Monitoring of Nitrate and Chloride in an Irrigated Farmland

Saffinga and Keeney (1977) monitored Cl and NO3 in shallow wells near a farm in central Wisconsin. In Fig. 16.4, the results from a well in an area not irrigated by the farm (well 7) are compared with the results from wells located in the irrigated farmland (wells 8 and 9, the latter was situated in a less cultivated part). The farming intensity dropped after 1972.

Discussion.

• The NO3 and Cl concentrations were correlated to irrigation intensity, since no increase was observed in well 7, located in a nonirrigated area, and as seen by the drop in Cl and NO3

Fig. 16.3 Change in nitrate and calcium concentration in water flowing from a watershed cleared of vegetation (thick line) and an adjacent watershed with preserved vegetation (thin line). The arrows mark the date of vegetation clearance. Nitrate and calcium increased, with a 5-month delay, indicating piston flow recharge. (From Bormann and Likens, 1970.)

Fig. 16.3 Change in nitrate and calcium concentration in water flowing from a watershed cleared of vegetation (thick line) and an adjacent watershed with preserved vegetation (thin line). The arrows mark the date of vegetation clearance. Nitrate and calcium increased, with a 5-month delay, indicating piston flow recharge. (From Bormann and Likens, 1970.)

concentrations with the decrease in irrigation between 1972 and 1975.

The Cl and NO3 covaried, indicating a common source, which was found to be two fertilizers applied in constant proportions: a nitrogen-rich fertilizer and a potassium chloride fertilizer. The recovery of the water quality in 1975 indicated that no salts were stored in the ground.

The rapid recovery also indicated that the irrigation water reached the local groundwater rapidly, changes being observed from month to month (Fig. 16.4).

Fig. 16.4 Nitrate (dots) and chloride (circles) in groundwater of a well (no. 7) in a nonirrigated area, and wells (nos. 8 and 9) located in an irrigated area, Hancock Experimental Farm. Irrigation caused an increase in nitrate and chloride, caused by nitrogen and potassium fertilizers, the latter containing Cl (KCl). The quality of water was restored because of a decrease in farming activities. (From Saffinga and Keeney, 1977.)

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