Clayton Giani Bortolini

Clorofila na folha como indicador do nível de nitrogênio em cereais

The development of a portable chlorophyll meter, which allows instantaneous measurement without leaf destruction, has been used as a new tool to assess plant N status. The reading in the equipment indicates a relationship with leaf chlorophyll and they are calculated based on the emission of light quantity through of the leaf in two wavelengths with different chlorophyll absorbance. Some researchers have established association between SPAD reading and chlorophyll content and between chlorophyll content and plant N content. In rice, wheat, oat and maize there were determined good associations between SPAD reading and grain yield. The critical level of a portable chlorophyll meter, correspondent with adequated N level, determined in rice (panicle differentiation), wheat (leaf flag) and maize (silking) are of, respectively, 40-42, 41-42 and 58-62. However, since it is a new tool, this equipment presents some limitations such as: little variation between readings, the readings are influenced by other factors besides N and, especifically for maize, to present low correlation with grain yield in the initial stages of plant development. These limitations were be to solve or minimize through the utilization of correction factores such as the use of strip reference, specific leaf weight, leaf area and plant dry matter. Despite of the limitations presented, the use of the leaf chlorophyll content shows high potential as an indicator for nitrogen fertilization recommendation in cereals, especially if associate as soil indicators.

Resposta de híbridos simples de milho à redução do espaçamento entre linhas

The objective of this work was to determine the effects of using narrow row spacing on grain yield, grain components and on other agronomic traits of maize single-cross hybrids. Two experiments were conducted in the state of Rio Grande do Sul, Brazil. In the 1997/98 growing season, treatments were composed by two singlecross hybrids (Cargill901 and BraskalbXL212) and four row spacings (40, 60, 80 and 100 cm). In the 1998/99growing season, two single-cross hybrids were tested at two plant densities (50,000 and 65,000pl./ha) and four row spacings (40, 60, 80 and 100 cm). Maize grain yield was influenced by hybrid and plant density. The reduction in row spacing promoted a high grain yield specially for hybrids with a low plant height sown at the density of 50,000pl./ha.

Efeitos do manejo mecânico e químico da aveia-preta no milho em sucessão e no controle do capim-papuã

n†The objective of this experiment was to evaluate the effects of mechanical and chemical management of oat straw and of sowing dates of maize after oat desiccation on maize grain yield and on alexandergrass (Brachiaria plantaginea Link) infestation. In 1997/98, treatments were composed by two mechanical management systems of oat (rolled or not) and bare area as the control, by two herbicides (glyphosate and paraquat) applied to desiccate oat straw and by two maize sowing dates after desiccation (one and 15 days). In the 1998/99†growing season, five management systems of oat straw (rolled, cleared and desiccated with glyphosate, glufosinate and paraquat) and a bare area used as check were tested. Delay of maize sowing date in 15 days after oat straw desiccation increased N accumulation, dry matter production per plant and grain yield of maize. Maize grain yield in succession to oat was not influenced by management system of oat straw. Rolling oat straw provided the best control of alexandergrass infestation.

Sistemas consorciados de aveia preta e ervilhaca comum como cobertura de solo e seus efeitos na cultura do milho em sucessão

With the increase of corn cultivation under the no-tillage system, various cover crop species have been evaluated to obtain a soil cover that benefits corn under succession and no-tillage. The objective of this work was to evaluate the effect of three sowing densities of black oat (Avena strigosa Scheig) and common vetch (Vicia sativa) in associated crops and as isolated crops and three levels of nitrogen fertilization (N), applied on corn (0, 60 and 160 kg ha-1 of N). Dry matter yield of the cover crop species was similar in associated systems and as isolated crops. The increase in the amount of N applied and the increase in the proportion of common vetch seeds in the associated systems increased the amount of N accumulated by corn plants. There was no interaction between the amount of N applied and the soil cover systems for corn grain yield. Without N fertilization, corn grain yield increased 321 kg ha-1 for each 10% of substitution of oat for common vetch in the associated systems. With 60 kg ha-1 of N, the response was quadratic. With the 160 kg ha-1 of N, there was no effect of soil cover on corn grain yield. Grain yield of corn cultivated after oat as isolated crop or associated with common vetch increased linearly with the increase of the amount of N fertilizer applied in corn. Under succession, using common vetch as an isolated crop, there was no response of corn grain yield to N fertilization.

Sistemas de aplicação de nitrogênio e seus efeitos sobre o acúmulo de N na planta de milho

Nitrogen accumulation in corn plant is highly influenced by N content in soil and by rate of its absorption by plant in a given growing stage. In order to compare the effects of N application methods on N accumulation and dry matter production by corn plant, an experiment was carried out in the state of Rio Grande do Sul, Brazil, over the 1998/99 growing season. Treatments consisted of two levels of water availability, one adequate to corn crop needs and the other with excessive water availability, and seven systems of N application to soil. The N application methods consisted of the following rates: 150 kg ha-1 topdress; 150 kg ha-1 applied before corn sowing (immediately after oat desiccation); 75 kg ha-1 applied before corn sowing + 75 kg ha-1 topdress; 60 kg ha-1 topdress; 60 kg ha-1 applied before corn sowing; 30 kg ha-1 applied before corn sowing + 30 kg ha-1 topdress; 60 kg ha-1 topdress; and check (without N before corn sowing or topdress). At sowing, 30 kg ha-1 of N were applied to all treatments. Urea was used as N source. Topdress N was applied manually, in a row, 5 cm from the corn row. There was no interaction between water level applied and N application systems. In the system with total N application before corn sowing, plants accumulated less N in relation to the system in which N was topdressed. The differences between the two systems were higher in the later stages of plant development, regardless of the water availability level.