Irrigation Patterns Research Articles

Effect of leachate irrigation on methane oxidation in tropical landfill cover soil

The effect of leachate irrigation on methanotrophic activity in sandy loam-based landfill cover soil with vegetation was investigated. Laboratory-scale experiments were conducted to investigate the methane oxidation reaction in cover soil with and without plants (tropical grass). The methane oxidation rate in soil columns was monitored during leachate application at different organic concentrations and using different irrigation patterns. The results showed that the growth of plants on the final cover layer of landfill was promoted when optimal supplement nutrients were provided through leachate irrigation. The vegetation also helped to promote methane oxidation in soil, whereas leachate application helped increase the methane oxidation rate in nonvegetated cover soil. Intermittent application of leachate (once every 4 days) improved the methane oxidation activity as compared to daily application. Nevertheless, the adverse effects of organic overloading on methane oxidation rate and plant growth were also observed.

Climate change impacts on pressurised irrigation systems

Investment in collective pressurised irrigation infrastructure has played a major role in intensifying agricultural production in southern Italy, with positive impacts on the rural economy and sustainability of livelihoods. However, due to observed climate trends and intensified agricultural practices, this region has been identified as being most susceptible to desertification in Europe. This work uses a case study to assess agronomic impacts of climate change on crop water demand and engineering impacts on the performance and sustainability of existing irrigation infrastructure to meet peak demands. Outputs from a general circulation model for selected Intergovernmental Panel on Climate Change emission scenarios were downscaled and applied to baseline climatology. A water balance model was used to assess changes in irrigation water requirements and hydraulic modelling was then used to assess the impacts of engineering design on the future sustainability of the system's performance. The results indicate that climate changes will increase the number of failing hydrants up to 54–60%. Furthermore, system costs will increase by 20–27% when designed according to the future irrigation demand. Water managers, farmers and agribusinesses need to develop adaptation strategies to cope with changes in future water reliability. The paper also discusses the implications of alternative options such as the use of low-energy systems, improving irrigation efficiency, switching to deficit irrigation and changing cropping patterns.

Effect of Long-Term Fertilizer Management and Crop Rotations on Accumulation and Downward Movement of Phosphorus in Semi-Arid Subtropical Irrigated Soils

Crop species and their varieties vary in phosphorus (P) requirements for optimum production and response to P application. As crop recovery of added P often ranges from 10 to 40%, the rest accumulates in soil and may create potential for P leaching, depending upon the soil characteristics, duration of P applications, and cropping systems. Accumulation and distribution of Olsen P (plant-available labile P), total inorganic P, and total organic P were investigated in soil profiles of three field experiments differing in rate (9–44 kg P ha–1), frequency (applied once or twice annually), and duration (4–34 years) of fertilizer P applications, crop rotations, soil characteristics, and irrigation pattern (upland irrigated and flooded-rice crop) in a subtropical region. Profile samples were collected from soil depths of 0–15, 15–30, 30–60, 60–90, 90–120, and 120–150 cm of different treatments in these experiments and analyzed for different forms of P and soil characteristics. The results revealed that (i) annual applications of fertilizer P either to one crop (alternative-applied P) or to both crops (cumulative) led to the accumulation of residual fertilizer P in the form of Olsen P, varying from 44 to 148 kg P ha–1, and the magnitude of accumulation was proportional to applied fertilizer P rate, frequency, and duration; (ii) majority of residual fertilizer P accumulated as inorganic P (74–89%) followed by organic P (11–26%) and Olsen P (9–19%), illustrating that the inorganic P pool is a major sink for fertilizer P; (iii) application of fertilizer nitrogen (N) and potassium (K) alone or in combination with fertilizer P did not affect residual fertilizer P accumulation in soil profile; (iv) incorporation of farmyard manure enhanced the P enrichment of soil profile; (v) irrigation pattern, soil pH (7.1–7.7), and calcium carbonate (CaCO3) (trace–0.33%) did not influence P movement to deeper soil layers; silt, clay, and soil organic C (SOC) showed strong relationships with Olsen P (r = 0.827, 0.938, and 0.464, P < 0.01) and enhanced the retention of labile P in the plow layer; and (vi) only 6–29% total residual P moved beyond 30 cm deep in fine-textured soils under 22-year rice (Oryza sativa L.)–wheat (Triticum aestivum L.) and 34-year maize (Zea maize L.)–wheat rotations, whereas 41, 27, 20, 9, and 3% were located in soil layers 0–30, 30–60, 60–90, 90–120, and 120–150 cm deep, respectively, in coarse-textured soil profile under 4-year peanut (Arachis hypogaea L.)–sunflower (Helianthus annuus L.) field. These findings confirmed that interplay between the fertilizer P management (alternative vis-à-vis cumulative P application and optimal vis-à-vis excessive rates of fertilizer P in different crop rotations), amount of labile P accumulated in soil profile, and soil characteristics (silt, clay, and SOC) largely controlled the downward movement and resultant potential for P leaching in subtropical irrigated soils.

Activities of key enzymes involved in starch synthesis in grains of wheat under different irrigation patterns

SUMMARYIt is generally accepted that sucrose phosphate synthase (SPS), sucrose synthase (SuSy), ADP-glucose pyrophosphorylase (AGPase), soluble starch synthase (SSS), granule-bound starch synthase (GBSS) and starch branching enzyme (SBE) play a key role in starch synthesis in wheat grains. Starch synthesis in wheat grains is influenced by genotype and environment. However, what is not known is the degree of variation in enzyme activities during starch accumulation of wheat cultivars field-grown in different water regimes. The present study was undertaken to determine whether irrigation patterns could cause differences in starch accumulation and activities of key enzymes involved in starch synthesis. Starch accumulation and related enzyme activities were investigated in two winter wheat varieties, JM20 and BY535, differing in grain starch content, under two irrigation patterns. Results showed that soil water deficit led to an increase at early grain filling and decrease during late grain filling in starch accumulation rate (SAR) and activities of key enzymes involved in starch synthesis, especially AGPase, SSS and SBE. Water deficit enhanced grain starch accumulation in two wheat cultivars, suggesting that rainfed treatments increase physiological activities during early grain filling and promote starch accumulation. Furthermore, the change of SAR is consistent with SuSy, AGPase, SSS and GBSS. The results suggest that these enzymes play a key role in starch synthesis, and the decrease of photosynthate produced in the source organ is not the factor inhibiting starch accumulation.

Effects of alternate furrow-irrigation on crop water consumption,yield and quality of cotton

A field experiment was carried out to study the effect of alternate furrow-irrigation (AFI) on water consumption characteristics, yield and quality of seed cotton in the oasis region of downstream Shiyang River Basin of Gansu Province. In the early stages of cotton growth (squaring to flowering stages), diurnal crop water consumption under conventional furrow-irrigation (CFI)is higher than in AFI. In the late stages (bolling to open-boll stages), diurnal crop water consumption under AFI is higher than in CFI. Under the same irrigation pattern, AFI improves yield of total seed cotton and seed cotton yield before frost. When irrigation is 375 m3·hm-2 and 480 m3·hm-2, seed cotton yield and water use efficiency (WUE) under AFI are significantly higher than in CFI. In the two years, the difference in percent lint between AFI and CFI is insignificant. In 2005, average fiber length under AFI is 2.6 mm longer than in CFI, with a significant difference when irrigation is 225 m3·hm-2. In 2006, no significant difference exists between AFI and CFI in fiber length. This can be attributed to different precipitation events in the two years. It is concluded that AFI is a feasible method of cotton cultivation in the oasis of Shiyang River Basin. With no reductions in fiber quality, AFI increases both seed cotton yield and water use efficiency.

A remote irrigation monitoring and control system (RIMCS) for continuous move systems. Part B: field testing and results

Precision irrigation systems can have inherent errors that affect the accuracy of variable water application rates controllers, as well as affect the controllers’ performance when evaluated on different continuous move irrigation systems configurations. The objective of this study was to assess the performance of a remote irrigation monitoring and control system (RIMCS) installed on two separate linear move (LM) irrigation systems. The RIMCS varies water application rates by pulsing nozzles controlled by solenoids connected via relays to a single board computer (SBC) with wireless Ethernet connection to a remote server. The system also monitors irrigation system flow, pressure, position and wireless field sensor networks. The system was installed on a LM irrigation system in Prosser, Washington, USA and on a LM in the Nesson Valley of North Dakota, USA. For the LM at Prosser, four pre-defined irrigation patterns were imposed and variable rates were applied as a percentage of the nozzle base application rate. Each nozzle was pulsed across the span length and along the LM travel direction. For the LM at the Nesson Valley, a quadratic pattern was imposed pulsing banks of nozzles along the LM travel direction. Standard catch can tests were performed and the system performance was evaluated by comparing measured catch can water depths with pre-determined target values. The RIMCS accuracy was found to be in the range of the LM uniform water depth application uniformity coefficients of 88–96%. The RIMCS was successfully transferred to another LM in North Dakota as indicated by the relatively low variable rate application errors of –8.8 ± 8.1% and −0.14 ± 6.7% for the two spans.

Software design for wireless sensor-based site-specific irrigation

In-field sensor-based site-specific irrigation management is of benefit to producers for efficient water management. Integration of the decision making process with the controls is a viable option for determining when and where to irrigate, and how much water to apply. This research presents the design of decision support software and its integration with an in-field wireless sensor network (WSN) to implement site-specific sprinkler irrigation control via Bluetooth wireless communication. Wireless in-field sensing and control (WISC) software was designed by four major design factors that provide real-time monitoring and control of both inputs (field data) and outputs (sprinkler controls) by simple click-and-play menu using graphical user interface (GUI), and optimized to adapt changes of crop design, irrigation pattern, and field location. The WISC software provides remote access to in-field micrometeorological information from the distributed WSN and variable-rate irrigation control. An algorithm for nozzle sequencing was developed to stagger nozzle-on operations so as evenly distributed over the 60-s cycle. Sensor-based closed-loop irrigation was highly correlated to catch can water with r 2 = 0.98.

The Regularity of Optimal Irrigation Patterns

A branched structure is observable in draining and irrigation systems, in electric power supply systems, and in natural objects like blood vessels, the river basins or the trees. Recent approaches of these networks derive their branched structure from an energy functional whose essential feature is to favor wide routes. Given a flow s in a river, a road, a tube or a wire, the transportation cost per unit length is supposed in these models to be proportional to s α with 0 < α < 1. The aim of this paper is to prove the regularity of paths (rivers, branches,...) when the irrigated measure is the Lebesgue density on a smooth open set and the irrigating measure is a single source. In that case we prove that all branches of optimal irrigation trees satisfy an elliptic equation and that their curvature is a bounded measure. In consequence all branching points in the network have a tangent cone made of a finite number of segments, and all other points have a tangent. An explicit counterexample disproves these regularity properties for non-Lebesgue irrigated measures.

Heavy metal content in soils under different wastewater irrigation patterns in Chihuahua, Mexico.

An area near the city of Chihuahua has been traditionally irrigated with wastewater to grow forage crops. It has been hypothesized that metal levels could be found in these soils high enough to cause potential health problems to the population. The objective of this study was to determine heavy metal concentrations in different soils due to irrigation practices. Four soil types were evaluated; a soil with a past and present history of wastewater irrigation (S1), a soil with a history of wastewater irrigation until 2003 (S2), a soil with no irrigation history (S3), and a soil similar to S1 and adjacent to the river where the wastewater is transported (S11). Three soil depths were evaluated; 0-15, 15-30 and 30-50 cm. Consequently, a total of 150 soil samples were analyzed evaluating pH, EC, OM and the following elements; Na, K, Cd, Pb, Ni, Cr, Cu and Fe. The pH (P=0.000) and EC (P=0.000) were different for each soil type but no differences were noted for soil depth and the interaction. Maximum pH levels were noted in S3 with a value of 8.74 while maximum EC was observed in S1 with a value of 0.850 dSm-1. The OM level was different for soil type (P=0.000), soil depth (P=0.005) and the interaction (P=0.014). S1 and S11 obtained maximum levels of OM while minimum levels were noted in S3. Maximum OM levels were observed at the 0-15 cm depth followed by the 15-30 cm depth and finally at the 30-50 cm depth. The highest concentration of metals was as follows: K in S1 (359.3 mg kg-1); Cd in S1 (4.48 mg kg-1); Pb in S11 (155.83 mg kg-1); Ni in S1 (10.74 mg kg-1); Cu in S1 (51.36 mg kg-1); B in S3 (41.5 mg kg-1); Fe in S3 (20,313.0 mg kg-1), Cr in S3 (44.26 mg kg-1) and Na in S3 (203.0 mg kg-1). The conclusion is that some metals are present in the soils due to anthropogenic activities but others are present in natural forms.

The impact of various sprinkler irrigation patterns on spatial soil moisture variation in Vertisols

The objective of this research was to assess the effect of soil cracks on soil moisture distribution under various sprinkler irrigation applications and to identify the optimal irrigation strategy that enhances soil moisture distribution and reduces water drainage for the upper soil layer 0–250 mm. The assessment was made for six irrigation events: the first two were for 10 and 46 mm water applications using a hand shift-set sprinkler system. The second set was for 43 and 19 mm water applications using the lateral move system with fixed sprayer heads and the third pair of events were for 43 and 32 mm water applications using the lateral move system with rotating sprinklers. The experiments were conducted on two adjacent fields at the University of Queensland, Gatton, Australia. Each field was divided into 2 m × 2 m grids that covered 62 sampling locations. For each event, the initial soil moisture content (SMC) was measured at each sampling location before irrigation. After irrigation, catch can readings were recorded for each sampling location. After 12 h overnight, the second set of soil moisture measurements was taken at each location. The area1 distribution of SMC for the studied applications was quantified. An attempt was made to identify the relationship between the applied water uniformity using catch cans and the soil moisture uniformity using gravimetric water content measurements. The study also took into consideration variables that could affect the soil physical and hydrological properties including the field slope, the soil texture, the infiltration rate, the salt content and the soil organic matter content of the two fields. Since the soils were cracking clay Vertisols, further analyses were conducted on the crack dynamics, size and distribution using image analysis techniques. The research findings demonstrated that the cracks were the main contributors to water drainage below 250 mm soil depth due to the micro-run off from the crust surface to the cracks. The cracks ranged from a few millimeters to more than 40 mm in width. It was observed that the cracks which were wider than 15 mm remained open after irrigation for the specified application rates. Improving the irrigation system application uniformity did not always result in higher uniformity of the surface SMC (0–250 mm). The event that best enhanced soil moisture distribution and thus improved soil moisture recharging was observed after the sixth irrigation event when the field received 32 mm water application. The soil was at a relatively high initial SMC of 25%, (which represented 43.3% of the plant available water range) and the sprinkler water uniformity was rather high above 87% Christiansen coefficient of uniformity (CUc). At this SMC, the extent of soil cracking is limited.

Antimicrobial efficacy of 4.2% sodium hypochlorite adjusted to pH 12, 7.5, and 6.5 in infected human root canals

The purpose of this study was to determine the antimicrobial efficacy of sodium hypochlorite adjusted to pH 12, 7.5, and 6.5 in human root canals infected by Enterococcus faecalis. One hundred sixty-five human single-rooted teeth were prepared and inoculated with E. faecalis for 48 h. Teeth were divided into 3 experimental groups according to the irrigation pattern used: group 1, 4.2% NaOCl pH 12; group 2, 4.2% NaOCl pH 7.5; and group 3, 4.2% NaOCl pH 6.5. Samples from the root canals were collected, and bacterial growth was analyzed by turbidity of the culture medium. None of the irrigating solutions used in this study demonstrated 100% effectiveness against E. faecalis. The antibacterial effectiveness of 4.2% NaOCl at pH 6.5 was significantly increased (P = .03) compared with 4.2% NaOCl at pH 12 (chi-squared test: P < .05). Bactericidal activity of NaOCl solution is enhanced by weak acidification of 4.2% NaOCl solution at pH 6.5.

Surface Boundary Conditions in Two‐Dimensional Dual‐Permeability Modeling of Tile Drain Bromide Leaching

The simulation of preferential flow in structured soil using dual‐porosity models requires separate sets of the hydraulic, transport, and mass transfer parameters and of the boundary conditions. Analyses of tracer experiments with two‐domain models are limited by constraints in specifying separate boundary conditions (BCs) for each pore domain. The appropriate boundary conditions for dual‐permeability models have not been systematically studied or addressed in experiments. The objective of this study was to numerically evaluate the effects on Br leaching from a tile‐drained field of different surface boundary conditions for a two‐dimensional dual‐permeability model. For the previously described Br tracer experiment at the Bokhorst site (Germany), effects of irrigation intensities, flux‐ and resident‐type solute BCs, and Br application domain on drain discharge and Br effluent concentrations were compared. The two‐dimensional dual‐permeability numerical model divides the soil into soil matrix (SM) and preferential flow (PF) domains. In case of ponding at the surface of the SM domain, water is redistributed toward the PF domain surface. The combination of detailed irrigation record, flux‐type solute BCs, and solute application to the PF domain resulted in the largest Br leaching. In contrast, the lowest Br leaching was predicted for averaged irrigation rates, flux‐type solute BCs and Br addition to the SM domain. For flux‐type (third‐type) solute BC application to both pore domains, enhanced Br leaching was obtained due to surface redistribution effects. Detailed irrigation patterns with realistic intensities predicted higher Br leaching than averaged intensities. In addition to surface effects, the temporal availability of Br in the preferential pathways seemed to control Br leaching patterns. The results suggest that the formulation of the upper BCs strongly affects two‐dimensional dual‐permeability Br leaching predictions. Proper experimental consideration of domain‐specific BCs may help improve descriptions of preferential flow.

Self-Organizing Map and Multi-Layer Perceptron Neural Network Based Data Mining to Envisage Agriculture Cultivation

Study on characteristics of soil, to determine the types of crops suitable for cultivation in a particular region can increase the yield to greater extent, which minimizes the expenditures involved in irrigation and application of fertilizers. With the tested techniques available for calibrating the quality of soil and the crops suitable for cultivation in it, it is possible to determine the exact crop, irrigation patterns and even the cycle and quantity of fertilizer application. This paper dealt with the application of SOM based clustering and Artificial Intelligence techniques, to analyze the patterns of soils distributed across huge geographical area and identify the suitable types of crops for the particular soil. Estimation of exact crop(s) suitable for a particular region can help stave off redundant maintenance and the inherent expenditures that would occur due to over irrigation and over usage of fertilizers, to fulfill the natural deficiencies. Our Focus is to improve the optimal utilization of innate characteristics in a soil through cultivation of appropriate crops, which will increase the volume and quality of yield, in particular for a developing country like India, where the huge majority of the population depends primarily on agriculture for livelihood.

Effect of different irrigation patterns on root distribution characteristics of cucumber in solar greenhouse on the Loess Plateau

采用土柱模拟试验和大田调查相结合的方法，研究了不同灌溉方式下温室嫁接黄瓜根系分布特征，结果表明：膜下暗灌和滴水灌溉温室黄瓜根系干重最大值分别出现在黄瓜定植后180 d和210 d，黄瓜拔蔓时根系干重后者较前者高29.0%。黄瓜不同发育时期根系垂直分布特征有明显差异，在初瓜期前，0～20 cm根系干重前者明显高于后者，20 cm以下根系干重二者无明显差异；结瓜盛期以后，0～20 cm根系干重二者差异不明显，20 cm以下根系干重后者显著高于前者。膜下暗灌和滴水灌溉黄瓜根系水平分布在0～15 cm，分别占总根干重的96.6%、94.2%。随着黄瓜生长发育的推进，膜下暗灌内侧根系分布数量逐渐下降，结瓜期以前内侧根系占植株根系总数量的61.1%,中后期占15.6%；而滴灌黄瓜全发育期，内外侧根系分布数量比较均衡。说明灌水方式对温室嫁接黄瓜根系分布特征有显著影响。

Effects of Irrigation Patterns during Grain Filling on Grain Quality and Concentration and Distribution of Cadmium in Different Organs of Rice

The objective of this study was to investigate whether grain quality could be improved and the proportion of cadmium (Cd) be reduced in grains through a proper irrigation management when rice ( Oryza sativa L.) was planted in Cd-contaminated soil. Two rice cultivars, Yangjing 9538 ( japonica) and Yangdao 6 ( indica), were pot-grown. A total of 150 mg kg −1 Cd was added into pots before seedling transplantation (Cd treatment), and Cd-free treatment was used as the control. Three irrigation patterns, well-watered (WW), moderate dry-wet alternate irrigation (MD, soil was re-watered when soil water potential reached −20 kPa), and severe dry-wet alternate irrigation (SD, soil was re-watered when soil water potential reached at −40 kPa), were carried out from 7 d after heading to maturity. Under the same Cd concentration in soil and compared to WW, MD significantly increased, but SD significantly reduced seed-setting rate, 1000-grain weight, grain yield, brown rice rate, milled rice rate, and head rice rate. Moderate dry-wet alternate irrigation markedly reduced, whereas SD increased chalkiness. There were no significant differences in seed-setting rate, 1000-grain weight, and quality traits of rice between the Cd treatment and the control. Under the Cd treatment and compared to WW, MD and SD significantly increased the concentration and proportion of Cd in roots, but significantly reduced Cd concentration in stems and leaves and reduced Cd proportion in grains. Cadmium concentrations in grains and milled rice were significantly higher under SD than under WW, and exhibited no significant difference between MD and WW. Severe dry-wet alternate irrigation resulted in lower proportion of Cd in milled rice compared to MD or WW. The results from this study indicate that moderate dry-wet alternate irrigation during grain filling increases grain yield and improves milling and appearance quality, but does not increase Cd concentration or even reduce Cd proportion in grains. The reasons for variations in grain yield, quality, and the concentration and proportion of Cd under different irrigation patterns were analyzed in terms of root activity, photosynthetic characters, and Cd translocation.

Effects of Soil Moisture and Irrigation Patterns during Grain Filling on Grain Yield and Quality of Rice and Their Physiological Mechanism

The objective of this study was to investigate whether a moderate soil-drying or an alternate wetting and moderate-drying irrigation during the grain filling period could improve the grain quality and increase yield in rice. Two rice cultivars, Wuyujing 3 (japonica) and Yangdao 6 (indica), were grown in pots and cement tanks. Three soil moisture treatments and three irrigation patterns, well-watered (WW, well-watered) and conventional irrigation (CI, continuous flooding), moderate soil-drying (MD, soil water potential at-10～-30 kPa) and alternate wetting and moderate-drying irrigation (W-MD, re-watered when soil water potential reached at-25 kPa), and severe soil-drying (SD, soil water potential at-40～-60 kPa) and alternate wetting and severe-drying irrigation (W-SD, re-watered when soil water potential reached at-50 kPa), were imposed during grain-filing. Compared with WW or CI, MD or W-MD significantly increased grain weight, peak viscosity, and breakdown values, and re-duced chalkiness and setback values. The results were reversed for SD or W-SD treatments. Activities of sucrose synthase (SuS), adenine diphosphoglucose pyrophosphorylase (AGP), starch synthase (StS), and starch branching enzyme (SBE) in grains in mid-dle and late grain-filling stages were significantly enhanced, whereas ethylene revolution rate of grains decreased, under MD or W-MD. The SD or W-SD had the opposite effects. The results indicate that both MD and W-MD can improve rice quality, result-ing from the physiological mechanism of enhancing activities of SuS, AGP, StS, and SBE and decreasing ethylene production in grains.

Tank irrigation in India: a time series analysis

Tanks are one of the important traditional sources of irrigation in India, irrigating nearly three million hectares even today. Though considered to be a low cost source with few environmental problems, the performance of tank irrigation has been poor and has deteriorated over the years. Several studies have analysed the performance of tank irrigation using field survey data, but not many studies seem to have analysed the trends and determinants of tank irrigation covering various states as well as national level data in recent times. In this study, therefore, using time series data from 1950/51 to 1999/2000, an attempt is made (a) to study the growth pattern of tank irrigation across different periods both at the national as well as across states level, (b) to study the nexus between rainfall and area under tank irrigation at a specific state, which has relatively larger area under tank irrigation, (c) to find out the losers and gainers of tank irrigation among different size of farmers, and (d) to suggest policy measures to rejuvenate tank irrigation in India.

In Situ Colloid Mobilization in Hanford Sediments under Unsaturated Transient Flow Conditions: Effect of Irrigation Pattern

Colloid transport may facilitate off-site transport of radioactive wastes at the Hanford site, Washington State. In this study, column experiments were conducted to examine the effect of irrigation schedule on releases of in situ colloids from two Hanford sediments during saturated and unsaturated transientflow and its dependence on solution ionic strength, irrigation rate, and sediment texture. Results show that transient flow mobilized more colloids than steady-state flow. The number of short-term hydrological pulses was more important than total irrigation volume for increasing the amount of mobilized colloids. This effect increased with decreasing ionic strength. At an irrigation rate equal to 5% of the saturated hydraulic conductivity, a transient multipulse flow in 100 mM NaNO3 was equivalent to a 50-fold reduction of ionic strength (from 100 mM to 2 mM) with a single-pulse flow in terms of their positive effects on colloid mobilization. Irrigation rate was more important for the initial release of colloids. In addition to water velocity, mechanical straining of colloids was partly responsible for the smaller colloid mobilization in the fine than in the coarse sands, although the fine sand contained much larger concentrations of colloids than the coarse sand.

Introducing greenhouse gas mitigation as a development objective in rice-based agriculture: II. Cost–benefit assessment for different technologies, regions and scales

New tools for land use analysis including detailed cost–benefit assessments are needed to integrate resource management for enhancing farmers’ income and mitigating greenhouse gas (GHG) emissions. The paper comprises an assessment of GHG emissions and economic returns under different mitigation technologies in three rice growing regions in Asia, i.e., Ilocos Norte province (Philippines), Zhejiang province (China) and Haryana state (India). Site-specific data on soil, climate and socio-economics were integrated in the previously developed spreadsheet model TechnoGAS (Technical Coefficient Generator for Mitigation Technologies of Greenhouse Gas Emissions from Agricultural Sectors). Three baseline technologies that differed in terms of inorganic/organic N supply have been compared to different mitigation technologies in form of Marginal Abatement Cost Curves (MACCs). For the baseline technology of inorganic N (urea) fertilization, amendment with phosphogypsum and nitrification inhibitors are the most promising mitigation options resulting in shadow prices of less than US$10 per ton of carbon dioxide equivalent (CE). Assuming a mix of urea and farm yard manure for the baseline, we have tested several options including different irrigation patterns and husk used as fossil fuel. Mid-season drainage had a better cost–benefit ratio (ca. US$20 per t CE) than alternate flooding, but was less profitable than husk utilization (ca. US$4 per t CE). Assuming high organic inputs, biogas technology is, in most cases, the preferable option (ca. US$10 per t CE). Finally, we compiled regional abatement cost curves for selected administrative units using the outcome from regional optimization models. Implementing the three most promising technologies required US$6000 for Dingras municipality, Ilocos Norte, in the Philippines (ca. 10 3 ha of rice land potentially providing emission savings of ca. 3000 t CE), US$50,000 for Pujiang county in China (ca. 10 4 ha providing ca. 27,000 t CE), and US$1.2 million for Karnal district in India (ca. 10 5 ha providing ca. 220,000 t CE).

Elementary properties of optimal irrigation patterns

In this paper we follow the approach in Maddalena et al. (Interfaces and Free Boundaries 5, 391–415, 2003) to the study of the ramified structures and we identify some geometrical properties enjoyed by optimal irrigation patterns. These properties are “elementary” in the sense that they are not concerned with the regularity at the ending points of such structures, where the presumable selfsimilarity properties should take place. This preliminary study already finds an application in G. Devillanova and S. Solimini (Math. J. Univ. Padua, to appear), where it is used in order to discuss the irrigability of a given measure.