Cover crops can generate both on-farm and water-quality benefits. However, their use in Iowa remains subdued, partly due to implementation costs faced by farmers. We tested the hypothesis that monetary incentives through cost-share programs are effective at increasing the area of farmland planted to cover crops in Iowa, as opposed to the alternative in which the participants of cost-share programs would have planted the same cover-crop acreage in the absence of payment. We found that cost-share payments induced a 15 percentage-point expansion in cover-crop acreage beyond what would have been planted in the absence of payment, among farmers who participated in cost-share programs. The estimated additionality rate was 54%, suggesting at least half of cost-share expenditures funded cover-crop acreage that would not have been planted without payment. Furthermore, we estimated the public cost to reduce nitrogen loads to Iowa waterways via cover crop, beyond what would have occurred in the absence of cost-share programs, to be $1.72–$4.70 lb−1 N ($3.79–$10.36 kg−1 N). Farmers absorbed about 70% of those costs as private losses, and cost-share payments offset the remaining 30%. Although the additionality rate estimated in this study is less than what has been found in other states, the cost-share programs in Iowa have been relatively cost-effective, due to their lower payment rate.

中文翻译：

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成本分摊计划会增加覆盖作物的使用吗？爱荷华州的经验证据

覆盖作物可以产生农场和水质效益。然而，它们在爱荷华州的使用仍然低迷，部分原因是农民面临实施成本。我们检验了这样一个假设，即通过成本分摊计划的货币激励措施可以有效地增加爱荷华州种植农田以覆盖作物的面积，而不是成本分摊计划的参与者将种植相同的覆盖作物面积的替代方案在没有付款的情况下。我们发现，在参与成本分摊计划的农民中，成本分摊支付导致覆盖作物的种植面积比没有支付的情况下增加了 15 个百分点。估计的额外费用率为 54%，这表明至少有一半的成本分摊支出资助了没有付款就不会种植的覆盖作物种植面积。-1N ($3.79–$10.36 公斤-1N)。农民承担了其中约 70% 的成本作为私人损失，成本分摊支付抵消了剩余的 30%。尽管本研究中估计的额外费用率低于其他州的情况，但由于支付率较低，爱荷华州的成本分摊计划相对具有成本效益。