Soil nutrition, weed control and sowing or seeding are important considerations when establishing forage crops.
Good soil nutrient levels are important to ensure vigorous forage crop establishment. While the fertiliser history of a paddock can provide an insight into the likely levels of key nutrients, the only way to be sure of the soil nutrient and mineral profile along with pH is to undertake a soil test. A soil test will reveal attributes of soil fertility, which may influence forage crop selection and determine fertiliser requirements.
These aspects are important as nutrient deficiencies or soil properties such as low pH may affect crop establishment and lead to weed invasion.
While understanding the fertiliser and cropping history of a paddock provides a useful indication of the likely status of various soil nutrients, the only way to be sure of the soil nutrient profile is to undertake a soil test.
Soil tests vary in complexity depending on producer requirements, but usually assess:
- available phosphorus
- available sulphur
- nitrogen levels
- exchangeable cations (Ca, Mn, Na and K).
Soil tests can be organised through local rural merchandise suppliers and rural consultants or a producer can order a soil test kit and take their own samples to send away for laboratory analysis.
The results from soil testing must be considered within the context of the local farm environment and it is advisable to have the results interpreted by a FertCare accredited advisor.
Good weed control prior to planting a forage crop minimises competition for nutrients and moisture and helps the crop become established. If weeds are not controlled prior to planting, crop production can be reduced, and in extreme cases, fail completely.
Weeds can sometimes be controlled after sowing, however, the options are limited and selective herbicides are generally expensive. It is always best to reduce the weed population and residual seeds bank in the soil through a planned control program prior to sowing.
Identifying target weeds
Different weeds have different commercial impacts. It is important to focus on those weeds that pose the greatest commercial threat to the business and the objectives of the enterprise. For example, weeds that are toxic to livestock or will potentially outcompete the forage crop should be the target of a weed control program.
The first step is to identify the kinds of weeds in the paddock where the forage crop is to be sown and to categorise these as either grasses or broadleaf weeds. Woody weeds may also pose a problem and may require specific control methods.
Weed control can be achieved with herbicides, strategic grazing or a combination of both.
Herbicides specifically targeting broadleaf weeds or grasses may be used or a knock down herbicide employed for the general control of broadleaf weeds and grasses. A range of additives that improve the effectiveness or aid the uptake of herbicides are available. Specialist advice from an agronomist or consultant should be sought when deciding upon the best control option for a particular situation.
Plants tend to have varying sensitivity to herbicides depending on their growth phase and this can be critical when planning control. Producers should react quickly following a rain event or cultivation to ensure that time critical control opportunities are not missed.
Strategic grazing can also be used as an effective weed control method. Spray-grazing is one useful technique, however, producers must always be careful to abide by grazing withholding periods (WHP) and include on the LPA NVD/Waybill if livestock are being sold. Export grazing intervals (EGI) must also be considering if spray-grazing.
Goats are particularly proficient when it comes to weed control, particularly for various hard-to-kill woody weeds.
Having selected a suitable forage cop, reduced weeds to an acceptable level and determined the fertiliser requirement, it is time to consider sowing.
Conventional, minimum till and no-till sowing can be used depending on the circumstance and personal preference. Soil to seed contact is the most critical aspect in achieving germination and this is often best achieved using conventional sowing techniques.
Assuming sufficient moisture at sowing time, achieving good soil-to-seed contact and the right sowing depth for the particular crop are the most important factors influencing germination and establishment. Broadcasting seed can be used, however, this method often results in poor soil-to-seed contact and germination, and is rarely used.
Some crops are better suited to particular sowing methods. For example, better establishment is generally achieved with brassicas when they are sown using conventional methods. While particular sowing methods are better suited to particular climates and soil types. It is advisable to seek local advice before deciding on the best sowing or seeding method for a particular situation.
Conventional sowing versus minimum and no-till sowing
|Conventional sowing (through cultivation and the use of harrows or press wheels)||
Minimum and no-till sowing