Irrigation management in arid areas affected by surface crust

The effects of supplemental irrigation and irrigation practices on soil water storage and barley crop yield were studied for a crust-forming soil at the University of Jordan Research Station near Al-Muwaqqar village during the 1996/97 growing season. An amount of 0.0, 48.9, 73.3, 122.2 and 167 mm supplemental irrigation water were applied. The 48.9, 73.3 and 122.2 mm applications were applied through surface irrigation into furrows with blocked ends, and the 0.0 and 167 mm applications via sprinkler irrigation. The greatest water infiltration and subsequent soil storage was achieved with the 122.2 mm application followed by the 73.3 mm irrigation, both surface applied. Application efficiency (the fraction of applied water that infiltrated into the soil and stored in the 600 mm soil profile) and soil water storage associated with supplemental blocked furrow irrigation was significantly greater than with supplemental sprinkler irrigation. For arid zone soil, which has little or no structural stability, application of supplemental irrigation water via short, blocked-end furrows prevents runoff and increases the opportunity time for infiltration, thereby increasing the amount of applied water that is infiltrated into the soil and stored in the soil profile. Supplemental irrigation, applied by a low-rate sprinkler system, was not as effective because of the low infiltration rates that resulted from the development of a surface throttle due to dispersion of soil aggregates at the soil surface. The differences in stored water had a significant effect on grain and straw yields of barley. Without supplemental irrigation, barley grain and straw yields were zero in natural rainfall cultivation with a total rainfall of 136.5 mm. Barley yields in the control treatment, with a 167 mm supplemental sprinkler irrigation were low being 0.19 and 1.09 ton/ha of barley grain and straw, respectively. Supplemental irrigation through blocked-end furrows increased barley grain and straw yields significantly compared with supplemental sprinkler irrigation to a maximum of 0.59 and 1.8 ton/ha, respectively. The improvement coming from the increased water storage associated with furrows. Since irrigation water is very limited if available, farmers are encouraged to form such furrows for reducing runoff from rainfall thereby increasing the amount of water available for forage and field crop production.     

Wheat water productivity and yield in a cool highland environment: Effect of early sowing with supplemental irrigation

The Central Anatolian Plateau of Turkey is a typical cool highland rainfed wheat area with an annual rainfall of 300–500 mm. Due to suboptimal seasonal rainfall amounts and distribution, wheat yields in the region are low and fluctuate substantially over seasons. Delayed sowing due to late rainfall affects early crop establishment before winter frost and causes substantial reduction in yield. A 4-year field study (1998/1999 to 2001/2002) was carried out at Ankara Research Institute of Rural Services to assess the impact of early sowing with supplemental irrigation (SI) and management options during other dry spells on the productivity of a bread wheat cultivar, “Bezostia”. Treatments included early sowing with 50 mm irrigation and normal sowing with no irrigation as main plots. Four spring (SI) levels occupied the sub-plots. These are rainfed (no-irrigation), full irrigation to sature crop water requirements and two deficit irrigation levels of 1/3 and 2/3 at the full irrigation treatments.Results showed that early establishment of the crop, using 50 mm of irrigation water at sowing, increased grain yield by over 65% and adding about 2.0 t/ha to the average rainfed yield of 3.2 t/ha. Early sowing with SI allowed early crop emergence and development of good stand before being subjected to the winter frost. As a result, the crop used rainwater more efficiently. Additional supplemental irrigation in the spring also increased yield significantly. Grain yields of 5120, 5170 and 5350 kg/ha were obtained by applying 1/3, 2/3 and full SI, respectively. The mean productivity of irrigation water given at sowing was 3.70 kg/m³ with maximum value of 4.5 kg/m³. Water productivity of 1/3, 2/3 and full SI were 2.39, 1.46 and 1.27 kg/m³, respectively, compared to rainwater productivity of 0.96 kg/m³.     

Effects of winter crop and supplemental irrigation on crop yield,water use efficiency and profitability in rainfed rice based cropping system of eastern India

Soil moisture availability is the main limiting factor for growing second crops in rainfed rice fallows of eastern India. Only rainfed rice is grown with traditional practices during the rainy season (June–October) with large areas (13 m ha⁻¹) remaining fallow during the subsequent dry season (November–March) inspite of annual rainfall of the order 1000–2000 mm. In this study an attempt was made to improve productivity of rainfed rice during rainy season and to grow second crops in rice fallow during dry (winter) season with supplemental irrigation from harvested rainwater. Rice was grown as first crop with improved as well as traditional farmers’ management practices to compare the productivity between these two treatments. Study revealed that 87.1–95.6% higher yield of rice was obtained with improved management over farmers’ practices. Five crops viz., maize, groundnut, sunflower, wheat and potato were grown in rice fallow during dry (winter) season with two, three and four supplemental irrigations and improved management. Sufficient amount of excess rainwater (runoff) was available (381 mm at 75% probability level) to store and recycle for supplementary irrigation to second crops grown after rice. Study revealed that supplemental irrigation had significant effect (P < 0.001) on grain yield of dry season crops and with two irrigation mean yields of 1845, 785, 905, 1420, 8050 kg ha⁻¹ were obtained with maize (grain), groundnut, sunflower, wheat and potato (tuber), respectively. With four irrigations 214, 89, 78, 81, 54% yield was enhanced over two irrigations in respective five crops. Water use efficiency (WUE) of 13.8, 3.35, 3.39, 5.85 and 28.7 kg ha⁻¹ was obtained in maize, groundnut, sunflower, wheat, potato (tuber), respectively with four irrigations. The different plant growth parameters like maximum above ground biomass, leaf area index and root length were also recorded with different levels of supplemental irrigation. The study amply revealed that there was scope to improve productivity of rainfed rice during rainy season and to grow another profitable crops during winter/dry season in rice fallow with supplemental irrigation from harvested rainwater of rainy season.     

Water–yield relations and optimal irrigation scheduling of wheat in the Mediterranean region

Crop yield is primarily water-limited in areas of West Asia and North Africa with a Mediterranean climate. Ten years of supplemental irrigation (SI) experiments in northern Syria were conducted to evaluate water–yield relations for bread wheat (Triticum aestivum L.) and durum wheat (Triticum turgidum L.), and optimal irrigation scheduling was proposed for various rainfall conditions. The sensitive growth stages of wheat to water stress were from stem elongation to booting, followed by anthesis, and grain-filling. Water stress to which crop subjected depends on rainfall and its distribution during the growing season; the stress started from early March (stem-elongation stage) or even in seedling stage in a dry year, and from mid-April (anthesis) in an average or wet year. Crop yield linearly increased with increase in evapotranspiration (ET), with an increase of 160 kg for bread wheat and of 116 kg for durum wheat per 10 mm increase of ET above the threshold of 200 mm. Water-use efficiency (WUE) with a yield ≥3 t ha⁻¹ was ca. 60% higher than that with yield <3 t ha⁻¹; this emphasises the importance of that to achieve effective use of water, optimal water supply and relatively high yields need to be ensured. Quadratic crop production functions with the total applied water were developed and used to estimate the levels of irrigation water for maximizing yield, net profit and levels to which the crops could be under-irrigated without reducing income below that which would be earned for full SI under limited water resources. The analysis suggested that irrigation scenarios for maximizing crop yield and/or the net profit under limited land resource conditions should not be recommended. The SI scenarios for maximizing the profit under limited water resource conditions or for a targeted yield of 4–5 t ha⁻¹ were recommended for sustainable utilization of water resources and higher WUE. The time of irrigation was also suggested on the basis of crop sensitivity index to water stress taking rainfall probability and available soil water into account.     

Effects of different ridge:furrow ratios and supplemental irrigation on crop production in ridge and furrow rainfall harvesting system with mulches

The ridge and furrow rainfall harvesting (RFRH) system with mulches is being promoted to increase water availability for crops for higher and stable agricultural production in many areas of the Loess Plateau in northwest China. In the system, plastic-covered ridges serve as rainfall-harvesting zones and stone-, straw- or film-mulched furrows serve as planting zones. To adopt this system more effectively, a field study (using corn as an indicator crop) was conducted to determine the effects of different ridge:furrow ratios and supplemental irrigation on crop yield and water use efficiency (WUE) in the RFRH system with mulches during the growing seasons of 1998 and 1999.The results indicated that the ridge:furrow ratios had a significant effect on crop yield and yield components. The 120:60 cm ridge and furrow (120 cm wide ridge and 60 cm wide furrow) system increased yield by 27.9%, seed weight per head by 14.8%, seed number per head by 7.4% and 1000-seed weight by 4.7%, compared with the 60:60 cm ridge and furrow (60 cm wide ridge and 60 cm wide furrow) system. No differences in WUE were found between the two ratio systems. For corn and winter wheat, the optimum ridge:furrow ratio seems to be 1:1 in the 300-mm rainfall area, 1:2 in the 400-mm rainfall area and 1:4 in the 500-mm rainfall area. The optimum ridge:furrow ratio seems to be 1:3 for millet in the 300-mm rainfall area, although it is unnecessary to adopt RFRH practice in regions with more than 400 mm rainfall. The most effective ridge size for crop production seems 60 cm in the Loess Plateau. Implementing supplemental irrigation in the RFRH system is also a useful way to deal with the temporal problem of moisture deficits. In the case of corn, supplemental irrigation at its critical growth stage can increase both grain yield and WUE by 20%. The combination of in situ RFRH system with supplemental irrigation practice will make the RFRH system more attractive.     

Scheduling the cropping calendar in wet-seeded rice schemes in Malaysia

The Besut Irrigation Scheme, Terengganu, Malaysia is one of the eight gazetted main rice-growing areas in Malaysia. These eight granaries are targeted to produce only 65% of the total rice requirements of the nation. This scheme faces water scarcity especially during the off-season with the present existing cropping schedule. This study discusses the ways and means to overcome the water scarcity problem by setting the calendar for cropping schedules taking into consideration rainfall, river flow available and irrigation water requirements. A water balance approach using 48 years of rainfall and weather data was pursued in this study. The present main season from land preparation to crop harvest lasts from 1st November to 6th April, with land preparation being carried out during the heaviest rains in early November. However, the heavier rains may result in the postponement of seeding. Delays in crop planting during this main season can result in the cancellation of the following off-season crop from May to October. Shifting the land preparation works from November 1 to an earlier date, September 15, would result in a better match of crop water needs with the prevailing rainfall season (normally most of the rainfall occurs between September and December). This proposed schedule (15th September–10th February) also increases the probability that land preparation and subsequent seeding can be done for a second crop in the revised off-season period, 15th March–10th August. The present off-season schedule is from 5th May to 7th October and water scarcity during the vegetative and reproductive phases of the crop growth can be a problem. With the shifting of the off-season to start on March 15, severe water shortage can be avoided. The proposed revised cropping schedules could reduce the irrigation water requirements for the main season and off-season by 30% (equivalent to 60 mm of water) and 19% (equivalent to 37 mm of water), respectively.     

The role of supplemental irrigation and nitrogen in producing bread wheat in the highlands of Iran

The West Asia and North Africa (WANA) region, with a Mediterranean climate type, has an increasing deficit in cereal production, especially bread wheat. Rainfed cropping in the highlands of this region coincides with the severely cold winter with mostly, snow from November to April. Cereal yields, are low and variable mainly as a result of inadequate and erratic seasonal rainfall and associated management factors, such as late sowing (or late crop emergence). In an area where water is limited, small amounts of supplemental irrigation (SI) water can make up for the deficits in seasonal rain and produce satisfactory and sustainable yields. This field study (1999–2002) on a deep clay silty soil in north west of Iran was conducted with four SI levels (rainfed, 1/3, 2/3 and full irrigation requirements) combined with different N rates (0, 30, 60, 90 and 120 kg ha⁻¹) with one wheat variety (Sabalan). Yields of rainfed wheat varied with seasonal rainfall and its distribution. A delay in the crop emergence from October (SI treatment) to November (rainfed) consistently reduced yields. With irrigation, crop responses to nitrogen were generally significant up to 60 kg N ha⁻¹. An addition of only limited irrigation (1/3 of full irrigation) significantly increased yields and maximized water use efficiency (WUE). Use efficiency for water and N was greatly increased by SI. Under deficit irrigation, maximum WUE would be achieved when 60 kg N ha⁻¹ is combined with 1/3 of full SI. Early crop germination is essential to ensure adequate crop stand before the winter frost and to achieve high yield. Early emergence can be achieved by applying a small amount (40–50 mm) of SI after sowing. Thus, when limited SI is combined with appropriate management, wheat production can be substantially and consistently increased in this highland semi-arid zone.     

Determining water consumption in olive orchards using the water balance approach

Efficient irrigation regimes are becoming increasingly important in commercial orchards. Accurate measurements of the components of the water balance equation in olive orchards are required for optimising water management and for validating models related to the water balance in orchards and to crop water consumption. The aim of this work was to determine the components of the water balance in an olive orchard with mature ‘Manzanilla’ olive trees under three water treatments: treatment I, trees irrigated daily to supply crop water demand; treatment D, trees irrigated three times during the dry season, receiving a total of about 30% of the irrigation amount in treatment I; and treatment R, rainfed trees. The relationships between soil water content and soil hydraulic conductivity and between soil water content and soil matric potential were determined at different depths in situ at different locations in the orchard in order to estimate the rate of water lost by drainage. The average size and shape of the wet bulb under the dripper was simulated using the Philip’s theory. The results were validated for a 3 l h⁻¹ dripper in the orchard. The water amounts supplied to the I trees during the irrigation seasons of 1997 and 1998 were calculated based on the actual rainfall, the potential evapotranspiration in the area and the reduction coefficients determined previously for the particular orchard conditions. The calculated irrigation needs were 418 mm in 1997 and 389 mm in 1998. With these water supplies, the values of soil water content in the wet bulbs remained constant during the two dry seasons. The water losses by drainage estimated for the irrigation periods of 1997 and 1998 were 61 and 51 mm, respectively. These low values of water loss indicate that the irrigation amounts applied were adequate. For the hydrological year 1997–1998, the crop evapotranspiration was 653 mm in treatment I, 405 mm in treatment D and 378 mm in treatment R. Water losses by drainage were 119 mm in treatment I, 81 mm in treatment D and 4 mm in treatment R. The estimated water runoff was 345 mm in treatments I and R, and 348 mm in treatment D. These high values were due to heavy rainfall recorded in winter. The total rainfall during the hydrological year was 730 mm, about 1.4 times the average in the area. The simulated dimensions of the wet bulb given by the model based on the Philip’s theory showed a good agreement with the values measured. In a period in which the reference evapotranspiration was 7.9 mm per day, estimations of tree transpiration from sap flow measurements, and of evaporation from the soil surface from a relationship obtained for the orchard conditions, yielded an average daily evapotranspiration of 70 l for one I tree, and 48 l for one R tree.     

Alternative cropping strategies for assured and efficient crop production in upland rainfed rice areas of eastern India based on rainfall analysis

The productivity of rice in rainfed upland soils of eastern India is very low (<1 t/ha) and unstable because of erratic monsoon, moisture deficit during dry spells, light textured with less fertile soils and several biological constraints (weeds, pests and diseases). Keeping the urgent need of augmenting the productivity of vast rainfed upland rice ecosystem of eastern India (4.3 million ha), crop diversification technology was generated through on-farm research trials in representative upland rice soils of eastern India after analyzing agro-climatic (rainfall variability, probability and onset of effective monsoon) and edaphic (soil water retention properties) constraints and prospects. Based on rainfall analysis, direct seeded, low water requiring, rice substituted alternative upland crops namely maize, groundnut, pigeonpea, greengram and blackgram (sole or intercropping) was sown in light textured upland rice soils on 24th meteorological weeks (11–17 June) in 3 years 2000–2002 with two to three summer ploughings during pre-monsoon shower (May). Study revealed that in deficit rainfall years (2000 and 2002), when rice yield was affected adversely in light textured upland, higher rice equivalent yield and rain water use efficiency were obtained from groundnut+pigeonpea intercropping followed by sole groundnut and sole pigeonpea. Study also revealed that productivity of rice substituted crops in the same upland did not fluctuate much between rainfall excess (2001) and rainfall deficit years (2002 and 2000). Double cropping in rainfed upland rice soils was also explored through maize–horsegram/sesamum rotation with increased productivity and rainwater use efficiency. The crop diversification technology was found to be very effective for drought mitigation.     

Risk analysis and economic viability of water harvesting for supplemental irrigation in semi-arid Burkina Faso and Kenya

Food insecurity affects a large portion of the population in sub-Saharan Africa (SSA). To meet future food requirements current rainfed farming systems need to upgrade yield output. One way is to improve water and fertiliser management in crop production. But adaptation among farmers will depend on perceived risk reduction of harvest failure as well as economic benefit for the household. Here, we present risk analysis and economical benefit estimates of a water harvesting (WH) system for supplemental irrigation (SI). Focus of the analysis is on reducing investment risk to improve self-sufficiency in staple food production. The analysis is based on data from two on-farm experimental sites with SI for cereals in currently practised smallholder farming system in semi-arid Burkina Faso and Kenya, respectively. The WH system enables for both SI of staple crop (sorghum and maize) and a fully irrigated off-season cash crop (tomatoes). Different investment scenarios are presented in a matrix of four reservoir sealants combined with three labour opportunity costs. It is shown that the WH system is labour intensive but risk-reducing investment at the two locations. The current cultivation practices do not attain food self-sufficiency in farm households. WH with SI resulted in a net profit of 151–626 USD year⁻¹ ha⁻¹ for the Burkina case and 109–477 USD year⁻¹ ha⁻¹ for the Kenya case depending on labour opportunity cost, compared to −83 to 15 USD year⁻¹ ha⁻¹ for the Burkina case and 40–130 USD year⁻¹ ha⁻¹ for the Kenyan case for current farming practices. Opportunity cost represents 0–66% of the investment cost in an SI system depending on type of sealant. The most economical strategy under local labour conditions was obtained using thin plastic sheeting as reservoir sealant. This resulted in a net profit of 390 and 73 USD year⁻¹ ha⁻¹ for the Burkina Faso and Kenyan respective site after household consumption was deducted. The analysis suggests a strong mutual dependence between investment in WH for SI and input of fertiliser. The WH system is only economically viable if combined with improved soil fertility management, but the investment in fertiliser inputs may only be viable in the long term when combined with SI.     

Soil water storage and surface runoff as influenced by irrigation method in arid soils with surface crust

The effects of irrigation methods, application rates and initial moisture content on soil water storage and surface runoff were studied in soils liable to surface crust formation during 1995–1996 at the University of Jordan Research Station near Al-Muwaqqar village. Four irrigation methods were tested (sprinkler, furrow, basin and trickle) and four application rates (6.2, 14.4, 24.4 and 28.4 mm/h). Two runs were performed (soil initially dry and soil initially wet). Basin irrigation provided the highest application efficiency followed by trickle, sprinkler and furrow irrigation methods. Entrapping water by the basin borders increased soil water storage by allowing more water to infiltrate through the surface crust. Decreasing the application rate from 28.4 to 6.2 mm/h increased soil water storage significantly in all 150 mm layers to a depth of 600 mm. If the soil was already wet, soil moisture storage decreased owing to siltation during the prewetting and formation of a surface crust and low soil water storage capacity. A sedimentary crust formed at the bottom of the furrows in the furrow irrigation treatment, which reduced soil water storage and increased surface runoff significantly owing to the reduction in infiltration. Increasing the application rate from 6.2 to 28.4 mm/h in the furrow surface irrigation treatment increased the runoff discharge 10-fold. Even with the lowest application rate the runoff coefficient under sprinkler irrigation was 20.3% indicating high susceptibility of Al-Muwaqqar soils to surface crust formation.     

Climatic water balance,probable rainfall,rice crop water requirements and cold periods in AER 12.0 in India

In this study an analysis was made on spatial variation of climatic water balance, (water surplus, actual evapotranspiration), probabilistic monthly monsoon rainfall and mapping of cold periods in agro-ecological region (AER) 12.0 of India using GIS and models. Since, rice is the dominant crop of the region, crop water requirements of rice was also spatially analyzed in different agro-ecological subregions (AESRs) of the AER 12.0 using CROPWAT 4.0 model and GIS. Study found that as per climatic water balance, large to moderate water surplus (520–70 mm) was available in AESR 12.1. The rainfall surplus of 220–370 mm was computed in AESR 12.2 and 370–520 mm in AESR 12.3 mm. Since winter rainfall is meagre and erratic, this amount of rainfall may be harvested and utilized for providing supplemental irrigation to winter crops or during dry spell of rainy season crops. Study also reveals that at 80% probability level (highly assured) in first month of southwest monsoon (June) 98–156 mm rainfall occurs in AESR 12.1, 103–144 mm in AESR 12.2 and 93–132 mm in AESR 12.3. These amounts of rainfall are sufficient to prepare land and sowing of direct seeded crops like maize, groundnut, blackgram, greengram, pigeonpea, cowpea, etc. that may be done from 24th standard week onwards (11th–7th June) after onset of southwest monsoon in the region. Based on existence of favorable temperature, among different AESRs, cold requiring crops may be tried in the districts of AER 12.1, but before cultivation of these crops, economic feasibility should be properly assessed. In normal rainfall year 450–550 mm, 600–720 mm and 775–875 mm crop water requirement was computed using CROPWAT 4.0 model for autumn rice, winter rice and summer rice, respectively in different AESRs of AER 12.0.     

Some hydrological parameters for the design and operation of small earthen dams in lower Shiwaliks of northern India

Construction of a series of small water harvesting structures (WHS) in the form of earthen dams, across the seasonal streams for managing runoff during the monsoon season, could improve the water availability in the lower Shiwaliks of northern India. However, the hydrological parameters needed for planning, design and operation of such structures were generally lacking. An effort has been made through this study to generate the needed information. Three water harvesting structures (core-wall type of earthen dams) having catchment areas of 77.2, 6.6 and 17.3 ha, were constructed: one at village Ballowal Sounkhri and Takarla each in district of Nawanshehr and one at Karoran in district of Ropar in Punjab in 1983–1984. The study showed that 73%, 77% and 85% of the total summer monsoon rains could produce runoff with runoff coefficients of 0.22 ± 0.03, 0.37 ± 0.04 and 0.35 ± 0.05, at the respective sites. On an average 1211, 2712 and 2769 m³ of water was harvested per hectare in the structures. From the harvested water 79%, 78% and 46% was lost through evaporation and seepage. The major mode of the water loss was seepage which varied from 61% to 86% at these sites. The water harvesting structures lost their gross storage capacity by 1.30%, 1.08% and 1.16% per year with siltation rate of 31, 37 and 47 t/ha of catchment area at Ballowal Sounkhri, Takarla and Karoran, respectively. The ratio of command to catchment area, for providing one irrigation was 0.51, 1.4 and 2.9 at the respective sites. Analysis of the rainfall-evaporation data have shown that pre-sowing irrigation (if required) or a single supplemental irrigation should be provided between October and December during the Rabi season. During that period, the moisture deficit as well as the probability of expecting at least one dry spell of 25 days duration are high. Additional irrigations at a later stage are not advised as the productivity of the water becomes low. Because of high variability in the hydrological parameters of the area in both time and space, some more longterm, location specific studies of these parameters are suggested.     

Determination of spatial water requirements at county and regional levels using crop models and GIS: An example for the State of Parana,Brazil

Due to the competitive use of available water resources, it has become important to define appropriate strategies for planning and management of irrigated farmland. To achieve effective planning, accurate information is needed for crop water use requirements, irrigation withdrawals, runoff and nitrate leaching as a function of crop, soil type and weather conditions at a regional level. Interfacing crop models with a geographic information system (GIS) extends the capabilities of the crop models to a regional level. The objective of this study was to determine the irrigation requirements, annual runoff and annual nitrate leaching for the most important crops of the Tibagi river basin in the State of Parana, Brazil. The computer tool selected for this study was the Decision Support System for Agrotechnology Transfer (DSSAT) version 3.5 (98.0) and its associated crop modeling and spatial application system AEGIS/WIN. It was assumed that farms within the same county use similar management practices. To achieve representative estimates of irrigation requirements, the weather data from stations located within each county or the nearest weather station were used. A weighting factor based on the proportion of soil type and crop acreage was applied to determine total annual irrigation withdrawals, annual runoff and nitrate leaching for each county in the river basin. The model predicted outputs, including yield, irrigation requirements, runoff and nitrate leached for different soil types in each county, were analyzed, using spatial analysis methods. This allowed for the display of thematic maps for irrigation requirements, annual runoff and nitrate leaching, and to relate this information with irrigation management and planning. The maximum annual irrigation withdrawal, runoff and nitrate leaching were 22,969 m³ per year, 31,152 m³ per year and 1488 t N per year in the Tibagi river basin. This study showed that crop simulation models linked to GIS can be an effective planning tool to help determine irrigation requirements for river basins and large watersheds.     

Rainwater,soil and nutrient conservation in rainfed rice lands in Eastern India

In rainfed rice ecosystem, conservation of rainwater to maximum extent can reduce the supplemental irrigation water requirement of the crop and drainage need of the catchment. The results of 3 years of experimental study on the above stated aspects in diked rice fields with various weir heights (6–30 cm at an interval of 4 cm) revealed that about 56.75% and 99.5% of the rainfall can be stored in 6 and 30 cm weir height plots, respectively. Sediment losses of 347.8 kg/ha and 3.3 kg/ha have been recorded in runoff water coming out of 6 cm and 30 cm weir height plots, respectively in a cropping season. Similarly, total Kjeldahl nitrogen (TKN) loss in runoff water from rice field ranged from 4.23 kg/ha (6 cm weir height plots) to 0.17 kg/ha (26 cm weir height plots) and available potassium loss ranged from 2.20 kg/ha (6 cm weir height plots) to 0.04 kg/ha (30 cm weir height plots). Conservation of rainwater in rice fields with various weir heights could not create any significant impact on grain yield differences, leaf area index and other biometric characters. Irrigation requirement of 18 cm and above weir height plots was found to be half of the requirement of 6 cm weir height plots. Keeping in view the aspects of conserving rainwater, sediment and nutrient and minimizing irrigation requirement, 22–26 cm of dike height is considered to be suitable for rice fields of Bhubaneswar region.     

Wastewater application and water use of Larrea tridentata

Treated wastewater has been applied to agronomic crops, rangelands, forests and recreation areas including parks and golf courses, and to disturbed lands such as mine spoil sites. While land application systems are conventional technology for many communities, there is limited information to guide land managers in arid and semiarid environments where wastewater may be the only source of supplemental irrigation. In order to develop a creosote climate-based water balance irrigation scheduling model to irrigate a desert ecosystem using wastewater, a crop coefficient (K_c) for the creosote bush (Larrea tridentata) must be determined. The objective of this study is to determine the K_c and evapotranspiration rate of L. tridentata in non-water limiting conditions and to use the data for wastewater irrigation scheduling in the Chihuahuan desert. The study site, located in Las Cruces, New Mexico is semiarid with an average annual rainfall of 220 mm. Thirty L. tridentata shrubs were purchased from a commercial greenhouse in 19 l pots. The pots were weighed before an irrigation and 24 h after irrigation. The weight change was converted to depth of Et based on the area of the plots. Reference Et was determined from climate data and a crop coefficient calculated. A third order polynomial described the change in the crop coefficient with both day of year and growing degree days using a base and minimum cutoff temperature of 0 °C, no upper cutoff temperature and only data when the day length was greater than 11 h. The coefficient of determination was 0.76 using day of year and 0.77 using GDD. The crop coefficient was used in a water balance irrigation scheduling model to predict creosote water use under rainfall condition in the Chihuahuan desert.     

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.     

Response of green bean (P. vulgaris L.) to subsurface drip irrigation and partial rootzone-drying irrigation

Effects on water use, green bean yield, irrigation water-use efficiency (IWUE), water-use efficiency (WUE), plant dry weight and crop water relationship were investigated for two-drip irrigation techniques and four irrigation water levels in the Mediterranean region of Turkey. The treatments were conventional (SDI) and alternating subsurface drip irrigation (SPRD). At each irrigation event, half of the volume of water applied to the SDI was applied to one side of the crop, representing the partial rootzone-drying treatment. All treatments received 295 mm of irrigation during crop establishment, prior to beginning the different irrigation regimes. Differing irrigation amounts corresponded to four crop-pan coefficients (Kcp₁ = 0.6, Kcp₂ = 0.8, Kcp₃ = 1.0 and Kcp₄ = 1.2), appropriate to pan data. Total water applied to the SDI and SPRD treatments ranged from 366 to 437 mm and from 331 to 366 mm, respectively, depending on Kcp values, with water uptake varying from 396 to 470 mm and 364 to 409 mm, respectively. While differences of green bean yield and dry plant weights were not significantly affected by the SDI and SPRD irrigation techniques, the overall irrigation water saving was found to be 16% for the SPRD irrigation treatment compared with the SDI treatment. SPRD irrigation techniques increased IWUE, WUE, and slopes of yield water relationships. Increase in slopes of the yield–irrigation water and yield–water-use function of SPRD according to the equivalent slopes of the SDI were 215.8 and 151.4%, respectively. SPRD increased the green bean yield response factor (ky) with value of 128.4% according to the equivalent slopes of the SDI. In conclusion, irrigation scheduling based on a 0.8 crop-pan coefficient is recommended for conventional SDI, with 1.0 being more appropriate for partial rootzone-drying practice.     

The effects of different irrigation regimes on cucumber (Cucumbis sativus L.) yield and yield characteristics under open field conditions

A study was conducted to determine the effects of different drip irrigation regimes on yield and yield components of cucumber (Cucumbis sativus L.) and to determine a threshold value for crop water stress index (CWSI) based on irrigation programming. Four different irrigation treatments as 50 (T-50), 75 (T-75), 100 (T-100) and 125% (T-125) of irrigation water applied/cumulative pan evaporation (IW/CPE) ratio with 3-day-period were studied.Seasonal crop evapotranspiration (ET_c) values were 633, 740, 815 and 903 mm in the 1st year and were 679, 777, 875 and 990 mm in the 2nd year for T-50, T-75, T-100 and T-125, respectively. Seasonal irrigation water amounts were 542, 677, 813 and 949 mm in 2002 and 576, 725, 875 and 1025 mm in 2003, respectively. Maximum marketable fruit yield was from T-100 treatment with 76.65 t ha⁻¹ in 2002 and 68.13 t ha⁻¹ in 2003. Fruit yield was reduced significantly, as irrigation rate was decreased. The water use efficiency (WUE) ranged from 7.37 to 9.40 kg m⁻³ and 6.32 to 7.79 kg m⁻³ in 2002 and 2003, respectively, while irrigation water use efficiencies (IWUE) were between 7.02 and 9.93 kg m⁻³ in 2002 and between 6.11 and 8.82 kg m⁻³ in 2003.When the irrigation rate was decreased, crop transpiration rate decreased as well resulting in increased crop canopy temperatures and CWSI values and resulted in reduced yield. The results indicated that a seasonal mean CWSI value of 0.20 would result in decreased yield. Therefore, a CWSI = 0.20 could be taken as a threshold value to start irrigation for cucumber grown in open field under semi-arid conditions.Results of this study demonstrate that 1.00 IW/CPE water applications by a drip system in a 3-day irrigation frequency would be optimal for growth in semiarid regions.     

Phenology based irrigation scheduling and determination of crop coefficient of winter maize in rice fallow of eastern India

Vast rainfed rice area (12 million ha) of eastern India remains fallow after rainy season rice due to lack of appropriate water and crop management strategies inspite of having favourable natural resources, human labourers and good market prospects. In this study, a short duration crop, maize, was tried as test crop with different levels of irrigation during winter season after rainy season rice to increase productivity and cropping intensity of rainfed rice area of the region. Maize hybrid of 120 days duration was grown with phenology based irrigation scheduling viz., one irrigation at early vegetative stage, one irrigation at tassel initiation, two irrigation at tassel initiation + grain filling, three irrigation at early vegetative + tassel initiation + grain filling and four irrigation at early vegetative + tassel initiation + silking + grain-filling stages. Study revealed that one irrigation at tassel initiation stage was more beneficial than that of at early vegetative stage. Upto three irrigation, water use efficiency (WUE) was increased linearly with increased number of irrigation. With four irrigations, the yield was higher, but WUE was lower than that of three irrigations, which might be due to increased water application resulted in increase crop water use without a corresponding increase of yield for the crop with four irrigations. The crop coefficients (K_c) at different stages of the crop were derived after computing actual water use using field water balance approach. The crop coefficients of 0.42–0.47, 0.90–0.97, 1.25–1.33, and 0.58–0.61 were derived at initial, development, mid and late season, respectively with three to four irrigation. Study showed that leaf area index (LAI) was significantly correlated with K_c values with the R² values of 0.93. When LAI exceeded 3.0, the K_c value was 1. Study revealed that the K_c values for the development and mid season stage were slightly higher to that obtained by the procedure proposed by FAO, which might be due to local advection.