Extra stored soil moisture vital for yield gains

Although we have recently had a run of wet years every milimetre of stored fallow soil moisture, or storing of soil moisture carryover from the past crop, can be vital.

Every millimetre used efficiently by the crop during the growing season is also vital.

Even for most higher rainfall areas, lack of moisture, soil and in-crop rain derived, at vital periods, like head emergence and grain fill, can commonly be critical.

Extra stored soil moisture can be a cost in a very wet year, like 2022, as it can contribute to waterlogging.

But more commonly, even in a wet year, it contributes to the ability to sow earlier, with appropriate varieties, which generally helps cope with wet conditions.

I have recently been on an extended trip through much of the South Australian wheat belt where many cropping areas have annual average rainfall of around 330 millimetre to 360mm. These are pretty dry environments in the eyes of many NSW farmers. Clearly efficient retention of carryover soil moisture, important in some years like after 2022, plus capture of any summer fallow moisture is critical.

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One of the most summer/early autumn SA crop scenes, not unlike much of NSW, is stubbles with no growing weeds and retention of good levels of ground cover (stubble residues).

Stubble retention is important for capturing fallow rains and protecting soil from wind and rain erosion. It is especially important to retain as much stubble as possible when following cereals with pulses.

Some of its carryover post pulse harvest will be especially valuable as pulses often leave little crop residue.

One aspect of high risk of low stubble loads retained for the fallow period is dual purpose crops or winter only fodder crops grazed completely out.

This commonly occurs in years with dry springs and when feed is scarce. In ours and many other districts this scenario was common in years like 2017, 2018, and 2019. Wind erosion over the summer was especially common and bad on many of these paddocks.

First weed control as soon as possible after harvest, to control fallow weeds and growth of germinated shelled and pinched grain, is vital because of their often rapid use of carryover soil moisture. Control of herbicide resistant weeds is also part of this challenge.

For example, double knock, where a herbicide application such as glyphosate is followed a week later by products like gramoxone is a common strategy to control weeds like fleabane.

While not always the case, aiming to sow winter crops in the early part of their sowing window, including choosing slower maturing varieties to increase sowing time options, is an important practice of better water use.

As a general rule, earlier sown crops root deeper than what is commonly considered normal sowing time, and especially deeper compared to late sown crops. Deeper roots commonly mean ability to capture more soil moisture and nutrients.

Soil fertility is also a key aspect for efficient crop water use. For example, crops low in phosphorus with insufficient appropriate fertiliser applied, or no fertiliser used, commonly have shallower roots and poorer ability to use soil water.

At the other extreme are soils too high in nitrogen, for a dry year, which can be more prone to haying off. They commonly result in little yield penalty.

Research undertaken by Grain Orana Alliance (central west NSW) shows high soil nitrogen in canola crops results in next to no yield penalty with unused nitrogen carrying over for the next crop.

As the research highlighted in earlier issues, crop rotations that help control crop diseases, build soil nitrogen (legume component), and cope with issues like nematodes (three major crop damaging species), are also important for maximising water use efficiency.

Maximising water use efficiency builds probability of highest possible yield.

A final point.

Every extra milimetre of fallow stored soil moisture, especially in a season with a dry spring, can be worth an extra 30kg/ha cereal grain yield.

Next week. Check pastures for possible upgrading