Fallow rain storage key to a top crop

Fallow rain storage key to a top crop


Cropping
Mid-winter 2019 view of dual-purpose winter cereal providing good winter grazing, largely because of soil moisture conserved over the summer fallow period. Timely weed control is a vital part of efficient soil water capture.

Mid-winter 2019 view of dual-purpose winter cereal providing good winter grazing, largely because of soil moisture conserved over the summer fallow period. Timely weed control is a vital part of efficient soil water capture.

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While we periodically get that odd wet year, far more often than not stored fallow soil moisture is a vital part of a successful winter and summer crop.

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While we periodically get that odd wet year, far more often than not stored fallow soil moisture is a vital part of a successful winter and summer crop.

Extensive research has shown that every millimetre of stored fallow water can be worth up to 30 kilograms a hectare of cereal grain.

Lesser but still significant and at least equally financially significant, gains occur in other crops like canola and pulses.

Across the Australian grain belt, including all of NSW, on average efficient fallow capture and storage of rainfall is, according to good research, worth more than 1.0 tonne a hectare extra grain.

In some years it can be the difference between sowing on time and not sowing, and between, in a dry year, an acceptable crop verses no crop.

Over the last three years, some areas have been so dry during the fallow as well as the crop growing season that no matter how efficient the capture of fallow moisture has been crop production has been impossible.

But the above comments remain applicable to the majority of seasons one is likely to experience and to the vast majority of cropping areas.

Efficient capture of fallow moisture is also equally applicable to dual purpose and grazing only crops.

Stubble cover can dramatically add to fallow water capture efficiency. In the background significant wind erosion is occurring in a paddock with no groundcover.

Stubble cover can dramatically add to fallow water capture efficiency. In the background significant wind erosion is occurring in a paddock with no groundcover.

Commonly, but not universally, mixed farmers are faced with the option of using fallow weeds and self-sown crop for livestock feed.

Coming from a drought or during a drought that can be quite tempting and maybe sometimes even economical.

However, as has happened in these last three drought years, and what happens most years, that fallow grazing comes at the expense of far less winter grazing because of lack of stored fallow moisture.

A way to avoid the need for tempting to use summer fallow feed is to have at least a portion of the property established to summer growing pastures.

These can be lucerne in suitable soils and where it fits the rotation, tropical grasses.

Efficient soil storage of fallow rain has a few important aspects. Unfortunately, some of these need a good season to allow "reset" of the aimed for strategy.

For example, as we have seen this past summer in many areas, stubble retention from previous crops or vegetation retention from a pasture phase moving into cropping, is vital for capturing storm rains.

Commonly storms, even relatively heavy to moderate non storm rains, rainfall mainly washed off paddocks with little or no stubble cover. Wind and water erosion were also commonly high.

Stored sub soil moisture was a vital part of the success of this canola crop last spring.

Stored sub soil moisture was a vital part of the success of this canola crop last spring.

Good stubble retention is also helpful for reducing rate of soil water evaporation and keeping soil waster closer to the soil surface. This can be critical for timely sowing.

Stubble retention is also helpful in reducing and maybe even slowly improving soil carbon levels.

Soil carbon build up is especially feasible when combining zero till stubble retention cropping with perennial pasture in a rotation.

Secondly, is the need to retain captured soil fallow water with prompt killing of fallow weeds.

Weeds use soil water reasonably quickly and as well are more easily killed by spraying them out while they are young and sappy.

Ploughing or scarifying rather than spraying is more long-term destructive of soil carbon and tilth as well as more wasteful of soil water.

Following a fallow rain event, it is worth immediately setting in place a weed control strategy.

For example, we use a contractor and immediately post rain request his services within 10-12 days time.

It takes three to four days for weeds to germinate, and a few more days to develop sufficient leaf area for herbicide capture.

While timing is not always perfect (wind holdups, take your turn and so on) this works pretty well.

Now, coming into spring is deciding when to commence fallowing (if not already commenced) when going from pasture to cropping.

Deep rooted plants like lucerne and some perennial grasses can dry down soil water to well over a couple of metres, therefore leaving the sub soil very dry.

Lower rainfall environments commonly require longer fallows for soil water rebuilding than moderate to higher rainfall areas.

Next week: Upgrading useless light country.

  • Bob Freebairn is an agricultural consultant based at Coonabarabran. Email robert.freebairn@bigpond.com or contact (0428) 752 149.
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