On-farm environmental assessment of corn silage production systems receiving liquid dairy manure

Abstract

Increased corn (Zea mays L.) silage and manure production accompanying the proliferation of large dairies has prompted concern regarding their environmental impacts. The objectives of this on-farm, field-scale study were (1) to quantify environmental impacts, e.g., soil chemical properties and offsite nutrient transport, of corn silage production with dairy manure application on artificially drained soils and (2) to assess the environmental benefits of and agronomic constraints on the adoption of winter rye (Secale cereale L.) cover cropping by a large dairy in west central Minnesota. From 2007 to 2009, corn for silage was grown on two adjacent 65 ha (160 ac) fields, with rye planted after corn on one field in 2007. Liquid manure was fall applied annually at average total nitrogen (N) and phosphorus (P) rates of 410 and 98 kg ha⁻¹ (365 and 87 lb ac⁻¹), respectively. Soil nitrate nitrogen (NO₃-N) and Olsen P accumulation did not occur with the studied cropping systems, but average annual NO₃-N and dissolved reactive P (DRP) subsurface drainage loads were 52 and 0.8 kg ha⁻¹ y⁻¹ (46 and 0.7 lb ac⁻¹ yr⁻¹), respectively. Soil organic carbon (C) concentration was maintained on the field without rye and increased 15% to a depth of 15 cm (6 in) on the field with rye, but C additions with manure likely contributed to the increase. Rye reduced spring soil NO₃-N by 46% and increased ground cover an average of fourfold compared with winter fallow. Subsurface drainage NO₃-N concentration was reduced from 53 mg L⁻¹ (53 ppm) without rye to 39 mg L⁻¹ (39 ppm) with rye, but rye had no impact on DRP concentration. Rye aboveground dry matter yield was 2 Mg ha⁻¹ (0.9 tn ac⁻¹). Corn dry matter yield was 16%, or 2.7 Mg ha⁻¹ (1.2 tn ac⁻¹), lower after rye than after winter fallow. This reduced yield and the persistence of high NO₃-N and DRP concentrations in subsurface drainage with rye indicate alternative conservation practices are warranted at this site. In general, cover cropping with winter rye provided environmental benefits over corn silage alone but also increased economic risks.