**3.7 Deep ECa zoning characteristics**

130 Current Issues of Water Management

concentration can be estimated. Hence, quick nutrients determination can be done through the ECa sensor detection. The average values of ECa are significantly different between shallow (0-30 cm) and deep depths (0-90 cm) signifying differences in soil structure and nutrient status. The sensor can measure the soil ECa through the field quickly for detailed

The study area was divided into 5 manageable zones by smart quantiles method (ESRI, 2001). Fig. 12 shows the shallow ECa and Fig. 13 shows the deep ECa. The map for the deep ECa shows the distribution clearly, especially for very low and low ECa levels. Fig. 13 shows the pattern of a former river clearly as a continuous line about 45 m wide at the northern

The on-the-go EC sensor can be used to replace the traditional way of acquiring soil data by intensive sampling technique and laboratory analysis, which is usually time consuming and laborious. The resulting ECa maps are useful in showing the management zones for improving crop productivity with minimum inputs. The delineation by ECa showed that some soil properties significantly differ from zone to zone. A total of 21 parameters were significantly predicted by using ECa which shows that the EC probe can predict multi-

Pearson's 2-tailed test for soil chemical, physical and ECa correlation showed that shallow ECa has positively significant correlation to pH, EC, CEC, Mg, Fe, clay and deep ECa and negatively significant correlation to Al, fine sand and sand, at 99%. It has positively significant correlation to P, K and total cation, at 95%. The highest r value was 0.70\*\* for deep ECa and followed by pH (r=0.39\*\*). Deep ECa has positively significant correlation to pH, EC, P, CEC, Mg, K, Na, Fe, total cation, clay, fine sand, sand and shallow ECa and negatively significant correlation to Al, at 99%. The highest r value was 0.70 for shallow ECa and followed by Mg (r=0.46\*\*). Eltaib (2003) found that laboratory EC has highest

The mean value for shallow ECa slightly increased from zone to zone and significantly isolated between zones. But, some mean values of soil properties (i.e. EC, OM, C, S, N, CEC, Ca, Na and etc.) within the shallow ECa zones did not show linear trend as per mean shallow ECa. The hypothesis for ECa zone establishment was that the soil properties within the zone were significantly different from zone to zone which indicated that soil ECa is a

The results indicate that the mean soil pH values within shallow ECa zone 1, 2 and 3 were not significantly different, but significantly higher than that in zone 4 and 5. However, zone 1 has significantly high OM, C, total S, total N, ESP, fine sand and sand, and significantly low Ca, total cation, BS and clay. Soil moisture, silt and coarse sand were not significantly different for all zones, at 0.05. The shallow ECa proved that zone 1 (former river) contained higher OM as compared to other parts of the study area. Therefore, to manage that area based on shallow ECa, it should be managed differently according to organic matter content. Mean shallow ECa for 5 zones has significantly negative correlation to soil pH (r = -0.95) and

good zone delineator, a new classification approach for paddy soil properties.

features of the paddy soil, and can be operated by just one worker.

variables, hence reduces time for sampling and analyses.

correlation to Mg (r = 0.79\*\*, n = 36) for this study area.

and central regions of the study area.

**3.5 Matrix correlation of soil properties** 

**3.6 Shallow ECa zoning characteristics** 

The stratification of total N, BS and coarse sand by deep ECa were homogenous between the zones when their mean values within the zone were not significantly different at 0.05. Mean soil OM, C and total S in zone 3 were significantly higher than those in other zones and they were different to shallow ECa zone where it indicated that zone 1 has significantly high OM, C and total S. Mean soil pH, EC, P, Mg, K, Fe, total cation and clay within zone 1 were significantly low as compared to other zones, but significantly high Al, fine sand and sand. Deep ECa has significantly positive correlation to soil pH and Fe at 0.01 and significantly negative correlation to coarse sand at 0.05.


Table 3. Significant Relationship of Soil Properties to ECa for the Study Area (n = 236)

Paddy Water Management for Precision Farming of Rice 133

Bulk density Clay Sand

Yield Deep ECa Shallow ECa

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

Season 1

Season 1

Season 2

Yield Deep ECa Shallow ECa

## **3.8 Model for soil properties estimations**

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