Inter-row treatments trialled in nursery
26 August, 2009
Viticulture nurseries typically maintain bare soil between vine rows using herbicide during spring and summer months. In line with sustainable practice policy, efforts are being made to reduce dependence on synthetic herbicides as a means to control weeds in the nursery. Non-herbicide inter-row treatments were trialled in the 2008/09 season to assess the suitability as an alternative to the current practice being undertaken.
Maintaining bare soil between crop rows of any kind has many advantages; crops are not subject to competition for water and nutrients, the risk of disease transmission is minimised and air movement is promoted within crop rows. The negative effects of bare inter-row soil can include poor water penetration, degradation of soil structure and organic matter, and reduced activity of beneficial soil organisms.
Methods
Treatments were applied to 90 meter rows within the trial block, with three repeats of each treatment applied in alternating sequence. Single vine rows were planted into raised black polythene mulch as per normal practice. The inter-row swards of all treatments were controlled twice during the summer using either mowers or weed-slashers. The more promising treatments were selected for comparison with the herbicide control when testing was carried out. A foliar fertiliser (Nitrosol) was applied to all treatments excluding the herbicide control on the 23rd February. Herbicide control vines showed no obvious nitrogen deficiency symptoms.
Treatment 1 Rye grass (25Kg/ha) with red white clover (4Kg/ha combined)
Treatment 2 Fescue grass (25Kg/ha) with red and white clover (4Kg/ha combined)
Treatment 3
Treatment 4 Straw mulch (5-10cm deep)
Control 1 Nil herbicide – weeds allowed to establish
Control 2 Weed control using herbicide
Measurable Outcomes
Leaf blade samples were collected 25th February from the control treatment and the
Inter-row soil samples were collected from the Straw treatment,
Graph 1. Comparison of inter-row soil from selected treatments June 2009
Vine growth during the season was significantly different between treatments. Vine growth of the Straw Mulch treatment was significantly greater than all other treatments including the controls. Partial yellowing of lower leaves and some leaf thickening were noted on the Straw Mulch vines but signs of nitrogen deficiency were less severe than noted on other treatments with inter-row swards. Vine canopies within treatments 1, 2, 3 and Control 1 were less dense and smaller than the herbicide Control and Straw Mulch treatment from January onward. Vines were wrenched after leaf drop and 100 vines samples collected from each treatment. Vine samples were pruned to two buds and roots were trimmed to 15cm before weighing each vine to determine the average trimmed vine mass.
Graph 2. Comparison of trimmed vine mass from selected treatments
The relative starch content of the vines was measured by viewing thin cross sections of vine stem under a microscope after applying iodine-potassium iodide stain. Ten vine samples were collected from each treatment and three sections were cut from each vine sample; one near the base, one below graft union and one above the graft union. Each sample was graded according to the percentage of starch accumulation within the stem sections to give a relative comparison between treatments. Results showed no significant difference in starch content between the Herbicide Control and Straw Mulch treatment.
Graph 3. Starch content of combined stem section samples
Discussion and conclusions
Inter-row sward species in treatments 1, 2, 3 and 4 all established and significantly reduced weed numbers. Rye grass established more quickly than Fescue grass and suppressed weeds more effectively combined with the clovers. A mower could be used to cut swards of all these treatments but a slasher was required to control weed growth within Control 1 where herbicide was not used.
Managed inter-row swards did compete with vines, limiting canopy growth and causing nitrogen deficiency. Starch testing suggests that vines grown with managed inter-row swards are less able to store carbohydrates than the control treatment and the mulch treatment. This is probably the result of increased vine stress when competition from the inter-row sward increases during summer, as indicated by the leaf blade tests and reduced canopy development.
Soil test results in June suggest that both the mulch treatment and the inter-row sward treatments had improved soil nitrogen levels compared with the herbicide control, despite nitrogen deficiency symptoms observed during the summer. It is possible that soil nitrogen was depleted by inter-row swards growing during summer but swards had provided additional nitrogen to soils by June when growth was slow. The sward may have helped retain nitrogen in the form of organic matter and active micro organisms.
The results suggest that straw mulch or similar organic mulch can produce stronger one-year old vines with similar carbohydrate levels to vines grown conventionally with herbicide. Subsequent incorporation and break-down of organic mulch would further increase soil organic matter over time. Whilst inter-row swards were not beneficial during this trial, increased soil nitrogen provided by the inter-row sward in June, highlights the potential benefit of well managed swards where competition can be controlled and the inclusion of cover crops during land rotations.
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