Effect of long-term agricultural cultivation and land use conversion on soil nutrient contents in the Sanjiang Plain

The cultivation patterns in the Sanjiang Plain of Northeast China have changed over the last three decades, resulting in variations in the land use and soil properties. Changes in cultivation patterns are an important concern for agricultural development in China. In order to highlight the impact of long-term land use on soil quality, the spatial pattern of permanent wetland, permanent forest, permanent dryland, wetland converted to dryland, wetland converted to paddy land, dryland converted to paddy land, and forest converted to dryland in the Sanjiang Plain from 1979 to 2009 was identified. Forty-one soil samples from these seven permanent and converted land use types were collected and eight indexes were analysed. The soil nutrient content of permanent forest, dryland reclaimed from forest, permanent wetland and dryland reclaimed from wetland was not significantly different. However, the soil nutrient content of permanent wetland, except for the available phosphorus, was higher than those of dryland and paddy land reclaimed from wetland. Compared to the permanent wetland, the soil organic matter and total nitrogen of dryland reclaimed from wetland decreased by 55.8% and 59.6%, respectively. For paddy land reclaimed from wetland, the decline in soil organic matter and total nitrogen was 63.6% and 67.6%, respectively. However, the total potassium and available phosphorus of permanent wetland were significantly lower than the amounts in dryland. After permanent forest and wetland were changed to dryland, the available phosphorus increased by 107.7% and 1032%, respectively. The one-way ANOVA was applied to assess the effect of different changes in land use patterns on the soil nutrient contents. This study suggests that the reclamation of wetland decreased soil nutrient content, but the conversion of dryland to paddy land and forest to paddy land increased the nutrient content. The findings can provide advice for agricultural land use managers and also enhance the understanding of nutrient balance. (C) 2012 Elsevier B.V. All rights reserved.