Potential for nitrate-nitrogen leaching in a silvopastoral system compared with open pasture and loblolly pine plantation

Potential for nitrate-nitrogen leaching in a silvopastoral system compared with open pasture and loblolly pine plantation

Summary

At 0.3 m below soil surface, soil solution nitrate-nitrogen was less in the silvopastures, and the open pasture than in the conventionally thinned pine plantation between June 16 and the end of 2004. Prior to fertilization, the open pasture had the highest soil solution nitrate-nitrogen concentrations in samples collected at 0.3 m below the soil surface. The first year results only partially corroborate our hypothesis of reduced nitrate-nitrogen leaching in silvopastures compared with the other investigated production systems.

Objectives/Performance Targets

• Determine differences in soil nitrate-nitrogen leaching among silvopasture, conventionally thinned loblolly pine plantation and open pasture. Determine effects of silvopasture fertilization for forage production on tree nutrition.

Accomplishments/Milestones

Prior to fertilization we found higher soil solution nitrate-nitrogen concentrations at 0.3 m below the soil surface in open pasture than silvopasture and the conventionally thinned pine plantation. On June 16, two and a half months after the first fertilization of warm-season forages and pine plantation, we detected higher soil solution nitrate-nitrogen concentrations at 0.3 m below the soil surface in the conventionally thinned pine plantation than any other production system. These differences in soil solution nitrate-nitrogen concentrations between the pine plantation and the other systems remained significant through the reminder of 2004. On two sampling dates in 2004 (June 16 and December 9), also at 1.2 m below the soil surface, soil solution nitrate-nitrogen concentrations were higher in the conventionally thinned pine plantation than any other investigated production system.

In February 2004, we collected pine foliage samples and analyzed them for five major macronutrients: N, P, K, Ca and Mg. These analyses revealed that prior to fertilization, tree foliar N in double-row silvopastoral system was slightly below the minimum recommended for loblolly pine. Foliar N in heavily thinned silvopasture and conventionally thinned pine plantation were adequate, but close to the minimum recommended. Also the other measured nutrients were at or above the minimums recommended. Only foliar K concentrations were almost twice as high as the minimum recommended for loblolly pine.

Impacts and Contributions/Outcomes

The first year results only partially corroborated our hypothesis that silvopastures reduce soil nitrate-nitrogen leaching compared with conventionally thinned pine plantation. We were unable to demonstrate the same benefit of reduced nitrate-nitrogen leaching in silvopastures compared with open pastures.

Borderline tree foliar macronutrient concentrations (especially N) we measured in 2004, indicated a need for fertilizer additions to boost tree nutritional status above that considered minimum for loblolly pine.

Collaborators: