If rain comes too late for winter crops and if good rains fall leading up to spring early summer is it feasible to sow summer crops far further south and far further west than is commonly considered the dryland summer cropping belt?
There currently are farmers as far south as between Parkes and Forbes, and even into Victoria, that regularly incorporate summer crops into their cropping system, let alone when seasonal conditions are against a winter crop but maybe look promising for a summer one.
Mark Swift, part of the farming business of Kebby and Watson Tichborne (between Parkes and Forbes) have for a number of years grown around 500 hectares grain sorghum as part of their cropping business. Last year, a very dry one with only 30mm of in-crop rainfall yield was 2.0 t/ha. He stresses that while summer cropping is an important part of their rotation, it requires planning and sound agronomics for best yield prospects and for other economic benefits such as improved weed and disease control in their more southern environment.
Katrina Swift, agronomist and entomologist of the business, stresses that summer cropping requires a business plan that includes rearranging holidays as timing for issues like pest control commonly coincide with Christmas holidays. Sometimes they also grow broadleaf crops like mung beans that especially require monitoring twice a week with prompt pest control if numbers are above threshold levels.
Mark Swift believes summer crops need to be considered as an important part of the rotation, properly budgeted for, including cash flow implications and work requirements, as well as impact on future crops such as sequencing back to winter crops. Their business is totally crop orientated with crop sequencing and rotations especially critical for profitability.
Soil water storage is important for all their cropping and includes monitoring via moisture probes. For summer cropping to be justified close to full water capacity in soils capable of excellent water storage are important Mr Swift emphasised. Some soils, for example a deep clay loam may be capable of storing 200mm of plant available water (PAW) to 1.5m depth. In contrast a sandy loam surface over a light clay may only store up to 100mm PAW.
Herbicide drift from fallow district spraying is an enormous risk to summer cropping Mr Swift says, even for sorghum but especially for crops like cotton and mung beans. Sowing time is an important aspect although Mr Swift is not that specific on aiming for the earliest sowing slot (each summer crop species, and even sorghum variety has its minimum soil temperature requirement). Heat waves and summer rainfall is so erratic it is impossible to predict from year to year best sowing time. Stubble retention, desirable for better rainfall capture) commonly results in cooler soil temperature, an issue sometimes for sowing early.
Research (involving 15 sites and five years in northern NSW) comparing sowing time (early or late to avoid highest probability of extreme heat), led by Loretta Serafin and colleagues, funded by GRDC and NSW DPI, showed overall similar yields given comparable starting sub soil moisture levels. Later sowing commonly has crop dry-down and high grain moisture implications, especially in southern NSW.
Agronomy issues with summer cropping include row configuration and sowing rate (plant population). Loretta Serafin noted their research had shown solid row configuration, 1.0m spacing, generally gave the greatest return in above average seasons. If the season turn out good, for example with solid plant yields of 5.0 t/ha, single skip can often yield 1.0 t/ha or less, and double skip even less yield. If yields are low (e.g. 2.0 t/ha or less) yield difference between row configurations is much smaller.