Antecedent water content effects on runoff and sediment yields from two Coastal Plain Ultisols

The highly weathered, low-carbon, intensively cropped, drought-prone Coastal Plain soils of Georgia are susceptible to runoff and soil loss, especially at certain times of the year when soil water contents are elevated. We quantified the effects of antecedent water content (AWC) on runoff (R) and sediment (E) losses from two loamy sands managed under conventional- (CT), strip- (ST), and/or no-till (NT) systems. Two AWC treatments were evaluated: field moist (FM) and pre-wet (PW), created with and without post pesticide application irrigations (∼12 mm of water added with the rainfall simulated over 30 min) for incorporation. Treatments (5) evaluated were: CT + FM, CT + PW, ST + FM, ST + PW, and NT + PW. Field plots, each 2-m × -3 m, were established on each treatment. Each 6-m² field plot received simulated rainfall at a variable rainfall intensity (I_v) pattern for 70 min (site 1) or a constant rainfall intensity (I_c) pattern for 60 min (site 2; I_c = 50.8 mm h⁻¹). Adding ∼12 mm of water as herbicide incorporation increased AWCs of the 0-2 (3-9-fold) and 2-15 (23-117%) cm soil depths of PW plots compared to existing field moist soil conditions. Increase in AWC increased R (as much as 60%) and maximum R rates (as much as 62%), and decreased E (at least 59%) and maximum E rates (as much as 2.1-fold) for corresponding tillage treatments. Compared to CT plots, ST and NT plots decreased R (at least 2.6-fold) and maximum R rates (as much as 3-fold), and decreased E (at least 2.7-fold) and maximum E rates (at least 3.2-fold). Runoff curves for pre-wetted CT and ST plots were always higher than corresponding FM curves, whereas E curves for field moist CT and ST plots were always higher than corresponding PW curves. Changes in AWC and tillage affected detachment and transport processes controlling runoff and sediment yields. A more accurate measure of rainfall partitioning and detachment and transport processes affecting R and E losses was obtained when commonly occurring field conditions (increased AWC with irrigation; I_v pattern derived from natural rainfall; commonly used tillage systems) were created and evaluated.     

Chickpea water use efficiency in relation to cropping system, cultivar, soil nitrogen and Rhizobial inoculation in semiarid environments

Crops grown in semiarid rainfed conditions are prone to water stress which could be alleviated by improving cultural practices. This study determined the effect of cropping system, cultivar, soil nitrogen status and Rhizobium inoculation (Rz) on water use and water use efficiency (WUE) of chickpea (Cicer arietinum L.) in semiarid environments. The cultivars Amit, CDC Anna, CDC Frontier, and CDC Xena were grown in no-till barley, no-till wheat, and tilled-fallow systems and under various rates of N fertilizer (0, 28, 56, 84, and 112 kg N ha⁻¹) coupled with or without Rz. The study was conducted at Swift Current and Shaunavon, Saskatchewan, from 2004 to 2006. On average, chickpea used about 10 mm of water from the top 0-15 cm soil depth. In the tilled-fallow system, chickpea extracted 20% more water in the 15-30 cm depth, 70% more in the 30-60 cm depth, and 156% more in the 60-120 cm depth than when it was grown in the no-till systems. CDC Xena had WUE of 5.3 kg ha⁻¹ mm⁻¹ or 20% less than the average WUE (6.6 kg ha⁻¹ mm⁻¹) of the three other cultivars, even though these cultivars used the same amounts of water. Water use efficiency increased from 4.7 to 6.8 kg ha⁻¹ mm⁻¹ as N fertilizer rate was increased from 0 to 112 kg N ha⁻¹ when chickpea was grown in the no-till barley or wheat systems, but chickpea grown in the tilled-fallow system did not respond to changes in the fertilizer N rates averaging WUE of 6.5 kg ha⁻¹ mm⁻¹. In the absence of N fertilizer, the application of Rz increased WUE by 33% for chickpea grown in the no-till barley system, 30% in the no-till wheat system, and 9% in the tilled-fallow system. Chickpea inoculated with Rhizobium achieved a WUE value similar to the crop fertilized at 84 kg N ha⁻¹. Without the use of Rz, chickpea increased WUE in a linear fashion with increasing fertilizer N rates from 0 to 84 kg N ha⁻¹. Cropping system, cultivar, and inoculation all had greater impact on WUE than on the amount of water extracted by the crop from the soil. The improvement of cultural practices to promote general plant health along with the development of cultivars with improved crop yields will be keys for improving water use efficiency of chickpea in semiarid environments.     

Field evaluation of sand-ditch water harvesting technique in Jordan

Water harvesting is viable alternatives for rainfed agricultural production in semiarid lands. A field experiment was conducted to evaluate the efficiency of a relatively new water harvesting technique, called sand ditch, for moisture and soil conservation. Twelve field plots of 10 m × 2 m were constructed in two adjacent fields having silt loam soils but varied in soil depth, 0.75 m and 2 m, and slope of 10% and 12%. A 130 L barrel was installed at the downslope end of the plots to collect water and sediments at the end of each rainstorm along the rainy season. Three types of treatments were used in duplicates (12 plots in total); sand-ditch plots in which a ditch of 2-m long, 1 m wide and 0.8 m deep was constructed in the middle of plots across the slope (2 in each field), two compacted plots and two plots covered with plastic mulch in addition to four control plots, 2 in each field. The total amount of runoff, sediment concentration, total infiltration and sediment loss for the experimental plots were measured or calculated after each storm during the winter season 2004/2005. Experimental results showed that sand-ditch technique significantly reduced runoff and sediment loss and increased infiltration and soil moisture compared to control or compacted plots. The overall average runoff and sediment reductions in the sand-ditch plots were 46% and 61% compared to control plots. Sediment losses from compacted plots were about 2.2 and 6 folds higher than control and sand-ditch plots, respectively making soil compaction unsuitable technique for rainfall harvesting under the current experimental and climatic conditions. Construction of sand ditch also increased the dry matter yield of native grass by an average of 62% and 40% in the two experimental fields compared to control.     

Role of irrigation and mulch on yield, evapotranspiration rate and water use pattern of tomato (Lycopersicon esculentum L.)

Irrigation management strategy invites the quantification of crop response to irrigation frequencies. Conventionally, mulches increase the yield and water use efficiency (WUE) to a great extent by augmenting the water status in the root zone profile. A field study was carried out during the winter season (November-March) of 2003-2004 and 2004-2005 at the Central Research Farm of Bidhan Chandra Krishi Viswavidyalaya (Latitude 22°58′N, Longitude 88°31′E and altitude 9.75 m amsl), Gayeshpur, India, to evaluate the effect of irrigation frequencies and mulches on evapotranspiration rate from tomato crop field as well as leaf area index (LAI), fruit yield and WUE of the crop. The experiment was laid out in a split-plot design where three irrigation treatments {rainfed (RF); CPE₅₀ and CPE₂₅ where irrigation was given at 50 and 25 mm of cumulative pan evaporation (CPE)} were kept in the main plots and the subplots contained four mulch managements {no mulch (NM), rice straw mulch (RSM), white polyethylene mulch (WPM) and black polyethylene mulch (BPM)}. Under CPE₂₅, tomato crop recorded significantly higher leaf area index (LAI) over CPE₅₀ and rainfed condition. LAI value under BPM was 9-30% more over other mulches. Maximum variation of LAI among different treatments was recorded at 60 days after transplanting (DAT). Fruit yield under CPE₂₅ was 39.4 Mg ha⁻¹; a reduction of 7 and 30% has been obtained under CPE₅₀ and RF condition. The use of mulch increased 23-57% yield in comparison to NM condition. Actual evapotranspiration rate (ET_R) was 1.82 mm day⁻¹ under CPE₂₅ and declined by 15 and 31% under CPE₅₀ and RF condition, respectively. The variation of ET_R among different mulches became more prominent under maximum water stressed (RF) condition, whereas the variation was negligible under CPE₂₅ frequency. Irrespective of mulching WUE was highest under moderately wet (CPE₅₀) soil environment. Among different mulches, BPM was responsible for attaining the highest WUE value (25.1 kg m⁻³), which declined by 22, 21 and 39% under WPM, RSM and NM, respectively.     

Soil water dynamics and water use efficiency in spring maize (Zea mays L.) fields subjected to different water management practices on the Loess Plateau, China

Soil water supply is the main limiting factor to crop production across the Loess Plateau, China. A 2-year field experiment was conducted at the Changwu agro-ecosystem research station to evaluate various water management practices for achieving favorable grain yield (GY) with high water use efficiency (WUE) of spring maize (Zea mays L.). Four practices were examined: a rain-fed (RF) system as the control; supplementary irrigation (SI); film mulching (FM); and straw mulching (SM) (in 2008 only). The soil profile water storage (W) and the crop evapotranspiration (ET) levels were studied during the maize growing season, and the GY as well as the WUE were also compared. The results showed that mean soil water storage in the top 200 cm of the profile was significantly (P < 0.05) increased in the SI (380 mm in 2007, 411 mm in 2008) and SM (414 mm in 2008) compared to the FM (361 mm in 2007, 381 mm in 2008) and RF (360 mm in 2007, 384 mm in 2008) treatments. The soil water content was lower at the end of growing season than before planting in the 60-140 cm part of the profile in both the RF and FM treatments. Cumulative ET and average crop coefficiency (K_c) throughout the whole maize growing season were significantly (P < 0.05) higher in the SI (ET, 501 mm in 2007, 431 mm in 2008; K_c, 1.0 in 2007, 0.9 in 2008) treatment than in the other treatments. Both FM and SI significantly improved the GY. The WUE were increased significantly (23-25%; P < 0.05) under the FM treatment. It was concluded that both SI and FM are beneficial for improving the yield of spring maize on the Loess Plateau. However, FM is preferable because of the shortage of available water in the area.     

Drought is a major yield loss factor for rainfed East African highland banana

Although drought stress has been identified among the production constraints of East African highland bananas (Musa spp., AAA-EA genome), no quantitative data were available to support this assumption. This study uses data from three on-station fertilizer trials (5-6 cycles) in Central and Southwest Uganda to quantify the effect of drought stress on banana production and explore possible interactions with nutrient availability. Production data were collected at individual plant basis from 1996 to 2002 in one trial and from 2004 to 2009 in two trials. Cumulative rainfall in the 12 months before harvest (CRF₁₂) was computed per plant from daily rainfall measurements. Average bunch weight ranged from 8.0 to 21.9 kg between trials and cycles and was 8-28% less in dry (CRF₁₂ ≤ 905 mm) than in normal (905 < CRF₁₂ ≤ 1365 mm) rainfall periods. Linear relations were observed between CRF₁₂ and maximum bunch weight over the whole range of observed CRF₁₂ (500-1750 mm), whereby every 100 mm decline in rainfall caused maximum bunch weight losses of 1.5-3.1 kg or 8-10%. Optimum annual rainfall for East African highland bananas may thus be well above 1200-1300 mm yr⁻¹ as suggested earlier. Relative drought-induced yield losses were independent of soil fertility. Absolute losses on fertile/fertilized soils were similar to those recorded in well fertilized irrigation studies in Latin America. Our study suggests that drought-induced yield losses in areas of the East African highlands with annual rainfall < 1100 mm are perhaps as high as 20-65% compared to the wetter areas in this region. To improve productivity of smallholder banana farmers in Africa, more attention should be given to research geared towards improved water/drought stress management.     

Water-use efficiency of wheat-based rotation systems in a Mediterranean environment

Crop production in Mediterranean-type environments is invariably limited by low and erratic rainfall (200-600 mm year⁻¹), and thus soil moisture, and by high evapotranspiration resulting from high temperature. Consequently, a major research challenge is to devise cropping systems that maximize water-use efficiency (WUE). In a long-term trial in northern Syria (1986-1998) we compared the effects of seven wheat-based rotations on soil water dynamics and WUE in both the wheat and non-wheat phase. The cropping systems were durum wheat (Triticum turgidum L.) in rotation with fallow, watermelon (Citrullus vulgaris), lentil (Lens culinaris), chickpea (Cicer arietinum), vetch (Vicia sativa), medic pasture (Medicago spp.), and wheat. Seasonal recharge/discharge were identified using the neutron probe. Depth of wetting varied with seasonal rainfall (233-503 mm). Based on crop yields, WUE was calculated for each cropping option in relation to the durum wheat crop.The greatest limitation to growth was the supply of water and not the soil moisture storage potential. Wheat grain yield was dictated by the extent to which the alternative crops in the rotation dried out the soil profile, in addition to seasonal rainfall and its distribution. Chickpea and medic extracted as much water as continuous wheat. Wheat after these crops was solely dependent on current seasonal rainfall, but fallow, lentil, watermelon, and vetch did not deplete soil moisture to the same extent, leaving some residual soil moisture for the succeeding wheat crop. This difference in soil water resulted in a significant difference in wheat yield and hence WUE, which decreased in the following crop rotation sequence: fallow, medic, lentil, chickpea, and continuous wheat. However, on the system basis, the wheat/lentil or wheat/vetch systems were most efficient at using rainfall, producing 27% more grain than the wheat/fallow, while the wheat/chickpea system was as efficient as wheat/fallow system, with continuous wheat being least efficient. With N added to the cereal phase, system WUE of the system increased, being least for continuous wheat and greatest for wheat/lentil. Wheat-legume rotation systems with additional N input in the wheat phase not only can maintain sustainable production system, but also are more efficient in utilizing limited rainfall.     

Nutrient management adaptation for dryland maize yields and water use efficiency to long-term rainfall variability in China

Rainfed crop production in northern China is constrained by low and variable rainfall, and by improper management practices. This study explored both the impact of long-term rainfall variability and the long-term effects of various combinations of maize stover, cattle manure and mineral fertiliser (NP) applications on maize (Zea mays L.) yields and water use efficiency (WUE) under reduced tillage practices, at Shouyang Dryland Farming Experimental Station in northern China from 1993 onwards. The experiment was set up according to an incomplete, optimal design, with 3 factors at five levels and 12 treatments including a control with two replications. Grain yields were greatly influenced by the amount of rain during the growing season, and by soil water at sowing. Annual mean grain yields ranged from 3 to 10 t ha⁻¹ and treatment mean yields from 4.2 to 7.2 t ha⁻¹. The WUE ranged from 40 in treatments with balanced nutrient inputs in dry (weather/or soil) years to 6.5 kg ha⁻¹ mm⁻¹ for the control treatments in wet years. The WUE averaged over the 15-year period ranged from 11 to 19 kg ha⁻¹ mm⁻¹. Balanced combination of stover (3000-6000 kg), manure (1500-6000 kg) and N fertiliser (105 kg) gave the highest yield and hence WUE. It is suggested that 100 kg N per ha should be a best choice, to be adapted according to availability of stover and manure. Possible management options under variable rainfall conditions to alleviate occurring moisture stress for crops must be tailored to the rainfall pattern. The potentials of split applications, targeted to the need of the growing crop (response nutrient management), should be explored to further improve grain yield and WUE.     

Furrow diking in conservation tillage

Crop production in the Southeastern U.S. can be limited by water; thus, supplemental irrigation is needed to sustain profitable crop production. Increased water capture would efficiently improve water use and reduce supplemental irrigation amounts/costs, thus improving producer's profit margin. We quantified infiltration (INF), runoff (R), and sediment (E) losses from furrow diked (+DT) and non-furrow diked (−DT) tilled conventional (CT) and strip tillage (ST) systems. In 2008, a field study (Tifton loamy sand, Typic Kandiudult) was established with DT, ST, and CT systems. In 2009, a field study (Faceville loamy sand, Typic Kandiudult) was established with DT and ST systems. Treatments (6) included: CT − DT, CT + DT, ST₁ (1-year old) − DT, ST₁ + DT, ST₁₀ (10-year old) − DT, and ST₁₀ + DT. Simulated rainfall (50 mm h⁻¹ for 1 h) was applied to each 2-m × 3-m plots (n = 3). Runoff and E were measured from each 6-m² plot. ST₁ + DT plots had 80-88% less R than ST₁ − DT plots. Any disturbance associated with DT in ST₁ systems did not negatively impact E values. For both soils, CT − DT plots represented the worst-case scenario in terms of measured R and E; ST + DT plots represented the best-case scenario. Trends for R, E, and estimated plant available water (PAW) values decreased in order of CT − DT, CT + DT, ST₁ − DT, ST₁ + DT, ST₁₀ − DT, and ST₁₀ + DT treatments. From a hydrology standpoint, ST₁ − DT plots behaved more similarly to CT plots than to other ST plots; from a sediment standpoint, ST₁ − DT plots behaved more similarly to other ST plots than to CT plots. DT had no effect on ST₁₀ plots. CT − DT and ST₁₀ + DT plots resulted in 5.9 (worst-case) and 8.1 (best-case) days of water for crop use, a difference of 2.2 days of water for crop use or 37%. Compared to the CT − DT treatment, an agricultural field managed to CT + DT, ST₁ − DT, ST₁ + DT, ST₁₀ − DT, and ST₁₀ + DT would save a producer farming the CT − DT field $5.30, $9.42, $13.55, $14.14, and $14.14 ha⁻¹, respectively, to pump the amount of water lost to R and not saved as INF back onto the field. The most water/cost savings occurred for CT and ST₁ plots as a result of DT. Savings for CT + DT, ST₁ − DT, and ST₁ + DT treatments represent 27%, 47%, and 68% of the cost of DT ($20 ha⁻¹) and 37%, 67%, and 96% of the savings a producer would have if managing the field to ST for 10 years without DT (ST₁₀ − DT) in a single 50-mm rainfall event. For row-crop producers in the Southeastern U.S. with runoff producing rainfall events during the crop growing season, DT is a management practice that is cost-effective from a natural resource and financial standpoint for those producers that continue to use CT systems and especially those that have recently adopted ST systems into their farming operations.     

Quantifying rainfall-runoff relationships on the Dera Calcic Fluvic Regosol ecotope in Ethiopia

Droughts, resulting in low crop yields, are common in the semi-arid areas of Ethiopia and adversely influence the well-being of many people. The objective of this study was to assess the benefit that in-field rainwater harvesting (IRWH) would have, compared to conventional tillage, on maize yields on a semi-arid ecotope at Dera situated on the eastern part of the Rift Valley. Rainfall-runoff measurements were made during 2003 and 2004 on 2 m × 2 m plots provided with a runoff measuring system and replicated three times for each treatment. There were two treatments: conventional tillage (CT) and no-till (NT), the latter with a flat surface that promotes runoff and therefore IRWH. Rainfall intensity was measured at 1 min intervals with an automatic tipping bucket instrument, and runoff was measured after each rain event. Measured runoff as a function of rainfall intensity and duration from half the rainfall-runoff events was used to determine the critical parameters of a appropriate runoff model. The calibrated model was found to be capable of predicting runoff in a satisfactory way.Rainfall-runoff measurements were made during the rain seasons in 2003 and 2004 during which there were 25 rain events with >9 mm of rain. There was no statistical difference between the runoff on the two treatments. The measured runoff (R) for the two rain seasons, expressed as a fraction of the rainfall during the measuring period (P), i.e. R/P, gave values of 0.46 and 0.39 for the NT and CT treatments, respectively.Results from 7 years of field experiments with IRWH at Glen in South Africa were used to estimate the yield benefit of NT for Dera compared to CT. The results were 696 and 494 kg ha⁻¹ for 2003 and 2004, respectively. Based on the estimated average long-term maize yield of 2000 kg ha⁻¹ at Dera, this was an estimated yield increase ranging from 25% to 35%.     

Runoff estimation in southern Brazil based on Smith's modified model and the Curve Number method

The objective of this work was to measure and model the runoff for different soils classes at different rainfall intensities (30, 60 and 120 mm h⁻¹) in Southern Brazil. A portable rainfall simulator with multiple nozzles was used to simulate these rainfall intensities. For each soil, the initial time and runoff rate, rainfall characteristics (total, duration and intensities), surface slope, crop residue amount and cover percentage, soil densities (bulk and particle), soil porosity (bulk, macro and micro), textural fractions (clay, silt and sand), and the initial and saturated soil water content were measured. The runoff measured was compared to Smith's modified and Curve Number (USDA-SCS) models. The cumulative runoff losses were 67, 45 and 27% of the total rainfall, for a Rhodic Paleudalf, Typic Quartzipsamment and Rhodic Hapludox, respectively. An inverse relationship was observed between initial runoff and the runoff rate, independently of the soil surface and rainfall conditions. Increasing rainfall intensity decreased the time to runoff and increased runoff rate. The Smith's modified model overestimated the cumulative runoff by about 4%. The Smith's modified model presented a better estimate for both higher and lower rainfall intensities (120 and 30 mm h⁻¹). The SCS Curve Number model overestimated the cumulative runoff by about 34%. This large overestimate is probably due to that the model did not take into account the soil tillage system used in the field by farmers, particularly for irrigated conditions. The combination of high porosity, low bulk density and presence of crop residue on soil surface decreased runoff losses, independently of the soil texture class. Smith's modified model better estimated the surface runoff for soil with a high soil water content, and it was considered satisfactory for Southern Brazil runoff estimations. The SCS Curve Number model overestimated the cumulative runoff and its use needs adjustments particularly for no-tillage management system.     

Forage quality, water use and nitrogen utilization efficiencies of pearl millet (Pennisetum americanum L.) grown under different soil moisture and nitrogen levels

The increasing scarcity of water for irrigation is becoming the most important problem for producing forage in all arid and semi-arid regions. Pearl millet is a key crop in these regions which needs relatively less water than other crops. In this research, a field study was conducted to identify the best combination of irrigation and nitrogen (N) management to achieve acceptable pearl millet forage both in quantity and quality aspects. Pearl millet was subjected to four irrigation treatments with interaction of N fertilizer (0, 75, 150 and 225 kg ha⁻¹). The irrigation treatments were 40%, 60%, 80% and 100% of total available soil water (I₄₀, I₆₀, I₈₀ and I₁₀₀, respectively). The results showed that increasing moisture stress (from I₄₀ to I₁₀₀) resulted in progressively less total dry matter (TDM), leaf area index (LAI), and nitrogen utilization efficiency (NUzE), while water use efficiency (WUE) and the percentage of crude protein (CP%) increased. The highest TDM and LAI were found to be 21.45 t ha⁻¹ and 8.65, in I₄₀ treatment, respectively. TDM, WUE, CP% and profit responses to N rates were positive. The maximum WUE of 4.19 kg DM/m³ was achieved at I₁₀₀ with 150 kg N ha⁻¹. The results of this research indicate that the maximum profit of forage production was obtained in plots which were fully irrigated (I₄₀) and received 225 kg N ha⁻¹. However, in the situation which water is often limited and not available, application of 150 kg N ha⁻¹ can produce high forage quality and guaranty acceptable benefits for farmers.     

Irrigation strategies to improve the water use efficiency of wheat-maize double cropping systems in North China Plain

Water is the most important limiting factor of wheat (Triticum aestivum L.) and maize (Zea mays L.) double cropping systems in the North China Plain (NCP). A two-year experiment with four irrigation levels based on crop growth stages was used to calibrate and validate RZWQM2, a hybrid model that combines the Root Zone Water Quality Model (RZWQM) and DSSAT4.0. The calibrated model was then used to investigate various irrigation strategies for high yield and water use efficiency (WUE) using weather data from 1961 to 1999. The model simulated soil moisture, crop yield, above-ground biomass and WUE in responses to irrigation schedules well, with root mean square errors (RMSEs) of 0.029 cm³ cm⁻³, 0.59 Mg ha⁻¹, 2.05 Mg ha⁻¹, and 0.19 kg m⁻³, respectively, for wheat; and 0.027 cm³ cm⁻³, 0.71 Mg ha⁻¹, 1.51 Mg ha⁻¹ and 0.35 kg m⁻³, respectively, for maize. WUE increased with the amount of irrigation applied during the dry growing season of 2001-2002, but was less sensitive to irrigation during the wet season of 2002-2003. Long-term simulation using weather data from 1961 to 1999 showed that initial soil water at planting was adequate (at 82% of crop available water) for wheat establishment due to the high rainfall during the previous maize season. Preseason irrigation for wheat commonly practiced by local farmers should be postponed to the most sensitive growth stage (stem extension) for higher yield and WUE in the area. Preseason irrigation for maize is needed in 40% of the years. With limited irrigation available (100, 150, 200, or 250 mm per year), 80% of the water allocated to the critical wheat growth stages and 20% applied at maize planting achieved the highest WUE and the least water drainage overall for the two crops.     

Simulation of bromide and nitrate leaching under heavy rainfall and high-intensity irrigation rates in North China Plain

Heavy rainfall and irrigations during the summer months in the North China Plain may cause losses of nitrogen because of nitrate leaching. The objectives of this study were to characterize the leaching of accumulated N in soil profiles, and to determine the usefulness of Br⁻ as a tracer of surface-applied N fertilizer under heavy rainfall and high irrigation rates. A field experiment with bare plots was conducted near Beijing from 5 July to 6 September 2006. The experiment included three treatments: no irrigation (rainfall only, I0), farmers’ practice irrigation (rainfall plus 100 mm irrigation, I100) and high-intensity irrigation (rainfall plus 500 mm irrigation, I500), with three replicates. Transport of surface-applied Br⁻ and NO₃⁻ (assuming no initial NO₃⁻ in the soil profile) and accumulated NO₃⁻ in soil profiles were all simulated with the HYDRUS-1D model. The model simulation results showed that Br⁻ leached through the soil profile faster than NO₃⁻. When Br⁻ was used as a tracer for surface-applied N fertilizer to estimate nitrate leaching losses, the amount of N leaching may be overestimated by about 10%. Water drainage and nitrate leaching were dramatically increased as the irrigation rate was increased. The amounts of N leaching out of the 2.1-m soil profile under I0, I100 and I500 treatments were 195 ± 84, 392 ± 136 and 612 ± 211 kg N ha⁻¹, equivalent to about 20 ± 5%, 40 ± 6% and 62 ± 7% of the accumulative N in the soil profile, respectively. N was leached more deeply as the irrigation rate increased. The larger amount of initial accumulated N was in soil profile, the higher percentage of N leaching was. N leaching was also simulated in summer under different weather conditions from 1986 to 2006. The results indicated that nitrate leaching in rainy years were significantly higher than those in dry and normal years. Increasing the irrigation times and decreasing the single irrigation rate after fertilizer application should be recommended.     

Effects of nutrition systems and irrigation programs on tomato in soilless culture

A research has been carried out to determine the effects of nutrition systems and irrigation programs on soilless grown tomato plants under polyethylene covered unheated greenhouse conditions. Two nutrition systems (open and closed) and three irrigation programs (high, medium and low) based on integrated indoor solar radiation triggering thresholds (1 MJ m⁻² [0.4 mm], 2 MJ m⁻² [0.8 mm] and 4 MJ m⁻² [1.6 mm]) in both nutrition systems have been tested. Applied and discharged nutrient solution, evapotranspiration, total and marketable yield have been measured and water use efficiency has been calculated. The highest total yield has been obtained from the open system with respectively 11% and 7.2% increases in autumn and spring. Applied nutrient solution volume and seasonal ET have been modified between 47.8-180.4 l plant⁻¹ and 41.7-145.5 l plant⁻¹ respectively during both growing seasons. As average of two growing seasons, respectively 826.5 and 330.6 m³ ha⁻¹ nutrient solutions have been discharged from the greenhouse in the open and closed systems. WUE of treatments varied between 33-55 kg m⁻³ in autumn and 26-35 kg m⁻³ in spring. Highest WUE values have been determined in 4 MJ m⁻² and in the closed system in both growing seasons. Results showed that the closed system and infrequent irrigations increased water use efficiency while decreasing yield and discharged nutrient solution.     

Environmental quality of Lower Little Bow River and riparian zone along an unfenced reach with off-stream watering

The goal of beneficial management practices (BMPs) such as off-stream watering without fencing is to direct cattle away from rivers, improve the environmental quality of the riparian zone, and prevent or reduce river pollution. We conducted a four year (2005-2008) study on an unfenced 1.3 km reach of the Lower Little Bow (LLB) River in southern Alberta, Canada where three off-stream watering systems were installed 290 to ≥730 m from the river in August, 2005. Our hypothesis was that off-stream watering would reduce cattle activity at the river, improve riparian health, prevent river pollution by cattle, and improve the soil, vegetative, and rainfall simulation runoff variables at a cattle access site near the river. Off-stream watering did not significantly (p > 0.10) reduce the median number of cattle on the river bank, in the river, or drinking from the river one year later. However, there was a reduction of 20% (p = 0.15) for median number of cattle on the river bank and a 72% reduction (p = 0.20) for cattle in the river. The BMP moderately improved the riparian health score from 60% (2005) to 65% (2007). Our spatial analysis (upstream-downstream) of base-flow during the post-BMP period (2006-2008) suggested that off-stream watering prevented river pollution by cattle for the majority of water quality variables measured. Canopy cover at the cattle access site near the river was significantly (p ≤ 0.10) increased by 26-53% one and two years after the BMP. Two years after the BMP was implemented, total basal area, biomass, and mulch were significantly increased by 37-106%, while bare soil and NO₃-N in surface soil were decreased by 38-89%, respectively. In contrast, other vegetative and soil properties were not significantly improved. Concentrations of the majority of N and P fractions in rainfall simulation runoff were not significantly reduced, and may be related to the high precipitation in the pre-BMP year of 2005. We accept the hypothesis that off-stream watering improved riparian health, prevented river pollution by cattle, and improved certain vegetative (canopy cover, total basal area, mulch, bare soil) and soil properties (soil NO₃-N) near the river. However, we reject the hypothesis that off-stream watering improved other vegetation (live basal area) and soil properties (bulk density, NH₄-N, total N and C), or improved rainfall simulation runoff quality near the river. Although we cannot statistically prove that the positive benefits of off-stream watering on certain environmental variables was due to reduced cattle activity, the non-significant reductions in cattle activity suggested this may be a possibility.     

Water use and distribution profile under pulse and oilseed crops in semiarid northern high latitude areas

Oilseed and pulse crops have been increasingly used to replace conventional summer fallow and diversify cropping systems in northern high latitude areas. The knowledge of water use (WU) and its distribution profile in the soil is essential for optimizing cropping systems aimed at improving water use efficiency (WUE). This study characterized water use and distribution profile for pulse and oilseed crops compared to spring wheat (Triticum aestivum L.) in a semiarid environment. Three oilseeds [canola (Brassica napus L.), mustard (Brassica juncea L.) and flax (Linum usitatissimum L.)], three pulses [chickpea (Cicer arietinum L.), dry pea (Pisum sativum L.) and lentil (Lens culinaris Medik.)], and spring wheat were seeded in removable 100 cm deep × 15 cm diameter lysimeters placed in an Aridic Haploboroll soil, in southwest Saskatchewan in 2006 and 2007. Crops were studied under rainfed and irrigated conditions where lysimeters were removed and sampled for plant biomass and WU at various soil depths. Wheat yields were greater than pulse crop yields which were greater than oilseed yields, and WUE averaged 4.08 kg ha⁻¹ mm⁻¹ for pulse crops, 3.64 kg ha⁻¹ mm⁻¹ for oilseeds, and ranged between 5.5 and 7.0 kg ha⁻¹ mm⁻¹ for wheat. Wheat used water faster than pulse and oilseed crops with crop growth. Pulse crops extracted water mostly from the upper 60 cm soil depths, and left more water unused in the profile at maturity compared to oilseeds or wheat. Among the three pulses, lentil used the least amount of water and appeared to have a shallower rooting depth than chickpea and dry pea. Soil WU and distribution profile under canola and mustard were generally similar; both using more water than flax. Differences in WU and distribution profile were similar for crops grown under rainfall and irrigation conditions. A deep rooting crop grown after pulses may receive more benefits from water conservation in the soil profile than when grown after oilseed or wheat. Alternating pulse crops with oilseeds or wheat in a well-planned crop sequence may improve WUE for the entire cropping systems in semiarid environments.     

Yield and water use efficiency of cauliflower under varying irrigation frequencies and water application methods in Lower Gangetic Plain of India

A field study (1999-2000 to 2001-2002) was carried out to optimize the irrigation frequency and suitable water application methods for cauliflower with a view to increase curd yield (CY) and water use efficiency (WUE). Check Basin (CB), Each Furrow (EF) and Alternate Furrow (AF) methods were tested with three irrigation frequencies depending on the attainment of soil matric potential (Ψ_m) value at 0.2 m depth as: −0.03 MPa (F₁), −0.05 MPa (F₂) and −0.07 MPa (F₃). Maximum CY was recorded under F₁ and decreased by 10.4 and 31.4%, respectively under F₂ and F₃ frequencies. In contrast, WUE decreased by 9.3% from F₃ to F₁. Highest CY and WUE obtained under CB followed by EF and AF methods. Furrow application methods saved 12-24% irrigation water over CB method. Maximum soil water stress coefficient (K_s) recorded at curd development stage in comparison to other stages. Both seasonal evapotranspiration (ET_a) and yield-moisture stress index (Kys) recorded positive linear relationships with CY. Present study shows a crop response factor of 0.822 for cauliflower. In this region, cauliflower should be irrigated with check basin method at an interval of 8-10 days.     

Corn yield responses under crop evapotranspiration-based irrigation management

Improving irrigation water management is becoming important to produce a profitable crop in South Texas as the water supplies shrink. This study was conducted to investigate grain yield responses of corn (Zea mays) under irrigation management based on crop evapotranspiration (ET_C) as well as a possibility to monitor plant water deficiencies using some of physiological and environmental factors. Three commercial corn cultivars were grown in a center-pivot-irrigated field with low energy precision application (LEPA) at Texas AgriLife Research Center in Uvalde, TX from 2002 to 2004. The field was treated with conventional and reduced tillage practices and irrigation regimes of 100%, 75%, and 50% ET_C. Grain yield was increased as irrigation increased. There were significant differences between 100% and 50% ET_C in volumetric water content (θ), leaf relative water content (RWC), and canopy temperature (T_C). It is considered that irrigation management of corn at 75% ET_C is feasible with 10% reduction of grain yield and with increased water use efficiency (WUE). The greatest WUE (1.6 g m⁻² mm⁻¹) achieved at 456 mm of water input while grain yield plateaued at less than 600 mm. The result demonstrates that ET_C-based irrigation can be one of the efficient water delivery schemes. The results also demonstrate that grain yield reduction of corn is qualitatively describable using the variables of RWC and T_C. Therefore, it appears that water status can be monitored with measurement of the variables, promising future development of real-time irrigation scheduling.     

Influence of irrigation frequencies and phosphate fertilization on actual evapotranspiration rate, yield and water use pattern of rajmash (Phaseolus vulgaris L.)

The hypothesis was tested, whether soil wetness and phosphorus status could regulate the evapotranspiration rate (ET_R), which is of special interest in the lower Gangetic Plain. Rajmash was grown during November-February of 2003-2004 and 2004-2005 on a sandy loam soil, and was irrigated when cumulative pan evaporation (CPE) attained the value of 33 mm (CPE₃₃); 44 mm (CPE₄₄) and 66 mm (CPE₆₆). Four levels of phosphate application were 0 kg P₂O₅ ha⁻¹ (P₀); 30 kg P₂O₅ ha⁻¹ (P₃₀); 60 kg P₂O₅ ha⁻¹ (P₆₀) and 90 kg P₂O₅ ha⁻¹ (P₉₀). Seed yield under CPE₃₃ was 1.37 Mg ha⁻¹ and reduced by 18% and 35%, respectively under CPE₄₄ and CPE₆₆. Continuous increasing trend in yield was recorded with an increase in phosphate level (PL). Irrespective of growth stages, similar trends were recorded for leaf area index (LAI). Maximum variation in LAI among the treatments was recorded at 60 days after sowing. On average, actual ET_R was 1.37 mm day⁻¹ under CPE₃₃ and declined by 13% and 16% under CPE₄₄ and CPE₆₆, respectively. Variation in ET_R under different PL was highest under CPE₃₃ and lowest under CPE₄₄. Except P₉₀, irrespective of PL, highest value of water use efficiency (WUE) was obtained under CPE₄₄. However, magnitude of net evapotranspiration efficiency (WUE_ET) and irrigation efficiency (WUE_I) attained the highest level under CPE₃₃ regime. All water use indices showed an increasing trend with the increase in phosphate level from 0 to 90 kg ha⁻¹. Impact of phosphorus on various parameters was pronounced under CPE₃₃.