A Study on the Water Retention Characteristics of Soils and their Improvements

Soil moisture plays a cardinal role in sustaining eclological balance and agricultural development – virtually the very existence of life on earth. Because of the growing shortage of water resources, we have to use the available water most efficiently by proper management. Better utilization of rainfall or irrigation management depends largely on the water retention characteristics of the soil.Soil water retention is essential to life and it provides an ongoing supply of water to plants between periods of irrigation so as to allow their continued growth and survival.It is essential to maintain readily available water in the soil if crops are to sustain satisfactory growth. The plant growth may be retarded if the soil moisture is either deficient or excessive. The optimum moisture content is that moisture which leads to optimum growth of plant. When watering is done, the amount of water supplied should be such that the water content is equal to the field capacity that is the water remained in the saturated soil after gravitational drainage. Water will gradually be utilized consumptively by plants after the water application, and the soil moisture will start falling. When the water content in the soil reaches the value known as permanent wilting point (when the plant starts wilting) fresh dose of irrigation may be done so that water content is again raised to the field capacity of soil.Soil differ themselves in some or all the properties depending on the difference in the geotechnical and environmental factors. Soils serve as a reservoir of the nutrients and water required for crops.Study of soil and its water holding capacity is essential for the efficient utilization of irrigation water. Hence the identification of the geotechnical parameters which influence the water retention capacity, chemical properties which influence the nutrients and the method to improve these properties have vital importance in irrigation / agricultural engineering. An attempt in this direction has been made in this study by conducting the required tests on different types of soil samples collected from various locations in Trivandrum district Kerala, with and without admixtures like coir pith, coir pith compost and vermi compost. Evaluation of the results are presented and a design procedure has been proposed for a better irrigation scheduling and management.

Degradation of atrazine and isoproturon in surface and sub-surface soil materials undergoing different moisture and aeration conditions

The influence of different moisture and aeration conditions on the degradation of atrazine and isoproturon was investigated in environmental samples aseptically collected from surface and sub-surface zones of agricultural land. The materials were maintained at two moisture contents corresponding to just above field capacity or 90% of field capacity. Another two groups of samples were adjusted with water to above field capacity, and, at zero time, exposed to drying-rewetting cycles. Atrazine was more persistent (t(1/2) = 22-3S days) than isoproturon (t(1/2) = 5-17 days) in samples maintained at constant moisture conditions. The rate of degradation for both herbicides was higher in samples maintained at a moisture content of 90% of field capacity than in samples with higher moisture contents. The reduction in moisture content in samples undergoing desiccation from above field capacity to much lower than field capacity enhanced the degradation of isoproturon (t(1/2) = 9-12 days) but reduced the rate of atrazine degradation (t(1/2) = 23-35-days). This demonstrates the variability between different micro-organisms in their susceptibility to desiccation. Under anaerobic conditions generated in anaerobic jars, atrazine degraded much more rapidly than isoproturon in materials taken from three soil profiles (0-250 cm depth). It is suggested that some specific micro-organisms are able to survive and degrade herbicide under severe conditions of desiccation. (C) 2004 Society of Chemical Industry.

Adsorption of water vapor by bare soil in an olive grove in southern Spain

Data for water vapor adsorption and evaporation are presented for a bare soil (sandy loam, clay content 15%) in a southern Spanish olive grove. Water losses and gains were measured using eight high-precision minilysimeters, placed around an olive tree, which had been irrigated until the soil reached field capacity (similar to 0.22 m(3) m(-3)). They were subsequently left to dry for 10 days. A pair of lysimeters was situated at each of the main points of the compass (N, E, S, W), at a distance of 1 m (the inner set of lysimeters; ILS) and 2 m (the outer set of lysimeters; OLS), respectively, from the tree trunk. Distinct periods of moisture loss (evaporation) and moisture gain (vapor adsorption) could be distinguished for each day. Vapor adsorption often started just after noon and generally lasted until the (early) evening. Values of up to 0.7 mm of adsorbed water per day were measured. Adsorption was generally largest for the OLS (up to 100% more on a daily basis), and increased during the dry down. This was mainly the result of lower OLS surface soil moisture contents (period-average absolute difference similar to 0.005 m(3) m(-3)), as illustrated using various analyses employing a set of micrometeorological equations describing the exchange of water vapor between bare soil and the atmosphere. These analyses also showed that the amount of water vapor adsorbed by soils is very sensitive to changes in atmospheric forcing and surface variables. The use of empirical equations to estimate vapor adsorption is therefore not recommended.

Simulating current global river runoff with a global hydrological model: model revisions, validation, and sensitivity analysis

Global hydrological models (GHMs) model the land surface hydrologic dynamics of continental-scale river basins. Here we describe one such GHM, the Macro-scale - Probability-Distributed Moisture model.09 (Mac-PDM.09). The model has undergone a number of revisions since it was last applied in the hydrological literature. This paper serves to provide a detailed description of the latest version of the model. The main revisions include the following: (1) the ability for the model to be run for n repetitions, which provides more robust estimates of extreme hydrological behaviour, (2) the ability of the model to use a gridded field of coefficient of variation (CV) of daily rainfall for the stochastic disaggregation of monthly precipitation to daily precipitation, and (3) the model can now be forced with daily input climate data as well as monthly input climate data. We demonstrate the effects that each of these three revisions has on simulated runoff relative to before the revisions were applied. Importantly, we show that when Mac-PDM.09 is forced with monthly input data, it results in a negative runoff bias relative to when daily forcings are applied, for regions of the globe where the day-to-day variability in relative humidity is high. The runoff bias can be up to - 80% for a small selection of catchments but the absolute magnitude of the bias may be small. As such, we recommend future applications of Mac-PDM.09 that use monthly climate forcings acknowledge the bias as a limitation of the model. The performance of Mac-PDM.09 is evaluated by validating simulated runoff against observed runoff for 50 catchments. We also present a sensitivity analysis that demonstrates that simulated runoff is considerably more sensitive to method of PE calculation than to perturbations in soil moisture and field capacity parameters.

Effects of restricted water availability and increased temperature on the grain filling, drying and quality of winter wheat

Experiments in controlled environments examined the effects of the timing and severity of drought, and increased temperature, on grain development of Hereward winter wheat. Environmental effects on grain specific weight, protein content, Hagberg Falling Number, SDS-sedimentation volume, and sulphur content were also studied. Drought and increased temperature applied before the end of grain filling shortened the grain filling period and reduced grain yield, mean grain weight and specific weight. Grain filling was most severely affected by drought between days 1-14 after anthesis. Protein content was increased by stresses before the end of grain growth, because nitrogen harvest index was less severely affected than was dry matter harvest index. Hagberg Falling Number was increased to the greatest extent by stresses applied 15-28 days after anthesis. Treatment effects on grain sulphur content were similar to those on protein content, such that N:S ratio was not significantly affected by drought nor temperature stresses. The effects of restricted water on grain yield and quality were linearly related to soil moisture between 44 and about 73% field capacity (FC) from days 15-28. Drought stress (but not temperature stress) before the end of grain filling decreased SDS-sedimentation volume relative to drought applied later. (C) 2003 Elsevier Science Ltd. All rights reserved.

Effects of restricted water availability and increased temperature on the grain filling, drying and quality of winter wheat

Experiments in controlled environments examined the effects of the timing and severity of drought, and increased temperature, on grain development of Hereward winter wheat. Environmental effects on grain specific weight, protein content, Hagberg Falling Number, SDS-sedimentation volume, and sulphur content were also studied. Drought and increased temperature applied before the end of grain filling shortened the grain filling period and reduced grain yield, mean grain weight and specific weight. Grain filling was most severely affected by drought between days 1-14 after anthesis. Protein content was increased by stresses before the end of grain growth, because nitrogen harvest index was less severely affected than was dry matter harvest index. Hagberg Falling Number was increased to the greatest extent by stresses applied 15-28 days after anthesis. Treatment effects on grain sulphur content were similar to those on protein content, such that N:S ratio was not significantly affected by drought nor temperature stresses. The effects of restricted water on grain yield and quality were linearly related to soil moisture between 44 and about 73% field capacity (FC) from days 15-28. Drought stress (but not temperature stress) before the end of grain filling decreased SDS-sedimentation volume relative to drought applied later. (C) 2003 Elsevier Science Ltd. All rights reserved.

Effect of Rht alleles on the tolerance of wheat grain set to high temperature and drought stress during booting and anthesis

Factorial pot experiments were conducted to compare the responses of GA-sensitive and GA-insensitive reduced height (Rht) alleles in wheat for susceptibility to heat and drought stress during booting and anthesis. Grain set (grains/spikelet) of near isogenic lines (NILs) was assessed following three day transfers to controlled environments imposing day temperatures (t) from 20 to 40°C. Transfers were during booting and/or anthesis and pots maintained at field capacity (FC) or had water withheld. Logistic responses (y = c/1+e-b(t -m)) described declining grain set with increasing t, and t5 was that fitted to give a 5% reduction in grain set. Averaged over NIL, t5 for anthesis at FC was 31.7±0.47°C (S.E.M, 26 d.f.). Drought at anthesis reduced t5 by <2°C. Maintaining FC at booting conferred considerable resistance to high temperatures (t5=33.9°C) but booting was particularly heat susceptible without water (t5 =26.5°C). In one background (cv. Mercia), for NILs varying at the Rht-D1 locus, there was progressive reduction in t5 with dwarfing and reduced gibberellic acid (GA) sensitivity (Rht-D1a, tall, 32.7±0.72; Rht-D1b, semi-dwarf, 29.5±0.85; Rht-D1c, severe dwarf, 24.2±0.72). This trend was not evident for the Rht-B1 locus, or for Rht-D1b in an alternative background (Maris Widgeon). The GA-sensitive severe dwarf Rht12 was more heat tolerant (t5=29.4±0.72) than the similarly statured GA-insensitive Rht-D1c. The GA-sensitive, semi-dwarfing Rht8 conferred greater drought tolerance in one experiment. Despite the effects of Rht-D1 alleles in Mercia on stress tolerance, the inconsistency of the effects over background and locus led to the conclusion that semi-dwarfing with GA-insensitivity did not necessarily increase sensitivity to stress at booting and flowering. In comparison to effects of semi-dwarfing alleles, responses to heat stress are much more dramatically affected by water availability and the precise growth stage at which the stress is experienced by the plants.

Commensalism in an agroecosystem: hydraulic redistribution by deep-rooted legumes improves survival of a droughted shallow-rooted legume companion

We investigated commensalism of water use among annual shallow-rooted and perennial deep-rooted pasture legumes by examining the effect of hydraulic lift by Cullen pallidum (N.T.Burb.) J.W.Grimes and Medicago sativa on growth, survival and nutrient uptake of Trifolium subterraneum L. A vertically split-root design allowed separate control of soil water in top and bottom soil. Thirty-five days after watering ceased in the top tube, but soil remained at field capacity in the bottom tube, an increase in shallow soil water content by hydraulic lift was 5.6 and 5.9 g kg−1 soil overnight for C. pallidum and M. sativa, respectively. Trifolium subterraneum in this treatment maintained higher leaf water potentials (with M. sativa) or exhibited a slower decline (with C. pallidum) than without companion perennial plants; and shoot biomass of T. subterraneum was 56% (with C. pallidum) and 67% (with M. sativa) of that when both top and bottom tubes were at field capacity. Uptake of rubidium (a potassium analog) and phosphorus by T. subterraneum was not facilitated by hydraulic lift. Interestingly, phosphorus content was threefold greater, and shoot biomass 1.5–3.3-fold greater when T. subterraneum was interplanted with C. pallidum compared with M. sativa, although dry weight of C. pallidum was much greater than that of M. sativa. This study showed that interplanting with deep-rooted perennial legumes has benefited the survival of T. subterraneum.

Dinâmica da água no solo em cultivos de milho sob plantio direto e preparo convencional

A dinâmica da água em sistema de plantio direto (PD) é alterada em relação ao preparo convencional (PC) devido a modificações na estrutura do solo e a presença de palha na superfície. Para avaliar estas diferenças foram conduzidos experimentos de campo, em 2001/02 e 2002/03, em Eldorado do Sul, RS. O objetivo geral foi quantificar alterações físico-hídricas no perfil e na superfície do solo em PD e PC, com ênfase na dinâmica da água e respostas das plantas de milho. Os sistemas de manejo do solo foram implantados na área em 1995. Foram avaliadas propriedades físicas, a movimentação e a armazenagem de água no solo. Mediu-se a infiltração e a capacidade de campo e monitorou-se a dinâmica da água durante o ciclo da cultura, enfocando a secagem do solo e a extração de água em períodos sem precipitação. Nestes períodos também foi determinada a evaporação da água na superfície e avaliadas respostas das plantas. Os efeitos do plantio direto se evidenciaram nas camadas de solo próximas à superfície. A mesoporosidade foi a propriedade física mais afetada, apresentando uma distribuição exponencial de mesoporos no plantio direto, enquanto no preparo convencional a mesma se aproximou de uma curva normal. Em geral, a condutividade hidráulica, a retenção e a disponibilidade de água foram mais elevadas em plantio direto, principalmente, próximo à superfície. O solo em PD também apresentou maior umidade volumétrica com menor energia de retenção, resultando em redução no avanço da frente de secagem do solo e extração de água. A evaporação também foi maior em PD, demonstrando que a maior umidade no solo em plantio direto se deve ao aumento na capacidade de armazenagem de água. O aprofundamento radicular foi sempre maior no preparo convencional. O plantio direto altera propriedades físicas ligadas à dinâmica da água, proporcionando maior disponibilidade hídrica no solo ao longo do tempo.

Indicadores fisiológicos da interação entre deficit hídrico e acidez do solo em cana-de-açúcar

O objetivo deste trabalho foi avaliar os indicadores fisiológicos da interação entre deficit hídrico e acidez do solo em plantas jovens de cana-de-açúcar. As plantas foram submetidas a três tratamentos de disponibilidade hídrica, medidos em percentagem de capacidade de campo (CC) - sem estresse (70% CC), estresse moderado (55% CC) e estresse severo (40% CC); e três tratamentos de acidez no solo, medidos em termos de saturação por bases (V) - baixa acidez (V = 55%), média acidez (V = 33%) e alta acidez (V = 23%). O experimento foi realizado em casa de vegetação a 29,7±4,3ºC e 75±10% UR. O delineamento experimental utilizado foi o de blocos ao acaso, em esquema fatorial 3x3, com quatro repetições. Após 60 dias, foram determinados os teores de solutos compatíveis - trealose, glicina betaína e prolina - na folha diagnóstico e o crescimento inicial da parte aérea. Os solutos compatíveis trealose, glicina betaína e prolina são indicadores do efeito da interação dos estresses hídrico e ácido no solo. O acúmulo dos solutos compatíveis nos tecidos foliares das plantas não é capaz de impedir a redução na produção de matéria seca da cana-de-açúcar, resultante do agravamento nas condições de disponibilidade hídrica e de acidez no solo.

Efeito simultâneo da deficiência hídrica e do alumínio tóxico no solo na cultivar IAC91-5155 de cana-de-açúcar

Sugarcane is a very important economic crop in Brazil. The effects of abiotic stresses cause negative reduction of the productivity in the sugarcane industry. In order to identify indicators of stresses tolerance, two physiological variables were evaluated, nitrate reductase activity and chlorophyll contents in young plants of sugarcane, cv. IAC91-5155. The simultaneous effect of abiotic stresses of high occurrence in Brazilian soils are, water deficiency and aluminum toxicity. The plants were submitted to three treatments of water availability (% field capacity, FC): no stress (70% FC), moderate stress (55% FC), and extreme stress (40% FC); and three acidity treatments in the soil (base saturation, V%): no acidity (V=55%), average acidity (V=33%), and high acidity (V=23%). The experiment was carried out in greenhouse, with 29.7 +/- 4.3 degrees C and 75 +/- 10% RH. The experimental design was in randomized blocks, in 3x3 factorial arrangement, with four replicates. After 60 days, nitrate reductase activity and chlorophyll contents were evaluated in the diagnostic leaf. The results demonstrate that the response of plants to a combination of drought and aluminum toxicity, similar to the conditions in many natural environments, is different from the response of plants to each of these stresses applied individually, as typically tested in the laboratory. The nitrate reductase activity can be used as a biochemical-physiological marker of water deficiency while chlorophyll contents can be used as a biochemical-physiological marker of both of them, water deficiency or aluminum toxicity in soil. Both parameters can not be as a biochemical-physiological marker for acclimation of young plants of sugarcane cv. IAC91-5155, under the combined stresses.

Desempenho do trator agrícola no manejo da cultura de cobertura e pressão de inflação do pneu da semeadora

O adequado manejo de culturas de cobertura no plantio direto tem-se mostrado excelente alternativa para melhorar as condições de semeadura. O objetivo do presente trabalho foi avaliar o desempenho do trator agrícola no manejo dos restos culturais do sorgo (rolo-faca e triturador de palhas) e a pressão de inflação (525 e 385 kPa) do pneu da semeadora-adubadora, no estabelecimento da cultura do milho em plantio direto. O experimento foi conduzido na UNESP - Jaboticabal, em delineamento de blocos ao acaso, com parcela subdividida, e os tratamentos consistiram nos manejos da cultura de cobertura do solo e pressões de inflação do pneu da semeadora, com quatro repetições. Foram mensurados nas máquinas: velocidade de deslocamento, capacidade de campo, consumo de combustível e patinhagem do trator; no solo e nas plantas, foi acrescido o tratamento de manejo com herbicida: cobertura inicial, número de dias para emergência das plântulas, população inicial e final de plantas, distribuição longitudinal e produtividade de grãos. No manejo da palhada da cultura do sorgo, o rolo-faca proporcionou maior capacidade de campo e menores consumos de combustível. Os tratamentos manejos e pressão não interferiram na cobertura do solo, no número de dias para emergência do milho e na distribuição longitudinal.

Semeadora-adubadora: exigências em função do preparo do solo, da pressão de inflação do pneu e da velocidade

As semeadoras-adubadoras, responsáveis pela correta adição de semente e adubo ao solo, possuem mecanismos dosadores acionados por suas rodas motrizes, que giram em função do contato com a superfície do solo. Esse contato é influenciado, entre outros fatores, pela pressão de inflação dos pneus. O objetivo do presente trabalho foi estudar o desempenho de uma semeadora-adubadora de precisão em função do preparo do solo (preparo convencional e plantio direto), das velocidades de deslocamento e da pressão de inflação do seu pneu. O trabalho foi realizado na UNESP de Jaboticabal (SP) no ano de 2006. Foram avaliadas as seguintes variáveis: força de tração e potência na barra, consumo de combustível (horário, ponderal, operacional e específico), capacidade de campo operacional, patinagem dos rodados do trator e da semeadora-adubadora, estande inicial e distribuição longitudinal de sementes. O sistema plantio direto demandou maior força (35 %), potência e consumo horário de combustível; o mesmo aconteceu na maior velocidade. A pressão de inflação das rodas da semeadora proporcionou menor patinagem e maior estande inicial de plântulas.

Decomposição de culturas de cobertura no sistema plantio direto, manejadas mecânica e quimicamente

O sistema plantio direto preconiza o uso de culturas de cobertura para produção de massa seca sobre o solo. O presente trabalho teve por objetivo estudar a produção e a taxa de decomposição de duas coberturas vegetais - crotalária juncea (Crotalária juncea L.) e mucuna-cinza (Stilozobium niveum L) - em três sistemas de manejo (rolo-faca, triturador de palhas e herbicida), e a capacidade de campo efetiva dos manejos. O experimento foi realizado na área do Laboratório de Máquinas e Mecanização Agrícola (LAMMA), do Departamento de Engenharia Rural, UNESP, Jaboticabal - SP, com delineamento em blocos ao acaso, em esquema fatorial 3x2, originando seis tratamentos, com quatro repetições. Foram analisadas as produções de massa seca das culturas de cobertura antes e após o manejo, a velocidade de deslocamento e a capacidade de campo efetiva para cada conjunto (trator-equipamento). As análises dos valores obtidos permitiram verificar que o fator manejo não interfere na decomposição da massa seca das coberturas vegetais e que as duas culturas de cobertura apresentaram massas semelhantes aos 30; 70 e 125 dias após a semeadura, diferindo aos 97 dias, época na qual a crotalária apresentou maior quantidade de massa seca. Aos 30; 51 e 71 dias após o manejo, as massas secas das culturas foram semelhantes. O manejo com herbicida apresentou maior capacidade de campo efetiva.

Demanda energética e eficiência da distribuição de sementes de milho sob variação de velocidade e condição de solo

O trabalho teve o objetivo de avaliar a demanda energética e a eficiência da distribuição de sementes de uma semeadora-adubadora para semeadura direta, submetida à variação de velocidade e condições de solo, na semeadura da cultura do milho. O estudo foi desenvolvido em um Nitossolo Vermelho distrófico, na Fazenda Experimental Lageado, no município de Botucatu - SP. O delineamento experimental foi em blocos casualizados, com oito repetições, combinando-se três velocidades de deslocamento (4,4; 6,1 e 8,1 km h-1) e duas condições de solo (solo manejado sob sistema de plantio direto há cinco anos e solo preparado com escarificador há 18 meses). Avaliaram-se a força de tração, a potência na barra de tração, o consumo de combustível, a capacidade de campo efetiva, a distribuição longitudinal de plantas, o coeficiente de variação, o índice de precisão e o número de plantas por hectare (estande inicial). Os resultados revelaram que, aumentando-se a velocidade de 4,4 para 8,1 km h-1, consegue-se aumentar em 86% a capacidade operacional, com incremento de 96% na demanda de potência na barra de tração e redução de 26% no consumo operacional de combustível. A maior velocidade (8,1 km h-1) proporcionou menor porcentual de espaçamentos normais e aumento no porcentual de espaçamentos múltiplos e falhos, maior coeficiente de variação e pior índice de precisão. A variação da velocidade não interferiu no número de plantas por hectare.