Continuous Submergence Research Articles

Soil Nutrients Availability, Rice Productivity and Water Saving under Deficit Irrigation Conditions

Two field experiments were carried out at Rice Research and Training Center, Sakha, Kafr El-Sheikh, Egypt during 2018 and 2019 cropping seasons. Experiments aimed to determine the impacts of different deficit irrigation treatments on the available soil nutrients, N, P, K and Zn uptakes, rice yield and water use efficiency. The field experiments were laid out in a strip-plot design with four replications. The horizontal plots were devoted to the four irrigation treatments: continuous submergence (W1), intermittent irrigation at 6-day intervals (W2), intermittent irrigation at 9-day intervals (W3) and intermittent irrigation at 12-day intervals (W4), while vertical plots were occupied by the three rice genotypes, namely Giza 177, Giza 179 and GZ10154. Intermittent irrigation at 6-days intervals (W2) treatment, recorded the highest available NH4+-N, NO3--N and K concentrations in the soil. The highest values of available-N and available-P concentrations in the soil were obtained with (W1) while (W4) recorded the lowest values. The N, P, K and Zn uptakes were significantly affected by the prolonged irrigation intervals. Rice yield and its attributes decreased significantly as irrigation intervals increased up to 12-day (W4) in both seasons. The highest values of plant height, number of panicles m-2, panicle weight (g), 1000-grain weight (g), number of filled grains panicle-1, grain and straw yields were obtained with (W1) followed by (W2) treatment, except panicle length and number of unfilled grains panicle-1 in both seasons. Water saved (%) ranged from 8.90% to 26.46% and from 17.47% to 27.25% in 2018 and 2019 seasons, respectively.

Designing Cropping Systems to Improve the Management of the Invasive Weed Phalaris minor Retz.

Because cropping systems can greatly affect the establishment and spread of alien species populations, the design of cropping systems to control invasive weeds is an important approach for invasive species management in agro-ecosystems to avoid excessive increases in other control measures such as herbicides. The annual weed Phalaris minor Retz. (P. minor) is one of the most troublesome invasive weed species of winter crops in Yunnan Province, China, but the development of cropping systems for ecological control of this weed have received limited research attention. Here, we studied seed dormancy, germination characteristics and reproductive responses of P. minor to various cropping systems to show how cropping systems could be better designed to control P. minor in China. Our research showed that cropping systems significantly affected seed dormancy in submerged paddy fields. Phalaris minor seed remained dormant and the germination rates (less than 10%) were significantly lower (p < 0.05) than in maize fields and dry, bare soil conditions. Wheat, faba bean and rapeseed crops had no significant influence (p < 0.05) on the seed germination rate of P. minor, but increasing soil depth significantly decreased (p < 0.05) the germination rate and germination index of this weed. Total biomass, spike biomass, spike number and seed number of P. minor were significantly reduced (p < 0.05) with increasing proportions of the three crops (wheat, faba bean and rapeseed), with rapeseed having the strongest inhibition effects among the three crops. The reproductive allocation and reproductive investment of P. minor were also significantly reduced (p < 0.05) in mixed culture with wheat and rapeseed. With increasing proportions of wheat or rapeseed, the specific leaf area of P. minor significantly increased (p < 0.05), but the reverse was true for leaf area and specific leaf weight. Moreover, the net photosynthetic rate, stomatal conductance and transpiration rate for P. minor also decreased significantly (p < 0.05) when grown with wheat or rapeseed. These results suggest that optimal cropping systems design could involve planting rapeseed in conjunction with deep plowing and planting rice (continuous submergence underwater) in summer. Such a system could reduce the field populations and seed bank of P. minor, thus providing a sustainable and environmentally friendly means of suppressing P. minor.

Nitrate pollution reduction using biological fertilizers in paddy fields, the South Caspian Sea basin, Guilan Province, Iran

Application of chemical fertilizers, especially urea, causes groundwater pollution. Therefore, to decrease environmental pollution, biological fertilizers may be employed. In order to investigate the effect of irrigation levels, Azospirillum and nitrogen levels on rice yield and its components, an experiment was conducted in the north of Iran during the crop season in 2013. The experiment was arranged in a split-split plot based on a completely randomized block design with 3 replications in which irrigation level was the main factor. The levels of factors used were: I1= continuous submergence and I2 = 11 days’ irrigation interval; A1 = application and A2= no application of Azospirillum as the sub factor; and nitrogen fertilizer levels as a sub-sub factor includingN1 = 0, N2 = 30, N3 = 60 and N4 = 90 kg ha-1. Continuous submergence and 11 days’ irrigation interval produced 4247 and 2720 kg ha-1, while the application of Azospirillum and the treatment without it produced 4064 and 2903 kg ha-1, respectively. Moreover, N4, N3, N2 and N1 produced 3950, 3800, 3225 and 2700 kg ha-1, while I1A1N4 and I1A1N3 had maximum and I2A2N1 had minimum mean values with 5381, 5330 and 1882 kg ha-1, respectively. Therefore, it is concluded that the application of a balanced nitrogen fertilizer with Azospirillum could prevent the indiscriminate use of chemical fertilizers and reduce nitrate pollution, leading towards more sustainable agriculture in the north of Iran.

Agronomic, Water Productivity and Economic Analysis of Irrigated Rice under Different Nitrogen and Water Management Methods

The most limiting factors for irrigated rice farming are water and nitrogen. Efficient water and nitrogen management has remained critical for sustainable rice production in irrigated rice farming system. Due to rapid global population growth and climate change, future rice production will depend heavily on developing strategies and practices that use water and nitrogen efficiently. The study therefore set to evaluate agronomic, water productivity and economic analysis of irrigated rice under various nitrogen and water management methods. To achieve the set objectives, field and pot experiments were carried out at the Soil and Irrigation Research Centre, University of Ghana, Kpong in 2015 and 2016 cropping season. The field experiment was laid in a split plot design with water management treatments as main plots and N fertilizer as subplot treatment. The pot experiment was carried out in a randomized complete block design with five replications. The water management treatments were; continuous submergence (SC), alternate wet and dry soil condition (AWD) and moist soil condition (MC). Nitrogen fertilizer rates were; no N fertilizer (N0), 60 kg N/ha (N1) and 90 kg N/ha (N2). Data such as yield and yield parameters of rice, water use, water productivity, costs and returns were recorded. Results obtained from both pot and field experiments revealed that rice yields were at par in AWD and SC but yields were lower in MC treatment. With N fertilizer, higher yields were observed with 90 kg N/ha. The interaction effect of submerged with 90 kg N/ha gave the highest grain yield. N fertilizer effect on water use and water productivity was ranked as N2 > N1 > N0 while water management effect on water use and water productivity was ranked in this order: SC > AWD > MC and MC > AWD > SC respectively.

Growth responses of the intertidal seagrass Zostera japonica to manipulated sea level rise conditions

Although most seagrasses inhabit subtidal areas, a few species occur in the intertidal zone. The seagrass, Zostera japonica Asch. & Graebn., is an intertidal seagrass species, and thus this species may be vulnerable to environmental changes associated with sea level rise due to climate change. We examined the effects of continuous submergence conditions, which might be caused by sea level rise, on the growth of the intertidal seagrass, Z. japonica. In the present study, submerged conditions were generated in a Z. japonica meadow in the intertidal zone using transparent cylindrical cores, and the growth responses to the inundation conditions were examined. Daily photon flux density and temperature were not significantly different between the manipulated submerged and the control intertidal conditions during the experimental period. Increases in shoot height, biomass, and leaf productivity were among the acclimatory responses of Z. japonica to the inundation conditions. Shoot density, however, decreased rapidly in the submerged conditions as a result of the self-shading induced by taller and larger shoot sizes. Thus, prolonged inundation, which would be induced by a rise in sea level, had both positive and negative effects on the growth of the intertidal seagrass, Z. japonica, which exhibited plasticity at the individual and population levels. According to the results of our study, the restricted distribution of Z. japonica in the intertidal zone may not be a consequence of tidal inundation stress in the subtidal zone.

Estimation of crop evapotranspiration and crop coefficients of rice (Oryza sativa L.) under low land condition

An attempt has been made to estimate the crop evapotranspiration (ETc) and Kc under alternate wetting and drying method (AWD) of water management of rice (Oryza sativa L.) under lowland condition during 2013 and 2014 at Rajendranagar, Hyderabad. The average seasonal ETc was highest in continuous submergence (Cs) of 3-cm depth from transplanting to panicle initiation (PI) and 5-cm from PI to physiological maturity (PM) (657.8 mm) followed by AWD irrigation regimes of flooding to a water depth of 5-cm between15 DAT to PM and when ponded water level drops to 5-cm below ground level in field water tube (628 mm). The results suggested that the roots of rice were able to extract adequate amount of water to satisfy its ETc needs for 2-7 days in different treatments of AWD. The mean crop coefficient values worked out were 1.35, 1.59, 1.81 and 1.33 at initial establishment stage, vegetative and panicle initiation stage, at panicle development stage and at ripening and maturity stage.

Invasive Smooth Cordgrass (Spartina alterniflora) Eradication and Native Crab Recovery

AbstractInvasive smooth cordgrass (Spartina alterniflora Loisel) eradication is important for the health of many coastal ecosystems. An integrated regime of continuous submergence after clear mowing, with three interval levels between mowing and submergence (5, 10, and 15 d) and three submergence depths (20, 30, and 50 cm), was implemented in cofferdams enclosing invader populations along a Chinese coast. In July of the following year, after the roots of mowed S. alterniflora had been submerged for 12 mo, some ramets grew under the regime with an interval of 15 d and the regime with a submergence depth of 20 cm, but no ramets occurred under the regimes with submergence depths of 30 or 50 cm and intervals of 5 or 10 d. Four crab species were documented: Helice tridens tientsinensis Rathbun, Sesarma dehaani H. Milne-Edwards, Ocypode stimpsoni Ortmann, and Chiromantes haematocheir de Haan. Biomass and abundance values of crab species in the cofferdams were similar to those in the mudflats but different from those in smooth cordgrass populations. Thus, the treatment of submergence after mowing, which was implemented in the cofferdams, can control S. alterniflora and provide a mudflat-like habitat that promotes crab recovery if this treatment uses the proper combination of submergence depth and interval between mowing and submergence.

Water use, energy use efficiency and carbon footprint of transplanted rice (Oryza sativa) in response to surface drainage

A field study was undertaken to determine the productivity, water use, energy efficiency, and carbon footprint under enforced surface drainage for 15 days at various growth stages of rice (Oryza sativa L.) during kharif 2011 and 2012. The continuous submergence improved the rice grain yield (3.41 t/ha) and straw yield (4.68 tonnes/ha) over the continuous drainage. The water-use was higher with continuous submergence (15350 m3) followed by alternate wetting and drying, whereas, the lowest water was used with continuous drainage (5400 m3). The continuous submergence consumed the highest total input energy (84.97 x 103 MJ/ha) and produced 1.23 fold higher output energy, 452.6 of human energy profitability and 0.04 kg/MJ of energy productivity than the continuous drainage. Alternate wetting and drying was the most energy efficient which produced the highest energy ratio (1.53) and energy productivity 0.53). However, the lowest energy intensiveness was noticed with continuous drainage. Similarly, alternate wetting and drying followed by continuous drainage had the lowest carbon footprint and carbon dioxide emission. Thus, submergence of 5-7 cm may be followed as per the availability of water, while, submergence may be avoided for 15 days at tillering under limited water to obtain optimum yield with better energy efficiency.

Transcriptomic and physiological studies identify cues for germination stage oxygen deficiency tolerance in rice

Submergence during germination imposes germination stage oxygen deficiency (GSOD). Natural variation in anaerobic germination potential (AGP), manifested by their differences in GSOD tolerance, is available in rice. Present study was performed to understand differential responses of two rice cultivars, Naveen and AC41620 (susceptible and tolerant to GSOD, respectively) subjecting them to 48-h continuous submergence during germination. Transcriptome analysis revealed more elaborate regulation of gene expression in AC41620 compared to Naveen. Validation of transcriptome data through q-PCR of selected genes and biochemical analysis related to carbohydrate metabolism, anaerobic respiration and oxidative stress tolerance were more significant in AC41620, than Naveen. The time-course enzyme assays for continued submergence suggested that the activity of α-amylase, pyruvate decarboxylase and alcohol dehydrogenase increased under continuous submergence. Efficient nitrogen metabolism supported by increased nitrate and nitrite reductase activities and better handling of reactive oxygen species (ROS) because of increased antioxidant enzyme activities were found to be associated with GSOD in AC41620. Increased ethylene production along with action of ABA, GA and G-proteins aided in GSOD tolerance of AC41620. The differentially expressed genes identified in the present study will serve as a useful genomic resource for extending our understanding of molecular mechanism of anaerobic germination vis-à-vis GSOD tolerance in rice.

Standardization of Alternate Wetting and Drying (AWD) Method of Water Management in Lowland Rice (ORYZA SativaL.) for Upscaling in Command Outlets

AbstractThe experiment was conducted in irrigated lowlands and followed alternate wetting and drying (AWD) practices by using field water tubes. The site had sandy clay soil. Grain yield was 6.0–7.2 t ha−1with AWD irrigation and 7.5 t ha−1with continuous submergence irrigation. Non‐significant (P > 0.05) difference was registered in yield attributes and grain yield between continuous submergence of irrigation and I5(AWD irrigation regime of 5 cm submergence depth from 15 DAT (days after transplanting) to physiological maturity when the ponded water level drops to 5 cm below ground level) and I6(AWD irrigation regime of 5 cm submergence depth from 15 DAT to physiological maturity when the ponded water level drops to 10 cm below ground level). There was a decrease in yield attributes and grain yield with the I4(AWD irrigation regime of 3 cm submergence depth from 15 DAT to physiological maturity when the ponded water level drops to 15 cm below ground level). Of various irrigation regimes, AWD irrigation regimes of I5(57 900 ha−1) and I6(56 500 ha−1) registered higher net returns with a B: C ratio of 1.27 and 1.29, respectively, owing to higher grain yield coupled with lower application of water. Copyright © 2017 John Wiley & Sons, Ltd.

Drying-submergence alternation enhanced crystalline ratio and varied surface properties of iron plaque on rice (Oryza sativa) roots.

Iron plaque (IP) is valuable in nutrient management and contaminant tolerance for rice (Oryza sativa) because it can adsorb various nutrients and toxic ions. Crystalline ratio (CR) can be defined as the proportion of crystalline iron (CI) to total IP to describe IP crystallinity. Although the knowledge on IP has abounded, the information on the relationship among its formation condition, surface properties, and CR remains insufficient. In this study, quartz sand-soil cultivation with rice was conducted to explore the effect of drying-submergence alternation (DSA) on CI, amorphous iron (AI), CR, root oxidizing capacity (ROC), and surface properties of IP with different treatment durations and at different stages. Fourteen-day DSA treatment increased CI to 2.20 times of that after continuous submergence (CS) but decreased AI to 72.3% of that after CS. Correspondingly, CR was raised to 6.89% from 4.08%. Remarkably, CR of IP after DSA ending in submergence and ending in drying was 6.89% and 4.23%, respectively. In addition, ROC after 14-day DSA was enhanced to twice of that after CS. Results from scanning electronic microscope suggested that 14-day DSA induced thinner sheets with finer particles in IP compared to that after CS. Results from X-ray diffraction revealed that IP contained higher proportions of goethite, lepidocrocite, magnetite, and hematite after DSA than those after CS. Variable charge and surface area of IP after DSA were only 26.5% and 32.0% of those after CS, respectively. Together, our results indicated that proper strength DSA promoted ROC and transformation from AI to CI, and consequently increased CR of IP, while it changed its surface properties.

Standardization of alternate wetting and drying (AWD) method of water management in low land rice (Oryza sativa (L.))

Alternate wettting and drying (AWD) systems save water compared with continuoussubmergence (CS) irrigation. However, the reported effect on yield varies widely and detailedcharacterizations of the hydrological conditions of AWD experiments are often lacking so thatgeneralizations are difficult to make. We compared the effects of AWD and CS on crop andwater productivity in rice in the field experimentations in India. The experiment was conductedin irrigated lowlands and followed AWD practices by using field water tube. Crop and waterproductivity was significantly differed between AWD and CS of irrigation. The average grainyield was 5.8–7.4 t ha-1 with AWD irrigation methods and 7.5–7.6 t ha-1 with CS. The pooledvalues of irrigation water applied, effective rainfall and seasonal volume of water input variedfrom 1390, 216 and 1646 mm, respectively under CS and 708 to 1142 mm, 238 to 300 mm and1048 to 1420 mm, respectively under AWD irrigation regimes. Irrigation water applied in AWDirrigation regimes amounted to 50.9 to 82.1% of CS (1390 mm), averaged over two seasons, thecrop in different AWD irrigation regimes used water 63.6 to 86.2% of the CS (1646 mm)suggesting that the AWD practice enabled water saving of 13.8 to 36.4% in different treatments.Therefore, in view of considerable water saving (26.6 to 35.0%) and higher water productivitythe AWD method of water management is the best practice to meet the cope of water scarcity inlowland rice production.

Towards a smart automated surface irrigation management in rice-growing areas in Italy

Italy is the leading rice producer in Europe, accounting for more than half of the total high-quality production of this crop. Rice is traditionally grown in fields that remain flooded starting with crop establishment until close to harvest, and this traditional irrigation technique (i.e., continuous submergence) is recognised as an important water resource sink (almost 40% of the irrigation water available worldwide is used for paddy areas). Meanwhile, the water management in rice areas requires a high level of labour because it is based on maintaining a predetermined water height in paddy fields and because the regulation of input and output flow is typically operated manually by the farmer. This study reveals the hardware and software characteristics of an automated and remote controlled technology tested for the first time in a rice farm near Pavia (Italy), during the 2016 growing season, aiming at a more efficient and less burdensome irrigation management system for rice fields. A water level sensor in the field provides the data required to govern the inflow regulation gate in real-time, according to the precise time to cut off the flow rate. Using a dedicated web page, the farmer can control flows, volumes and water levels in the fields by operating directly on the gate if necessary or setting the irrigation program according to his agronomic practices.

Yield and water use efficiency of rice (Oryza sativa L.) relative to scheduling of irrigations

Irrigation scheduled at seven days’ interval during vegetative stage and four days’ interval during reproductive stage resulted in significantly higher panicle number and panicle weight, filled grains panicle-1 and grain yield. Permanent irrigation and interval irrigation methods had higher yield in comparison with saturated irrigation method in rice. Dry seeded rice significantly increased the water productivity with respect to irrigation water over wet seeded and transplanted rice. Intermittent irrigation in rice cultivation may reduce irrigation water use considerably (27-37%) compared with flooded rice cultivation. aerobic rice significantly required less water (67.91 ha-1 cm) to produce higher or on par yield as compared to transplanted puddled rice (122.59 ha-1 cm). Similarly, WUE was significantly higher in aerobic rice (81.31 kg ha-1 cm) as compared to transplanted rice (36.12 kg ha-1 cm). The irrigation schedule having three days’ drainage period after disappearance of ponded water yielded rice higher with maximum water use efficiency compared to continuous submergence or submergence at critical stages such as tillering, panicle initiation, flowering and milk, followed by saturation or field capacity between intermittent periods.

Water balance implications of switching from continuous submergence to flush irrigation in a rice-growing district

Studies conducted at the field scale report significant reductions in the irrigation requirements of rice when continuous submergence (CS) is replaced by less water-demanding regimes such as flush-irrigation (FI, i.e. intermittent irrigations of rice growing in non-submerged soils). However, the effects of their extensive application in paddy areas with shallow groundwater is much less studied. We present a scenario analysis investigating the impacts on irrigation requirements induced by a shift from CS to FI in an irrigation district of Northern Italy where rice is the main crop, followed by maize and poplar. The area is characterised by a shallow water Table whose depth fluctuates between two meters (in winter) and less than 1m (in summer). We applied a three-stage procedure, where we first analysed present state conditions using the SWAP (Soil, Water, Atmosphere, Plant) model to simulate irrigation deliveries and percolation fluxes. Then, we calibrated an empirical relationship between estimated percolation fluxes and measured depths to groundwater. Finally, we applied this relationship, in combination with the SWAP model, to predict the variation of district irrigation requirements due to a widespread shift from CS to FI. Results show that neglecting the feedback between groundwater recharge due to irrigation and groundwater depth led to overestimating the reduction of irrigation requirements of rice, which decreased from around 80% when no feedback was considered to around 60% when it was accounted for. Moreover, increased groundwater depths resulted in higher irrigation requirements for maize with an estimated growth of more than 50% due to the need of shortening the irrigation turn. These results demonstrate the importance of considering the impacts on the hydrological processes at larger scales when planning the conversion of CS into more efficient field irrigation methods.

Calibration and Testing of the Aquacrop Model for Rice under Water and Nitrogen Management

ABSTRACTThe objective of this study was to adapt and test the ability of the AquaCrop model under different nitrogen and irrigation management conditions in northern Iran. A three-year field experiment was conducted at the experimental farm of the Iranian Rice Research Institute in Rasht, Iran, from 2005 to 2007. Irrigation treatments comprised continuous submergence, irrigation at 5-day intervals, and irrigation at 8-day intervals. Nitrogen (N) application levels were 0, 45, 60, and 75 kg N ha−1. The goodness of fit between observed and simulated canopy cover, total and panicle biomass, grain yield, and final biomass was assessed by means of the coefficient of determination (R2) and the absolute and normalized root mean square errors (RMSEn). Results of the statistical test of the model for total and panicle biomass showed moderately high R2 (≥0.90) and moderate RMSEn (6–36%) values, confirming that the model simulated the total and panicle biomass accurately. The model was simulated for CC with RMSEn and R2 of 28 and 0.82, respectively. The agreement between predicted and observed rice grain yield and final biomass were with R2 of 0.81 and 0.82 and RMSEn of 13 and 10% respectively.

Response of water stress parameters to alternate wetting and drying (AWD) method of water management in low land rice (Oryza sativa)

Response of Water Stress Parameters to Alternate Wetting and Drying (AWD) Method of Water Management in Low land Rice (Oryza sativa). Alternate Wetting and Drying (AWD) is an irrigation technique where water is applied to the field a number of days after disappearance of ponded water. The treatments consisted of continuous submergence besides AWD irrigation regimes with two ponded water depths of 3 and 5 cm and drop in ponded water levels in field water tube below ground level to 5, 10 and 15 cm depth. The eight treatments were laid out in randomized block design with three replications. The irrigation water applied effective rainfall and seasonal volume of water input varied from 708 to 1390 mm, 216 to 300 mm and 1048 to 1646 mm, respectively on pooled basis. Irrigation water applied in AWD irrigation regimes amounted to 50.9 to 82.1% of continuous submergence (1390 mm).Water stress parameters viz., relative water content (90.00 to 91.81% in 2013 and 92.19 to 92.77% in 2014) and leaf water potential (10.0 to 11.8 –bars in 2013 and 10.3 to 12.6 –bars in 2014) reflecting plant water balance were higher in continuous submergence depth of 3 cm from transplanting to PI and 5 cm from PI to PM, comparable values of RWC and LWP were also registered when the crop was flooded to a water depth of 5 cm between 15 DAT to PM as and when ponded water level drops to 5 cm BGL in field water tube and 10 cm BGL in field water tube. Likewise in AWD irrigation regime flooding to a water depth of 3 cm from 15 DAT to PI and 5 cm from PI to PM as and when ponded water level drops to 15 cm BGL in field water tube markedly lower the relative water content and leaf water potential...

Response of Three Rice Cultivars to the Intermittent Irrigation in Southern Iraq

A field trial was conducted at Al-Mishkhab Rice Research Station during 2011 season, to assess the effects of irrigation intervals on water productivity and yield components of three local rice varieties (Anber 33, Yasamin, and Furat 1). Two irrigation methods were practiced: continuous ponding and intermittent water application where irrigation water was scheduled at three different intervals (3, 5 and 7 days).The trial was performed as split plot based on a complete randomized blocks design (RCBD) having three replications. Seedlings were transplanted 20 days following germination into rows. 30 cm a part with 20 cm distance between plants within rows. The results showed that the 3-days, 5-days and 7-days intervals of irrigation consumed 50%, 45% and 36% as much water, as continuous flood. The 3-days irrigation interval increased yield by 2% compared with continuous flood while the 7-days irrigation interval decreased yield by 15% compared with continuous flood. Furat1 and Yasamin varieties manifested higher water compared with Anber33. Water productivity of Furat 1 and Yasamin were 0.6108kg.m-3 and 0.5667kg.m-3 respectively. It is concluded that replacing current continuous submergence of rice crops with 3-days interval irrigation will lead to a substantial saving of water, about 50%, while raising yields; and having 7-days interval irrigation could indeed give much-improved productivity of water (grain produced per unit of water).This latter option should be considered even if it does not maximize grain produced per unit of land area in as much as water is becoming a resource more limiting than land for Iraqi agriculture. This water management strategy could help to deal with the shortage in water that is facing Iraqi farmers now and in the foreseeable future.

Irrigation scheduling in direct seeded rice (Oryza sativaL.)-A review

Rice establishment can be done by many methods such as direct seeding of rice, transplanting, SRI (System of rice intensification) etc. For saving both water and labour, direct seeding is the most promising approach. There is possibility of reducing water requirement of direct seeded rice without affecting the grain yield in comparison to the continuous sub-mergence. Depending upon the amount and distribution of rains as well as toposequence of the land, the DSR may be subjected to varying degree of moisture stress at different growth stages. The stress experienced at different growth stages may lead to decrease in plant height, panicle number, panicle length, test weight, number of tillers, total dry matter whereas non-puddled conditions result in the non-formation of hard pan at 15-20 cm soil layer which may restrict the root growth. Direct seeding rice culture showed irrigation water saving to the tune of 9-57 %.

Kinetics of zinc transformation in calciorthids soils of western Rajasthan, India

The present study was undertaken to investigate the kinetics of transformation process of applied and native Zn as influenced by soil moisture regime, available moisture and organic matter additions in Aridisols of western Rajasthan. The incubation experiment was conducted with exact amount of the soil samples (250 g), put in a number of small containers, made of corning glass. Three levels of moisture regimes i.e. field capacity (W0), continuous submergence (W1), alternate submergence and saturation (W2) and two levels of organic matter as starch at 0 per cent (M1) and 0.5 per cent (M2) of the soil weight; and two levels of zinc i.e. native (N) and applied (A) (Zn @ 5 mg kg-1 soil as ZnSO4.7 H2O). The soils then incubated for 30, 60 and 90 days. Destructive sampling was done after each incubation period, and then different fractions of Zn were sequentially extracted by different extracting solutions and determined with the help of atomic absorption spectrophotometer. Based on the results, it can be concluded that the transformation of Zn is largely controlled by organic matter, moisture regimes and Zn application due to considerable changes in the chemical and electrochemical properties of soil and thereby influence the transformation of zinc. Organic matter application significantly increased Zn fractions due to the retention of Zn on exchange complex owing to producing organic acid by decomposition of organic matter in soil. Further, the results showed that if such condition was maintained in the field, and it increased the availability of Zn for different crops in Aridisols.