Irrigation control of cowpea plants using the measurement of leaf thickness under greenhouse conditions

In this study, the thickness of cowpea leaves was measured with high data- and time-resolution, and the dynamics of leaf thickness was subsequently used as an input parameter for automated irrigation control at the greenhouse level. Under non-stressful environmental conditions, leaf thickness showed only minor diurnal and almost no nocturnal fluctuations. In an extreme water deficit stress scenario, leaf thickness decreased dramatically by as much as 45% within a short period of time. In a more realistic situation, leaf thickness was kept fairly constant for several days, but decreased substantially when water deficit stress became too severe for the plants to cope with any longer. This characteristic collapse of leaf thickness was used as an input parameter for the automated initiation of irrigation. Upon automated irrigation, plants re-established their nominal leaf thickness quickly and kept this leaf thickness constant for several days, until signaling the need for the next irrigation by a subsequent decrease of leaf thickness. By using the measurement of leaf thickness for irrigation control, between 25 and 45% of irrigation water could be conserved compared with a typical timed irrigation schedule.     

Simulated crop production under saline high water table conditions

Summary Many irrigated lands in semi-arid regions of the world are underlain with saline high water tables. Water management is critical to maintain crop productivity under these conditions. A multi-seasonal, transient state model was used to simulate cotton and alfalfa production under various irrigation management regimes. The variables included in-season water application of 1.0 or 0.6 potential evapotranspiration (PET), and 18 or 33 cm pre-irrigation amounts for cotton. The water table was initially at a 1.5m depth and a 9 dS/m salinity. A impermeable lower boundary at 2.5 m depth was imposed. Irrigation water salinity was 0.4 dS/m. Climatic conditions typical to the San Joaquin Valley of California were used for PET and precipitation values. The simulations were for no-lateral flow and also lateral flow whereby the water table was raised to its initial level prior to each irrigation event. Uniform application of 1.0 PET provided for relative cotton lint yields and alfalfa yields of 95% or more for at least 4 years. In-season irrigation of cotton with 0.6 PET had higher yields when associated with a 33 cm rather than an 18 cm pre-irrigation. Lateral flow provided for higher cotton lint yields production than the no-lateral flow case for each pre-irrigation treatment. The beneficial effects of lateral flow diminished with time because of the additional salt which accumulated and became detrimental to crop production. Substantial alfalfa yield reductions occurred after the first year when irrigation was set at 0.6 PET regardless of other conditions. Evaporation losses from the soil during the cotton fallow season were higher when the soil water content entering the fallow season were higher.Research was supported by the University of California Salinity/ Drainage Task Force     

Water relations of drought-resistant and drought-sensitive wheat cultivars sprinkled with saline water

Summary Water potential, osmotic potential, turgor potential, and stomatal resistance were measured on leaves of a drought-sensitive (Ponca) and a drought-resistant (KanKing) cultivar of winter wheat (Triticum aestivum L.) treated with foliar applications of NaCl to determine the effect of salt on the water status of two cultivars varying in drought resistance. Plants were grown under controlled conditions in soil, which was watered or allowed to dry. Water potential of the soil was determined. Given an ample water supply, water potential and osmotic potential of leaves of both cultivars with NaCl were lower, and stomatal resistance was higher, than without NaCl. The combination of salt and drought killed both cultivars, but the turgor potential of the drought-sensitive cultivar with the two stresses reached zero before that of the drought-resistant cultivar. Under limited water supply, both cultivars with foliar applications of salt extracted more water from soil than they did with no salt, and the drought-resistant cultivar took up more water than did the drought-sensitive cultivar. The drought-resistant cultivar with foliar NaCl maintained a higher turgor potential and extracted more water from the drying soil than did the drought-sensitive cultivar with foliar NaCl, suggesting that the drought-resistant cultivar was also more salt tolerant.     

Responses of five almond cultivars to irrigation: Photosynthesis and leaf water potential

In the Trás-os-Montes region, almond orchards are usually planted in the dry soils on the upper valley of the Douro river and are typically cultivated under non-irrigated conditions, leading to low yields. This study aimed to compare the physiological responses of five almond varieties (Francoli, Ferragnès, Glorieta, Lauranne and Masbovera) growing under non-irrigated and irrigated conditions. In irrigated conditions, all cultivars had higher photosynthetic rates, with maximum rates in a range of 10–12 μmol CO₂ m⁻² s⁻¹. Study of daily photosynthesis (June–August) indicates that, irrigated plants showed maximal values at 11 h (32 °C), while in water stressed ones highest values were found at 9 h (28 °C). The irrigation induced an increase in photosynthesis of around 173% in Lauranne, 187% in Francoli, 204% in Glorieta, 266% in Masbovera and 331% in Ferragnès. In relation to values of water potential that allow half-rate of photosynthesis (ψ_w50), they were calculated as −2.95, −2.50, −3.10, −3.20 and −3.30 MPa for Ferragnès, Glorieta, Masbovera, Francoli and Lauranne, respectively.     

盐渍化土壤水肥耦合对向日葵叶水势的影响

采用312-D最优饱和设计方案进行田间对比试验。对盐渍化土壤水肥耦合效应下向日葵叶水势的影响因素及变化规律进行了研究。结果表明,盐渍化地区油料向日葵叶水势的主要影响因素除气象因素外。还包括土壤盐分、土壤水分和施肥量。叶水势与大气水势、叶温呈线性关系。土壤基质势越高,叶水势越高;土壤基质势越低叶水势也越低。施肥在一定程度上可以缓解水盐的胁迫,施肥量的增加使叶水势降低。     

Estimation of a production function for wheat under saline conditions

Salinity is a major problem for irrigated agriculture in many parts of the world. Farmers face economic questions such as optimal water applications for given irrigation water quality, reuse of drainage water, reduction in income from using drainage saline waters and rate of mixing good quality water. Crop yield response to water quality and quantity is required to answer these questions. Therefore, this paper is concerned with estimating a set of production functions relating wheat yield to initial soil salinity and water quantity and quality. Crop-water production functions are estimated from experimental data from wheat crop at Sampla village in Rohtak district of Haryana (India).     

Water use — Yield relations for cowpea and maize

Three cowpea varieties and one maize variety were subjected to varying irrigation treatments, ranging from water deficits to over-irrigation, on a silty loam soil classified as an Alfisol at Ile-Ife, Nigeria. There was a strong curvilinear relation between cowpea yield and evapotranspiration (R² = 0.86 for dry matter yield and R² = 0.87 for dry seed yield). The values of the correlation coefficient dropped to 0.62 and 0.66 for dry matter and seed yields, respectively, when a linear relation was used. When data for over-irrigated fields were omitted from the calculation, a linear relationship yielded R² values close to unity (R² = 0.99). Similar results were obtained on maize dry matter and grain yields in relation to evaporation.     

Influence of irrigation on leaf water relations and dry matter production in coconut palms

Summary The effect of different frequencies of irrigation on the leaf water relations and dry matter production of the West Coast Tall coconut palms (Cocos nucifera L.) was studied during two growing seasons. Irrigation was applied in amounts of 60 mm at a ratio of irrigation water to cumulative pan evaporation (I/E) of 1.0, 0.75, 0.50 and 0.0. Measurements were made of stomatal resistance, leaf water potential and epicuticular wax content, and vegetative and reproductive dry matter production. Irrigation treatments resulted in a four-to five-fold increase in the soil water deficit at I/E ratios of 0.5 and 0.0 as compared to 1.0. Coconut palms experienced severe moisture stress at an irrigation level of 0.50, resulting in a greater stomatal resistance (111%) and epicuticular wax content (32%) and reduced transpiration rate (10%), leaf water potential (68%), and reproductive dry matter production (22%), compared with well watered palms. Based on the relationship between the soil water deficit and the stomatal resistance, the critical soil water deficit for irrigation scheduling was deduced to be 110 mm. However vegetative dry matter production was reduced at much lower soil water deficits than this value.     

Midday measurements of leaf water potential and stomatal conductance are highly correlated with daily water use of Thompson Seedless grapevines

A study was conducted to determine the relationship between midday measurements of vine water status and daily water use of grapevines measured with a weighing lysimeter. Water applications to the vines were terminated on August 24th for 9 days and again on September 14th for 22 days. Daily water use of the vines in the lysimeter (ET_LYS) was approximately 40 L vine⁻¹ (5.3 mm) prior to turning the pump off, and it decreased to 22.3 L vine⁻¹ by September 2nd. Pre-dawn leaf water potential (Ψ_PD) and midday Ψ_l on August 24th were −0.075 and −0.76 MPa, respectively, with midday Ψ_l decreasing to −1.28 MPa on September 2nd. Leaf g _s decreased from ~500 to ~200 mmol m⁻² s⁻¹ during the two dry-down periods. Midday measurements of g _s and Ψ_l were significantly correlated with one another (r = 0.96) and both with ET_LYS/ET_o (r = ~0.9). The decreases in Ψ_l, g _s, and ET_LYS/ET_o in this study were also a linear function of the decrease in volumetric soil water content. The results indicate that even modest water stress can greatly reduce grapevine water use and that short-term measures of vine water status taken at midday are a reflection of daily grapevine water use.     

Modelling of root ABA synthesis, stomatal conductance, transpiration and potato production under water saving irrigation regimes

Application of water saving irrigation strategies in agriculture has become increasingly important. Both modelling and experimental work are needed to gain more insights into the biological and physical mechanisms in the soil-plant system, which regulates water flow in the system and plays a central role in reducing crop transpiration. This paper presented a mechanistic model (Daisy) developed based on data obtained in the SAFIR project on measured leaf gas exchange and soil water dynamics in irrigated potato crops grown in a semi-field environment subjected to different irrigation regimes. Experimental data was compared to simulated results from the new enhanced Daisy model which include modelling 2D soil water flow, abscisic acid (ABA) signalling and its effect on stomatal conductance and hence on transpiration and assimilation, and finally crop yield. The results demonstrated that the enhanced Daisy model is capable of simulating the mechanisms underlying the water saving effects of the partial root-zone drying (PRD) irrigation as compared with the conventional full irrigation (FI). However the simulated effect on both crop yield and water use in this particular experiment was negligible indicating more experimental studies are necessary in order to improve on the model.     

Narrow row cotton (Gossypium hirsutum L.) under saline conditions

Summary Cotton (Gossypium hirsutum L.), although known to be one of the most salt tolerant crops, shows a significant reduction in plant size and yield when grown on highly saline soils. A field plot study was therefore conducted to determine the feasibility of increasing yield on highly saline soils by increasing population density by decreasing the distance between rows. Three row widths and four salinity levels were imposed on a nonsaline Pachappa fine sandy loam (mixed, thermic, Mollic Haploxerall). Canopy closure, plant height, earliness, and several yield components were measured. A significant yield increase was obtained at all salinity levels by decreasing the distance between rows from 102 to 86 or 71 cm.     

Leaching rates under a perennial pasture irrigated with saline water

Summary Dilution of saline groundwater (2.5 dS m^–1) for irrigation is a common practice in the Shepparton Region of Northern Victoria. There is little information describing the leaching rates and hence longterm soil salinity levels that will result from such practices. There is also little information to suggest the effect of irrigating with saline water on groundwater recharge.Leaching rates under perennial pastures grown on a Paleustalf were estimated using three methods based on the mass conservation of chloride. Five treatments were irrigated with water ranging from 0.22 dS m^–1 to 4.84 dS m^–1. Leaching rates were greater the higher the salinity of the irrigation water (Table 3). Increased leaching resulted from both increased electrolyte levels in the water and decreased water uptake by plants.A model based on non-steady state solute movement usefully predicted the approach of steady-state conditions in the root zone several years earlier than simple observation of the solute data allowed (Table 5).     

Interaction of applied water amounts and leaf removal in the fruiting zone on grapevine water relations and productivity of Merlot

A study was conducted in the San Joaquin Valley of California on Merlot to determine the interaction of applied water amounts [at 0.4, 0.8, and 1.2 of estimated vineyard evapotranspiration (ET_c)] and leaf removal (at berry set or veraison) in the fruiting zone on productivity. Shaded area was measured beneath the canopy of the 1.2 irrigation treatment at solar noon throughout the study to provide an estimate of seasonal crop coefficients (K _c). Vine water status was assessed across treatments and years by measuring midday leaf water potential (Ψ_l). The maximum K _c determined from the percent shaded area was 0.7 at the row spacing of 3.66?m and canopy type that developed a “California Sprawl.” Irrigation treatment had a significant effect on midday Ψ_l and no such effect for leaf removal. Clusters exposed to direct solar radiation had significantly higher temperatures and lower cluster Ψ than clusters in the shade. Irrigation treatment had a significant effect on berry weight, soluble solids, and titratable acidity. Yields of vines significantly increased as applied water amounts increased. In this wine grape production area, profitability is dependent upon yield. This study provided a reliable estimate of ET_c and applied water amounts to maximize yield.     

Shoot growth and fruit development of muskmelon under saline and non-saline soil water deficit

In irrigated agriculture, the production of biomass and marketable yield depend largely on the quantity and salinity of the irrigation water. The sensitivity of field-grown muskmelon (Cucumis melo L. cv. Galia) to water deficit was compared, using non-saline (EC_i= 1.2 dS m^–1) and saline (EC_i=6.3 dS m^–1) water. Drip irrigation was applied at 2-day intervals at seven different water application rates for each water quality, including a late water-stress treatment. Neutron scattering measurements showed that the soil layers below the root zone remained dry throughout the experiment, indicating negligible deep percolation. Thus, the sum of the seasonal amount of applied water and the change in soil moisture approximated the cumulative evapotranspiration (ET). Gradual buildup of water and salt stresses resulted in small treatment effects on the size of the vegetative cover and large effects on leaf deterioration and fruit production. Crop responses to salinity may result from an osmotic component of the soil water potential or from other salt effects on the crop physiology. Relating plant data to cumulative ET allowed a distinction to be made between the effect on water availability and specific salinity effects. The relation between fruit fresh weight and ET was not sensitive to EC_i. The slopes for fruit dry weights were also insensitive to EC_i but the intercept was larger for saline treatments. At any given ET saline water increased fruit number, increased fruit dry matter content and decreased fruit netting, in comparison with non-saline water. The combination of salinity and soil-water deficit was detrimental to fruit quality. Saline soil-water deficit decreased the percentage of marketable (netted) fruit and caused an early end to the period of marketable fruit production. Non-saline soil-water deficit increased the percentage of marketable fruit and had no effect on the duration of the production period. Late non-saline water stress caused a pronounced increase in the percentage of marketable fruit.     

Movement of water in restructured saline and sodic clay topsoils under a rainfall simulator

The nature of water movement through freely draining saturated and field moist aggregates of saline sodic clay topsoil was studied using 200 mm long columns filled with soil aggregates. Water containing tritium as a tracer was supplied either by means of rainfall simulator or directly to the surface of the soil under a negative pressure head of 500 Pa.The proportion of macropore and micropore flow was elucidated. The micropores of the aggregates were shown to convey very little water (0.013 mm h⁻) and hence, even at low rainfall intensities water was expected to move down through the macropores. In practice, at a low water application rate of 0.6 mm h⁻ drainage did not begin from the base of the column until the aggregates had become fully saturated due to mobile water in the macropores being continuously absorbed into the micropores. The results, however, indicated that extensive rapid bypassing does occur at medium and high rainfall intensities ( > 2.3 mm ⁻) , with the result that a large proportion of the water falling on the unsaturated plough layers of clay soils is drained before the topsoil becomes saturated.The soil absorbed water continuously during the application of the equivalent of a wetter than average winter's rain (400 mm), the rate of absorption being directly proportional to the amount of salt leached.Tritium, used as a tracer, was found to be preferentially absorbed by the clay during the leaching process, the concentration in the soil water rising to 1.8 times that of the applied tritiated water.     

The effect of water stress and rootstock on the development of leaf injuries in grapevines irrigated with saline effluent

Deficit irrigation is increasingly being practiced in water-limited areas to overcome water scarcities. Although, this practice reduces yield losses, there is limited information currently available on how this practice can affect crops when the irrigation water contains elevated levels of salts. An experiment was set up to investigate salt uptake and distribution and salt tolerance of potted Soultanina vines grafted on different rootstocks (41B, 1103P, 110R) and irrigated with effluent containing relatively high concentrations of salts and fresh water at different fractions of evapotranspiration (0.50, 0.75 and 1.00ET). Irrigation with recycled water induced the development of leaf burns, which were more intense in 1998 despite the lower leaf-Na and -Cl content. This may have been due to the more severe water deficit and/or to the more adverse climatic conditions which prevailed during that season. Decreasing the irrigation level induced the development of leaf burns causing only minor changes to leaf-Na or -Cl content. Differences in salt uptake, accumulation and distribution were observed among the rootstocks investigated in this work, suggesting that differences exist in the mechanisms regulating salt uptake and distribution in the shoot. Despite these differences, a distinct superiority in terms of salinity tolerance among rootstocks was only observed at the 0.50ET irrigation level, where vines grafted on 41B developed earlier and more acute leaf burns than the other rootstocks. These findings suggest that leaf salt content alone it is not to classify genotypes according to their tolerance to salinity and that salinity-induced damage is linked with prevailing environmental conditions. Furthermore, it can be inferred that grapevines have additional mechanisms to cope with salt stress which may counteract differences in salt uptake and accumulation in the shoot.     

Evaluation of the CERES-Maize water and nitrogen balances under tile-drained conditions

The CERES-Maize model was developed to investigate how variations in environmental conditions, management decisions, and genetics interact to affect crop development and growth. A tile drainage subroutine was incorporated into CERES-Maize to improve soil-water and nitrogen leaching under subsurface tile drainage conditions. The purpose of this work was to evaluate the soil-water, soil-nitrogen, tile drainage, and tile-nitrogen loss routines of CERES-Maize for tile-drained fields in Iowa. An analysis was conducted based on information collected from a study of 36 plots consisting of five management systems during a 4-year period from 1993 to 1996, at Nashua, IA. The model was calibrated for each plot using data from 1994 and 1995, and validated using data from 1993 and 1996. Temporal soil-water contents and water flow from tile drains were calibrated to an average root mean square error (RMSE) of 0.036 cm³ cm⁻³ and 2.62 cm, respectively, compared to measured values. Validation trials gave an average RMSE for soil-water and tile drainage of 0.046 cm³ cm⁻³ and 5.3 cm, respectively. Soil-nitrate and tile-nitrogen flows were calibrated, with an RMSE of 6.27 μg NO₃ g⁻¹ soil⁻¹ and 3.21 kg N ha⁻¹ soil⁻¹, respectively. For the validation trials, the RMSE for soil-nitrate content and cumulative tile-nitrate flow was 6.82 μg NO₃ g⁻¹ soil⁻¹ and 8.8 kg N ha⁻¹, respectively. These results indicate that the new tile drainage algorithms describe water and nitrate movement reasonably well, which will improve the performance of CERES-Maize for artificially drained fields.     

Performance of sugarcane genotypes grown under sodic soil and water conditions

An experiment was conducted to evaluate the effect of residual sodium carbonates (RSC) of irrigation water on the growth and yield of sugarcane grown on sierozem light textured alkaline soil with sodic ground water and to study the performance of some promising sugarcane genotypes under these conditions. Treatments consisted of five levels of irrigations water viz RSC 2.8, 6.5, 12 me l⁻¹ and RSC 6.5 and 12.0 me l⁻¹ fully amended with gypsum. Plant and ratoon crops of eight genotypes of sugarcane were harvested. Cane yield and yield attributing characters like cane height, number of internodes per cane and number of millable canes were recorded. Juice quality viz percent juice extraction, percent sucrose, and commercial cane sugar (CCS%) in juice were determined at the harvest of crop. For both plant and ratoon crops, the average cane yield of all the genotypes of sugarcane and cane yield attributing characters decreased significantly with the increase in RSC of irrigation water to 6.5 and 12.0 me l⁻¹ (35% and 51% decline in the average cane yield for plant crop). For ratoon crop, the corresponding decrease in the average cane yield was less than the plant crop (only 14% and 21%). Amending RSC with gypsum increased the yield in all genotypes. The cane yield of various genotypes obtained under amended RSC with gypsum treatments were almost equal to the yield obtained under RSC 2.8 me l⁻¹ treatment (89% to 92% average cane yield for plant crop and 93% to 96% for ratoon crop). The effect of RSC of irrigation was variable for different genotypes (for example, for the plant crop of CoH 97, 65% and 76% and for CoH 108, 9% and 20% decline in the cane yield was observed with the application of high RSC irrigation water). As compared to plant crop, the ratoon crop of all genotypes recorded higher average cane yield and lesser decline in the cane yield with the application of high RSC irrigation water. Average juice extraction % decreased from 40.5% to 35.8%, and sugar yield decreased significantly (5.61 to 2.91 t ha⁻¹ for plant crop and 6.18 to 5.38 t ha⁻¹ for ratoon crop) with the increase in RSC of irrigation water, and amending RSC with gypsum increased the juice extraction % and sugar yield per unit area.     

On quantifying soil water deficit of a partially wetted root zone by the response of canopy or leaf conductance

Quantifying the soil water deficit (SWD) and its relation to canopy or leaf conductance is essential for application of the Penman–Monteith equation to water-stressed plants. As the water uptake of a single root depends on the water content of the soil in its immediate vicinity, the non-uniform distribution of water and roots in the soil profile does not allow simple quantification of SWD from soil-based measurements. Using measurements of stem sap flux (with a heat pulse technique), soil evaporation (with micro-lysimeters) and meteorological parameters the canopy conductance was obtained through inversion of the Penman–Monteith equation. SWD was evaluated by averaging the soil water content profile of the root zone (monitored by layers with the TDR sensors) weighted by root distribution of the layers. The average canopy conductance at midday (11:00–15:00, Israel Summer Time), denoted as G_noon, was computed for each day of the experimental period. Stable summer weather, typical of the Mediterranean region, and the fully developed crop canopy, made water stress the only plausible cause of a G_noon decline. However, the daily decline of G_noon did not occur at the same weighted average soil water content during the successive drying cycles. For the cycle with less irrigation, the decline in G_noon occurred at higher soil moisture levels. Alternatively, when SWD was determined from the water balance, i.e., by defining water deficit as irrigation minus accumulated evapotranspiration, the G_noon decline occurred at the same value of water deficit for all irrigation cycles. We conclude that a climate-based soil water balance model is a better means of quantifying SWD than a solely soil-based measurement.     

On-farm water management in saline groundwater area under scarce canal water supply condition in the Northwest India

The study investigates the possibility of enhancing crop water productivity in the parts of Northwest India where groundwater quality is marginal and canal water supply is severely scarce. Soil, Water, Atmosphere and Plant (SWAP) model was calibrated and validated in three farmers’ fields with varying canal water availability and groundwater quality in the Kaithal Irrigation Circle of the Bhakra Canal system, Haryana. On the basis of predicted and observed soil water content, pressure heads, salt concentration at 2 week intervals and crop yields, the model was found suitable for use in the region. A few nomographs were prepared to provide a graphical method to predict the effect of different combinations of water quality and depth of water application on crop yield and soil salinity and to help develop some guidelines to the farming community. Water management alternatives at the field level were suggested to increase the yield and to maintain soil salinity below threshold level. The application of frequent irrigation in precisely leveled field would help in achieving 10% higher yield even when saline groundwater of 11 dS/m is used for irrigation.