Yield Formation Stages Research Articles

A forward-inverse dynamic model for the hydraulic damping(magnetorheological) actuator based on cyclic stress–strain

Magnetorheological dampers (MRDs) are applied to hydraulic systems, which not only improve the underdamped characteristics of valve-controlled cylinder systems, but also help hydraulic actuators to resist high load impact. However, the high power density leads to the complexity of the internal flow channel of the damper, which seriously affects the output accuracy of the damping force. It can lead to the fact that existing dynamics models cannot accurately describe the hysteresis characteristics of the MRD. Therefore, this study proposes a simple and general dynamic model of MRD, which solves the problem that existing models are complex and difficult to invert. Firstly, the hydraulic damping actuator with the series MRD is taken as the research object. Based on the stress–strain hysteresis characteristics under the cyclic constitutive model, the hyperbolic tangent curve is reorganized and normalized. It can accurately describe the yield formation and yield dissipation stages of the hysteresis loop. Secondly, the relationship between the parameters of the dynamic model and the current is obtained according to the mechanical experimental data. Then the inverse model of the MRD is established by using the method of section-backstepping. Finally, in the static experiment, the mean absolute percentage error (MAPE) of the force at different velocity is less than 7.5%; in the dynamic experimental test, the MAPE of the force is 9.7%. The inverse dynamics model is verified to have high tracking performance under both static and dynamic forces. And it also indirectly confirms the effectiveness of the forward model.

Trocas gasosas, crescimento e produção de genótipos de algodoeiro sob déficit hídrico nas fases fenológicas

ABSTRACT Cotton cultivation in the Brazilian Northeast region faces water scarcity problems caused by the irregularity of the rainy season, leading to losses in yield. In this context, the objective of the present study was to evaluate the gas exchange, growth, and production of colored-fiber cotton genotypes under water stress, varying the water deficit management strategies in the different phenological stages of the plant. The study was carried out in the experimental area of the Federal University of Campina Grande, located in the municipality of Pombal, Paraíba, Brazil. A randomized block design was used, in a 3 × 7 factorial scheme, corresponding to three colored cotton genotypes (‘BRS Rubi’, ‘BRS Jade’, and ‘BRS Safira’) and application of water deficit (40% of actual evapotranspiration - ETr) management strategies in seven phenological stages of the crop. The ‘BRS Jade’ genotype is the most suitable for cultivation under water deficit conditions with 40% of the actual evapotranspiration. Colored-fiber cotton cultivation under water deficit in the flowering stage caused a reduction in physiological variables and growth. Water deficit during the vegetative and yield formation stages promoted lower losses in the production of seed cotton and total seed weight of the genotypes ‘BRS Rubi’, ‘BRS Jade’, and ‘BRS Safira’.

Transcriptome-based analysis of key pathways relating to yield formation stage of foxtail millet under different drought stress conditions.

Although foxtail millet, as small Panicoid crop, is of drought resilient, drought stress has a significant effect on panicle of foxtail millet at the yield formation stage. In this study, the changes of panicle morphology, photosynthesis, antioxidant protective enzyme system, reactive oxygen species (ROS) system, and osmotic regulatory substance and RNA-seq of functional leaves under light drought stress (LD), heavy drought stress (HD), light drought control (LDCK) and heavy drought control (HDCK) were studied to get a snap-shot of specific panicle morphological changes, physiological responses and related molecular mechanisms. The results showed that the length and weight of panicle had decreased, but with increased empty abortive rate, and then yield dropped off 14.9% and 36.9%, respectively. The photosynthesis of millet was significantly decreased, like net photosynthesis rate, stomatal conductance and transpiration rate, especially under HD treatment with reluctant recovery from rehydration. Under LD and HD treatment, the peroxidase (POD) was increased by 34% and 14% and the same as H2O2 by 34.7% and 17.2% compared with LDCK and HDCK. The ability to produce and inhibit O2- free radicals under LD treatment was higher than HD. The content of soluble sugar was higher under LD treatment but the proline was higher under HD treatment. Through RNA-seq analysis, there were 2,393 and 3,078 different genes expressed under LD and HD treatment. According to the correlation analysis between weighted gene coexpression network analysis (WGCNA) and physiological traits, the co-expression network of several modules with high correlation was constructed, and some hub genes of millet in response to drought stress were found. The expression changes relating to carbon fixation, sucrose and starch synthesis, lignin synthesis, gibberellin synthesis, and proline synthesis of millet were specifically analyzed. These findings provide a full perspective on how drought affects the yield formation of foxtail millet by constructing one work model thereby providing theoretical foundation for hub genes exploration and drought resistance breeding of foxtail millet.

Evaluation of the Nutrient Composition of Maize in Different NPK Fertilizer Levels Based on Multivariate Method Analysis

One of the critical issues in using micronutrient fertilisers is the comparison of methods and amounts of fertiliser use, which is very important from the aspect of increasing production and economic viewpoint. The aim of this research was to analyse the nutrient composition of different parts of the maize (Zea mays L. FAO 490) during the growing season with six-level nitrogen fertilisation supplies at five phenological stages. The study included essential nutrients as nitrogen (N), phosphorus (P), potassium (K), and sulphur (S) (in first cluster) and calcium (Ca) and magnesium (Mg) (in second cluster) in treatments on different leaf stage. Growth stages have different nutrient demands based on their actual demand. The first cluster included nitrogen and sulphur and the second included calcium and zinc in the NPK treatments on the stalk of plants. Nitrogen and potassium had their maximum effect on the stalk of maize during the growing season. Magnesium and copper were the second most important and desirable factors during the different growth stages and treatments in relation to the stalk. Nitrogen and calcium had their maximum impact during the yield formation stage and nitrogen and phosphorus had their most desirable effect during the grain filling stage. The effect of nitrogen on the quantitative and qualitative properties of maize showed that nitrogen increases the production of dry matter, grain yield, and its components. The maximum amount of absorption in the plants occurs before the accumulation of applied fertiliser, which is the prelude to the production of maximum biomass.

Mathematical Modelling of Crop Water Productivity for Processing Tomato

Crop water productivity models (CWPMs) are of great importance in evaluating different irrigation programs. The mean goal of the study was to evaluate the performance of the Jensen, Minhas, Blank, Stewart and Rao CWPMs in predicting fruit yield of processing tomato. Field experiments were conducted for two consecutive growing seasons. The soil water stress sensitivity indices of the CWPMs were determined using experimental data from the second crop growing season. Yields simulated by the CWPMs were compared with the experimental data for the first season. The sensitivity indices for the crop growth stages were taken into account as appropriate weights of the soil water sensitivity of the vegetative, flowering, yield formation and ripening stages of the processing tomato crop. The results give evidence that processing tomato is much more sensitive to soil water stress during flowering and yield formation stages whereas the adverse impact of water stress on yield is very limited at vegetative stage. The highest modelling efficiency (0.96) between field-measured and simulated yield by the model, the lowest arithmetic mean of errors (0.04), mean absolute deviation (0.07), mean square error (0.02), absolute percentage error (12.76), root mean square error (0.15) and coefficient of residual mass (0.05) were achieved by Minhas model and followed by Rao model based on same parameters of statistical analyses. Both the Minhas and the Rao models with their soil water stress sensitivity indices generated for the different growth stages obtained in this study are recommended for the processing tomato in the sub-humid environments.

Leaf Photosynthesis Response to Change of Soil Moisture Content in Sugarcane

It is necessary to practice efficient irrigation in any agricultural development strategy under the context of climate change and competition from other economic sectors. Irrigation based on the relationship between photosynthetic activity and change of soil moisture could be an effective practice. Herein, we investigated the response of sugarcane photosynthetic parameters on drought stress at yield formation stage. The experiment was carried out by withholding water for 3 weeks from 190 days after transplanting and then re-watering until the end of experimental period. Data were collected for photosynthetic parameters including potential photosynthetic rate, stomatal conductance, transpiration rate, internal CO2 concentration, SPAD, and soil physical parameters. The results showed that sugarcane photosynthetic parameters decreased with decreasing soil moisture content to certain extent and the stayed static before dropping off again. Internal CO2 concentration increased when soil moisture reached the most severe, and it caused a standstill in photosynthesis. However, photosynthesis also recovered with soil moisture recovery. Photosynthetic parameters could be used as indicators to evaluate drought stress’s effect as well as to determine the time to re-irrigate to maintain normal growth of the plants. Soil volume moisture content of 15% (recorded by the 5TE sensor) or at pF of 2.8 (recorded by the MPS-6 sensor) seems to be the initial time to start irrigation to keep standard growth. Soil moistures at 10% and 3.8 pF, respectively, could be the critical points beyond which irrigation was found to result in photosynthetic disorders.

Productivity and production components of safflower genotypes affected by irrigation at phenological stages

Drought and the scarce resource of water for irrigation can limit agricultural production under tropical conditions. The objective of this study was to investigate the growth and yield response of safflower genotypes to water deficit in the soil profile during vegetative, flowering and yield formation stages, both in clayey and sandy soils. The experiments were carried out in Engenheiro Coelho, SP, Brazil, in autumn-winter 2014. The experimental design was a randomized block in a factorial arrangement, consisting of the genotypes IMA-2232, IMA-4409, IMA-2109 and IAPAR, and irrigation schemes water deficit (WD), irrigation at the vegetative stage (V), irrigation at the grain formation stage (G), irrigation at the vegetative and flowering (VF) stages, irrigation at the vegetative and grain formation (VG) stages, irrigation at the flowering and grain formation (FG) stages and irrigation at the vegetative, flowering and grain formation (VFG) stages (control). The growth of safflower genotypes, yield components and grain and oil yield were weaken by gradual water restriction at the stages, especially at the vegetative stage in both soils. The water regime with irrigation at the flowering stage and grain formation (FG) only did not reduce the oil content in the genotypes in clayey soil. The IAPAR genotype produced more grains (2.7Mgha−1), while the IMA-4409 genotype had higher oil content (42.8%) but they both had similar oil yield (0.75 and 0.79Mgha−1, respectively) on the clayey soil with irrigation throughout the cycle (VFG). Oil yield in the sandy soil treatment was similar to that of clayey soil (0.72Mgha−1) in VFG, in particular for the IMA-4409 genotype. The IAPAR and IMA-4409 genotypes were generally less sensitive to interruption of water supply at the growth stages. In general, the higher total water storage in soil profile of clayey soil, compared to sandy soil, did not benefit the safflower crop. On an average, irrigation only at vegetative and flowering stage (VG) stages can save 15% of water but with a corresponding 50% reduction in yield, both in clayey soil and sandy soil. The irrigation during the VFG stages might be practiced to attain the highest yield of safflower genotypes.

Changes in yield variability of major crops for 1981–2010 explained by climate change

While changes in temperature and precipitation extremes are evident, their influence on crop yield variability remains unclear. Here we present a global analysis detecting yield variability change and attributing it to recent climate change using spatially-explicit global data sets of historical yields and an agro-climatic index based on daily weather data. The agro-climatic index used here is the sum of effective global radiation intercepted by the crop canopy during the yield formation stage that includes thresholds for extreme temperatures and extreme soil moisture deficit. Results show that year-to-year variations in yields of maize, soybean, rice and wheat in 1981–2010 significantly decreased in 19%–33% of the global harvested area with varying extent of area by crop. However, in 9%–22% of harvested area, significant increase in yield variability was detected. Major crop-producing regions with increased yield variability include maize and soybean in Argentina and Northeast China, rice in Indonesia and Southern China, and wheat in Australia, France and Ukraine. Examples of relatively food-insecure regions with increased yield variability are maize in Kenya and Tanzania and rice in Bangladesh and Myanmar. On a global scale, over 21% of the yield variability change could be explained by the change in variability of the agro-climatic index. More specifically, the change in variability of temperatures exceeding the optimal range for yield formation was more important in explaining the yield variability change than other abiotic stresses, such as temperature below the optimal range for yield formation and soil water deficit. Our findings show that while a decrease in yield variability is the main trend worldwide across crops, yields in some regions of the world have become more unstable, suggesting the need for long-term global yield monitoring and a better understanding of the contributions of technology, management, policy and climate to ongoing yield variability change.

Monitoring of late-season agricultural drought in cotton-growing districts of Andhra Pradesh state, India, using vegetation, water and soil moisture indices

Persistent soil moisture deficits during flowering and yield formation stage are referred to as late-season agricultural drought. This study aims to assess late-season agricultural drought in cotton- and millet-growing districts of Andhra Pradesh, India, during summer cropping season 2011. Satellite-based indices like the Normalized Difference Vegetation Index, Normalized Difference Water Index and their Vegetation Condition Index from MODIS were analyzed. The root zone Soil Moisture Index (SMI) using soil water balance model for cotton and millet (sorghum and pearl millet) crops was derived to evaluate the soil moisture status. The analysis was carried out by comparing the satellite-derived indices with the previous normal years, and the assessments were made. The satellite-based indices clearly brought out the stress that the crop endured during late October and November, while SMI indicated soil water stress in early October. The soil- and crop-specific SMI’s were able to clearly indicate the exact period of water stress. The results show that millet crop was able to escape drought due to sufficient rainfall and its shorter duration, while cotton crop did not have enough soil moisture during the critical stage of flowering and boll formation and suffered severe yield loss due to the late-season agricultural drought.

Climate trends and impacts on crop production in the Koshi River basin of Nepal

Understanding crop responses to climate is essential to cope with anticipated changes in temperature and precipitation. We investigated the climate–crop yield relationship and the impact of historical climate on yields of rice, maize and wheat in the Koshi basin of Nepal. The results show significant impact of growing season temperature and precipitation on crop production in the region. Rice, maize and wheat cultivated at altitudes below 1,100, 1,350 and 1,700 m amsl (above mean sea level), respectively, suffer from stress due to higher temperatures particularly during flowering and yield formation stages. Responses of crop yields to a unitary increment in growing season mean temperature vary from -6 to 16 %, -4 to 11 % and -12 to 3 % for rice, maize and wheat, respectively, depending on the location and elevation in the basin. In most parts of the basin, we observe warming trends in growing season mean temperatures of rice, maize and wheat over the last few decades with clear evidence of negative impacts on yields. However, at some high-elevation areas, positive impacts of warming are also observed on rice and maize yields. If the observed trends in temperature continue in future, the impact is likely to be mostly negative on crop production in the basin. However, crop production may gain from the warming at relatively higher altitudes provided other conditions, e.g., water availability, soil fertility, are favorable.

The response of processing tomato to deficit irrigation at various phenological stages in a sub-humid environment

Field studies were conducted to determine the response of processing tomato (Lycopersicon esculentum Mill.) to deficit irrigation (DI) to guide programs for the development of improved irrigation management practices for sub-humid zones. Field experiments were conducted in Bursa province, Turkey. Industrial tomato plants (cv. Shasta) were subjected to different levels of irrigation using a drip system in the field on a clay–loam Entisol soil for 2 years. Well-watered plants were irrigated at100% crop evapotranspiration (ETc) with 3-day intervals. In other treatments, irrigation was not applied during the vegetative, flowering, yield formation or ripening stages or during combinations of these stages. Fruit weight, marketable yield (MY) and net income decreased with decreases in the amount of irrigation depending on the irrigation timing, but the effect of soil water deficit on the shape index was minor. The highest MY and fruit weight were obtained with the full irrigation (100% ETc) treatment. Water deficit by non-irrigation during the flowering and/or yield formation stages substantially reduced MY values in both years. The results showed that full irrigation during the whole growing season is preferable for higher yield and net income. However, in regions of water scarcity, irrigation managers should adopt the DI approach to achieve economically sustainable crop production. As an alternative to full irrigation during the entire growing season, the application of full irrigation until the beginning of the fruit ripening stage and the cessation of full irrigation after that time can be recommended as optimal because it achieved irrigation water savings of 33%, an increase of 42% in irrigation water use efficiency (IWUE), a satisfactory fruit soluble solids content (SSC) and an acceptable net income with a yield loss of only approximately 5% compared with full irrigation.

Late season sugarcane performance as affected by soil water deficit at the yield formation stage in commercial farms of northern Ivory Coast

A field trial was carried out in Ferke 2 Sugar mill located in northern Ivory Coast, in order to study sugarcane growth and yield response to deficit irrigation imposed over the yield formation stage. The crop used was a first ratoon Co 957 , a non flowering late season sugarcane variety. The experiment was completely randomized following a one-factor design with 4 water deficit treatments in 3 replicates. It came out that the optimum water deficit treatment reached 20%, i.e., 80% of crop water requirements were satisfied through irrigation. That treatment gave an irrigation water use efficiency of 7.9 kg cane/m 3 or 0.98 kg sugar/m 3 . Relatively low crop growth rates (0.2 – 0.4 cm/day) as well as low cane yields (24.5 – 78.4 t/ha) were obtained as a result of an intensive and persistent dry season occurred over the yield formation stage. In line with prevailing climatic conditions, cane juice quality measured was particularly high (15.7 – 16.7 pol%) on Co 957 which used to be a moderately performing variety in Ferke 2 sugar mill. Keywords : Water deficit, yield formation, growth rate, cane yield, water use efficiency, Ivory Coast

Effects of irrigation regimes on yield and water productivity of safflower (Carthamus tinctorius L.) under Mediterranean climatic conditions

A field study was carried out in order to determine the effect of deficit irrigation regimes on grain yield and seasonal evapotranspiration of safflower (Carthamus tinctorius L.) in Thrace Region of Turkey. The field trials were conducted on a loam Entisol soil, on Dincer, the most popular variety in the research area. A randomised complete block design with three replications was used. Combination of four well-known growth stages of the plant, namely vegetative (Va), late vegetative (Vb), flowering (F) and yield formation (Y) were considered to form a total of 16 (including rain fed) irrigation treatments. The effect of irrigation and water stress at any stage of development on grain yield per hectare and 1000 kernels weight was evaluated. Results showed that safflower was significantly affected by water stress during the sensitive late vegetative stage. The highest yield was obtained in VaVbFY treatment. Seasonal irrigation water use and evapotranspiration were 501 and 721 mm, respectively, for the non-stressed treatment. Safflower grain yield of this treatment was 5.22 Mg ha-1 and weight of 1000 kernels was 55 g. The seasonal yield�water response factor value was 0.87. The total water use efficiency was 7.2 kg ha-1 mm-1. Irrigation schedule of the non-stressed treatment may be as follows: the first irrigation is at the vegetative stage, when after 40�50 days from sowing/elongation and branching stage, that is the end of May; the second irrigation is at the late vegetative stage, after 70�80 days from sowing/heading stage, that is in the middle of June; the third irrigation is at the flowering stage, approximately 50% level, that is the first half of July; and the fourth irrigation is at the yield formation stage, seed filling, that is the last week of July.

Impact of Climate Change on Crop Yield: A Case Study of Rainfed Corn in Central Illinois

Abstract This paper assesses the effect of climate change on crop yield from a soil water balance perspective. The uncertainties of regional-scale climate models, local-scale climate variability, emissions scenarios, and crop growth models are combined to explore the possible range of climate change effects on rainfed corn yield in central Illinois in 2055. The results show that a drier and warmer summer during the corn growth season and wetter and warmer precrop and postcrop seasons will likely occur. Greater temperature and precipitation variability may lead to more variable soil moisture and crop yield, and larger soil moisture deficit and crop yield reduction are likely to occur more frequently. The increased water stress is likely to be most pronounced during the flowering and yield formation stages. The expected rainfed corn yield in 2055 is likely to decline by 23%–34%, and the probability that the yield may not reach 50% of the potential yield ranges from 32% to 70% if no adaptation measures are instituted. Among the multiple uncertainty sources, the greenhouse gas emissions projection may have the strongest effect on the risk estimate of crop yield reduction. The effects from the various uncertainties can be offset to some degree when the uncertainties are considered jointly. An ensemble of GCMs with an equal weight may overestimate the risk of soil moisture deficits and crop yield reduction in comparison with an ensemble of GCMs with different weight determined by the root-mean-square error minimization method. The risk estimate presented in this paper implies that climate change adaptation is needed to avoid reduced corn yields and the resulting profit losses in central Illinois.

Developing crop production functions of wheat using experimentally determined yield response factors

Yield response factors at vegetative and yield formation stages of wheat (var. Protiva) were determined in clay loam soil of Rajshahi and in silty clay loam soil of Joydebpur. The value of the factor at vegetative stage was the same (0.18) in both the locations. But those at yield formation stage were 0.46 in Rajshahi and 0.45 in Joydebpur. Using these values in conjunction with the potential yield and stage wise evapotranspiration of wheat, the crop production functions were obtained as: Yv = 3.36+0.009 ETav; 50 mm ≤ ETav ≤ 83 mm and Yyf = 2.22 + 0.0214 ETayf; 53 mm ≤ ETayf ≤ 88 mm in Rajshahi and Yv = 2.76 +0.0075 ETav; 48 ≤ ETav ≤ 80 and Yyf = 1.82 + 0.02 ETyf; 47 ≤ ETayf ≤ 78 in Joydebpur Where, Yv is the expected yield (t/ha) of wheat for water deficit in vegetative stage, Yyf is the expected yield (t/ha) for water deficit in yield formation stage, ETav and ETayf are the crop evapotranspirations (mm) at vegetative and yield formation stages, respectively. All other stages except that received deficit irrigation were irrigated a per stage requirement. Bangladesh J. Agril. Res. 32(2) 2007: 171-182

Agro-hydrological evaluation of on-farm rainwater storage systems for supplemental irrigation in Laikipia district, Kenya

Semi-arid agro-ecosystems are characterized by erratic rainfall and high evaporation rates leading to unreliable agricultural production. Total seasonal rainfall may be enough to sustain crop production, but its distribution and occurrence of intra-season dry spells (ISDS) and off-season dry spells (ODS) affect crop production. Rainwater harvesting (RWH) and management, especially on-farm storage ponds for supplemental irrigation offers an opportunity to mitigate the recurrent dry spells. Farm ponds are small runoff storage structures of capacities ranging from 30 to 100 m 3 used mainly for supplemental irrigation of kitchen gardens, and sometimes for domestic and livestock water supply. The main objective of the study was to evaluate the hydrological and economic performance of farm ponds with the view of assessing their contributions to water and food security in semi-arid agro-systems of Kenya. Agro-hydrological evaluation of on-farm runoff storage systems entailed field survey, monitoring of water losses, analysis of rainy seasons and dry spell occurrence, soil moisture and water balance, estimation of supplemental irrigation requirement (SIR) and farm-level cost-benefit analysis of cabbage production using low-head drip irrigation system. Significant water losses through seepage and evaporation, which accounted on average for 30–50% of the stored runoff, is one of the factors that affect the adoption and up-scaling of on-farm water storage systems. Frequency analysis of rainfall revealed that there is 80% probability of occurrence of dry spells exceeding 10 and 12 days during the long rains and short rains, respectively. The occurrence of off-season (after rainfall cessation) dry spells was more pronounced than intra-seasonal (within the rainy season) dry spells. The length of intra-seasonal (10–15 days) was less than off-season dry spells (20–30 days). The occurrence of off-season dry spells coincides with the critical crop growth stage, in particular flowering and yield formation stages. A 50 m 3 farm pond with a drip system irrigation system was found adequate to meet supplemental irrigation requirement for a kitchen garden of 300–600 m 2 planted with a 90 days growing period cabbages. The cost-benefit analysis showed that farm ponds are feasible solutions to persistent crop failures in semi-arid areas which dominant most countries in Sub-Saharan Africa (SSA).

Daily Evapotranspiration Prediction from Louisiana Flooded Rice Field

During 1995, daily evapotranspiration (Et) from a flooded rice field was calculated with a water balance equation using measured values of water level, precipitation, irrigation, seepage, and tailwater runoff. Stagewise Et was 6.3, 8.1, and 6.8 mm/d for the vegetative, flowering, and yield formation stages, respectively; average daily Et was 6.8 mm/d. Grass reference Et (Etr) combination models Penman-Monteith, FAO-Penman, and 1963 Penman were evaluated for their capabilities to predict rice Et using daily weather data. Daily Etr was also calculated by summing up hourly values with the Penman-Monteith method. The Penman-Monteith (daily) method had a coefficient of determination (R2) of 63.7%, as compared with 62.9, 60.0, and 61.7% for Penman-Monteith (hourly), FAO-Penman, and 1963 Penman methods, respectively. Crop coefficients (Kc) using the Penman-Monteith (daily) model were 1.39, 1.51, and 1.43 for the vegetative, flowering, and yield formation stages, respectively. Developed Kc values were verified using limited rice Et data in 1996. The Kc values underpredicted rice Et by 3.7%, which was acceptable for water management.

Efeito de épocas de deficiência hídrica na evapotranspiração atual da cultura do feijão cv. imbabello

O presente trabalho teve por objetivo identificar os estádios da cultura de feijão que apresentam a menor sensibilidade ao estresse de água no solo, nos quais a irrigação pode ser omitida sem um significativo decréscimo na evapotranspiração, para melhor definir práticas de irrigação em situação de água escassa. O experimento foi realizado em um solo franco arenoso (Typic Haplustoll), em Tumbaco-Pichincha, Equador, entre julho e novembro de 1994, região caracterizada por um clima temperado e seco (temperatura média anual de 16ºC, umidade relativa média do ar 74% e chuva de 123 mm durante o peláodo do experimento). Sete regimes de irrigação foram utilizados, incluindo irrigação ótima durante todo o ciclo, irrigação deficiente durante todo o ciclo, irrigação tradicional da região, deficiência lúdrica no período vegetativo, na floração e formação de vagens, no enchimento de vagens e na maturidade. As parcelas experimentais foram de 33,6 m2 (8 linhas de 7 metros de comprimento, distantes entre si 0,6 m) com uma população de 120.000 plantas/ha. Os tratamentos de irrigação foram aplicados depois da germinação uniforme das sementes e estabelecimento da cultura. A umidade do solo foi monitorada com sonda de nêutrons, até a profundidade de 50 em, 24 horas antes e depois de cada irrigação. A evapotranspiração atual da cultura foi estimada pela técnica do balanço hídrico. Da análise dos resultados obtidos, concluiu-se que a deficiência de água no solo, durante a fase de enchimento da vagem, afetou a produtividade do feijoeiro. Nesta fase a eficiência de uso de água pela planta (Ec = 0,46 kg/m3) foi a mais baixa. Deficiência de irrigação no estádio vegetativo não reduziu a produtividade, permitindo uma economia de água de 30%.

EFEITO DE ÉPOCAS DE DEFICIÊNCIA HÍDRICA NA EFICIÊNCIA DO USO DO NITROGÊNIO DA CULTURA DO FEIJÃO cv. IMBABELLO

Visando identificar estádios da cultura de feijão que apresentam a menor sensibilidade ao estresse de água no solo, nos quais a irrigação pode ser omitida sem um significativo decréscimo na eficiência de uso de nitrogênio e na produtividade final, foi realizado experimento em um solo franco arenoso (Typic Haplustoll) na Estação Experimental da Universidade Central do Equador, "La Tola", em Tumbaco-Pichincha, Equador, entre julho e novembro de 1994. Os tratamentos consistiram da combinação de sete regimes de irrigação, incluindo irrigação ótima durante todo o ciclo, irrigação deficiente durante todo o ciclo, irrigação tradicional da região, deficiência hídrica no período vegetativo, na floração e formação de vagens, no enchimento de vagens e na maturidade; e de dois níveis de adubação nitrogenada (20 kg N/ha e 80 kg N/ha). Os quatorze tratamentos resultantes foram arranjados e analisados num esquema de parcelas sub-divididas com quatro repetições. O tamanho da parcela experimental foi de 33,6 m2 (8 linhas de 7 metros de comprimento, distantes entre si 0,6 m) com uma população de 120.000 plantas/ha. O nitrogênio fixado do ar pelo feijoeiro foi calculado pelo método de diluição isotópica do 15N, no tratamento com adubação de 20 kg N/ha. A solução marcada foi de sulfato de amônio, com abundância de 5% de átomos de 15N. Como planta-controle, foi utilizado o trigo, semeado no sulco central. Da análise dos resultados obtidos, concluiu-se que: A deficiência de água no solo, durante a fase vegetativa, não afetou a eficiência de uso de nitrogênio, a fixação biológica do nitrogênio, nem a produção de sementes, permitindo uma economia de água de 30%. A deficiência de água durante a floração e enchimento de vagens, afetou drasticamente a fixação biológica do nitrogênio, que comparativamente ao controle, foi reduzida 2,2 vezes.

An analysis of the effects of water stress on leaf growth and yield of three barley cultivars

The main objective of the study was to evaluate the sensitivity of Iraqi local barley cultivar (Black) to soil water deficit as compared to other barley cultivars, namely: CM-72 and Arivat. The local cultivar proved to be susceptible during germination and emergence, but it developed resistance during the vegetative growth and yield formation stages. Growth analysis of individual leaves clearly showed that Black barley produced leaves of long growth duration which could affect the growth processes especially cell division. Thus, the reduction in the number of cells composing those leaves was small in the cultivar Black. Leaf growth rates as soil matric potential decreased, were reduced considerably, although, no clear trends were observed between cultivars. On the other hand, the smaller cell volume of local cultivar may have a role in its ability to tolerate water deficit. Some evidence that the local cultivar is post-flowering resistant is discussed.