So far there's been two studies on it and neither give the ringing endorsement that NSF proponents claim, firstly there was the CSIRO expert panel report, which, while it does have some good things to say about the concept:
(note: at the time the report was written the practice was know as "The Natural Farming Sequence" it was later changed to Natural Sequence Farming")
The panel believes that NFS is a successful and sustainable farming system for the current enterprise at Tarwyn Park, where it has led to substantial agronomic and environmental improvements on the property.
Central to the implementation of NFS at Tarwyn Park is the manipulation of the hydrologic regime, that has increased aquifer water storage providing effective sub-surface pasture irrigation. This has substantially increased pasture productivity, and avoids the evaporative water losses that occur with surface irrigation.(page 1)
isn't exactly unequivocal in it's support. Let's see what else they have to say:
The panel made its assessment on the basis of professional interpretations of verbal and written descriptions of NFS, and an inspection of Tarwyn Park on 23 May 2002. The lack of quantitative data and the limited resources for the study precluded quantitative assessment.
The panel only assessed NFS as implemented as Tarwyn Park, and comments on the applicability of the particular practices used at Tarwyn Park in other landscape settings. The practices required for the application of NFS in other settings have not been demonstrated or documented, and so cannot be assessed.
NFS has done little to address issues of native biodiversity and landscape ecology at Tarwyn Park. There is low species diversity in the riparian and stream plant communities, and a near absence of remnant native trees on the farmed hillslopes. These plant communities are therefore expected to provide little habitat for birds and other terrestrial fauna.
The suite of practices implemented for NFS at Tarwyn Park are only appropriate for local groundwater systems (recharge and discharge areas within a few kilometres of each other) dominated by fresh groundwater in porous floodplain sediments.
As the panel only visited Tarwyn Park, the assessment of NFS is limited to its implementation at Tarwyn Park. In the panel’s opinion, most of the reports of prior scientific studies are of poor quality. Because of this, and the resource restraints placed on the panel, the assessments are qualitative, based on professional interpretation of observations made at Tarwyn Park. Furthermore, it should be noted that very little data to describe conditions at Tarwyn Park before the implementation of NFS exist, and the panel did not have the opportunity to view comparable properties in the region–with or without NFS.
There is little data to describe the current water, salt, and nutrient balances of Tarwyn Park, and no data to describe levels of productivity. Furthermore, there are no data to describe conditions at Tarwyn Park before the implementation of NFS. Our assessments of the changes that have occurred at Tarwyn Park are therefore qualitative, based on observation and our interpretation of the verbal and written descriptions of changes due to NFS with which we were provided. These changes are summarised below in terms of material balances (water, salt, sediment, and nutrients), productivity, landscape biodiversity, and farm economics.
While the implementation of NFS at Tarwyn Park has increased the functional diversity of plant species within the pasture, biodiversity has not been increased on the property. The number of native plant species on the property is low, with all plant communities – floodplains, hillslopes, stream channel, and riparian zone– characterised by moderate to low species diversity. The pasture communities are the most diverse, although native species diversity and abundance in the pasture is very low. Because of the dominance of broad-leaf annuals in the pasture mix at certain times, it is likely that there is a significant export of the seeds of these species (for example, Paterson’s curse (Echium plantagineum) and thistles (Centaurea spp.)) to downstream properties. To downstream landholders pursuing more conventional agriculture, this is undesirable.
The riparian vegetation is dominated by a canopy of exotic willows (Salix spp.) and native river oak (Casuarina cunninghamania), very little understorey, and a mix of native and exotic grasses as ground cover. There is an absence of trees on the hillslopes adjacent to the floodplain, although native eucalypts dominate the forest up the steeper slopes towards the escarpments. The lack of trees implies poor habitat on the property for birds and other terrestrial fauna.
It is the opinion of the panel that suite of Tarwyn Park practices can only work for local groundwater flow systems where the water balance is dominated by fresh groundwater held in highly transmissive floodplain sediments. Local groundwater systems are those which have recharge and discharge areas within a few kilometres of each other……..The sediments must also be sufficiently deep to allow substantial subsurface water storage. The valley and floodplain topography must be such that it is possible to move the majority of the stream flow out onto the floodplain. The salinity of the groundwater in the floodplain sediments must also be low. Furthermore, the salt sources must be discrete such that those areas of highest salt mass can be effectively quarantined from the water cycle that is operating on the floodplains.
In addition to the hydrogeologic setting, the suite of Tarwyn Park management measures are only suitable in fluvially confined floodplain systems that prior to disturbance were characterised by a “chain of ponds” stream system. In systems that previously had incised channels, stream energies would be sufficiently high to preclude the stability and effectiveness of low-cost grade control structures.
Tarwyn Park benefits from the increased volumes of water and loads of sediment and nutrients, and provides an environmental service by acting as at least a medium-term store for a proportion of the salt load it receives from upstream. It is the panel’s view that implementation of NFS higher up the Bylong River catchment would reduce these inputs to Tarwyn Park. With reduced flow and nutrient inputs from upstream, sustainable productivity on Tarwyn Park would be lower. In addition, with less incoming water, the ability to store salt would most probably be reduced. Thus if the properties upstream implemented NFS, there would be a negative impact on Tarwyn Park. Similarly, implementing NFS on Tarwyn Park has reduced sediment and nutrient loads downstream of the property. These changes are believed to be towards the pre-European condition, nonetheless from a downstream agricultural perspective they could be viewed as detrimental.
Not exactly a ringing endorsement is it? In short it does work on Tarwin Park however applicability to other landscapes is limited and the property shows low biodiversity.
Since this report there has been research undertaken on Barramul Stud by a range of researchers which makes for interesting reading, but that's for next time.