NITROGEN soil level is commonly the factor most likely to impact on yield of cereal and canola crops. Adding extra nitrogen commonly is the largest cropping cost and its application depends on soil nitrogen status and equally important on soil water levels.
A critical aspect is to have a good understanding on what soil water level is at a given crop stage. Soil tests might have indicated a likely need for 40 to 100 kilograms per hectare nitrogen (sometimes even more) but for that investment to pay off requires sufficient moisture.
While many areas have received good to excellent rains over the fallow period, much of it came in storm events and soil capture ranged dramatically. Note previous article that showed capture of 237 millimetres of rain that fell between January 9 and February 20 in Tamworth DPI Dr Sean Murphy's pasture trials ranged from very poor where there was little ground cover (40mm) to very good with high, even with ground hugging groundcover (130mm). In cropping terms that difference commonly equates to 2.0t/ha grain or more. Assessing soil moisture levels at any given time is possible via a number of ways. Simplest is a simulation model, like CliMate (How Wet/Nitrate section), designed by Dr David Freebairn and colleagues at the University of Southern Queensland. For example, for a farm near Dubbo with model predictions based on many years of research, CliMate predicts a deep red loam soil may have conserved 142mm of soil water from a five-month fallow leading up to mid-April on a paddock with no stubble retention.
However, the model indicates with 90 per cent ground cover it would have conserved 180mm of stored soil moisture with an almost full water profile. That's a pretty reasonable estimate and illustrates the critical role of groundcover retention. In a dryish winter-spring that extra water could be worth more than 2.0t/ha extra yield.
Other extremely valuable tools include permanent moisture probes placed in paddocks via individual farmers and groups like FarmLink in southern NSW. FarmLink provides members with updates of likely soil water levels in members areas. A simple push probe, just a rod with a slightly bulbous tip point, is far better than nothing. It works via being able to be pushed through the soil profile to a depth where stored soil water ends. Knowledge of soil type and its water holding ability, combined with experience that helps judge level of stored water (100pc when easy to push, less when more difficult).
Knowledge of stored soil water, especially when contemplating adding nitrogen, either at sowing or post establishment, is critical when deciding on nitrogen rate or if even to apply. Soil test data, surface and deep nitrogen soil test, as well as a likely rain following application are all important for nitrogen decision making. While rain does not have to fall immediately post application, it is best if it does in reasonable time.
Monitoring crops for diseases like stem, leaf or stripe rust in wheat is also an important part of cropping. In wheat for example, it is helpful if one has the rating of diseases for a given variety. These are readily available in the NSW DPI Winter Crop Variety Guide. Should it turn out a wetter year, especially late winter and early spring, diseases like rust can badly impact on yield in susceptible varieties. While not as good as having resistant varieties, reasonably economic fungicide programs can be used if a disease like rust gets going in a susceptible variety.
Earlier weeds can be controlled with appropriate herbicides, are also a commonly important aspect from the yield perspective. Again, the DPI Winter Crop Herbicide guide is a good "bible" to help choose best bet products for a given weed situation.
There clearly are many other factors that go into achieving a good crop yield. For example, having used enough phosphorus at sowing helps achieve best results from added nitrogen. Sowing where possible towards the earlier part of the window for a specific variety is not always, but generally more so than not, best for reliable top yields. Earlier sowing within a variety's sowing window commonly means deeper rooting and better access to deep soil water and nutrients.
Next week. Getting the best from native pastures.
Bob Freebairn is an agricultural consultant based at Coonabarabran. Email robert.freebairn@bigpond.com or phone 0428) 752 149.
