Assessing Soil Quality in Conversion of Burned Forestlands to Rice Croplands: A Case Study in Northern Iran

Conversion of burned forestlands into rice croplands is often practised to increase food production. However, this practice can lead to a severe decline in soil quality and functioning. Unfortunately, no research has previously evaluated how and to what extent physico-chemical properties and overall quality of forest soils change when converted to rice paddy fields. This study has evaluated the changes in key soil properties and Soil Quality Index (SQI) when burned forests are converted to rice croplands in Guilan Province (Northern Iran). This conversion results in noticeable worsening of soil structure (shown by the decreases in size and stability of macro-aggregates, ~50%) and reductions in organic matter (−30%) and nutrient contents (−43% of TN and −49% of P) of soil in rice paddy fields in comparison to burned forest soils. In contrast, soil salinity increased by 180% and potassium by 12%, while pH remained unchanged between forestland and rice fields. The calculation of the SQI showed that the overall quality of the soil was severely affected by this change. The main message of this study is that replacement of forest ecosystems with rice croplands should be carefully controlled, in order to avoid noticeable impacts on soil properties and theiroverall quality. In sites where this conversion has occurred, sustainable land management practices, such as moderate supply of organic amendments and fertilisers, should be implemented to mitigate soil degradation.