So, good stored soil moisture to 1.5-metre depth (say 170mm for a typical red brown earth, but potentially much more for some quality clays), plus in-crop rainfall of 250mm can potentially yield 7.68 t/ha (170+250-100) x 24 =7680 kilograms per hectare).
That sounds impossible, but such yields were achieved by some growers this past season, where close to ideal conditions occurred and high standard agronomy was practised. Clearly conditions are rarely ideal but such a target is worth aiming for.
Plant breeders endeavour to improve yield potential and modern agronomy is responsible for about 50 per cent of yield improvement (estimated at one per cent per year) for the last decade or so. It is generally accepted variety yield potential is only part of the story, with soil fertility and disease prevention equally part of high yields. Agronomy research indicates, in many areas, earlier sowing with slower maturing varieties, or those with winter habit in central southern environments, has the potential to lift yields. Earlier sowing and later maturity means crops can flower at the same time as more traditionally later-sown, quicker-maturing crops.
Earlier sowing allows plants to root deeper and better access subsoil moisture and nutrients. Also in many areas, earlier sown appropriate variety crops (all cereals and canola) can commonly provide valuable winter grazing with little detriment to yield.
Highest efficiency fallow water storage is in most years part of achieving highest crop water-use efficiency. Stored soil water is especially useful for common moisture stress during the growing season, especially during flowering and early grain fill. Highest fallow moisture storage efficiency depends on early weed control, often involving more herbicide treatments, stubble retention and sound use of herbicides to maximise effectiveness.
Soil fertility is closely linked to highest possible yields, with phosphorus and nitrogen the main likely limiting nutrients for many areas. Matching nitrogen application to crop needs is a difficult task and may involve split applications (some up-front, some mid-crop) with the in-crop application rate related to how the season is progressing. Where moisture is sufficient, timing of nitrogen is commonly a secondary factor. Disease prevention is clearly a vital part of maximising water-use efficiency. Root and crown rot diseases such as take-all crown rot and common root rot as well as nematodes, especially in central northern NSW, can take a big toll on water-use efficiency if not controlled by rotations. Disease control also generally requires good fallow as well as in-crop weed control, as they can be carried by many of them, especially grass weeds.
The three rusts (stem, stripe and leaf), yellow leaf spot and septoria tritici can also devastate crop yields (water-use efficiency) and variety resistance can help. Unfortunately it is still difficult to protect against all of these in the one variety for a given sowing window or environment, but choice continues to improve.
As NSW DPI Wagga-based agronomist Helen Turner continually reminds us, soil factors such as acidity can impact on crop water-use efficiency unless appropriate varieties (for some crops) combined with sound lime use and application technique are practised. Soil monitoring via soil testing at appropriate layers is important. Other soil factors impinging on water-use efficiency include sub and top soil sodicity, sub soil adverse salt layers, and boron toxicity.
Also important are sowing depth and good soil to seed to water contact. Simple aspects but ones that commonly can go astray.
Next week. Manage pastures for combining summer and winter species.
- Bob Freebairn is an agricultural consultant based at Coonabarabran. Email robert.freebairn@bigpond.com or contact (0428) 752 149.
