Daroub, S., B.G. Ellis, and G.P. Robertson
Presented at the All Scientist Meeting (1999-07-20 to 1999-07-21 )
We evaluated the effect of conventional, no-tillage, and low-input organic row crop agriculture and perennial farming systems on soil phosphorus (P). We also compared soil P under conventional agriculture to an adjacent forest site in south west Michigan, USA. Sequential fractionation analysis of soil inorganic and organic P fractions (Hedley et al. 1982) was performed on treatments 1 through 8 of the KBS LTER plots and the deciduous forest. Long-term conventional row crop agriculture resulted in the reduction of NaOH-extractable organic P by 79% compared to adjacent forested sites (Table 1). The calcium phosphate pool and the residual P fraction on the other hand increased under conventional agriculture compared to the forest site, probably due to fertilizer inputs. The adoption of no-tillage and low-input organic based systems for seven years did not significantly increase organic P in any of the fractions extracted from the annual cropping systems. However, organic P extracted by NaOH increased to 22.1% after the adoption of continuous alfalfa for the same period compared to 11.4% extracted in the conventional tillage treatment (Fig. 1). This increase was attributed to the turnover of the extensive alfalfa root system. The residual P content decreased under alfalfa cropping which suggests that alfalfa can take up P from this stable pool. Alfalfa may be tapping into this stable pool not just for P, but perhaps for Ca released through apatite dissolution. We conclude that continuous alfalfa can restore soils to their native P fertility levels by taking up P from the stable residual fraction and transforming it into moderately labile organic P through root death.
Back to meeting | Show |