Agricultural & Environmental Letters最新文献

Soil nutrient concentrations are often expressed as parts per million (ppm) in soil test reports. For incorporation into nutrient management decisions, ppm-based concentrations have to be converted into pounds per acre, and a conversion factor (multiplier) of 2.0 is typically recommended universally to do so. However, this conversion factor stems from an assumed value of bulk density (ρ_b) corresponding to silt loam soil and is invariant to any deviation beyond assumed ρ_b. Here, we quantify and evaluate the potential ramifications of assuming a constant ρ_b value on calculating soil nitrogen credits. A true dynamic conversion factor that is sensitive to variation in ρ_b ranges between 1.28 and 2.68 for soils across US cropland. Failure to account for this dynamic conversion factor was shown to result in an underestimation of soil N credits by up to 40%. In addition to spatial variation, management-induced changes in ρ_b are also important to incorporate into the conversion factor.

Understanding the long-term effects of manure applications on the soil microbial component in semiarid climates will be key to sustain essential processes that affect their productivity and soil health. In this paper, soil health indicators encompassed both selected chemical and biological indicators. From 2004 to 2009, solid dairy manure treatments were applied to plots at cumulative rates of 0, 134, and 237 dry Mg ha⁻¹ (34–56 dry Mg ha⁻¹ year⁻¹) in a randomized complete block with three replicates. Soil samples were taken from each manure rate in the spring of 2020 at 0–15 and 15–30 cm. Eleven years after manure applications ceased, many of the soil chemical and biological indicators were different between the manure and control treatments. In general, soil organic carbon and biological indicators were significantly greater in the 134 and 237 Mg ha⁻¹ treatments as compared to the 0 Mg ha⁻¹ treatment.

A changing climate offers new opportunities to expand agriculture in northern latitudes, and understanding forest-to-agriculture land conversion impacts is critical to ensure soil sustainability. Using the Comprehensive Assessment of Soil Health (CASH) framework, we identified a minimum suite of indicators with little collinearity to reliably predict soil impacts during the conversion of boreal forest to agriculture and a time since conversion gradient (forest, <10 years, >10 and <50 years, and >50 years since conversion). We sampled paired forest and agricultural sites and used multiple linear regression to assess 16 indicators and found four- and six-indicator models predicted the CASH score with varying but reasonable accuracy depending on conversion class. Organic matter, water aggregate stability, and pH were consistent predictors across all classes, as well as one or more micronutrients. The CASH framework appears to be more suitable for agricultural soils and as time since conversion proceeds.

The editorial board of Agricultural & Environmental Letters is pleased to announce the recipients of the 2023 Editor's Citation for Excellence. These awards recognize the outstanding professional commitment and dedication of volunteer reviewers and editors who, through their excellent insights and comments, have helped maintain the high standard and quality of papers published in the journal. Recipients were nominated based on their thorough, competent, and timely reviews or editing of manuscripts.

In the last two decades, permanganate has been used to define what is assumed to be a labile or “active” soil carbon (C) pool, commonly referred to as “permanganate-oxidizable carbon” (POXC). However, uncertainties in the reduction reaction (Mn⁷⁺ → Mn⁴⁺/Mn²⁺) and even greater uncertainties in the oxidation reaction (C^? → C^?) as well as the reaction of non-C reductants in the soil sample preclude the calculation of milligram C per kilogram of soil oxidized. Combined variation in the reduction–oxidation reactions can entail up to fivefold variation in how much soil organic C is oxidized per unit permanganate reduced. Without determining final reduction state of Mn and the initial and final oxidation states of C, the amount of C oxidized cannot be calculated. Unless a concrete understanding of the reduction and oxidation half-reactions is achieved, an alternative expression of permanganate reactivity of a soil sample (i.e., not mg C kg⁻¹ soil) is needed.

Cover crops are promoted by agronomists and governments due to their on-farm and off-farm benefits. Incentive programs were created because high planting costs have hindered cover crop adoption in the United States. Crop insurance discount programs are novel incentives that subsidize farmers’ crop insurance premiums by $5 per acre ($12.36 ha⁻¹) on cover cropped land. While this payment is smaller than those typically offered through the Natural Resources Conservation Service and state-level cost-share programs, crop insurance discount programs have the potential to reach a significant proportion of farmers who purchase crop insurance. This paper uses data from a survey of Iowa farmers to quantify whether participation in the Iowa Crop Insurance Discount Program (ICIDP) affects the area planted to cover crops. I find that 11% of the ICIDP area would not have been planted to cover crops in the absence of the program, which is similar to other programs after considering the lower payment rate.