Irrigation and the role of groundwater

Our data also demonstrate the importance of groundwater in supplying irrigation to northern China's agricultural sector. According to the respondents, nearly half (49%) of China's cultivated area is irrigated (slightly higher than the figure given in China National Statistical Bureau, 2004 - 42%). However, with our data we can understand the water economy more fully, since our survey covers more than what is available in official sources. For example, since national statistics do not collect irrigation data by type of irrigation water, we asked village leaders to carefully document the source of their irrigated area: either surface, groundwater or conjunctive use of both. On the basis of their responses, in 1995, of all of the cultivated land that is irrigated, only 40% came from surface water diversions (or was lifted from canals by pumps onto the fields). The remaining 60% came from groundwater sources. Between 1995 and 2004 the importance of groundwater has continued to grow. In 2004, 68% of irrigation in northern China was from groundwater.

Crop-specific incidences of irrigated area

Our data can also produce estimates of crop-specific sown area statistics by irrigated and non-irrigated portions. For example, major food grains in northern China are mostly irrigated (Table 3.2). Approximately 96% of rice and 80% of wheat are irrigated, levels that are above the national average (Table 3.2, column 1, rows 1 and 2). Hence, our data support the findings of Huang et al. (2006) that investment in irrigation has been central for China to maintain food security. Although it is well known that China's food crops are heavily irrigated and that this is an important factor in China being able to produce a large fraction of its own food, these crop-specific estimates are important because China's own statistical bureau does not report sown area by irrigated and non-irrigated portions.

In contrast to the case of food grains, a majority of feed grains and lower-valued staple crop area is not irrigated (Table 3.2, column 1, rows 3, 5 and 6). For example, despite its growing importance in China's agricultural economy, only 49% of China's maize is irrigated.10 An even lower proportion of coarse grains and potatoes (including white and sweet potatoes) is irrigated. Although the proportion of irrigated area in cash crops also varies by crop, much of the

Table 3.2. Share of irrigated sown area by crop type in north China. (From authors' survey in 2004.)

Crop

Percent of cropland that is irrigated

Percent of irrigated sown area Surface water Groundwater

Rice

96

76

24

Wheat

80

28

72

Maize

49

30

70

Cotton

58

30

70

Potato

22

27

73

Soybean

24

32

67

Oil crops

47

38

62

Field vegetables

66

33

67

area of China's main cash crops is irrigated (e.g. 58% of cotton area, 47% of oil crop area and 66% of field vegetable area - Table 3.2, rows 4, 6 and 7).

Perhaps more importantly, in northern China irrigation for most crops mainly depends on groundwater resources (Table 3.2, column 3). For grains and other staple crops, except for rice, at least 70% of the producers in irrigated areas use groundwater resources (72% for wheat; 70% for maize; 73% for potatoes). For cash crops, groundwater is the major source of water for irrigation. For example, groundwater irrigates 70% of cotton area, 62% of oil crop area and 67% of field vegetable area.

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