Thiago Isquierdo Fraga

Atributos físicos do solo e rendimento de soja em sistema plantio direto em integração lavoura-pecuária com diferentes pressões de pastejo

The integration of farming and cattle production activities in no-tillage system areas with winter cover crops can be an income supplement for summer grain farmers. However, many of them are afraid of adopting this integration system, because of possible negative effects of animal treading on soil attributes, mainly of those related to soil compaction. This study was conducted: (1) to determine the alterations in the soil physical attributes promoted by animal treading; (2) to verify if the alterations in soil attributes due to animal treading affect soybean establishment and grain yield. The experiment was carried out with a Rhodic Hapludox (Oxisol), under black oat + ryegrass pasture grazed at different heights (10, 20, 30 and 40 cm) and an ungrazed area. After one cycle of animal treading there were no significant modifications in soil bulk density, porosity and compressibility at different grazing heights. However, soil density and compressibility were higher and the porosity lower in the grazed plots. The soybean population and grain yield were not affected by modifications in the soil physical attributes.

Flooded rice yield as affected by levels of water salinity in different stages of its cycle

Losses of productivity of flooded rice in the State of Rio Grande do Sul, Brazil, may occur in the Coastal Plains and in the Southern region due to the use of saline water from coastal rivers, ponds and the Laguna dos Patos lagoon, and the sensibility of the plants are variable according to its stage of development. The purpose of this research was to evaluate the production of rice grains and its components, spikelet sterility and the phenological development of rice at different levels of salinity in different periods of its cycle. The experiment was conducted in a greenhouse, in pots filled with 11 dm3 of an Albaqualf. The levels of salinity were 0.3 (control), 0.75, 1.5, 3.0 and 4.5 dS m-1 kept in the water layer by adding a salt solution of sodium chloride, except for the control, in different periods of rice development: tillering initiation to panicle initiation; tillering initiation to full flowering; tillering initiation to physiological maturity; panicle initiation to full flowering; panicle initiation to physiological maturity and full flowering to physiological maturity. The number of panicles per pot, the number of spikelets per panicle, the 1,000-kernel weight, the spikelet sterility, the grain yield and phenology were evaluated. All characteristics were negatively affected, in a quadratic manner, with increased salinity in all periods of rice development. Among the yield components evaluated, the one most closely related to grain yields of rice was the spikelet sterility.

Recuperação de atributos físicos de um Argissolo em função do seu revolvimento e do tempo de semeadura direta

A melhoria da qualidade estrutural do solo pelo uso continuado do sistema semeadura direta ocorre junto com o processo de sua (re)acidificacao. Em algumas circunstâncias, ocorre tambem compactacao superficial devido ao trafego de maquinas, que necessita ser corrigida pela mobilizacao do solo. Assim, em experimento conduzido ha 12 anos sob diferentes sistemas de manejo do solo, avaliou-se o tempo necessario para o solo readquirir os atributos fisicos iniciais, alterados no processo de revolvimento do solo, por ocasiao da reaplicacao de calcario. O experimento foi realizado na Estacao Experimental Agronomica da UFRGS, em Eldorado do Sul - RS, em um Argissolo Vermelho distrofico tipico. Os sistemas de manejo avaliados foram: (a) preparo convencional durante 12 anos, (b) sistema semeadura direta com revolvimento do solo para incorporar calcario a cada quatro anos, (c) sistema semeadura direta durante oito anos e (d) sistema semeadura direta durante 12 anos. Determinaram-se, imediatamente antes e 6, 12, 24, 36 e 48 meses depois da terceira reaplicacao de calcario, a densidade, a porosidade total, a macroporosidade, a microporosidade, a estabilidade de agregados e o teor de C orgânico em tres camadas (0,0-2,5; 2,5-7,5 e 7,5-15,0 cm) de solo. O revolvimento do solo para incorporacao do calcario no sistema semeadura direta de quatro anos propiciou condicoes mais favoraveis de densidade e porosidade do solo, mas diminuiu a estabilidade de agregados. Houve necessidade de um periodo de quatro anos de cultivo do solo no sistema semeadura direta para o retorno da estabilidade de agregados a condicao original. Os atributos fisicos do solo foram mais uniformes no perfil no preparo convencional, porem com menor estabilidade de agregados na camada superficial, que foi relacionada ao teor de C orgânico.

Suprimento de potássio e mineralogia de solos de várzea sob cultivos sucessivos de arroz irrigado

The low capacity to predict potassium (K) availability for rice by different evaluation methods is due to the greater potassium diffusion in the flooded soil solution and to potassium supply through non-exchangeable forms in the soil. The purpose of this study was to evaluate the supply capacity of exchangeable and non-exchangeable potassium forms by flooded soils with different characteristics, in successive rice crops. Rice plants were grown in a greenhouse in 12 dm3 pots in three soils (Typic Hapludales, Aquic Udorthents and Lithic Udorthents) that represent soils from different rice producing regions in the state of Rio Grande do Sul (Brazil), where the yield response to potassium fertilization is low. Soils were fertilized with potassium in three successive rice crops. Soil texture and mineralogy were characterized and rice plants were grown until flowering. Potassium was determined in the plant tissues and in exchangeable form in the soil, before and after rice cultivation. It was found that the soils differed in terms of potassium supply capacity to flooded rice and the contribution of non-exchangeable forms was significant. The short-term supply capacity (first crop) was related to the exchangeable form, and in the long term (2nd and 3rd crop) mostly by the potassium saturation ratio in the cation exchange capacity (K/CECpH 7,0) and by non-exchangeable forms, particularly, potassium feldspars, smectites and smectite interlayered with Al-hydroxy , found in different amounts in the analyzed fractions.