Study on intermittent irrigation for Paddy Rice: Ⅱ. Crop Responses

Effect of intermittent irrigation on the production of paddy rice was studied in a well-puddled paddy field with four treatments and 2 replicates: continuous flooding irrigation (CFI), and intermittent irrigation Ⅱ-O, Ⅱ-1 and Ⅱ-2, in which plants were re-irrigated when the soil water potential fell below 0, -10, and -20 kPa, respectively, at soil depth of about 5 cm. Results showed that the reduction in soil water potential to about -10 or -20 kPa did not significantly affect the number of grains and the percentage of ripened grains. While, a lower crop growth rate (CGR) resulted from a decrease in the net assimilation rate (NAR) during intermittent irrigation Ⅱ-1 and Ⅱ-2, and there was also a reduction in the leaf area index (LAI) during intermittent irrigation Ⅱ-2. Senescence of lower leaves on stems was promoted in treatments Ⅱ-1 and Ⅱ-2 at the ripening stage. Early senescence at ripening stage and water stress around midday decreased the rate of photosynthesis in leaves, causing the lower NAR. These physiological responses of the plants were responsible for the reduction in the dry matter production and grain yield in the intermittent irrigation treatments.

Study on Intermittent Irrigation for Paddy Rice: I. Water Use Efficiency

A field experiment was conducted in a well-puddled paddy field developed on the Tama River alluvial soil in the Farm of Tokyo University of Agriculture and Technology, Japan, to study the effect of intermittent irrigation on water use efficiency of paddy rice. Four treatments were arranged with 2 replicates: continuous flooding irrigation treatments (CFI), and three intermittent irrigation treatments Ⅱ-0, Ⅱ-1 and Ⅱ-2, in which plants were re-irrigated when the soil water potential fell below 0, -10, and -20 kPa, respectively, at soil depth of about 5 cm. Water consumption was lower in treatment Ⅱ-0 than in treatment CFI because the percolation rate was reduced by the reduction in the hydraulic head of ponded water. Intermittent irrigation led to soil repeated shrinking and swelling in Ⅱ-1 and Ⅱ-2 plots and, therefore, soil cracks developed rapidly. Since they became the major routes of water percolation, the soil cracks increased water consumption in treatments Ⅱ-1 and Ⅱ-2. There were no significant differences in dry matter production and grain yields between treatment Ⅱ-0 and treatment CFI, but the dry matter production and grain yields in treatments Ⅱ-0 and CFI were significantly higher than those in treatments Ⅱ-1 and Ⅱ-2. Therefore, the water use efficiency in the treatments was in the order of Ⅱ-0 > CFI > Ⅱ- 2 > Ⅱ- 1.

Estimating Crop Coefficient in Intermittent Irrigation Paddy Fields Using Excel Solver

The current study proposes a novel method using Excel Solver to estimate, from limited data, crop coefficient （Kc） in paddy fields under intermittent irrigation （11）. The proposed method was examined in a field experiment conducted at Karang Sari Village, Bekasi, West Java, Indonesia during the first rice season of 2007/2008 （December 2007 to April 2008） in the rainy season. As the control, continuous flooding irrigation （CF） was applied to the conventional rice cultivation fields. Based on the observed water storage, Excel Solver was used to estimate crop evapotranspiration. Estimated crop evapotranspiration was used to compute Kc value, then the average Kc values at each growth stage were compared with that for the CF treatment. The estimation method was evaluated by comparing estimated crop evapotranspiration and the crop evapotranspiration derived by the well established FAO procedure. Excel Solver estimated crop evapotranspiration accurately with R2 values higher than 0.81. Accordingly, more than 81% of the FAO crop evapotranspiration was described by the proposed method. Thus, Kc value could be well determined from those estimated crop evapotranspiration. Under the II treatment, the average Kc values were 0.70, 1.06, 1.24 and 1：22 for the initial, crop development, reproductive and late stages, respectively. These values were lower than those under the CF treatment for initial and crop development stages because of a minimal soil evaporation and intense dryness during these stages. However, average Kc values under the II treatment were higher than those under the CF treatment at the reproductive and late stages, indicating that the II treatment promoted more plant activity particularly for dry biomass production as indicated by a greater number of tillers per hill.

Technologies for Efficient Use of Irrigation Water and Energy in China

While the shortage of water and energy is a well-recognized worldwide natural resources issue, little attention has been given to irrigation energy efficiency. In this paper, we examine the potential energy savings that can be achieved by implementing improved irrigation technologies in China. The use of improved irrigation management measures such as a flow meter, irrigation scheduling, and/or regular maintenance and upgrades, typically reduces the amount of water pumped over the course of a growing season. The total energy saved by applying these improved measures could reach 20%, as compared with traditional irrigation methods. Two methods of irrigation water conveyance by traditional earth canal and low pressure pipeline irrigation （LPPI） were also evaluated. Our study indicated that LPPI could save 6.48x 109 kWh yr1 when applied to 11 Chinese provinces. Also, the COz emission was reduced by 6.72 metric tons per year. Among these 11 surveyed provinces, the energy saving potential for two provinces, Hebei and Shandong, could reach 1.45 x 109 kWh yr^-1. Using LPPI, potential energy saved and CO2 emissions reduced in the other 20 Chinese provinces were estimated at about 2.97×109 kWh yr-1 and 2.69 metric tons per year, respectively. The energy saving potential for Heilongjiang, a major agriculture province, could reach 1.77× 109 kWh yr-1, which is the largest in all provinces. If LPPI is applied to the entire country, average annual energy saving of more than 9 billion kWh and average annual CO2 emission reduction of more than 9.0 metric tons could be realized. Rice is one of the largest users of the world＇s fresh water resources. Compared with continuous flooding irrigation, intermittent irrigation （ITI） can improve yield and water-use efficiency in paddy fields. The total increments of net output energy and yield by ITI in paddy fields across China could reach 2.5× 1016 calories and l07 tons, respectively. So far only a small part of agricultural land in China has adopted water and energy saving technologies. Therefore, potential water and energy savings in China by adapting improved irrigation technology could be significant and should be carefully studied and applied.

Water Management for Improvement of Rice Yield,Appearance Quality and Palatability with High Temperature During Ripening Period

To clarify the optimal water management in large-scale fields under high temperatures at the ripening period,effective water managements during this period for improvement of yield,appearance quality and palatability were investigated.Compared with intermittent irrigation and flooded irrigation,the soil temperature with saturated irrigation remained low throughout the day,and the decrease rate of the bleeding rate of hills was the lowest.These results suggested that the saturated irrigation maintained root activity.For the three irrigation types,the number of spikelets per m2 and 1000-grain weight were similar,however,saturated irrigation resulted in significantly higher rice yield due to improvement in the percentage of ripened grains.The saturated irrigation produced a high percentage of perfect rice grains and thicker brown rice grain,furthermore,the palatability of cooked rice was excellent because protein content and hardness/adhesion ratio were both low.Thus,under high-temperature ripening conditions,soil temperature was lowered and root activity was maintained when applying saturated irrigation after heading time.The results indicated that saturated irrigation is an effective countermeasure against high-temperature ripening damage.

Rice and Barnyardgrass:Water Stress and Initial Establishment

The present work aimed to evaluate the effect of different water stress levels on the development of both rice and barnyardgrass. The study was established into greenhouse, in completely randomized design, in factorial scheme 2 × 5, with four replications. Factor “A” comprised the plant species (rice cv. BRS Querência, or the weed Echinochloa crusgalli), and factor “B” comprised the water stress levels: (T1) continuous flood (CF);(T2) 0 kPa (saturated soil);(T3) 10 kPa;(T4) 40 kPa;and (T5) 100 kPa. Plant emergence was assessed every day;plant length was measured 30 days after planting. At the end of the experiment, the number of leaves per plant, root length and shoot and root dry mass were determined. Our data supply evidence that under moderate water stress, up to approximately 40 kPa, rice tends to perform better than barnyardgrass in the initial stage of crop growth, when under equivalent plant density. However, barnyardgrass is usually present in much higher plant density than crop plants in fields traditionally cropped with rice. Thus, efficient control of barnyardgrass should be accomplished to avoid damage to rice crop by competition for environmental resources.