MANY farmers achieved record or near record crop yields in 2020. Even in northern NSW, where in-crop rainfall was generally well below average, yields were commonly good given the season. Evaluating one's potential yield, and assessing how to improve even further, for a given season, is a valuable exercise for every property.

There are many factors that account for crop yield other than just seasonal conditions and are worth assessing for future upgrading - such as stored soil water, soil fertility, sowing time for different varieties and crops, pests like root lesion nematodes, diseases like rusts, yellow leaf spot and Septoria, variety yield and quality ability, root and stem rot diseases, soil constraints like acidity and sodicity, including sub soils, and weeds.

While stored subsoil water is not an issue in a very wet in-crop rainfall year, a rarity for most areas, commonly it is critical, especially from late tillering onwards. Agronomist colleagues and farmers even last year noted how critical that extra soil water was to get crops through and/or to maximise probability of achieving very high yields. Some research has shown every millimetre of stored soil water can be worth up to 30kg/ha extra grain, especially in a tight finish.

Also important is if fallow weeds have got away maybe due to inability to herbicide treat on time in wet and windy conditions, available soil nitrogen for the next crop is likely to be lower, and the greater risk of diseases and pests.

Frost caused sizable yield loss in many areas in 2020 including in our area. Even with the best advice and planning it can be impossible to eliminate this risk. In some areas there is a tendency to sow late to minimise frost risk, especially in low lying paddocks. As occurred in 2020, it was sometimes the later sown crop that copped most frost damage from a late normally unexpected frost. In our case frosts occurred between September 25 to 29 much later than normal.

Crops flowering at this later date appeared to be more frost affected than those that had already set grain, although all crops at various heading dates often suffered damage. Delaying heading later, for this area, as an example, would lead to regular yield losses from heat and moisture stress, so common in most districts.

Addressing soil fertility, with a focus to mesh fertiliser rates to soil deficiency levels (soil test data) and grain removal rates, especially after a big crop, will be a big 2021 issue. While phosphorus needs to be supplied early (pre-sowing or sowing), in close proximity to developing roots, nitrogen can be applied progressively as the season develops. Aiming for high yields (depending on soil water and seasonal progress) commonly means adding 100 to 200 kg/ha nitrogen rather than traditional 40kg/ha.

Choice of variety has a big effect on yield with some recent releases several per cent higher than many older varieties. Most importantly choosing varieties with best resistances to likely disease and pest threats can usually better protect crops. The two major root lesion nematode threats can cause big yield losses in susceptible varieties. Using the Predicta B soil and crown residue test (north and southern laboratory's) help choose best variety depending on analysis for nematodes and diseases like crown rot.

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Variety and crop choice can also play a role in lifting crop yields if factors like topsoil and subsoil acidity are a paddock or part paddock issue. Within a crop type like wheat, there is considerable variation in variety tolerance to soil acidity. If acidity is severe, either or in both top and sub soil, some species are far more tolerant than others. For example triticale in quite tolerant, and so are most oat varieties.

Other subsoil constraints, such as high salt levels, can adversely affect crops. Barley is the most tolerant to chlorine toxicity, followed by bread wheat and canola, with durum and chickpeas most sensitive (data based on limited variety testing). Bearing in mind frost constraints, as a general rule earlier sowing of a variety, within its sowing window, tends to correlate with higher yield. A feature of earlier sowing tends to be greater rooting depth resulting in greater moisture and nutrient scavenging capability.

Next week: Preparing for autumn pasture upgrades.