Irrigation In Arid Areas Research Articles

Dynamic Simulation of Soil Salt Transport in Arid Irrigation Areas under the HYDRUS-2D-Based Rotation Irrigation Mode

This research aims to explore the dynamic transport of water and salt in soil under different irrigation modes and disclose the desalting effect of different irrigation factors in inland arid irrigation areas. Jingdian Irrigation District in Gansu Province, which is located in the arid region of Northwest China, is selected as a typical experimental area. Soil water and salt dynamic migration model is constructed based on HYDRUS-2D software, and field irrigation experiments are designed according to actual irrigation conditions in crop growth period. The model is used to simulate the salt transport process between saturated soil and unsaturated soil as well as the effects of different irrigation quotas, irrigation rounds and quota allocations on soil desalting. Through simulation, the vertical movement pattern of water and salt in the soil of the test area is analyzed, and the optimal design of the soil desalting irrigation plan is carried out. The results demonstrate that: after two-round irrigation, the average soil salinity of the tillage layer at each test points decreases significantly under evapotranspiration; the infiltration of irrigation water has an obvious impact on soil desalting; the deviation between the simulated and the measured value is less than 0.5%, which proves the model fitting result reliable; with fixed irrigation cycle and times, the soil desalting efficiency is higher when the irrigation quota falls in the range of 4000 ~ 6000 m3/hm2; when the first round of irrigation water only saturates the moisture content and gradually increases the irrigation quota in the subsequent rounds, it is more conducive to the dissolution and discharge of soil salinity. In summary, the results of this study can provide technical support for the protection of water and soil resources, as well as the improvement of saline-alkali land in inland arid irrigation areas.

Geostatistical analysis of variations in soil salinity in a typical irrigation area in Xinjiang, northwest China

Characterizing spatial and temporal variability of soil salinity is tremendously important for a variety of agronomic andenvironmental concerns in arid irrigation areas. This paper reviews the characteristics and spatial and temporal variationsof soil salinization in the Ili River Irrigation Area by applying a geostatistical approach. Results showed that： （1） the soilsalinity varied widely, with maximum value of 28.10 g/kg and minimum value of 0.10 g/kg, and was distributed mainly atthe surface soil layer. Anions were mainly SO4^2- and Cl^-, while cations were mainly Na^＋ and Ca^2＋; （2） the abundance ofsalinity of the root zone soil layer for different land use types was in the following order： grassland 〉 cropland 〉 forestland.The abundance of salinity of root zone soil layers for different periods was in the following order： March 〉 June 〉 September;（3） the spherical model was the most suitable variogram model to describe the salinity of the 0-3 cm and 3-20 cmsoil layers in March and June, and the 3-20 cm soil layer in September, while the exponential model was the most suitablevariogram model to describe the salinity of the 0-3 cm soil layer in September. Relatively strong spatial and temporalstructure existed for soil salinity due to lower nugget effects; and （4） the maps of kriged soil salinity showed that higher soilsalinity was distributed in the central parts of the study area and lower soil salinity was distributed in the marginal parts.Soil salinity tended to increase from the marginal parts to the central parts across the study area. Applying the krigingmethod is very helpful in detecting the problematic areas and is a good tool for soil resources management. Managingefforts on the appropriate use of soil and water resources in such areas is very important for sustainable agriculture, andmore attention should be paid to these areas to prevent future problems.

Wheat-Maize Intercropping With Reduced Tillage and Straw Retention: A Step Towards Enhancing Economic and Environmental Benefits in Arid Areas.

Intercropping is considered a promising system for boosting crop productivity. However, intercropping usually requires higher inputs of resources that emit more CO2. It is unclear whether an improved agricultural pattern could relieve this issue and enhance agricultural sustainability in an arid irrigation area. A field experiment using a well-designed agricultural practice was carried out in northwest China; reduced tillage, coupled with wheat straw residue retention measures, was integrated with a strip intercropping pattern. We determined the crop productivity, water use, economic benefits, and carbon emissions (CEs). The wheat-maize intercropping coupled with straw covering (i.e., NTSI treatment), boosted grain yield by 27–38% and 153–160% more than the conventional monoculture of maize and wheat, respectively, and it also increased by 9.9–11.9% over the conventional intercropping treatment. Similarly, this pattern also improved the water use efficiency by 15.4–22.4% in comparison with the conventional monoculture of maize by 45.7–48.3% in comparison with the conventional monoculture of wheat and by 14.7–15.9% in comparison with the conventional intercropping treatment. Meanwhile, NTSI treatment caused 7.4–13.7% and 37.0–47.7% greater solar energy use efficiency than the conventional monoculture of maize and wheat, respectively. Furthermore, the NTSI treatment had a higher net return (NR) by 54–71% and 281–338% and a higher benefit per cubic meter of water (BPW) by 35–51% and 119–147% more than the conventional monoculture of maize and wheat, respectively. Similarly, it increased the NR and BPW by 8–14% and 14–16% in comparison with the conventional intercropping treatment, respectively. An additional feature of the NTSI treatment is that it reduced CEs by 13.4–23.8% and 7.3–17.5% while improving CE efficiency by 62.6–66.9% and 23.2–33.2% more than the conventional monoculture maize and intercropping treatments, respectively. We can draw a conclusion that intercropping maize and wheat, with a straw covering soil surface, can be used to enhance crop production and NRs while effectively lowering CO2 emissions in arid oasis irrigation region.

Estimation of daily evapotranspiration and irrigation water efficiency at a Landsat-like scale for an arid irrigation area using multi-source remote sensing data

The estimation of land-surface evapotranspiration (ET) at high spatial and temporal resolutions is important for management and planning of agricultural water resources, but available remote sensing data generally have either high spatial resolution or high temporal resolution. To overcome this limitation, we evaluated the use of a data fusion scheme, Enhanced Spatial and Temporal Adaptive Reflectance Fusion Model (ESTARFM), to determine the surface parameters needed to estimate daily ET at a Landsat-like scale (100 m). In particular, we fused Moderate Resolution Imaging Spectroradiometer (MODIS) data with Landsat Enhanced Thematic Mapper Plus (ETM+) data in analysis of the Heihe River Basin (HRB), an arid region of Northwest China. The surface parameters were then used to drive the revised Surface Energy Balance System (SEBS) model to estimate daily ET at a spatial resolution of 100 m for this an arid irrigation area during the crop growth period (April to October) in 2012. The results showed that the daily ET estimates had a mean absolute percent error (MAPE) of 12% and a root mean square error (RMSE) of 0.81 mm/day relative to ground measurements from 18 eddy covariance (EC) sites in the study area. The validation results indicated good accuracy for land cover types of maize and vegetables, a slight overestimation for residential and wetland sites, and a slight underestimation for orchard site. Our comparison of the input parameter fusion approach (IPFA) and the ET fusion approach (ETFA) with field measurements indicated the IPFA was superior than the ETFA for land surfaces with high spatial heterogeneity. Furthermore, our high spatiotemporal ET estimates indicated that irrigation water efficiencies of the irrigation districts (mean: 70%) and villages (mean: 62%) had large spatial heterogeneity. These results point to the need for calculating ET at a high spatiotemporal resolution for monitoring and improving irrigation water efficiency at local scales. Our findings suggest that the proposed framework of estimating daily ET at a Landsat-like scale using multi-source data may also be applicable to other heterogeneous landscapes by providing a foundation for management of water resources at the basin or finer scales.

Potential of forage cactus pear accessions under saline water irrigation in arid areas

Forage cactus pear has potential in arid areas of the world to be as one of the alternate foddersin the existing forage/fodder production system. Thirty three cactus accessions introducedunder Arabian Peninsula Research Program of International Center for Agriculture Researchin the Dry Areas in Oman in 2005 with an objective to identify suitable species for therehabilitation of degraded rangelands in arid and saline areas were planted in randomizedcomplete block design under plant density of 40,000 ha-1 with three replications on a sandyloam site under drip irrigation on December 2011 at Rumais Livestock Research Center inOman and evaluated annually during three consecutive years (2012 to 2014) followingstandard agronomic practices recommended worldwide for cactus cultivation. The irrigationwater electrical conductivity was 5.37 dSm-1 at the beginning of the experiment while it was6.01 dSm-1, 10.45 dSm-1 and 14.75 dSm-1, for the annual harvests on December 2012, 2013and 2014, respectively. The observations on plant height (cm) at harvest, number of pads/plant,weight/pad (kg) and green matter weight/plot were recorded at each harvest. The dry matterweight was estimated based on dry matter percentage of green samples. Green and dry matteryield/ha were estimated for their respective weights from experimental plots (3m x 3m). Theresults revealed that the cactus accessions were different (p<0.05) with respect to all thecharacters, such as plant height (45.75 to 82.00 cm), number of pads/plant (2.00 to 10.56),weight/pad (0.32 to 0.59 kg), green matter yield (46.99 to 331.58 t ha-1), dry matter yield (4.40to 33.38 t ha-1) and dry matter (8.29 to 13.00%). Ten cactus accessions had three-year freshannual fodder yield over 150 t ha-1. The accession No. 74112 from Mexico had significantlyhighest (p<0.05) annual pad yield (331.58 t ha-1) of all other accessions studied. Otheraccessions which were not different (p>0.05) but with important production were 4321 fromTunisia (197.67 t ha-1), 75018 from Morocco (195.33 t ha-1), 68247 from Algeria (185.78 t ha-1),73049 from Mexico (180.78 t ha-1) and 69241 from Tunisia (173.22 t ha-1). Results indicatedthe potential of cactus for fodder production under saline water in arid conditions (from 5.37 to14.75 dSm-1 during crop growth), with an average green fodder yield of 117.31 t ha-1 yr-1, ascompared with existing perennial Rhodes grass with an average of 80 to 100 t ha-1 yr-1. Hence,these cactus accessions could be included in the existing fodder production system or used for afforestation of degraded rangelands of Oman besides the farms affected by salinity to theextent of over 5.37 dSm-1.

The growth characteristics and yield potential of rice (Oryza sativa) under non-flooded irrigation in arid region

The objectives of this field experiment were to study the growth characteristics and yield potential of rice plants under non-flooded irrigation in arid area. Non-flooded treatments included drip irrigation with plastic mulching treatments (DIs), furrow irrigation with plastic mulching treatment (FIM) and furrow irrigation with non-mulching treatment (FIN). Conventional flooded cultivation (F) was check treatment (CK). The four drip irrigation treatments differed in the amount of water applied before and after panicle initiation. Root length density, leaf dry weight, shoot dry weight and root activity were generally higher in the non-flood-irrigated treatments (especially the drip-irrigated treatments) than in the flood-irrigated treatment at mid-tillering. However, the growth and development of rice plants were limited after jointing in the non-flooded irrigation treatments. Increasing the root/shoot ratio and root length density in the 20–40 cm depth and decreasing specific root length at 0–20 cm soil layer were important mechanisms for helping the rice plants to adapt to the non-flooded environmental stresses. Finally, the grain yield in the non-flooded irrigation treatments was lower than that in the F treatment. These low yields were mainly attributed to the low root length density at 0–20 cm depth and root activity. Generally speaking, the restricted degrees in the DIs were smaller than that in the FIM and FIN treatments. Among the DIs, both the highest grain yield (8223–8900 kg ha−1) and the highest water use efficiency (WUE) (0.63) were observed when the soil water content was kept at −30 kPa before panicle initiation and at −15 kPa after panicle initiation (referred to as the DI2 treatment). The yield in the DI2 treatment was not significantly different than that in the flood-irrigated treatment. However, WUE was 2.5 times higher in the DI2 treatment than in the F treatment. These results suggest that drip irrigation technology can be considered as a better water-saving cultivation of rice plants in arid region.

Dynamics of an oasis vegetation degradation model with stage structure and impulsive irrigation in arid area

In this work, we consider the influence of the water resources on the oasis vegetation, and establish oasis vegetation degradation model with stage structure and impulsive irrigation in arid area. We prove that all solutions of (2.1) are uniformly ultimately bounded, and prove the oasis vegetation-extinction periodic solution is globally attractive. The condition for permanence of system (2.2) is also obtained. It is concluded that the approach of impulsive irrigation provides reliable tactic basis for preventing the oasis vegetation from degradation while the rainfall decreases in arid area.

Soil salt and groundwater change in flood irrigation field and uncultivated land: a case study based on 4-year field observations

Salt transport in soil profile and shallow groundwater changes are significant seasonal response to flood irrigation in arid area. Understanding soil salt and groundwater level change is useful to determine irrigation schedule and agricultural development. In this study, based on observation data at six fixed sites from 2007 to 2010, soil salt and groundwater depths change were investigated in irrigation fields and uncultivated lands of upper, middle and lower reaches in the arid irrigation district of Hetao irrigation district. The results indicated that the fluctuation of soil salinity in each layer in irrigation fields was more frequent, while the soil salinity in uncultivated lands presented a surface accumulation phenomenon. The groundwater level had similar trends in 4 years and the groundwater changed gradually deeper from upstream to downstream. Meanwhile, relationships between soil surface salinity and groundwater depth were various for irrigation field and uncultivated land. Furthermore, the groundwater recharge and evapotranspiration were calculated with water table fluctuation method. In all the crop growth periods, the influence of groundwater recharge on evapotranspiration was significant. For the irrigation fields, the mean contributions of groundwater to evapotranspiration of 4 years in upper, middle and lower reaches were 25.57, 11.96 and 15.23 %, respectively, while the values were 53.92, 21.61 and 36.84 % at the uncultivated land, respectively. The results can contribute to determine the water resources management plan for sustainable development of the irrigation district with shallow groundwater.

SPATE IRRIGATION OF BARLEY THROUGH FLOODWATER HARVESTING IN THE GAREH-BYGONE PLAIN, IRAN

Utilizing passive floodwater for spate irrigation in arid areas is an opportunity to use marginal water for production of crops. These techniques have only partially been studied in an extensive way. This paper describes a floodwater harvesting and spreading system for spate irrigation and field experiments for cultivation of barley. The field experiments were carried out during a three-year period. The area is noteworthy for its erratic and scarce rainfall. Due to the scarce and late rainfall, only in the second year experiment barley yield was achieved. On December 5, 2009, barley was planted in one trial plot and subsequently received spate irrigation on December 8. On December 16, 2009, barley was planted in a second trial plot and in a control plot outside the system. During the growth period, the second trial plot and the control plot only received moisture from rainfall. The total weight of barley seed and straw in the trial plots was about 1616 and 2052 kg ha-1, respectively. The total weight of barley seed and straw in the control plot, however, was only about 821 kg ha-1. The results consequently displayed a significant increase in yield for the trial plots as compared with the control plot. (Less)

Adaptation of the Submerged Pumps Intended for the Irrigation in the Arid Regions

The first area of work is to study only submersible pumps PUVAL "Pumps Valves" of Berrouaghia. While tracing the effects of abrasion on submersible pumps installed in the shelters in drilling and suffered the consequences are for irrigation in arid areas. The second line stain work to answer the following position: "Should we fight against the causes and not against the consequences?" The result of the proposals will help manufacturers to pump Algerian, one with the best hydraulic performance for the chosen material. Certainly, there have been abrasion tests on samples, but determining the duration of wear and the wear rate of the types of materials is always a line of news. Increasing the life of the pump while remaining within the proper range of operation.

Performance of Wheat/Maize Intercropping is a Function of Belowground Interspecies Interactions

ABSTRACTIntercropping is shown to have yield advantages over sole cropping, but it is unknown how much yield increase is due to belowground interspecies interactions. This study determined land equivalent ratio (LER) and water use efficiency (WUE) of spring wheat (Triticum aestivum L.)/maize (Zea mays L.) intercropping and quantified the magnitude of yield increases due to belowground interspecies interactions. Field experiments, conducted at Wuwei (37°96′N, 102°64′E) in 2008 to 2010, included sole wheat (W), sole maize (M), wheat/maize intercropping with no root‐barrier (W/M), with a plastic sheet barrier (PW/M), or with a nylon mesh barrier (NW/M), vertically placed to one meter deep between the intercrops. Wheat/maize intercropping increased grain yields by 46% in 2008, 26% in 2009, and 64% in 2010, and improved WUE by 49, 30, and 20% in the respective years, compared with the corresponding sole cropping. The LER values ranged from 1.24 to 1.60 for W/M, suggesting that the grain yield of intercropping per hectare is equivalent to the yield that sole wheat or sole maize would produce on 1.24 and 1.60 ha. The W/M system had total yield of 10.6, 11.1, and 16.9 t ha−1 in 2008, 2009, and 2010, respectively; they were 20, 14, and 15% greater compared with the PW/M system; belowground interspecies interactions contributed 32% of the increased yield in 2008, 29% in 2009, and 40% in 2010. With the large, positive belowground interspecies interactions, wheat/maize intercropping is shown to be a promising farming practice for improving crop productivity and WUE in arid irrigation areas.

Higher yield and lower carbon emission by intercropping maize with rape, pea, and wheat in arid irrigation areas

Food security has become a global issue, seriously threatening developing countries owing to fast-growing human populations and declining availability of land for agriculture. Increasing crop yields could be achieved by intensive systems, but these usually need higher energy and emit more carbon (C). Here, we studied crop productivity, energy yields, and C emissions of intercropping versus sole cropping. We tested maize–wheat, maize–rape, maize–pea, and soybean–wheat intercropping, and sole crops as controls in field experiments at Wuwei experimental station in from 2009 to 2011 in a randomized block design with three replicates. We used an evaluation index integrating yield and environmental factors. Results showed a yield increase of 27 % for maize–wheat, 41 % for maize–rape, and 42 % for maize–pea versus sole crops. Water use efficiency increased by 25 % for maize–wheat intercropping over sole wheat, 152 % for maize–rape over sole rape, and 95 % for maize–pea over sole pea. The three maize–crop intercrops produced 68, 308, and 256 % more energy yield than did the sole wheat, sole rape, and sole pea crops, respectively. They emitted 42, 52, and 45 % less C per unit of water in 2009, 2010, and 2011, respectively, compared with the sole maize crop. The maize-based intercropping received a the highest evaluation index (0.82 out of 1.0) among the systems evaluated, clearly showing that the maize-based intercropping is the most effective and sustainable cropping system for arid irrigation areas.

Relationships among soil respiration, soil temperature and dry matter accumulation for wheat-maize intercropping in an arid environment

Liu, S. B., Chai, Q. and Huang, G. B. 2013. Relationships among soil respiration, soil temperature and dry matter accumulation for wheat-maize intercropping in an arid environment. Can. J. Plant Sci. 93: 715–724. Spring wheat (Triticum aestivum L.) intercropped with maize (Zea mays L.) offers an opportunity to boost grain production in short-season areas, but little is known about the sustainability of the intercropping system. This study, conducted at an arid irrigation site in 2009 and 2010, determined water consumption and soil respiration (Rs) characteristics and their relationships to soil temperature (Ts) and above-ground dry matter (DM) accumulation for wheat/maize (W/M) intercropping compared with sole wheat and sole maize. The W/M intercropping had a co-growth period of 70-80 d, allowing the two intercropped species to complete their life cycles. Maximum DM rate for the wheat in the W/M system was significantly greater than that for sole wheat (57 vs. 51 g d−1), which occurred at around 72 to 77 d after sowing (DAS), whereas the maximum DM rate for the maize in the W/M system was between 31.6 and 44.9 g m−2 d−1, or 30 to 43% lower than that of sole maize. The ercroppedhe umulation of a thetime to reach maximum DM was 96 DAS in 2009 and 80 DAS in 2010 for sole maize, and the corresponding time for the intercropped maize was delayed by 6 to 10 d. Soil respiration and DM was a curvilinear relationship; with the increase in DM accumulation, Rs increased, reached a peak at the early flowering stage for wheat and at the silking stage for maize, and then declined. Soil respiration increased linearly with increases in soil temperature during the growth period for both sole and intercropping, suggesting that farming practices aimed at reducing soil temperature will be effective in reducing carbon emissions. Evapotranspiration during the co-growth period averaged 44.1 mm for sole wheat and 48.5 mm for the intercropped wheat and 57.0 mm for sole maize and 48.0 mm for the intercropped maize, but soil water status had little or no effect on Rs. Wheat/maize intercropping had greater grain yield with lower soil respiration over the corresponding sole plantings, and it can serve as a sustainable cropping system for arid irrigation areas.

Model Development and Application for Saline Water Irrigation in Arid Area in Inner Mongolia

Taken Hongwei test field in the He Tao irrigation area of Inner Mongolia for research example, soil water and salt movement model system in regional unsaturated zone is established and tested, through the method of regional zoning. Detection results indicate that the calculated results from the model system agree well with the measured data. It is concluded that simulating and forecasting soil water and salt movement in regional unsaturated zone with this model system is feasible and authentic.

Integrated hydrochemical method of water quality assessment for irrigation in arid areas: application to the Jilh aquifer, Saudi Arabia

Water samples from 72 wells tapping the Jilh aquifer were collected and analyzed for 10 different water quality parameters. Using these data, a regional irrigation water quality was assessed using three techniques: (i) United States Department of Agriculture method (USDA), (ii) Food and Agriculture Organization (FAO) guidelines for water quality assessment, and (iii) Water-Types approach. The USDA method revealed that the aquifer water salinity, as represented by electrical conductivity, ECw, ranges from high salinity (C3: ECw>0.75–2.25 dS/m) to a very high salinity (C4: ECw>2.25 dS/m). The sodium adsorption ratio (SAR) varied from low (S1) to very high (S4) sodicity. Therefore, the water of the Jilh aquifer is dominantly of the C4–S2 class representing 56% of the total wells followed by C4–S1, C4–S3, C3–S1 and C4–S4 classes at 19%, 14%, 8%, and 3% of the wells respectively. The FAO system indicated moderate to severe restriction on the use for irrigation and slight to moderate ion toxicities for Na+, Cl−, B+, NO3− and HCO3−. It is clear that, both USDA and FAO systems condemn the Jilh groundwater as hazardous for irrigation due to its high salt content, unless certain measures for salinity control are undertaken. The dominant salt constituents in the water are Mg–Cl2, Na–Cl and Ca–Cl2 as per the Water-Types method. However, due to the complexity in classifying the aquifer groundwater for irrigation, a simplified approach acknowledging three class groups (I-suitable water, II-conditionally suitable water and III-unsuitable water) adopted from the three methods, is suggested in this paper. The simplified approach combines C–S classes of the USDA method among these three groups according to the lowest ratings. The salinity of the FAO method has been split arbitrarily into slight and moderate subclasses with values of 0.7–2.25 and >2.25 dS/m, respectively; to match with the C3-class of the USDA system. The Water-Types were classified assuming that Ca–Cl2 is the least hazardous salt, followed by Mg–Cl2 and Na–Cl. Using this integrated hydrochemical method, the majority of the wells (92%) contain unsuitable water for irrigation (Group III) while the remaining wells (8%) are in Group II with water considered conditionally suitable for irrigation.

Soil water distribution, uniformity and water-use efficiency under alternate furrow irrigation in arid areas

Soil water distribution, irrigation water advance and uniformity, yield production and water-use efficiency (WUE) were tested with a new irrigation method for irrigated maize in an arid area with seasonal rainfall of 77.5–88.0 mm for 2 years (1997 and 1998). Irrigation was applied through furrows in three ways: alternate furrow irrigation (AFI), fixed furrow irrigation (FFI) and conventional furrow irrigation (CFI). AFI means that one of the two neighboring furrows was alternately irrigated during consecutive watering. FFI means that irrigation was fixed to one of the two neighboring furrows. CFI was the conventional method where every furrow was irrigated during each watering. Each irrigation method was further divided into three treatments using different irrigation amounts: i.e. 45, 30, and 22.5 mm water for each watering. Results showed that the soil water contents in the two neighboring furrows of AFI remained different until the next irrigation with a higher water content in the previously irrigated furrow. Infiltration in CFI was deeper than that in AFI and FFI. The time of water advance did not differ between AFI, FFI and CFI at all distances monitored, and water advanced at a similar rate in all the treatments. The Christiansen uniformity coefficient of water content in the soil (CUs) was used to evaluate the uniformity of irrigated water distribution and showed no decrease in AFI and FFI, although irrigation water use was smaller than in CFI. Root development was significantly enhanced by AFI treatment. Primary root numbers, total root dry weight and root density were all higher in AFI than in the FFI and CFI treatments. Less irrigation significantly reduced the total root dry weight and plant height in both the FFI and CFI treatments but this was less substantial with AFI treatments. The most surprising result was that AFI maintained high grain yield with up to a 50% reduction in irrigation amount, while the FFI and CFI treatments all showed a substantial decrease of yield with reduced irrigation. As a result, WUE for irrigated water was substantially increased. We conclude that AFI is an effective water-saving irrigation method in arid areas where maize production relies heavily on repeated irrigation.

Weed invasion in East Africa: insights from herbarium records

The invasion process was documented from data on the labels of specimens stored in the East African Herbarium at the National Museums of Kenya. We analysed data from seven abundant alien plant species: Ageratum conyzoides L. (Asteraceae), Capsella bursa‐pastoris (L.) Med. (Brassicaceae), Datura stramonium L. (Solanaceae), Galinsoga parviflora Cav. (Asteraceae), Tagetes minuta L. (Asteraceae), Spergula arvensis L. (Caryophyllaceae) and Stellaria media (L.) Vill. (Caryophyllaceae) and compared these data with the spread of two native weeds: Cynoglossum coeruleum A.DC. (Boraginaceae) and Senecio discifolius Oliv. (Asteraceae). Although all investigated species had been already recorded before the Second World War, most specimens were collected between 1960 and 1980. This regional spread is correlated with a change in the agricultural systems of Kenya. The early records of alien weeds were restricted to higher altitudes. With the increasing human population and the associated increase of agricultural activities (e.g. irrigation in arid areas) the weed species from South America were able to spread to lower altitudes.

Drainage Load-flow Relationships in Arid Irrigated Areas

The load-flow relationship of salt in drainage water was studied using drainage water flow and salinity data from an irrigation district on the west side of the San Joaquin Valley of California. Flow and salinity data were collected from the main district drain, individual drainage sumps, and two field sites. Linear regression was used to describe the salt load-flow relationship at each drainage site. The slope of the regression line for the salt flow in the main drain was different compared to the subsurface drainage sites because of the inclusion of surface runoff from irrigation in the main drain. The EC in the water from the subsurface drains was not correlated with the flow rate. Cluster analysis of the load-flow relationships of 45 individual drainage sumps indicated that the load-flow relationship for flow from the district could be characterized by one of three relationships.