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Extreme weather (high rainfall and temperatures) and challenging soils are sources of uncertainties in the use of current crop models that have been developed for more favorable environments. This may limit their applicability to guide and support decision making for the development of new agricultural regions in tropical environments. We evaluated the accuracy of the Agricultural Production Systems Simulator (APSIM) framework in representing yield and development of a range of crops across multiple locations in the Northern Territory of Australia, a tropical region with large potential for agricultural development. Observations of yield, biomass, and phenology for a range of crops from 28 experiments undertaken at three locations were compiled and used to develop simulations undertaken using APSIM version 7.10. Model performance varied with coefficients of determination and concordance correlation coefficients ranging from 0.36 to 0.98 and 0.37 to 0.93, respectively. Instances where model performance was less than ideal were associated with conditions presenting a limited number of observed values. Deviations by the model from yield observations were larger for situations with high‐yielding crops and low daily maximum temperatures during vegetative growth stages. Deviations in phenology were larger for conditions associated with water and N stress. APSIM was capable of representing the yield, biomass, and development of cereal and pulse crops and can be used with confidence to assist the expansion of agriculture in tropical environments such as the Northern Territory of Australia. Core Ideas: The accuracy of crop models for environments frequented by challenging weather and soils is rarely reported.We showed that the Agricultural Production Systems Simulator (APSIM) performs well in one such environment, the Northern Territory of Australia.APSIM can be used with confidence in environments with challenging weather and soil conditions. [ABSTRACT FROM AUTHOR]

Prospects for improving the productivity of species mixtures in transitions between phases by changing row configuration at sowing were examined in two series of field experiments in rain-fed, semi-arid environments in south-eastern Australia. The first series explored how the choice of cover crop and use of alternate drill row configurations affected establishment and yields of sward components in the transition from a cropping into a pasture phase. Cover-crop species included wheat (Triticum aestivum L.), barley (Hordeum vulgare L.), c anola (Brassica napus L.) a nd l upins (Lupinus augustifolius L.), e ach s own i n m ixed o r a lternate d rill r ows w ith l ucerne (Medicago sativa L.) and subterranean clover (Trifolium subterraneum L.). The second series of experiments examined the productivity implications when returning from the pasture phase back into cropping following 10 contrasting pastures sown to various combinations of lucerne, subterranean clover or phalaris (Phalaris aquatica L.) sown in mixed, alternate (1:1) or double skip (1:2) row configurations in the absence of cover crops. All experiments were sown on a 0.25-m row spacing. In the transition into the pasture phase, grain yields of cover crops in the mixed drill row treatment were similar to those achieved by crops grown in the absence of pasture species but were reduced by an average of 24% in the alternate drill row configuration. Canola and lupin crop biomass were lower, compared with wheat and barley, leading to increased pasture yields in year 1, highlighting an opportunity for increased use of these species as cover/companion crops in semi-arid environments. Pasture yields beyond year 1 were reduced by ~20% in the alternate drill row treatments compared with where species were sown in mixed drill rows, with greater yield differences under more favourable growing conditions. This response largely reflected yield reductions in lucerne where it was concentrated in fewer drill rows. The alternate drill row configuration increased the abundance of subterranean clover in year 1, but this species remained a minor component of all swards beyond the establishment year. In the transition into the cropping phase, effects on grain quality could only be attributed to row configuration of the previous pasture to the extent that row configuration changed pasture composition. Grain size was smallest and protein concentration highest where previous pastures contained both lucerne and subterranean clover without phalaris. Taken together, there was little advantage in total productivity attributable to spatially separating species in drill rows at sowing. [ABSTRACT FROM AUTHOR]

Growth of alfalfa (Medicago sativa L.) following the correction of a water deficit will depend in part on the characteristics of the canopy grown during the water deficit. The current study was undertaken to determine the extent to which canopy structure and photosynthetic capacity are affected in alfalfa plants regrowing following defoliation while exposed to a water deficit. The effects of five levels of water application (100, 75, 50, 25, and 0% of the replacement water requirement) during the regrowth of two alfalfa cultivars with contrasting levels of fall dormancy was investigated in a controlled environment. Mass per shoot and shoots per plant were both significantly (P < 0.05) reduced by water applications 75% or less of the replacement water requirement. Dry matter accumulation was reduced in proportion to the level of the water deficit the plants were exposed to. The rate of CO2 assimilation and maximum efficiency of photosystem II were unaffected (P > 0.05) by water deficits except for the unwatered plants on which leaf senescence occurred. The only inhibition in the plants' capacity for photosynthesis from a water deficit was reduced leaf area. Shoot density and reduced overall canopy photosynthesis were the only canopy characteristics that were altered by water deficit in a way that could continue to inhibit plant growth following the correction of the water deficit. [ABSTRACT FROM AUTHOR]