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OCT- Farm Monitoring |
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 Tasmanian Organic Farm Monitoring Project. This three year project commenced in 1995 and was sponsored by the Tasmanian Organic-Dynamic Producers co-operative (TOP) with funding from the Natural Heritage Trust. Background The organic grower members of the co-operative had often expressed their desire for more technical support and mentoring of new growers. However, as the co-operative depended primarily on voluntary input, their members were not able to sustain the effort required. In addition, there was a concern that organic farmers were not paying sufficient attention to good farm management. Funds were therefore sought from the NHT under the banner Organic Farming: Preventative Landcare Along with the provision of technical support, the project sought to collect benchmark data for the industry. An additional aim of the project was to expose professional agriculture to organic farming systems. A total of 61 properties were contacted during the project. The median size of the properties was 1.6ha covering 14 different agricultural enterprises and the average duration under organic production was 8 years. Soil nutrient tests Gardens were assessed by sampling garden beds across the whole garden operation. Pasture samples were taken from a representative paddock within the farm. Approximately 20 cores were taken per sample to a depth of 15cm.
The data for available phosphorus and potassium in Table 1 are quite high, especially for the grazing properties when most have not used fertilisers of any kind (closed input systems). The range, especially for available nutrients, was very large. The lowest readings suggest that these paddocks/garden beds were not sustainable under the present management regime. The higher levels (especially for phosphorus under intensive market garden management) indicate excessive use of compost/manures. Inputs One of the prime philosophies of the organic movement is to limit the dependence on farm inputs, particularly fertilisers (‘closed input systems’). The higher levels of farm inputs observed (intensive enterprises) amounted to annual applications of 18kg/m2 , which was primarily applied as compost. At the other extreme was one grazing enterprise (Ray and Elma Mason’s dairy farm, West Pine) that had operated for 30 years without any inputs. Records of tests from one paddock (9 samples of 15-20 cores each) over 21 years were taken by the agricultural department and are shown in figure 1 below. Fig.1: Available Phosphorus
Prior to going organic in 1968, the farm used typical application rates of superphosphate for potato production. Since the predominant soil is a red basaltic clay-loam, much of this phosphorus would have been ‘fixed’ by the clay particles, and subsequently released over time. The graph indicates a significant drop in available phosphorus over the first 20 years of operating as a closed input system. The last reading (in 1997) suggests that levels may be increasing, however they are not significantly different from the 1991 levels.
The krasnozem soils were on the north west coast with rainfall of over 1000mm/year. Available or total phosphorus? Many organic farmers are wary of soil tests based on available nutrients only. They consider that total nutrient tests are more appropriate for organic farming systems as they are more likely to maintain higher, and more diverse, populations of soil micro-organisms that are more able to mobilise nutrients from the insoluble, total, pool of nutrients. For this reason the project tested for the two pools of phosphorus on 12 properties, as outlined in table 3.
Botanical composition Organically managed pasture (since the use of herbicides is not allowed) inevitably vary from the non-organic perception of ‘good’ grazing swards. The composition of pasture was assessed using the ‘dot-point’ method. A summary of the results over 21 properties is given in table 4 with a comparison with typical ‘non-organic’ dairy pasture receiving approximately 500kg fertiliser/ha/year.
The ‘improved’ grasses included perennial ryegrass and cocksfoot. The ‘unimproved’ grasses included yorkshire fog, browntop, onion twitch and sweet vernal. From this data it is readily seen that organic pasture are more ‘weedy’ and are more inclined to contain a higher proportion of ‘unimproved’ pasture species. This would be due to both the prohibition of the use of herbicides to control weeds, and the lower overall soluble ‘fertility’ of the soil that would favour the newer cultivars of pasture species bred specifically for the use of such high rates of soluble inputs. Productivity Data was collected for levels of productivity as shown in table 5.
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© copyright The Organic Coalition of Tasmania, 2005- 2008
