Search

Take home messages The nitrogen (N) fertiliser demand for cereal cropping systems can increase due to two factors: 1. A reduction in the amount of soil organic N mineralised due to the continued decline of natural capital (soil organic carbon and total nitrogen) that occurs under cropping; and 2. An increased crop N demand due to higher yield potentials resulting from optimising other components of the cropping system. The amount of biological N fixation by pulse crops (chickpea/mungbean) is related to the crop yield and biomass and the availability of soil mineral N from mineralisation or carry-over of residual fertiliser. Where deep phosphorus (P) and potassium (K) application increases chickpea biomass (and grain yield), there is generally more N fixed. While some of this is re-exported in grain, the greater residue return means more N is carried forward to the next crop. Growers have a selection of fertiliser N management practices that have differing strengths and weaknesses – it is not a one-size-fits-all model for CQ (or northern region) farming systems. The 4R framework allows choice of rate, source, time and place for any nutrient applied to be implemented suiting each growers’ preferences, with on-going research addressing several themes in regional Qld.

The efficiency of soil water accumulation during fallow periods, and the availability of that soil water for use by crops are key drivers of northern farming system productivity and profitability. In 2015 seven farming systems experiments were established from central Queensland to central New South Wales to answer the question; Can system performance be improved by modifying farming systems in the northern grains region? To assess this soil water dynamics were monitored under different farming systems, along with soil nitrogen, pathogens, crop biomass, grain yield and variable costs, as measures of system performance. Analysis of soil water accumulation during the fallows and its subsequent use by sorghum, wheat and chickpea crops, showed a cost to all crops for converting biomass to grain yield. This cost was least for chickpea (50 mm), followed by wheat (100 mm) and highest for sorghum (150 mm), and should be deducted from crop water use to calculate water-use-efficiency (WUE). The WUE was lowest for pulse crops (10 kg/mm), but sorghum and wheat returned the same WUE (17 kg/mm). Northern growers typically store plant-available-water (PAW) in the fallow as a buffer against variable quantity and timing of in-crop rainfall. Crops produced a better than average WUE when planted with at least 60 mm PAW in a high in-crop rainfall season, or 120 mm of PAW with low in-crop rainfall.

Take home messages • At average fertiliser costs, return on investment to nitrogen applications exceed 5:1, i.e. every dollar spent on nitrogen results in $5 of additional profit • When N prices double, growers are still receiving $2.10 in profit for every dollar spent on nitrogen, and at triple the cost nitrogen is still expected to return $0.85 in additional profit for every dollar spent • With higher N prices profitable N responses to winter cereals are only expected under favourable grain prices or seasonal conditions • Soil testing and precision/variable nutrient application become more valuable as nutrition costs rise.

Sclerotinia stem rot (SSR), caused by the necrotrophic fungus Sclerotinia sclerotiorum, is a major, but unpredictable disease of canola in Australia. However, there is no disease rating system for current canola varieties. Over the last four years the most common varieties of canola grown in Western Australia were assessed in the field using natural disease occurrence, and in glasshouse experiments using manual inoculations, to determine their susceptibility to SSR. The results highlighted the complexity and unpredictable nature of SSR with infection levels and varietal response varying depending on seasonal conditions and time of infection, despite limited levels of genetic resistance to SSR in current varieties. It is suggested that a disease rating system should not be based purely on inseason plant infection, but should also include potential for future infections through the contribution of sclerotia from infected plants to the system.

Take home message Shorter season, faster maturing crops can leave residual surface water from unutilised late season rain and/or residual deep water due to shallower roots and quicker maturity Legumes such as lentils, fababeans, field pea, and chickpea often leave 20-40 mm extra residual soil water compared to canola and winter cereals Higher residual water may not remain at sowing of next crop – fallow efficiency differences between crops and seasons can influence this – e.g. low cover after legumes For summer crops, mungbean typically leaves 20mm more residual water than sorghum/maize while cotton leaves 20mm less (i.e. mungbean > sorghum/maize > cotton) Early-sown, slower maturing crops (e.g. early sown winter crops) can dry the profile deeper (>2m) and utilise deep stored soil to support higher yield in dry springs. The legacy of drier soil may warrant changes to crop sequence and management to avoid yield penalties Extra residual water at sowing can increase grain yield of subsequent crops when water is limited during the critical period for yield determination so the marginal WUE (i.e. extra yield per mm of extra soil water available) can be very high (>60kg/ha/mm) As the value of the residual water is seasonally dependent, understanding how management (crop choice, sowing dates, N management) can be adjusted to capture value from such legacies across a sequence of crops is the goal of current farming systems research.