Pastures represent an important component of many rotations, and normally take 1–5 years to break up extended periods of cropping. Incorporating pastures can help restore soil fertility (organic matter and soil nitrogen) that may have declined due to frequent cropping, and in turn improve the competitive ability of crops.
Pastures provide a valuable opportunity to manage weed problems using strategies not able to be used in cropping situations, such as grazing or mechanical manipulation.
Dense stands of well-adapted pasture species compete against weeds, reducing weed numbers and weed seed-set. Where desirable species dominate pasture (greater than
80%), weeds have less opportunity to establish. It follows then that weeds may be best controlled by pasture plants themselves which compete for light, moisture, space and nutrients. Strong competition against weeds is encouraged by:
High plant densities of desirable plants
Use of fertilisers to provide the best possible soil conditions for vigorous growth of legumes and desirable grasses
Strategic grazing that incorporates ‘grazing-free’ periods – this enables desirable species to increase in size, favours root development and competitive ability, and allows for seed-set and subsequent seedling recruitment (see Grazing).
Competitive pastures greatly improve the effectiveness of other procedures used to manage weeds in the pasture phase. The best scenario for weed competition is high densities of desirable annual pasture plants germinating at the same time as weeds. Fertiliser (and lime where required) may be applied to increase the vigour of desirable species.
Whole-farm benefits
Improved feed quality and quantity
Higher stocking rates with better pastures
Forage preservation (hay or silage) due to higher production
Less supplementary feeding.
Select species and varieties to suit your conditions. Select the most appropriate species and varieties according to soil type, climatic conditions and farming system (eg permanent pasture or rotation with grain crops). Desirable species need to be managed to ensure the development of an adequate seedbank because large seedbanks are required to drive high density pasture regeneration.
Once a pasture gets below a threshold density for a desirable pasture species it should be manipulated to build up seed reserves, or reseeded with improved cultivars. Pasture re-establishment (re-sowing desirable species) will improve pastures that are severely degraded. Optimise this operation by implementing weed control prior to sowing (eg cultivation).
In a pasture–crop rotation, if the pasture density declines to a level where weeds invade (eg due to drought, poor establishment or overgrazing), it may be necessary to shorten the pasture phase using mechanical procedures and move into the cropping phase early.
Mixtures of pasture species will add diversity to the pasture base and improve the capacity for desirable plants to fill gaps created by disturbance (eg drought, cropping). Species mixtures can improve the resilience of pastures by providing a range of seed characteristics (and/or pest and disease tolerances). Mixtures should include perennial and annual grasses and legumes.
Whole-Farm Considerations
Ensure that appropriate grazing management (deferred and rotational grazing) is used
Devise strategies and paddock plans for pasture re-establishment
Ensure that pasture legumes are inoculated with their correct rhizobium.