Reimar Carlesso

Estimation of water retention and availability in soils of Rio Grande do Sul

Dispersed information on water retention and availability in soils may be compiled in databases to generate pedotransfer functions. The objectives of this study were: to generate pedotransfer functions to estimate soil water retention based on easily measurable soil properties; to evaluate the efficiency of existing pedotransfer functions for different geographical regions for the estimation of water retention in soils of Rio Grande do Sul (RS); and to estimate plant-available water capacity based on soil particle-size distribution. Two databases were set up for soil properties, including water retention: one based on literature data (725 entries) and the other with soil data from an irrigation scheduling and management system (239 entries). From the literature database, pedotransfer functions were generated, nine pedofunctions available in the literature were evaluated and the plant-available water capacity was calculated. The coefficient of determination of some pedotransfer functions ranged from 0.56 to 0.66. Pedotransfer functions generated based on soils from other regions were not appropriate for estimating the water retention for RS soils. The plant-available water content varied with soil texture classes, from 0.089 kg kg-1 for the sand class to 0.191 kg kg-1 for the silty clay class. These variations were more related to sand and silt than to clay content. The soils with a greater silt/clay ratio, which were less weathered and with a greater quantity of smectite clay minerals, had high water retention and plant-available water capacity.

Absorção de água pelas plantas: água disponível versus extraível e a produtividade das culturas

An important issue to understanding the effect of water shortage on crop yield is how crops balance the supply of water from the soil to match the demand for water from the atmosphere. Supply is determined by the crop ability to utilise the stored soil water and, demand, on the other hand, is determined by a combination of metereological factors interacting with the crop canopy. Different criteria have been used to determine the timing and duration of water deficits despite the abundant literature available. Much attention has been given to the quantification of crop water consumption in different stages of development. However, considerations about the total amount of plant water available (extractable) in the soil profile to affect plant growth and development have recieved little attention. A discussion of water extraction must first consider the problem of accurately defining the limits to soil water availability. This review presents a critical analysis of the limitations usually encountered in using the limits concept of soil water availability. The relationship between water available and extractable is analysed based on results of transpiration rates and fraction of available water, depth of water extraction and, extraction per unit soil depth.

Critical limits of soil penetration resistance in a rhodic Eutrudox

Soil penetration resistance is an important indicator of soil physical quality and the critical limit of 2 MPa has been widely used to characterize the soil physical quality, in both no-tillage and conventional systems. The aim of this study was to quantify the influence of different tillage and cropping systems on the soil penetration resistance in a Rhodic Eutrudox. The experiment was carried out in a 5 × 2 factorial, completely randomized block design (tillage systems vs cropping systems), with four replications. The tillage systems consisted of: conventional tillage disk harrow; minimum tillage with annual chiseling; minimum tillage with chiseling every three years; no-tillage for 11 consecutive years; and no-tillage for 24 consecutive years. The factor cropping systems was represented by: crop rotation and crop succession. The soil penetration resistance (SPR) was determined in 20 soil samples per treatment and layer (0.0-0.10; 0.10-0.20 and 0.20-0.30 m) for each soil matric potential: -6, -10, -33, -100, -500 kPa. The SPR was determined at a volumetric soil water content equivalent to the fraction of plant-available water of 0.7. There were no differences of soil penetration resistance between the two cropping systems. Differences in soil penetration resistance among tillage systems were related to the matric potential at which the samples were equilibrated. The critical SPR limit of 2 MPa normally used for conventional tillage should be maintained. However, this value of 2 MPa is inappropriate for the physical quality characterization of Rhodic Eutrudox under no-tillage and/or minimum tillage with chiseling. Regardless of the cropping systems, the critical SPR limit should be raised to 3 MPa for minimum tillage with chiseling and to 3.5 MPa for no-tillage.

Funções de pedotransferência para estimativa da retenção de água em alguns solos do Rio Grande do Sul

Soil physical hydraulic properties are determinations considered expensive and difficult to obtain. The use of pedotransfer functions (PTFs) is an alternative for obtaining such properties more easily and practically costless. The objective of this study was to develop and validate PTFs to estimate soil water retention of different textural soil classes in the State of Rio Grande do Sul, Brazil. The research was carried out using data from physical analysis of soils belonging to the database of Sistema Irriga laboratory, Universidade Federal de Santa Maria. This database consists of soil texture information (sand, silt and clay), density (of soil and of particles), soil porosity (macro, micro and total), besides of water content information at the matrix potential of 0, -1, -6,-33, -100, -500 e -1500kPa. Soil samples were collected on the surface layer of cultivated soils of RS. The variables were submitted to a correlation test, and were subsequently analyzed in multiple regressions test to obtain the PTFs, using the stepwise option of the SAS statistical program. The generated PTFs showed greater associations of soil attributes only related to soil structure such as soil water retention for higher potential (0 and -1kPa) and textural and structural attributes for lower potential (-33, -100, -500 e -1500kPa). The PTFs showed high accuracy in estimating soil water holding capacity of the considered potentials.

População de plantas e espaçamento entre linhas do feijoeiro irrigado. II: rendimento de grãos e componentes do rendimento

The objective of this experiment was to evaluate the effect of different plant populations and row spacing on dry matter accumulation, grain yield and yield components of irrigated drybean. The experiment was conducted during the 1997/98 growing season in the experimental field of the Rural Engineering Department of the Federal University of Santa Maria, Santa Maria - RS, Brayl. The cultivar BR-FEPAGRO 44 - Guapo brilhante, (type II) was submitted to three plant populations (175, 250 and 325 thousand plants ha-1) and three row spacing (35, 50 and 65cm). A factorial completely randomized design was used with four replications. Sprinuer irrigations were appiied when maximum crop evapofranspiration, determined based on class A evaporation pan, indicated na accumulated value of 25mm. Results demonstrated that the different plant populations and row spacing did not affect grain yield and grain weight. However, the number ofseeds per legume and legumes per plant increased as plant population decreased. The reduction in row spacing increased shoot dry matter during grain filling period. The cultivar BR-FEPAGRO 44 - Guapo brilhante presented great plasticity of grain yield components mainly because the reduction in plant population resulted in higher grain yield of individual plants.

População de plantas e espaçamento entre linhas do feijoeiro irrigado. I: comportamento morfológico das plantas

Engenheiro Agronomo, Programa de Mestrado em Engenharia Agricola, UFSM.RESUMOO experimento foi conduzido com o objetivo deavaliar variacoes no indice de area foliar, altura das plantas,numero de nos, comprimento dos entrenos na haste principal ealtura das vagens em relacao a superficie do solo do feijoeiroirrigado e cultivado em diferentes populacoes de plantas eespacamentos entre linhas de cultivo. O experimento foiconduzido no ano agricola 1997/98, em area experimental doDepartamento de Engenharia Rural da Universidade Federal deSanta Maria, Santa Maria, RS. A cultivar de feijao preto BR-FEPAGRO 44 - Guapo brilhante, de crescimento indeterminado(tipo II), foi cultivada em tres populacoes de plantas (175, 250 e325 mil plantas ha

Use of penetrometers in agriculture: a review

Soil physical quality can be easily and quickly evaluated by using simple equipment to identify levels of soil compaction. Hence, it is necessary to know the variables responsible for changes in the soil penetration resistance (SPR). The aim of this review is to identify the main factors related to the various equipment used for assessing SPR as a soil physical quality indicator in agriculture. This literature review describes the different types of equipment used and its relationship with SPR. A wide range of procedures, devices, and equipments are available. Much of variability in SPR results is related to the equipment model, cone angle and diameter, and penetration rate. Usually, restrictions to root growth are correlated with SPR values above 2-3 MPa. However, comparisons of SPR values obtained under different soil moisture regimes in the same soil type have provided conflicting results of difficult interpretation. In order to minimize these problems, there is a need for standardization of measurement procedures and interpretation, and/or correction of SPR values according to a soil water content of reference.

Qualidade física de solos irrigados do Estado do Rio Grande do Sul

As areas irrigadas caracterizam-se pela intensificacao dos cultivos e, por consequencia, por uma intensa utilizacao do solo. Isso resulta em uma maior pressao de degradacao da estrutura do solo, ocasionando muitas vezes a compactacao dos solos. O objetivo deste trabalho foi realizar a caracterizacao fisica dos solos irrigados de algumas regioes do Estado do Rio Grande do Sul, com vistas a promover uma base de informacoes para orientar a tomada de decisoes relativas ao manejo de areas irrigadas. Os perfis dos solos foram divididos em tres camadas: (superficial, intermediaria e inferior), nas quais determinaram-se a textura do solo, a densidade do solo (Ds) e de particulas e porosidade. Os solos foram agrupados em faixas de teor de argila, sendo que, para cada faixa de teor de argila, estabeleceu-se um valor critico de densidade do solo (Ds) e de macroporosidade (Macro). As amostras com valores DS maiores que o valor citrico e com valores de macro menores que o valor citrico foram caracterizados com indicacao de compactacao. As amostras de solo coletadas foram classificadas, com maior frequencia na faixa de 400-500g kg-1 de argila, nas camadas superficial e intermediaria e na faixa de argila superior a 700g kg-1 na camada inferior. Do total das areas amostradas, 66,5% apresentaram indicacao de compactacao do solo na camada superficial, 20,5% na camada intermediaria e 9,5% na camada inferior.

Physical quality of irrigated soils in some regions of Central Brazil.

Intensive soil cultivation using heavy machinery, especially when soil moisture content is relatively high, has caused degradation of the physical properties of soil, mainly soil compaction. The objective of this study was to evaluate the physical quality of soil of some irrigated regions of Brazil and to collect information necessary to guide soil management decisions. This study was carried out in areas irrigated by center pivots in the States of Goias, Minas Gerais and Sao Paulo. The soil profile was divided into three soil layers: superficial, intermediate and inferior. The following determinations were conducted: soil texture, bulk density, particle density and soil porosity. Soil types were grouped according to clay content. For each group of clay content, critical values of bulk density and soil macroporosity were established above which (bulk density) and below which (macroporosity) the soil sample were characterized as compacted. Considering the entire area sampled in the superficial layer, 14.2% of the samples collected in Goias, 9.5% of soil samples collected in Minas Gerais and 34% of the samples collected in Sao Paulo presented indications of soil compaction as a function of bulk density and macroporosity.

The Use of a Meteorological Station Network to Provide Crop Water Requirement Information for Irrigation Management

Despite of the water use increment for other sectors than agriculture, the water use for irrigation is the main water consumer in global scale. However, irrigation has been pressured by the civil society to improve water use efficiency in agriculture, to prevent water scarcity for human population that grows continuously, mainly in developing areas of the planet. On the other hand, the irrigation practice is considered the main tool to increase water use efficiency, either for increasing crop production or for keeping rural works in the agricultural areas. The water use efficiency can be improved through the adoption of an efficient irrigation management and programming that results in water conservation. Several methods of irrigation management have been developed and used in the last few decades, but the adoption of the majority of then by the irrigated grower was limited by the cost, time of installation, maintenance and local difficulties that the selection of a specific method involves. In arid regions, the decision of “when” and “how much” to irrigate is relatively simple. However, in wet regions when complementary irrigation is used, the irrigation scheduling is a complex task, mainly due to the water added from rainfall events. The Sistema Irriga™ is basically a service of irrigation management developed by the Federal University of Santa Maria, Brazil. The criteria used by this method to decide the amount of each irrigation application is based on crop parameters of the irrigated crop, soil physical characteristics, meteorological conditions and characteristics of the irrigation system and irrigation method, combined with a mathematical model to determine the reference and crop evapotranspiration. This paper describes all factors and parameters used by the Sistema Irriga™ service, since the data acquisition (plant, soil, weather and irrigation system information), data processing and how the irrigation recommendation is available to the farmers.