**3.2 Restoration of areas damaged by erosion**

The cereal yields varied much between the different types of restoration measures at Øksna. When the measures were grouped into three: eroded topsoil or no damage (Types No. 2, 3, 5), leveled areas (Types No. 6 and 8), filled erosion craters (Types No. 1, 4, 7, 9, 10, 11), significant difference was found between the undamaged areas (eroded topsoil/no damage) and the restored areas. Average of the restoration measures gave 85% of the yields compared to the areas with eroded topsoil or intact soil (**Table 5**). There was large variation within the group filled erosion craters. Type No. 4 gave 5340 kg ha−1 yield of cereals as mean for the period 1999–2002 and type No. 11 gave only 2920 kg ha−1 cereal yield in the same period. The results indicated that it is possible to find combination of treatments that can fully restore the productivity after severe erosion caused by flooding.

The two types of sewage sludge had different effects on the yields. The limed and calcareous type had positive effect. The types Nos. 1 and 4 were filled with the similar loamy fine sand [**Table 5**], while sewage sludge was mixed in the topsoil at No 4. Although the difference was not statistically significant, the average yield for No. 4 was about 500 kg ha−1 higher in the period 1999–2002 than for No. 1. Most of the treatments had low levels of readily available P in the topsoil (<5 mg 100 g−1), which may result in


**Table 5.**

*Average yield of cereals (spring barley and oats) (kg ha−1, 15% water content) at plots with different restoration measures at Øksna, Elverum, for the period 1999–2002. Means followed by different letters are statistically significant (p < 0.05).*


#### **Table 6.**

*Soil texture, bulk density, porosity, TOC, and pH in topsoil (Ap-horizon) at Øksna for different restoration types.*

*Flood Damage on Agricultural Land and Methods for Restoration of Agricultural Soils… DOI: http://dx.doi.org/10.5772/intechopen.109111*

P-deficiency for the crop [10]. The limed sewage sludge increased the level of readily available P in the topsoil significantly, resulting in very high levels of P-AL (>35 mg 100 g−1). The other type of sewage sludge gave no additional yield compared to the other types of restoration measures. Although both sludges contained much phosphorus, soil analyses indicated deficiency of phosphorus after application of the sludge with Al salts used as coagulants. The plant availability of P in sludges produced from wastewater using Al salts as coagulants is often low compared with that in mineral fertilizer, while liming can increase the P fertilization effect of sludges [11]. This may explain the difference in effect between the two types of sewage sludge applied at Øksna.

There was no significant difference in TOC in the topsoil between areas with intact or eroded A-horizon and areas where the topsoil was amended with sludge during the restoration and the content of TOC was rather low, mainly 1 ± 0.3 g 100 g−1 (**Table 6**). The type No. 11 where peat material had been mixed in the topsoil had low pH initially and was limed before the growing season 2000. Although this treatment had good physical properties for plant growth, this treatment had the lowest content of available plant nutrients and different plant deficiency symptoms were observed on the cereal plants (P, K, Zn) resulting in low yield of cereals.
