Replacement Of Crop Evapotranspiration Research Articles

Produção de grãos verdes de feijão-caupi fertirrigado por gotejamento contínuo e pulsado

Abstract The objective of this work was to evaluate the production of green cowpea beans under conventional fertilization, different fertigation depths, and replacement of crop evapotranspiration (ETc) through continuous and pulse drip irrigation. The experimental design was a randomized complete block with 12 treatments distributed in a 5x2+2 factorial arrangement, with five ETc replacement irrigation depths (40, 60, 80, 100, and 120%), combined with two types of fertigation application (pulse and continuous) plus two additional treatments with pulse (control 1) and continuous (control 2) irrigation at 100% of ETc under conventional fertilization. The analyzed variables were: number of pods, number of grains, fresh and dry mass of pods and grains, and total shoot fresh and dry mass. Cowpea showed a better productive performance at the fertigation depths between 80 and 100% of ETc. Moreover, pulse fertigation promotes higher yields for all production variables analyzed. Regardless of the type of application (pulse or continuous), the productive variables show better results at the fertigation depths estimated for maximum physical efficiency than in the treatments with conventional fertilization and irrigation with a depth of 100% of ETc.

Water Stress Alters Physiological, Spectral, and Agronomic Indexes of Wheat Genotypes.

Selecting drought-tolerant and more water-efficient wheat genotypes is a research priority, specifically in regions with irregular rainfall or areas where climate change is expected to result in reduced water availability. The objective of this work was to use high-throughput measurements with morphophysiological traits to characterize wheat genotypes in relation to water stress. Field experiments were conducted from May to September 2018 and 2019, using a sprinkler bar irrigation system to control water availability to eighteen wheat genotypes: BRS 254; BRS 264; CPAC 01019; CPAC 01047; CPAC 07258; CPAC 08318; CPAC 9110; BRS 394 (irrigated biotypes), and Aliança; BR 18_Terena; BRS 404; MGS Brilhante; PF 020037; PF 020062; PF 120337; PF 100368; PF 080492; and TBIO Sintonia (rainfed biotypes). The water regimes varied from 22 to 100% of the crop evapotranspiration replacement. Water stress negatively affected gas exchange, vegetation indices, and grain yield. High throughput variables TCARI, NDVI, OSAVI, SAVI, PRI, NDRE, and GNDVI had higher yield and morphophysiological measurement correlations. The drought resistance index indicated that genotypes Aliança, BRS 254, BRS 404, CPAC 01019, PF 020062, and PF 080492 were more drought tolerant.

Water Use, Growth, and Yield of Ratooned Guayule under Subsurface Drip and Furrow Irrigation in the US Southwest Desert

Guayule (Parthenium argentatum, A. Gray) is a perennial desert shrub with ratoon-cropping potential for multiple harvests of its natural rubber, resin, and bagasse byproducts. However, yield expectations, water use requirements, and irrigation scheduling information for ratooned guayule are extremely limited. The objectives of this study were to evaluate dry biomass (DB), contents of rubber (R) and resin (Re) and yields of rubber (RY) and resin (ReY) responses to irrigation treatments, and develop irrigation management criteria for ratooned guayule. The water productivity (WP) of the yield components were also evaluated. Guayule plants that were direct-seeded in April 2018 were ratooned and regrown starting in April 2020, after an initial 2-year harvest at two locations in Arizona: Maricopa and Eloy on sandy loam and clay soils, respectively. Plots were irrigated with subsurface drip irrigation (SDI) at 50, 75, and 100% replacement of crop evapotranspiration (ETc), respectively, and furrow irrigation at 100% ETc replacement, as determined by soil water balance measurements. The Eloy location did not include the 100% irrigation treatment under SDI due to unsuccessful regrowth for this specific treatment. The irrigation treatments at the locations were replicated three times in a randomized complete block design. After 21–22 months of regrowth, the guayule plants were harvested in plots. The results showed that DB increased with the amount of total water applied (TWA, irrigation plus precipitation), while R and Re were reduced at the highest TWA received at both locations. Ultimately, the SDI treatments with 75% ETc replacement resulted in the best irrigation management in terms of maximizing RY and ReY, and WP for both locations and soil types. Compared to the initial 2-year direct-seeded guayule crop, ratooned guayule required less TWA and attained higher DB, RY, and ReY, as well as higher WP, with average increases of 25% in dry biomass, 33% in rubber yield, and 32% in resin yield. A grower’s costs for planting the initial direct-seeded guayule crop would be offset by the additional yield revenue of the ratooned crop, which would have comparatively small startup costs.

Analysis of Principal Components for the Assessment of Silage Corn Hybrid Performance under Water Deficit

Corn is an important crop for animal production systems. Owing to climate change, it is important to understand the behavior of commercial corn hybrids under low soil water availability. The objective of this study was to evaluate the morphogenic characteristics and yields of silage corn hybrids subjected to different water conditions using univariate and multivariate analyses. The experimental design was randomized blocks in a 5 × 2 factorial scheme with four replications. Corn hybrids (AGRI104, AGRI320, AGRI330, AGRI340, and AGRI360) and water replacement levels (50% and 100% replacement of crop evapotranspiration—ETc) were considered as factors. A water replacement level of 50% ETc was defined as a severe water deficit that persisted for 46 days from V7 until harvesting (R3). Plant height, stem diameter, leaf area, chlorophyll index, water productivity, fresh and dry mass, and dry matter of the shoot and root systems were evaluated. An analysis of variance and a mean test of isolated variables were carried out, and a multivariate perspective, through principal components was performed. In general, the replacement of 50% ETc changed the morphophysiological characteristics of the plants; however, it was only possible to classify the hybrids through a principal components analysis. The best performing hybrids, regardless of the water replacement levels, were AGRI340 and AGRI360.

ÍNDICE DE ESTRESSE HÍDRICO DO FEIJÃO-CAUPI EM DIFERENTES DISPONIBILIDADES HÍDRICAS EM CASTANHAL-PA

ABSTRACT Cowpea is a crop of great socioeconomic relevance for the populations of the North and Northeast of the country, and its low yield is commonly related to environmental stresses, especially water. The objective of this study was to evaluate the water stress index of cowpea, cultivar BR3 - Tracuateua, subjected to different irrigation levels (100, 50, 25 and 0% of ETc) in three reproductive phenological stages (R7, R8 and R9) in Castanhal-PA, Brazil. The experimental design was in randomized blocks, with six replications and four treatments corresponding to 100, 50, 25 and 0% of daily replacement of crop evapotranspiration, during the reproductive period, through an irrigation system. The surface temperature readings were made with infrared thermometer, during the reproductive stage. The smallest absolute temperature differences between canopy and air occurred in stages R7 and R8. The highest values of water stress index (CWSI) were verified when the plant was under water deficit, regardless of phenological stages. The effect of water deficit caused reductions in stomatal conductance of 58.82% (R7), 83.57% (R8) and 84.87% (R9), in leaf transpiration of 45.97% (R7), 64.21% (R8) and 65.90% (R9) and in the net photosynthetic rate of 40.75% (R7), 66.92% (R8) and 74% (R9). The CWSI varied with the availability of water, showing the highest value (0.75) in the treatment without irrigation, in the R8 stage. The CWSI proved to be a good indicator of the water status of the plant.

Water Stress Alters Morphophysiological, Grain Quality and Vegetation Indices of Soybean Cultivars.

Rainfall is among the climatic factors that most affect production, as in the Brazilian Cerrado. Non-destructive and automated phenotyping methods are fast and efficient for genotype selection. The objective of this work was to evaluate, under field conditions, the morphophysiological changes, yield, and grain quality of soybean (Glycine max L. Merrill) under water stress in the Brazilian Cerrado. The plots comprised six soybean cultivars and the subplots of four water regimes, corresponding to 31, 44, 64 and 100% of crop evapotranspiration replacement. The experiments were conducted from May to September 2018 and 2019. An irrigation system with a bar of sprinklers with different flow rates was used. Gas exchange, vegetation indices (measured using a hyperspectral sensor embedded in a drone), yield and grain quality were evaluated. Water stress had different effects on gas exchange, vegetation indices, grain yield and chemical composition among the cultivars. Embrapa cultivar BRS 7280 Roundup ready (RR) and Nidera cultivar NA 5909 RG (glyphosate resistant) are yield stable and have a greater tolerance to drought. BRS 7280RR showed a higher tolerance to drought and higher water use efficiency (WUE) than all other tested cultivars. Vegetation indices, such as the NDVI (Normalized Difference Vegetation Index), correlated with the morphophysiological traits, such as plant height, were the most responsive variables to water stress. The NDVI can be used to predict soybean yield as a tool in a selection program under drought.

Irrigation effects on seasonal growth and rubber production of direct-seeded guayule

Understanding guayule’s response to environmental factors, such as location, soil type, drought stress, and seasonal growth variation is critical for irrigation management to maximize and estimate rubber and resin accumulation throughout the growing seasons. A study was conducted at two sites with different soil types (sandy loam soil at Maricopa, AZ and a clay soil at Eloy, AZ) to compare plant growth and rubber accumulation among different irrigation treatments during a two-year growing season. The above- and below-ground biomass, biomass growth, rubber/resin content, and rubber/resin accumulation were measured every other month from establishment to final harvest in well-watered treatments, which received 100% replacement of crop evapotranspiration (ETc) and irrigated with subsurface drip and furrow (denoted as D100 and F100, respectively), and compared to reduced irrigation treatments (D50 and F50), which received 50% replacement of ETc. Drip irrigation with high water input (D100) decreased root mass partition, but leaf, stem, and flower partitions were not significantly affected by irrigation treatment. Biomass yield was higher in the well-watered treatments as expected, while rubber and resin content were lower, indicating rubber and resin dilution by higher biomass. For all treatments, rubber and resin yield increased linearly over the two-year growing season. However, the rates of increase were different among the irrigation treatments. The D100 treatment had a higher rubber yield increase rate compared to F100 and D50 in sandy loam soil at Maricopa, while the D100 treatment had the lowest increase rate compared to the F100, F50, and D50 treatments in clay soil at Eloy. Top branches of guayule plants in the D100 treatment at Eloy lodged in the second year and likely contributed to lower rubber content and rubber yield in the treatment. The drip irrigation treatments D50 and D100 had higher water productivity for rubber yield at Maricopa. However, the D50 and F50 treatment had the highest water productivity for guayule rubber yield, while the D100 treatment had the lowest due to lower rubber content at Eloy. Root rubber content was 31–39% lower than stem at the two locations. This study indicates that rubber biosynthesis occurred in guayule year-round and that it is possible in clay soils to reduce irrigation without a significant loss in rubber yield.

Physiological changes in soybean cultivated with soil remineralizer in the Cerrado under variable water regimes

Abstract: The objective of this work was to evaluate the influence of the soil remineralizer fine-graded mica schist (FMS) on soybean (Glycine max) physiology, yield, and grain quality under different water regimes (WRs) in the Brazilian Cerrado. The experiment was conducted under field conditions for two years, using four WRs and three treatments: mica schist, conventional fertilization, and control. In 2017 and 2018, the following WRs were evaluated: WR1, WR2, WR3, and WR4, corresponding to a mean value of 100, 65, 44, and 28% of crop evapotranspiration replacement, respectively. Photosynthesis, stomatal conductance, transpiration, internal CO2 concentration, effective quantum yield of photosystem II (PSII) (Fv’/Fm’), quantum yield (PSII) (ᶲFSII), and electron transport rate reduced as a function of the advanced phenological stage of soybean and the reduction in WR. Grain quality was only affected by the WR. The mica schist was statistically similar to conventional fertilization and the control in 2017 and 2018. Yield decreased due to the anticipation of soybean phenological age and WR, but there were no differences between the three treatments in 2017 and 2018. The reduction in soybean yield is attributed to stomatal closure, loss of photoprotective capacity, and damage to the photosynthetic machinery caused by drought.

Mitigating Heat Wave and Exposure Damage to "Cabernet Sauvignon" Wine Grape With Partial Shading Under Two Irrigation Amounts.

Rising temperatures in most agricultural regions of the world are associated with a higher incidence of extreme weather events such as heat waves. We performed an experiment to mitigate the impact of heat waves and exposure of berries in grapevine (Vitis vinifera cv. “Cabernet Sauvignon”) with untreated vines (Exposed) or with fruit-zone partial shading (Shaded) under 40 and 80% replacement of crop evapotranspiration (ETc) with sustained deficit irrigation in a factorially arranged experiment. The trial was performed in a vineyard with vertically shoot positioned trellis with a row orientation that concentrated solar radiation exposure on the southwest aspect of the fruit zone. Leaf stomatal conductance (gs) and net carbon assimilation (AN) were significantly lower in shaded leaves under partial fruit-zone shading that resulted in lower pruning mass for Shaded treatments. Stem water potential (Ψstem) responded to a large extent to increased irrigation. However, grapevines with partial fruit-zone shading had transiently better water status under 40% ETc. Cluster maximum temperatures were 3.9°C greater in Exposed grapevines. Exposed clusters had transiently lower acidity and higher pH. However, Exposed clusters on 40% ETc had higher total soluble solids (TSS). The experimental vineyard suffered a 4-day heat wave 21 days before harvest, resulting in 25% of the clusters being damaged in Exposed treatment, regardless of irrigation amount. Furthermore, berries in Exposed treatments suffered a great loss of anthocyanins and flavonols even if they were not damaged by direct solar exposure. The pre-planting decision of using a vertically shoot positioned trellis that concentrated solar radiation on the Southwest aspect offered mild protection in a hot climate region with a sunny growing season with extreme heat events during the execution of study. The extreme conditions under which this study was conducted are not unusual, and have become more expected. Our work provided evidence of the vulnerability of grape berry to heat waves and exposure during heat wave events and possible protection methods to mitigate these effects in situ in context of climate change.

Bradyrhizobium Inoculation Plus Foliar Application of Salicylic Acid Mitigates Water Deficit Effects on Cowpea

To evaluate the interaction between foliar application of salicylic acid and Bradyrhizobium inoculation on the morphophysiology of cowpea under water stress conditions, four genotypes (BRS Rouxinol, BRS Marataoa, BRS Arace and BR 17 Gurgueia) were subjected to five combinations of water availability: 100% replacement of crop evapotranspiration (control); 50% replacement of crop evapotranspiration (water stress); water stress + salicylic acid; water stress + Bradyrhizobium inoculation; and water stress + salicylic acid + Bradyrhizobium inoculation. The experiment was set up in a 4 × 5 factorial randomized block design, with four replicates and four plants per plot. Water stress negatively affected the leaf water potential, growth, proline contents and antioxidant activity of the cowpea genotypes, and BRS Marataoa was the most sensitive. Under water stress conditions, Bradyrhizobium inoculation was efficient for BRS Rouxinol, but was only efficient for BRS Marataoa, BRS Arace and BR 17 Gurgueia when associated with foliar application of salicylic acid, maintaining their values of leaf water potential, growth, proline content and activities of superoxide dismutase, ascorbate peroxidase, and catalase similar to those of the control treatment.

Potato production affected by fertilization methods, masses of seed tubers and water regimes

ABSTRACT Increasing potato yield while saving natural resources is a challenge for all those involved in the potato production chain. A field experiment was carried out in order to evaluate the effect of different levels of fertilization, mass of seed tubers and the water regime on the production of potato cv. Orchestra. We tested fertilization methods (F1= conventional fertilization; F2= fertigation according to the rate of absorption by the crop; F3= fertigation split into 3 applications), seed tuber mass (ST1= <50 g; ST2= >50 g), and water regimes [WR1= 50%; WR2= 100% replacement of crop evapotranspiration (ETc)]. The study was conducted using a split-plot randomized block design, with fertilizers in the plot and seed tuber mass in the subplot, with six replications. The highest tuber yields (48.18 t ha-1) and greatest potatoes (43.67 t ha-1) were obtained in the treatment F2 and for seed tuber masses >50 g (48.61 and 42.78 t ha-1) under 100% ETc water regime. However, for plants subjected to 50% ETc, the factors fertilization and seed tuber mass caused no difference in tuber yield (P>0.05). The highest water use efficiency (39.82 kg m-3 of water) was found under WR of 50% ETc for seed tuber masses >50 g. The highest cover ratio was obtained with tubers under 100% ETc being 89 days the cycle duration. The fertilization method and seed tuber mass that positively influenced the studied variables were fertigation according to the culture absorption rate and seed tuber masses >50 g for both water conditions (100% and 50% ETc).

Irrigation Water Use Efficiency and Water Productivity of Commercial Sugarcane Hybrids under Water-Limited Conditions

HighlightsSugarcane hybrids with improved IWUE have greater scope in sugarcane agriculture as irrigation water is getting scarce.Among sugarcane hybrids, Co 8371 registered high mean water productivity of 4.18 kg m-3, followed by Co 85019 (3.92 kg m-3), while in I2, six hybrids had significantly higher water productivity (Co 85019, Co 0212, Co 86249, Co 10026, Co 0218 and Co V92102) above 4 kg m-3.Deficit irrigation scheduling (irrigation at recommended interval, with 50% crop evapotranspiration replacement) appears to be far more useful than reducing frequency as well as quantity of irrigation water alone. Hybrid mean water productivity was 3.2, 2.7, and 2.1 kg m-3 in I0, I1, and I2, respectively.ABSTRACT. The escalating deficit rainfall scenario in India indicates that drought is a recurrent phenomenon associated with tropical sugarcane farming, and the availability of irrigation water for sugarcane cultivation will be much less in coming years. To meet the challenge of limited and costly water supply, tropical sugarcane growers will have to find ways of increasing the efficiency of irrigation to maintain high cane yields. More efficient irrigation systems, accurate irrigation scheduling, and the right choice of sugarcane hybrids are potential means of increasing irrigation water use efficiency (IWUE), water productivity (WP), and global water security. With the objective of optimizing irrigation water use, a field experiment evaluating the physiological efficiency of commercial sugarcane hybrids for WP in a sandy clay soil under water-limited conditions was conducted during 2016-2017 at the ICAR-Sugarcane Breeding Institute in Coimbatore, India. The replicated field experiment was laid out in split-plot design with three irrigation levels as the main plot and 33 sugarcane hybrids as subplots. The prevailing climatic conditions during the experiment represented a tropical wet and dry climate, with the wet season lasting from October to December due to the northeast monsoon. The results showed that full irrigation at recommended intervals with 100% crop evapotranspiration (ET) replacement (I0) produced significantly higher cane yield than deficit irrigation at recommended intervals with 50% crop ET replacement (I1) and skipping alternate irrigations with 50% crop ET replacement (I2). The deficit irrigation treatments (I1 and I2) had declines in cane yield of 41.2% and 56.4%, respectively. IWUE was similar in I0 and I1, while I2 had reduced IWUE by 23%. WP was significantly influenced by irrigation level; reduction in irrigation water reduced WP by 17.5% and 36.3% in I1 and I2 compared to I0. Among sugarcane hybrids, Co 85019, Co 13006, Co 10026, Co 99004, CoLk 8102, Co 86249, Co 8371, Co 94008, and Co 95020 yielded higher than the genotypic mean under both deficit irrigation treatments, suggesting their usefulness in deficit irrigation strategies. Sugarcane hybrids with high WP can play a pivotal role in sustaining sugarcane productivity and can reduce the large volumes of irrigation water consumed in water-scarce tropical India. Thus, considering water security, the implications of the results are of paramount importance in promoting the coordinated development and management of water, land, and related resources to maximize economic benefits and social welfare in an equitable manner without compromising the sustainability of vital ecosystems at local as well as national levels. Keywords: Cane yield, Global water security, Sugarcane, Water-limited condition.

Performance of arugula genotypes under irrigation depths on Brazilian Cerrado

ABSTRACT Due to the water balance in the Brazilian Cerrado, it is not necessary to cultivate arugula in a rainfed system. Together with the lack of research on with this crop, it is necessary to study the response of genotypes to irrigation in this biome. Thus, the objective of this study was to determine the optimal irrigation depth and to identify the best arugula genotypes. Three arugula genotypes were field-tested during two cycles under the effect of four irrigation depths based on crop evapotranspiration. The parameters evaluated were root depth, SPAD index, number of plants and leaves per plant, plant diameter, fresh shoot mass and water use efficiency. The arugula presented the same demand for irrigation in the two cycles, and the genotypes and/or irrigation depths affected the evaluated parameters. The results support that the Folha Larga variety should be preferred by Brazilian Cerrado producers and irrigated with 90% replacement of crop evapotranspiration.

Water productivity for sugar and biomass of sugarcane varieties

ABSTRACT The aim of this study was to evaluate the water productivity into biomass and into sugar for 23 sugarcane varieties (second ratoon crop) under two levels of drip irrigation. Two experiments were conducted in a greenhouse. Experiment 1 comprised nine sugarcane varieties grown in a clay soil and Experiment 2 was composed of 14 varieties in a sandy-loam soil. Moreover, two irrigation treatments were adopted: T100 - full irrigation with 100% crop evapotranspiration replacement, maintaining soil moisture near field capacity for each variety; and T70 - irrigation with 70% T100 water depth. Water productivity was evaluated in terms of stem fresh biomass (WPFB) and sugar (WPGSY). The results showed that WPFB ranged from 11.45 to 18.45 kg m-3. The highest values were observed for varieties CTC14, CTC6, RB867515, and SP81-3250 (in T100) and for the varieties CTC6 and CTC14 (in T70). The WPGSY values ranged from 1.68 to 2.22 kg m-3, with emphasis placed on CTC6, RB9675-15, SP81-3250, and RB925211 (in T100) and on CTC6, CTC14, and SP81-3250 (in T70).

PHYSIOLOGICAL RESPONSES OF DWARF COCONUT PLANTS UNDER WATER DEFICIT IN SALT-AFFECTED SOILS

ABSTRACT The objective of this study was to characterize the physiological acclimation responses of young plants of the dwarf coconut cultivar Jiqui Green‘ associated with tolerance to conditions of multiple abiotic stresses (drought and soil salinity), acting either independently or in combination. The study was conducted under controlled conditions and evaluated the following parameters: leaf gas exchange, quantum yield of chlorophyll a fluorescence, and relative contents of total chlorophyll (SPAD index). The experiment was conducted under a randomized block experimental design, in a split plot arrangement. In the plots, plants were exposed to different levels of water stress, by imposing potential crop evapotranspiration replacement levels equivalent to 100%, 80%, 60%, 40%, and 20%, whereas in subplots, plants were exposed to different levels of soil salinity (1.72, 6.25, 25.80, and 40.70 dS m-1). Physiological mechanisms were effectively limited when water deficit and salinity acted separately and/or together. Compared with soil salinity, water stress was more effective in reducing the measured physiological parameters. The magnitudes of the responses of plants to water supply and salinity depended on the intensity of stress and evaluation period. The physiological acclimation responses of plants were mainly related to stomatal regulation. The coconut tree has a number of physiological adjustment mechanisms that give the species partial tolerance to drought stress and/or salt, thereby enabling it to revegetate salinated areas, provided that its water requirements are at least partially met.

Produtividade e qualidade da cana-de-açúcar irrigada com efluente de estação de tratamento de esgoto

O objetivo deste trabalho foi avaliar o desempenho produtivo e qualitativo da cana-de-açúcar (Saccharum spp.), irrigada por gotejamento subsuperficial com efluente de estação de tratamento de esgoto (EETE). Testaram-se lâminas de irrigação entre 0, na testemunha sem irrigação, e 200% da evapotranspiração máxima da cultura, em dois ciclos de cultivo de cana soca, adubada com metade da quantidade recomendada de nitrogênio (N). A produtividade, em cada ciclo, foi ajustada a um modelo que considera a produtividade da cana planta como covariável. Por esse modelo, os ganhos em produtividade, proporcionados pela reposição da evapotranspiração com EETE, foram de 17,13 e 25,76 Mg ha-1. A aplicação de 200% de EETE resultou no ganho estimado de 19,84 Mg ha-1 na primeira soca e 40,47 Mg ha-1 na segunda. Houve redução de sólidos solúveis do caldo da cana, com o uso da irrigação na primeira soca. No entanto, outros parâmetros indicativos da qualidade industrial não foram significativamente alterados pela irrigação. A irrigação com EETE proporciona ganhos de produtividade da cana-de-açúcar e reduz a adubação nitrogenada recomendada no cultivo da primeira e segunda socas.

Crescimento e produção de bagas da mamoneira irrigada com água residuária doméstica

Objetivou-se avaliar os efeitos da irrigação com água de esgoto doméstico sobre o crescimento e a produção de bagas da mamoneira (Ricinus communis L), em ambiente protegido. A pesquisa foi desenvolvida entre novembro/2005 e maio/2006, no Centro de Tecnologia e Recursos Naturais (CTRN) da UFCG-PB. Foram estudados 5 níveis de reposição da evapotranspiração da cultura - ETc, (0,60, 0,75, 0,90, 1,05 e 1,20) em duas cultivares de mamoneira (BRS Nordestina e BRS Paraguaçu), constituindo um fatorial 5 x 2, com três repetições, no delineamento estatístico de blocos ao acaso. Avaliaram-se altura de planta, diâmetro caulinar, número de folhas e área foliar aos 48, 90, 132 e 174 dias após a semeadura (DAS). A produção de sementes foi avaliada na última data. A mamoneira irrigada com 0,60 ETc, em relação a 1,05 da ETc, aos 174 DAS, teve a altura de planta, o diâmetro caulinar, o número de folhas, a área foliar e produção de sementes reduzidos em 23,45, 16,14, 26,23, 44,06 e 50,59%, respectivamente. O crescimento em altura da cultivar BRS Paraguaçu foi significativamente maior, ao longo do ensaio, enquanto a BRS Nordestina se destacou em área foliar, no início do ciclo. A produção de bagas foi semelhante nas duas cultivares Não houve interação significativa entre os fatores estudados.

Sorghum Management Practices Suited to Varying Irrigation Strategies: A Simulation Analysis

Increasing pumping costs and declining well capacities in regions like the Southern High Plains of Texas are requiring producers to adapt cropping practices for use with irrigation levels that vary between complete replacement of crop evapotranspiration (ET) to none (i.e., dryland production). Grain sorghum [Sorghum bicolor (L.) Moench] is a crop suited to both dryland and various deficit irrigation production systems. Our objectives were to (i) identify cultural practices (planting date, population, and cultivar maturity) that maximize sorghum grain yield for widely varying irrigation strategies; and (ii) consider effective means to allocate available water among irrigation strategies that maximizes the ratio of yield to ET, that is, water use efficiency (WUE). Using the model SORKAM and long‐term (1958–1999) weather records from Bushland, TX, we simulated sorghum grain yields on a Pullman soil (fine, mixed, superactive, thermic Torrertic Paleustoll) under dryland (rain) and three deficit irrigation levels (rain + irrigation = 2.5, 3.75, or 5.0 mm d−1) for all combinations of planting date (mid‐May, 15 May; early June, 5 June; and late June, 25 June), cultivar maturity (early, 95 d; medium, 105 d; late, 120 d), and plant density (12 and 16 plants m−2). For 2.5 mm d−1 irrigation level, simulated grain yields were maximized with either early or medium‐maturing cultivars planted in early June. In contrast, simulated sorghum yield and WUE increased with a mid‐May planting date and later‐maturing cultivars for irrigation levels of 3.75 and 5.0 mm d−1. We conclude that spreading water to uniformly irrigate a field with 2.5 mm d−1 produces ∼16% less grain than concentrating the same water resources to variably irrigate a field at 3.75 or 5.0 mm d−1 with complementary (2:1 and 1:1) dryland areas.

A Comparison of Onion Production Under Sprinkler, Subsurface Drip, and Furrow Irrigation

Onion yield and grade were compared under sprinkler, subsurface drip, and furrow irrigation in 1992, 1993, and 1994. Furrow-irrigated onions were planted on two double rows on 1.12-m-wide beds at 352,000 seeds/ha. Sprinkler- and drip-irrigated onions were planted in nine single rows on a 2.24-m-wide bed at 432,100 seeds/acre. Drip plots had three drip lines buried 0.10 m deep in each 2.24-m bed. Soil water potential at 0.2-m depth was measured by tensiometers and granular matrix sensors (Watermark Model 200SS, Irrometer Co., Riverside, Calif.). Furrow irrigations were started when the soil water potential at the 0.2-m depth reached –25 kPa. Drip-irrigated onions had soil water potential at the 0.2-m depth kept wetter than –25 kPa by daily replacement of crop evapotranspiration (Etc). Sprinkler irrigations were started when the accumulated Etc reached 25 mm. Sprinkler irrigation resulted in significantly higher onion yield than furrow irrigation in 1993 and 1994. Sprinkler irrigation resulted in higher marketable onion yield than furrow irrigation in 1993. Drip irrigation resulted in significantly higher onion yield than furrow irrigation every year. Drip irrigation resulted in higher marketable onion yield than furrow irrigation in 1992 and 1994. Marketable onion yield was reduced in 1993 due to rot during storage.

Potato Production and Deficit Irrigation

Potato response to water stress and changes in soil available-N levels in relation to irrigation management were evaluated in 1992, 1993, and 1994. Potatoes were grown on silt loam with sprinkler irrigation in an adequately irrigated check (100% of crop evapotranspiration replaced at –60 kPa) and three deficit irrigation regimes. Water stress treatments were achieved by partial or complete replacement of crop evapotranspiration when soil water potential reached –80 kPa. In 1992 and 1994, relatively warm years, tuber yield and grade were significantly reduced by water stress. In 1993, a relatively cool year, yield was reduced by water stress, but grade was not. Each year, soil available-N accounting for the season showed large surpluses for all treatments. Potato cultivars grown as subplots varied in their response to deficit irrigation.