Calibração de uma sonda de capacitância em um Argissolo

Sensores de capacitância são alternativas aos métodos comuns de quantificação do teor de água do solo (teta, m³ m-3), provendo leituras em profundidade de forma segura e rápida. Neste estudo, uma sonda de capacitância (Diviner 2000) foi calibrada em um Argissolo vermelho-amarelo do Estado do Piauí, Brasil. Seis tubos de acesso foram instalados em uma grade de 5 m × 2 m. Três níveis de umidade (saturado, úmido e seco) foram aplicados em duas repetições. Efetuaram-se leituras do equipamento, para cada 0.1 m de solo, até 1.0 m de profundidade, juntamente com amostras de solo para a determinação de teta. Uma equação de potência foi desenvolvida para cada profundidade como também para o todo perfil do solo (RMSE = 0.014, R² = 0.93) em um intervalo de 0.068 a 0.264 m³ m-3 of teta. A calibração para cada profundidade melhora o coeficiente de correlação e minimiza o erro das estimativas. Calibrações locais melhoram a acurácia do monitoramento da água no solo.The use of capacitance sensors is one of the methods used to quantitatively measure soil water contents (theta, m³ m-3). Sensors provide readings at desired depths and time intervals. A capacitance probe (Diviner 2000) was calibrated for a Rhodic Paleudult from the Piaui State, Brazil. Six access tubes were installed in a 5 × 2 m grid arrangement. Three moisture levels (saturated, moist and dry) were used in two replications. Probe readings and soil samplings to determine theta were made at 0.1 m depth intervals down to a depth of 1.0 m. A power calibration equation was developed for each depth as well as for the entire soil profile (Root Mean Square Error = 0.014, R² = 0.93) for a theta range of 0.068 to 0.264 m³m-3. A separate calibration for each depth improves the correlation coefficient and minimizes RMSE. Site-specific calibration improves the accuracy for soil water monitoring

Effect of water regimes and plant densities on cowpea production

Cowpea has been cultivated in a rudimentary form in the main producing regions of Brazil, resulting in lower grain yields, when compared to the crop potential. The use of technologies such as water regimes, adequate plant density and soil management are alternatives to increase this crop yield. This study aimed at evaluating the effects of different water regimes and plant densities on the yield components of cowpea cultivated under conventional and no-tillage systems. A randomized block design in a split-plot factorial, with four replications, was used. The treatments consisted of five water regimes in the plots (157.00 mm, 189.00 mm, 234.00 mm, 274.00 mm and 320.00 mm) and five plant densities as subplots (12 plants m-2, 16 plants m-2, 20 plants m-2, 24 plants m-2 and 28 plants m-2). The evaluated variables were: number of pods per plant, number of pods per area, pod length and grain yield. The combination between 270 mm of irrigation water depth with a density of 280,000 plants ha-1 resulted in higher grain yield using the no-tillage system, while the combination between the density of 280,000 plants ha-1 and 320 mm of water depth favored the highest grain yields in the conventional growing system

Rendimento agroindustrial da cana-de-açúcar fertirrigada por gotejamento subsuperficial com nitrogênio e potássio

The objective of this work was to evaluate the stalk yield, technological quality parameters, and sugar and alcohol productions in the first sugarcane (Saccharum officinarum) crop cycle, according to the response to N and K2O applications by subsurface drip fertigation. The experiment was carried out in a dystrophic Ultisol, in a randomized complete block design with four replicates. The treatments consisted of a 2X + 2X + 1 incomplete factorial arrangement with the application of 60, 80, 120, 160, and 180 kg ha-1 N and 60, 80, 120, 160, and 180 kg ha-1 K2O. The maximum estimated yield (217.5 Mg ha-1) was obtained with the application of 180 kg ha-1 N and 60 kg ha-1 K2O. Sugar and alcohol productions increased with N application above 120 kg ha-1. The technological quality characteristics of soluble solids content, apparent sucrose in the juice/broth, apparent sucrose in sugarcane, purity, and fiber show the highest averages with the application of 180 kg ha-1 N and 60 kg ha-1 K2O.O objetivo deste trabalho foi avaliar a produtividade de colmos, os parâmetros tecnológicos de qualidade e o rendimento de açúcar e álcool no primeiro ciclo de cana-planta (Saccharum officinarum), em resposta à aplicação de N e K2O em fertirrigação por gotejamento subsuperficial. O experimento foi realizado em um Argissolo Vermelho-Amarelo distrófico, em um delineamento experimental de blocos ao acaso, com quatro repetições. Os tratamentos consistiram de um arranjo fatorial incompleto 2x + 2X + 1 com a aplicação de 60, 80, 120, 160 e 180 kg ha-1 de N e de 60, 80, 120, 160, 180 kg ha-1 de K2O. A máxima produtividade de colmos estimada (217,5 Mg ha-1) foi obtida com a aplicação de 180 kg ha-1 N e 60 kg ha-1 K2O. Os rendimentos de açúcar e álcool aumentaram com a aplicação de adubação nitrogenada acima de 120 kg ha-1. As características tecnológicas de qualidade dos sólidos solúveis totais, sacarose aparente no caldo, sacarose aparente na cana, pureza e fibra apresentam médias mais elevadas com a aplicação de 180 kg ha-1 de N e 60 kg ha-1 de K2O

Optimal irrigation strategies for watermelon crop

O trabalho teve como objetivo determinar estratégias ótimas de irrigação para a cultura da melancia (Citrullus lanatus Thumb. Mansf.), considerando a água como fator limitante da produção e diferentes valores para o preço do produto e custos da energia elétrica. Utilizou-se uma função de produção quadrática e função de custo linear obtidas para as condições edafoclimáticas dos Tabuleiros Costeiros do Piauí. A irrigação com déficit proporcionou as maiores rendas líquidas, com significativa economia de água, no intervalo de variação de preços do produto de US$0,05 kg-1 a US$ 0,35 kg-1, nas três formas de tarifação da energia elétrica. Acima desse intervalo, deve-se utilizar a lâmina que maximiza a produção de frutos.This paper aimed to determine optimal strategies for irrigation management watermelon crop (Citrullus lanatus Thumb. Mansf.), when water is limiting resource under different values of the crop and electrical energy price. The analysis involved quadratic production function and linear cost function developed to the soil and climate characteristics of the Coastal Tablelands, at Piauí State, Brazil. The highest net incomes were achieved with deficit irrigation, in the range crop prices of the US$0.05 kg-1 to US$ 0.35 kg-1, independently of electrical energy price. Up this range, irrigation depth that maximizes fruits yield must be used

Modeling of water quality parameters of dissolved oxygen and biochemical oxygen demand in the sub-basin of Poxim river, Brazil

The major cause of scarcity of the water resources, especially in large urban centers, is caused by the degradation of water quality; this is because of the inadequate release of industrial effluents and domestic sewage. The application of models that consider aspects of quantity and water quality are extremely important in case to understand and try to solve this problem. Thus, this paper aims are to show how computational modeling can be used to assess pollution by sewage water resources in the sub-basin of Rio Poxim, contributing in this way to solve environmental problems. To conduct the study, we employ the data monitored DO and BOD during the period from July 2009 to June 2010, which were inserted in the AcquaNet for calibration and validation. The simulations were performed for the current situation, (calibrated) with two scenarios increase of 10 thousand and 20 thousand inhabitants in the area of influence. The results of parameter calibration and validation of 00 showed a good correlation between the observed and calculated data, the same can not be observed for the parameter BOD. The results show that the parameters DO and BOD present critical situations at Station E4 mainly for the month of May where they were observed DO and BOD concentrations of 0.0 mg L-1 and 16.52 mg .L-1 with respective population increases. Computer modelings allows monitoring of water quality parameters in rivers and seek some solutions for that serious problems related to the quality of life and environmental health in areas where the risk of contamination by sewage is higher. For those reasons it is recommended to study what are the best treatment solutions or launch strategy and develop specific levels of monitoring for future situations

Armazenamento de água em Plintossolo Argilúvico cultivado com cana-de-açúcar sob níveis de palhada

The objective of this work was to evaluate water storage in a Plinthaqualf under different straw levels during the fourth ratoon season of a sugarcane (Saccharum officinarum) crop. The study was conducted in the 2013/2014 crop season, with the cultivar SP-813250, at two soil depths (0.0–0.3 and 0.3–0.6 m), in a randomized complete block design, with five straw levels (0.0, 4.2, 9.5, 13.0, and 18.4 Mg ha-1) and four replicates. Soil moisture content was monitored with a time-domain reflectometer. The straw provided gains of up to 20 Mg ha-1 stems and kept increased water storage in the soil, in comparison with the soil without straw, in all evaluated periods. Maintenance of up to 50% (9.5 Mg ha-1) of sugarcane straw on soil surface promotes better water retention in the soil per Mg of straw added and delays the reach of critical water storage in the soil by up to 11 days, when compared with soil without straw cover.O objetivo deste trabalho foi avaliar o armazenamento de água em um Plintossolo Argilúvico sob diferentes níveis de palhada durante o ciclo de quarta soca da cana-de-açúcar (Saccharum officinarum). O estudo foi conduzido na safra 2013/2014, com a cultivar SP-813250, em duas profundidades (0,0‒0,3 e 0,3‒0,6 m), em delineamento de blocos ao acaso, com cinco níveis de palhada (0,0, 4,2, 9,5, 13,0, e 18,4 Mg ha-1) e quatro repetições. A umidade do solo foi monitorada com reflectômetro de domínio de tempo. A palhada proporcionou ganho de até 20 Mg ha-1 de colmos e manteve o solo com maior armazenamento de água do que o sem palhada, em todos os períodos avaliados. A manutenção de até 50% (9,5 Mg ha-1) de palhada de cana-de-açúcar sobre a superfície do solo promove melhor conservação de água no solo por Mg de palha adicionada e retarda em até 11 dias o alcance do armazenamento crítico de água no solo, em comparação ao solo sem cobertura de palha

Macro and Micro-Nutrient Accumulation and Partitioning in Soybean Affected by Water and Nitrogen Supply

This study aimed to investigate the influence of water availability and nitrogen fertilization on plant growth, nutrient dynamics, and variables related to soybean crop yield. Trials were performed in Teresina, Piauí, Brazil, using randomized blocks in a split-split plot arrangement. The plots corresponded to water regimes (full and deficient), the split plots to N fertilization (0 and 1000 kg ha-1 N-urea), and the split-split plots to harvest times of soybean plants (16, 23, 30, 37, 44, 58, 65, 79 and 86 days after emergence), with three replicates. In general, the accumulation and partitioning of nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), sulphur (S), copper (Cu), iron (Fe), manganese (Mn), zinc (Zn) and boron (B) were decreased in plants subjected to water deficit and without N fertilization. Although nitrogen fertilization promoted elevated N accumulation in tissues, it did not result in any significant yield gain, and the highest seed yields were found in plants under full irrigation, regardless of N supplementation. However, deficient irrigation decreased the seed oil content of N-fertilized plants. In conclusion, N fertilization is critical for nutrient homeostasis, and water availability impairs biomass and nutrient accumulation, thereby limiting soybean yield performance