Assessing the impact of land management practices on bacterial community structure in New Zealand soils

Background/Question/Methods

Agriculture efficiency is a key component of New Zealand’s economy. These systems rely on healthy soils and their sustainability requires understanding the long-term impacts of agriculture on soils, including their microbial communities. Using ARISA, a molecular fingerprinting technique, we compared soil bacterial community structure in soils after 18 years of mowing and nitrogen fertilizer treatments. Our experimental design consisted of eight treatments replicated four times each in a randomized block design. Treatments were combinations of (i) three levels of mowing, never mown (Mo), mown regularly (Mr), or mown irregularly (Mi); (ii) clippings left or removed from the irregularly mown plots, (iii) and no fertilization (N₀) or 50 kg urea-N ha^-1 yr^-1 (N₁).

Results/Conclusions

Multivariate analysis revealed significant variation in bacterial community structure related to the mowing and clippings treatments. Whether clippings were left or removed accounted for nearly twice as much variability as frequency of mowing. Application of nitrogen did not significantly impact soil bacterial communities in this study and no significant interactions were detected among treatments. The amount of variability differed within treatments, with least variability observed in bacterial community data observed for plots in which no mowing occurred (MVDisp: Mo = 0.67, Mi = 1.1, Mr = 1.1). Regardless of the level of mowing or clippings, there was more variability in bacterial community data from plots to which nitrogen had been applied (MVDisp: N₁ = 1.14, N₀ = 0.87). Changes in soil chemistry described 33% of the variation in the bacterial community structure with Olsen P and NH₄ explaining 10% and 7%, respectively. Our results suggest that removal of plant biomass has a greater long-term impact on soil bacterial community structure than application of nitrogen fertilizers. This may be related to changes in available inorganic P levels, which were significantly lower plots with clippings removed, while total nitrogen, total carbon, and inorganic pools nitrogen did not differ between treatments.