**4.1 Strategies for water saving**

Water saving practices, which require greater water control is associated with improving agronomic practices and the use efficiency of other inputs. Available strategies include developing improved varieties, improving agronomic management, changing the crop planting date, reducing water use for land preparation, changing rice planting practices with wet or dry seeding, reducing water use during crop growth through intermittent flooding, maintaining the soil in sub-saturated condition, alternate drying and wetting, optimum use of rainfall, supplementary irrigation of rain-fed low-land rice, water distribution strategies, water reuse or recycling and conjunctive use and alternative methods to flooding for growing irrigated rice under aerobic conditions.

High rice yield are obtained with good on-farm water management. Many researchers reported that continuous submergence with 5 to 7 cm of water is probably best for irrigated rice considering all factors. Submergence allows better weed control, higher efficiency of fertilizer use, and better insect and weed control with granular chemicals. Research has shown no difference in yield of rice grown at saturated soil condition with minimum water use but weed control is expected to be more costly.

Other researchers found optimum rice growth and production at 9 cm of ponded water depth. High values of water productivity were also found at this depth under different water regimes and fertigation levels. High water levels are required after transplanting for recovery and rooting stage and booting stage up to flowering stage. Low depths are required for tillering, panicle development and milk stage. Shallow depths promote

Results from the curve estimation for the independent variables of shallow and deep ECa indicate that ECa can be used to estimate multi-variables, 21 out of 24 variables. Shallow ECa has lesser soil properties compared to deep ECa, where there were 16 and 21 variables, respectively. Most of the variables have high R2 values, except pH, EC, N, CEC and ESP when the estimation is using deep ECa as independent variable. The relationship functions differed for some variables while others remained. The high R2 values for deep ECa indicate that variables were significantly estimated using deep ECa rather than shallow ECa. The best model was judged based on their R2 where the estimation of soil Mg by deep ECa was the

A study was conducted to compare yield variability resulting from variability of soil ECa and other parameters for both the dry and wet seasons in the same 140 ha study area (Gholizadeh, 2011). Fig. 14 shows typical variability maps of the harvested yield compared to the variability in the bulk soil electrical conductivity, bulk soil density and soil texture. High yielding areas are associated with mid-range ECa, high clay and low sand, and low bulk density. Low yielding areas are associated with low ECa and high sand content. High yield is also associated with high pH, high EC and high OC, and vice versa. Hence water

Water saving practices, which require greater water control is associated with improving agronomic practices and the use efficiency of other inputs. Available strategies include developing improved varieties, improving agronomic management, changing the crop planting date, reducing water use for land preparation, changing rice planting practices with wet or dry seeding, reducing water use during crop growth through intermittent flooding, maintaining the soil in sub-saturated condition, alternate drying and wetting, optimum use of rainfall, supplementary irrigation of rain-fed low-land rice, water distribution strategies, water reuse or recycling and conjunctive use and alternative methods

High rice yield are obtained with good on-farm water management. Many researchers reported that continuous submergence with 5 to 7 cm of water is probably best for irrigated rice considering all factors. Submergence allows better weed control, higher efficiency of fertilizer use, and better insect and weed control with granular chemicals. Research has shown no difference in yield of rice grown at saturated soil condition with minimum water

Other researchers found optimum rice growth and production at 9 cm of ponded water depth. High values of water productivity were also found at this depth under different water regimes and fertigation levels. High water levels are required after transplanting for recovery and rooting stage and booting stage up to flowering stage. Low depths are required for tillering, panicle development and milk stage. Shallow depths promote

management that will allow increase in pH of the paddy soil is desirable.

to flooding for growing irrigated rice under aerobic conditions.

use but weed control is expected to be more costly.

**3.8 Model for soil properties estimations** 

highest following by Fe, clay, pH and so on (Table 3).

**3.9 Yield variability and soil management zones** 

**4. Water saving practices 4.1 Strategies for water saving** 

Fig. 14. (continues on next page)Variability in rice yield compared to ECa and soil physical properties in a 140 ha paddy fields for two seasons. Higher yielding areas are associated with mid-range ECad, medium ECas, low Db, high clay and low sand. Low yielding areas are associated with low ECad, low ECas, high Db, medium clay, medium sand

Paddy Water Management for Precision Farming of Rice 135

Maruyama and Tanji (1997) showed that the growth stages of rice can be divided into ten growth stages associated with water management practices in Japan as shown in Fig. 15. The paddy farmers must control the field water depth precisely according to the growth

Mao Zhi (2000) stated that rice is one of the most important food crops contributing over 39% of the total food grain production in China. Out of 113 million hectares of area sown under food crops 28% is covered by rice. The traditional irrigation regime for rice, termed as "continuous deep flooding irrigation" was applied in China before 1970s. Since 1980s, the industry water supply, urban and rural domestic water consumption has been increasing continuously. The shortage of water resources became an important problem and many water efficient irrigation regimes for rice have been tested, advanced, applied and spread in

Based on the results of experiment and the experience of spread of these new irrigation

• Three essential water efficient irrigation regimes (WEI) for rice as shown in Fig. 16, which include the regimes of combining shallow water depth with wetting and drying (SWD), alternate wetting and drying (AWD) and semi—dry cultivation (SDC), have

• In comparison to the traditional irrigation regime (TRI), rice yield can be increased slightly, water consumption and irrigation water use of paddy field can be decreased greatly and the water productivity of paddy field can be increased remarkably under

• The main causes of decrease of water consumption and irrigation water use are the decrease of the percolation rate in paddy field and increase in the utilization of rainfall. • A positive environmental impact is obtained by adopting WEI, the main cause of getting bumper yields were that the ecological environment under WEI is more

• For avoiding the decrease of yield under WEI, some measures, as timely irrigation, coordinating irrigation with fertilization and weed control must be used since shortage of water resources in China is becoming more serious each year, the water efficient irrigation techniques should be further investigated and adopted on large

With global warming and climate change, greater competition is expected among water users, and paddy irrigation may be sacrificed during water shortage in dry months favouring domestic and industrial users. However, rice granaries practicing multiple cropping have yet to improve on the use of "effective rainfall". Currently, the measurement of rain falling in a rice growing area is based solely on the available rain gauge network. These gauges are located at convenient locations which may not be representative of the whole rice growing

favourable for the growth and development of rice than that under TRI.

**4.2 Rice growing calendar and water management** 

different regions of China.

the WEI.

areas.

**4.4 Distribution variability of effective rainfall** 

stage in order to reap the benefit of higher water productivity.

regimes, the following conclusions were drawn by the author:

been adopted in the different rice growing regions of China.

**4.3 Water-efficient irrigation regimes to increase water productivity** 

Fig. 14. (continued) Variability in rice yield compared to ECa and soil physical properties in a 140 ha paddy fields for two seasons. Higher yielding areas are associated with mid-range ECad, medium ECas, low Db, high clay and low sand. Low yielding areas are associated with low ECad, low ECas, high Db, medium clay, medium sand

vigorous tillering. Mid-season drainage is important to cut-off the supply of ammonia-N to secure desirable plant characteristics, viz. short and erect upper 3 leaves, including flag leaf, and short lower inter-node to prevent lodging, to induce favourable ear (panicle) formation conditions, and to supply soils with oxygen to ensure healthy root growth.

Mid-season drainage removes hydrogen sulphide and other harmful substances, which are produced by microbial action under reductive conditions of submergence. Water (5 cm) is needed at milk stage for translocation of nutrients stored in plant body to ear or panicle for healthy development of developing grain or spikelet.

Fig. 15. Rice growth, agricultural works and water management (Maruyama and Tanji, 1997)

Bulk density Clay Sand

Fig. 14. (continued) Variability in rice yield compared to ECa and soil physical properties in a 140 ha paddy fields for two seasons. Higher yielding areas are associated with mid-range ECad, medium ECas, low Db, high clay and low sand. Low yielding areas are associated

vigorous tillering. Mid-season drainage is important to cut-off the supply of ammonia-N to secure desirable plant characteristics, viz. short and erect upper 3 leaves, including flag leaf, and short lower inter-node to prevent lodging, to induce favourable ear (panicle) formation

Mid-season drainage removes hydrogen sulphide and other harmful substances, which are produced by microbial action under reductive conditions of submergence. Water (5 cm) is needed at milk stage for translocation of nutrients stored in plant body to ear or panicle for

Fig. 15. Rice growth, agricultural works and water management (Maruyama and Tanji, 1997)

with low ECad, low ECas, high Db, medium clay, medium sand

healthy development of developing grain or spikelet.

conditions, and to supply soils with oxygen to ensure healthy root growth.

Season 2
