17:15 〜 19:15
[AGE34-P04] GeoWEPPを用いたカバークロップによる土壌侵食抑制効果の定量評価
キーワード：土壌侵食防止、カバークロップ、GeoWEPP、持続可能な農業、嬬恋村
Agricultural fields in Tsumagoi, Gunma Prefecture, are situated on sloping terrain, making them vulnerable to severe soil erosion. This threatens future cabbage productivity. Addressing soil erosion issue is essential for ensuring the long-term sustainability of agriculture in the region.
Though cover crops are known as beneficial for soil conservation, few studies have quantitatively demonstrated their effectiveness. The lack of cost-effectiveness data has led to farmers' reluctance to adopt cover crops as a soil conservation measure. To address this, we used the process-based model GeoWEPP to estimate the impact of cover crops on sediment yield reduction.
We measured sediment yields from 2021 to 2023 at the outlet of the Yokkosawa watershed (170 ha). We calibrated the GeoWEPP using these data, achieving high accuracy with R² = 0.93, NSE = 0.92, and PBIAS = 22.8%. Using this calibrated model, we simulated soil loss under a scenario where oats were planted as a cover crop after cabbage harvest.
The results showed that from 2019 to 2023, the total accumulated sediment yield decreased from 108 t ha-1 to 67.5 t ha-1, a 37.8% reduction. Notably, during Typhoon Hagibis on October 12, 2019, cover crops reduced soil loss from 71.9 t ha-1 to 16.8 t ha-1 in a single day, demonstrating a 63.9% reduction. Furthermore, based on the annual average sediment loss over five years, we estimated topsoil reduction over 50 years in the watershed. Assuming a dry bulk density of 0.5 g cm-³, approximately 22 cm of topsoil is expected to be lost without cover crops, whereas, with cover crops, the loss is reduced to 14 cm. In Tsumagoi, there is a case where 21 cm loss of topsoil resulted in a 23% decrease in cabbage yield (unpublished data). These findings quantitatively highlight the soil conservation benefits of cover crops and are expected to facilitate farmers' decision-making regarding soil erosion control measures.
Though cover crops are known as beneficial for soil conservation, few studies have quantitatively demonstrated their effectiveness. The lack of cost-effectiveness data has led to farmers' reluctance to adopt cover crops as a soil conservation measure. To address this, we used the process-based model GeoWEPP to estimate the impact of cover crops on sediment yield reduction.
We measured sediment yields from 2021 to 2023 at the outlet of the Yokkosawa watershed (170 ha). We calibrated the GeoWEPP using these data, achieving high accuracy with R² = 0.93, NSE = 0.92, and PBIAS = 22.8%. Using this calibrated model, we simulated soil loss under a scenario where oats were planted as a cover crop after cabbage harvest.
The results showed that from 2019 to 2023, the total accumulated sediment yield decreased from 108 t ha-1 to 67.5 t ha-1, a 37.8% reduction. Notably, during Typhoon Hagibis on October 12, 2019, cover crops reduced soil loss from 71.9 t ha-1 to 16.8 t ha-1 in a single day, demonstrating a 63.9% reduction. Furthermore, based on the annual average sediment loss over five years, we estimated topsoil reduction over 50 years in the watershed. Assuming a dry bulk density of 0.5 g cm-³, approximately 22 cm of topsoil is expected to be lost without cover crops, whereas, with cover crops, the loss is reduced to 14 cm. In Tsumagoi, there is a case where 21 cm loss of topsoil resulted in a 23% decrease in cabbage yield (unpublished data). These findings quantitatively highlight the soil conservation benefits of cover crops and are expected to facilitate farmers' decision-making regarding soil erosion control measures.