I am a soil ecologist and also am associated with the Global Soil Biodiversity Initiative. In New Zealand, we have conducted studies of links between pastoral agriculture (sheep and dairy), soil biodiversity, and soil ecosystem services such as nutrient and water supply. Soil invertebrates make important contributions to nutrient supply and water movement in the soil, as they feed on the soil organic matter and burrow through the soil. Soils and soil fauna of New Zealand pastures are coming under increasing pressures, as farmers increase fertiliser application and stocking rates to increase productivity. We have found that soil invertebrates with similar characteristics were consistent in their response to pasture management practices, particularly to changes in soil porosity due to livestock treading. We also found that the invertebrate contributions to nutrient supply in pastures remained important even in fertilised soils where nutrients were not limiting. Below are some examples of these studies.
1) Biodiversity is an important contributor to food security and improved nutrition. Could you share examples/activities in your work where
biodiversity is contributing in achieving food security and improved nutrition?
Soil invertebrates contribute to a wide range of soil services vital in agricultural soils, such as nutrient recycling through feeding, excretion, burrowing, casting, and litter incorporation. We investigated the influence of invertebrates on N cycling in a low-N and high-N environment in constructed ryegrass–white clover soil mesocosms (Schon et al. 2011a). We found that invertebrates improved N availability and N uptake by plants. At high bulk density and low N, the N made available by invertebrates resulted in higher plant growth, without any increases in N losses to the environment. The influence of invertebrates was dependent on bulk density, suggesting that invertebrates in compacted soils improved soil structure and N availability. In the high bulk density mesocosms, soil invertebrates stimulated the mineralisation of organic N and the uptake of N by plants at both low and high N fertility, but their contribution to N mineralisation was also more likely to be lost via leachate and gaseous emissions. This study highlights the importance of invertebrates in N supply and nutrient cycling in compacted and high fertility soils.
We also sampled invertebrates (macrofauna, mesofauna and microfauna) from four paired commercial organically and conventionally managed dairy farms on different soil types in New Zealand (Schon et al. 2012), and calculated rates of invertebrate-mediated N mineralisation. The organic dairy operations used fewer nutrient inputs and had lower cow stocking rates than conventional farms, which meant lower calculated pasture production and less available plant litter entering the soil food web. Despite lower plant litter inputs, earthworm biomass was higher under organic management. Nitrogen mineralisation was higher in organic systems, with earthworms contributing the most (24–98 kg N/ha/year). As the cow stocking rate increased under conventional management, physical loading on the soil increased, and the ability of the soil to provide ecosystem services (i.e. N mineralisation and litter decomposition) became compromised. We concluded that organic management on four soil types stimulated soil biological activity and provision of ecosystem services such as N mineralisation. The higher stock treading pressure under conventional management reduced soil invertebrate activity and their influence on N mineralisation, which was not compensated by higher food supply.
2) All agricultural sectors (crop and livestock, forestry, fisheries and aquaculture) rely on biodiversity and on the ecosystem functions and services, they underpin. At the same time, these sectors may affect biodiversity through various direct and indirect drivers. Could you share examples/activities in your work
where a (sustainable) production system played a key role for the conservation of the biodiversity surrounding it? Please provide detailed information you may have or know of and identify the agricultural sector.
In another study (Schon et al. 2008), the low-intensity pasture system with higher soil C:N ratio and lower sheep stocking rate supported lower earthworm numbers, but higher density and diversity of soil mesofauna and oribatid mites, which are considered indicators of soil disturbance. By comparison, the intensive pasture system had higher densities of introduced earthworms, but the native species Octochaetus multiporus had declined.
where a(n) (unsustainable) production system played a key role for the degradation of the biodiversity surrounding it? Please provide detailed information you may have or know of and identify the agricultural sector.
Earthworms play an important role as primary decomposers in agricultural systems; they incorporate plant litter into the soil and mix soil layers. In Schon et al (2011b) we explored the response of earthworms to increasing fertiliser inputs, pasture production and livestock numbers in 21 sheep- and dairy-grazed pastures in a variety of soils and management regimes in New Zealand. Native earthworms were only found in some low-fertility pastures. Introduced earthworms (when present) dominated pasture soils. Anecic earthworms showed a positive response to the increasing pasture intensification (higher potential dry matter inputs and livestock loading), while epigeic earthworms declined. We suggest that due to their lower susceptibility to livestock treading pressure, anecic species may be a suitable substitute for incorporation of surface litter into the soil in pasture systems where livestock treading limits epigeic earthworm populations.
References:
Schon, N.L., A.D. Mackay, M.A. Minor, G. A. Yeates, and M.J. Hedley. 2008. Soil fauna in grazed New Zealand hill country pastures at two management intensities. Applied Soil Ecology 40(2):218-228.
Schon, N.L., A.D. Mackay, M.J. Hedley, and M.A. Minor. 2011a. Influence of soil faunal communities on nitrogen dynamics in legume-based mesocosms. Soil. Res. (New York) 2:1–12.
Schon, N.L., A.D. Mackay, and M.A. Minor. 2011b. Soil fauna in sheep-grazed hill pastures under organic and conventional livestock management and in an adjacent ungrazed pasture. Pedobiologia 54(3):161-168.
Schon, N.L., A.D. Mackay, M.J. Hedley, and M.A. Minor. 2012. The soil invertebrate contribution to nitrogen mineralisation differs between soils under organic and conventional dairy management. Biology and Fertility of Soils 48(1):31-42.
Dr. Maria Minor