Animal‐Based Organic Amendments and Their Potential for Excessive Nitrogen Leaching and Phosphorus Loading

Abstract

Nitrate contamination of groundwater has been attributed to application of poultry litter to amend soil organic matter on raspberry farms in British Columbia, Canada. A field study assessed the risk of organic amendments that cause nitrate leaching and nutrient accumulation. The amendments, poultry litter, municipal compost, horse manure, and three types of dairy manure solids, were applied at 25 or 50 Mg dry matter ha–1 to match farm rates before new plantings. Plots were either unseeded or seeded with a grass mix to simulate berry establishment with grass alley crop. Soil was sampled at 0‐ to 15‐, 15‐ to 30‐, and 30‐ to 60‐cm depths 15 times over 14 mo and analyzed for concentrations of NH4+ and NO3–, and at 0 to 15 cm for total C, N, and P at 6 mo after application. Three grass harvests were analyzed for yield and N offtake. Poultry litter supplied more than twice the total mineral N and total P compared to the dairy solids and horse manure, while the compost was intermediate. At 25 Mg ha–1, poultry litter increased concentrations of soil (0–15 cm) NH4+ and NO3– (>150 and >300 mg kg–1, respectively), compared with small short‐term increases by compost (∼70 and 100 mg kg–1, respectively). There was almost no increase from dairy and horse amendments. Grass N offtake reduced soil NO3– concentrations but did not eliminate the risk of leaching from poultry litter. We conclude that dairy solids and horse manure present less risk of nitrate leaching and P loading than poultry litter or municipal compost. Core Ideas Poultry manure and compost amendments greatly increased soil NH4+, NO3– and P. Grass ‘alley’ crop did no sufficiently mitigate soil mineral N from poultry manure. Little risk of nitrate leaching or P loading with dairy solids or horse amendments.

Integrated Crop-Livestock Systems: Lessons From New York, British Columbia, and the South-Eastern United States

“…4). Soil nitrate dissipated in the soil horizon soon after rainfall increased in the autumn [42] . Other amendments did not show elevated soil nitrate concentration above that of the control treatment, indicating they did not pose leaching risk, even at very high application rate (Table 2).…”

“…Clearly, the berry industry needs an alternative source of organic C that does not contain large amounts of labile N. Although the supply of compost is limited and expensive, there is potentially an abundant supply of low-cost organic amendment with low labile N from nearby dairy operations, whereby solids can be removed from slurry by filtration. A study was conducted to test the potential of three types of dairy solids and local horse manure relative to municipal compost and poultry manure in terms of risk to nitrate leaching and soil P accumulation at typical high doses used for amending soil organic matter [42,43] . Dairy solids were either separated with a screw-press (with and without drying) or obtained from bed-pack barns.…”

“…All products were applied at similar rates of C, but poultry manure and compost had greater N and P concentrations and lower C:N than other products (Table 1). Table 1 Chemical properties of soil amendments (dry matter basis) tested for leaching risk [42] Property Soil nitrate (NO3 -) concentration by KCl extraction peaked rapidly in the surface soil layer after application of poultry manure and to a lesser extent after application of compost ( Fig. 4).…”

“…Composting manure was considered uneconomical. [42] . Control is without amendment, PLTY is poultry manure amendment, CPST is municipal compost amendment, HRSE is horse manure amendment, DARY-BM is dairy bed-pack amendment, DARY-Scrp is screw-pressed dairy solids amendment, and DARY-Flt is filtered dairy solids amendment.…”

“…Standard errors for each date are at the top of each panel. Data from Zhang et al [42] . Table 2 Soil amendment application rates of dry matter, total C, total N, NH4 + -N, and total P [42] Amendment property respectively.…”