While for many 2016 might have been a rare exception, stored soil water over the fallow period, year in year out, for almost all cropping areas of Australia is a key to maximising crop yields.
Even last year in many districts, including our own at the northern end of the central west, stored soil moisture was critical. For example it was possible to sow dual-purpose crops mid-March on a light rain event if stored soil moisture was reasonably close to the surface.
Following rains came more than a month later and early sowing meant these early sown crops were ready for grazing mid May onwards. Some of these provided 80 days’ grazing at about 25 dry sheep equivalents/ha before closing and yielded upwards of 5.0 t/ha of grain. Combined gross income over $1700/ha was not uncommon.
In contrast, crops not sown on this early rain event would not be sown until much later with then little grazing possible before needing to be closed for grain recovery.
Research (CSIRO, NSW DPI and others) has shown that efficiently storing soil moisture from rain falling between post crop ripening and over the fallow period for most Australian cropping areas on average can be worth an extra 1.0 t/ha of grain or more. On average in most NSW areas stored soil moisture is especially critical in dry springs and or a dry autumn, typical of our environment. Every millimetre of stored soil moisture can be worth as much as 30kg/ha extra grain (or/and in grazing production). For some areas with soils of good water holding capacity (deep clay and clay loams) it is possible to grow a reasonable crop on a full moisture profile with hardly any in-crop rainfall.
Stubble retention and prompt fallow weed control are important. Timely weed control is also important for maximising available soil nitrogen at sowing and is a vital part of reducing the weed soil seed bank. Research has shown timely weed control can result in 40kg/ha or more available soil nitrogen compared with poor fallow weed control.
Disease control is another big factor required for best crop yields. Rotations are increasingly appreciated for disease control and so is choice of variety. This past winter crop for example, it was commonly difficult to apply fungicides for disease control on time because of lack of product or too much demand on contractors.
Varieties with good resistance to diseases such as stem stripe and leaf rust and yellow leaf spot in wheat (also septoria for southern farmers) are available, often combine with required quality and are equal to best in yield. A number of slower-maturing varieties for several crops, including wheat, have been released and lengthen the sowing window. Mostly they provide an earlier sowing opportunity with little increase in spring frost risk and early sowing is increasingly appreciated associated with higher yields.
Coming off a mainly high yielding year in 2016, soil fertility will be even more critical in 2017. Nutrient budgeting is a useful starting point for appreciating crop nutrient removal. For example 5.0 t/ha of 13-per-cent protein wheat removed 114 kg/ha nitrogen off a paddock. Late winter spring leeching may have resulted in further nitrogen removal. Soil testing before sowing is a useful tool for fertiliser decisions.
Next week. Fallow and winter crop grazing no detriment to grain yield.
- Bob Freebairn is an agricultural consultant based at Coonabarabran. Email robert.freebairn@bigpond.com or contact (0428) 752 149.
