A review of tillage research (including no-till) shows enormous advantages of no-till or zero till compared to the once traditional multiple tillage per crop farming system. But research has also highlighted problems associated with zero till can occur and these have to be addressed as part of high yield cropping systems.
Soil scientist Dr David Freebairn University of Southern Queensland, who undertook the review for GRDC, examined results from all known and adequately documented tillage research studies undertaken over the last 40 years.
Strongest finding from many of the studies was that stubble cover and reduced tillage improve water storage, with very few exceptions.
For example starting soil water over three years at three sites in northern NSW was 30mm higher in no till with stubble compared to tilled and stubble burnt. Given the “safe” nature of stored soil water, Dr Freebairn notes the extra 30mm can be equivalent to 100mm of extra in-season rain. That’s often the difference between a good crop and one running out of vital moisture.
Improved water capture leads to improved yields, especially in drier years, but negative responses to stubble retention are commonly observed in southern regions the paper notes.
Lower soil nitrate and lower protein commonly occur, especially in wheat following wheat. Higher root and leaf disease and nematode levels were observed in stubble retained and reduced tillage plots.
Researchers and farmers have overcome these negative consequences in many cases by choosing upgraded rotations that nullify these adverse factors.
Researchers John Holland and Warwick Felton (NSW DPI Tamworth) for example found that when sorghum was sown into no-till cereal stubble, yields were 0.7-1.8 t/ha greater compared with cultivated stubble retained fallows.
Pulses are not adversely impacted by lower soil nitrate levels and provided nematodes are not an issue can yield higher sown into stubble.
Chickpea and faba beans commonly for example perform better sown into cereal stubble with yields often 10 - 20 percent higher. Also legumes fix more nitrogen, and pulses on wide rows (64 cm) sown into retained stubble are easier to sow and increase herbicide options.
Catastrophic erosion in cultivation farming systems, after typically sharp summer storms, highlighted the need for a better system to keep soil in place so it can store water for another day the report notes.
Some experiments recorded soil losses of 100 t/ha following summer storms in cultivated farming compared to almost no loss in a zero till stubble retained system.
GRDC funded research indicates that in most situations occasional tillage to deal with issues associated with no tillage does not have any long term negative impacts and benefits outweigh negatives.
For example occasional tillage as a part of weed control strategy, especially for troublesome herbicide resistant weeds (like fleabane, feather top Rhodes grass, windmill grass), results in improved weed control and no negative effects on yield (except in some cases loss of some critical soil stored moisture).
Optimizing compaction issues (controlled traffic) is another positive of zero till.
Zero till or no-till with stubble retention also generally results in improved water quality running off a paddock should excess fallow rainfall occur.
Full details of this report will appear in proceeding of the recent rounds of GRDC update seminars via the GRDC web site.
Next week: Budgeting crop nitrogen needs.
- Bob Freebairn is an agricultural consultant based at Coonabarabran. Email email@example.com or contact (0428) 752 149.