do Sul State, Brazil, in the 1996/97 growing season, in a Rhodic Paleudult soil . The experimental design was a split split-plot randomized complete block, with four replicates. Treatments were tested at three soil fertility levels (without fertilization, the recommended fertilization and twice the recommended fertilization), two plant populations (30 and 40 plants m) and two row spacing (20 and 40 cm). The cultivar tested was FT-Saray (early), in notill. Mean potential yields were 15.007 kg ha in R2, 10.282 kg ha -1 in R5 and 5.330 kg ha -1 in R8 (maturity). Plant populations as well as row spacing affected the soybean potential yield. The population of 40 plants m was greater than the 30 plants m in R5 but this advantage was not observed at maturity, because at this stage there was no difference between populations. With 20 cm rows the potential yield was greater than with 40 cm in R5, resulting in higher yield in R8.

Effect of plant density and spacing on the potential yield of soyabeans during development.

The objective of this study was to evaluate the effects of the row spacing reduction, plant populations and soil fertility on soybean potential yield at three stages of development. The experiment was performed at the Estação Experimental Agronômica of Universidade Federal do Rio Grande do Sul, in Eldorado do Sul, Rio Grande do Sul State, Brazil, in the 1996/97 growing season, in a Rhodic Paleudult soil . The experimental design was a split split-plot randomized complete block, with four replicates. Treatments were tested at three soil fertility levels (without fertilization, the recommended fertilization and twice the recommended fertilization), two plant populations (30 and 40 plants m) and two row spacing (20 and 40 cm). The cultivar tested was FT-Saray (early), in notill. Mean potential yields were 15.007 kg ha in R2, 10.282 kg ha -1 in R5 and 5.330 kg ha -1 in R8 (maturity). Plant populations as well as row spacing affected the soybean potential yield. The population of 40 plants m was greater than the 30 plants m in R5 but this advantage was not observed at maturity, because at this stage there was no difference between populations. With 20 cm rows the potential yield was greater than with 40 cm in R5, resulting in higher yield in R8.