Biography:

In the past S.P. Milroy has collaborated on articles with B.T. Steer and S. Asseng. One of their most recent publications is A model to simulate the development, growth and yield of irrigated sunflower. Which was published in journal Field Crops Research.

More information about S.P. Milroy research including statistics on their citations can be found on their Copernicus Academic profile page.

S.P. Milroy's Articles: (4)

A model to simulate the development, growth and yield of irrigated sunflower

AbstractA simulation model of the development, growth and yield of sunflower cv. Hysun 30 is presented. In the model, crop growth rate is a function of radiation use efficiency, incident radiation, the canopy extinction coefficient and leaf area index. The radiation use efficiency of a sunflower canopy was measured and found to change during the growth of the crop. It is higher after floret initiation than before, and reaches a maximum at anthesis. The changing radiation use efficiency has been incorporated into the model. The leaf area index each day is a function of the number of leaves produced and the rate and duration of expansion of each leaf. A nitrogen and plant population factor modulates crop growth through its effect on the expansion rate of each leaf and the rate of leaf senescence after anthesis. In this way the nitrogen concentration in leaves at floret initiation and population density affect the dry-matter accumulation by the crop. Crop dry matter at the end of floret initiation and at physiological maturity are used to calculate the components of yield from relationships previously demonstrated in greenhouse experiments. The mean daily temperature affects the rate of leaf production and the radiation use efficiency, as well as determining the time of phenological stages through thermal time. Although the model was developed for the hybrid Hysun 30, it has been extended to some other hybrids by changing the size and activity of the generative area producing florets in the floral meristem. The simulated yields of four hybrids are close to the measured yields of irrigated crops.

Regular ArticleProfiles of Leaf Nitrogen and Light in Reproductive Canopies of Cotton (Gossypium hirsutum)

AbstractDuring vegetative growth, the vertical profile of leaf nitrogen (N) often parallels the profile of light distribution within the canopy. This is more advantageous in terms of canopy photosynthesis than a uniform distribution of leaf N. We investigated the influence of both reproductive growth and N supply on the profiles of N and light in canopies of irrigated cotton crops (Gossypium hirsutum L.). Regular samplings were made from soon after the onset of reproductive growth until crop maturity. Every 2 weeks, a 1 m2sample of the canopy was cut in four successive vertical layers of equal thickness. Leaf area and N concentration (%) in each layer were measured. The vertical N gradient became more marked with ongoing reproductive development. It is hypothesized that because of the high rate of growth after the onset of reproductive development and the long duration of this phase compared to other species, the whole canopy photosynthetic benefit that would accrue from maintaining the N gradient is likely to be accentuated. The rate of decline in leaf N concentration in a layer was not related to either the initial concentration in the leaves nor the boll load within the layer.

Systems analysis of wheat production on low water-holding soils in a Mediterranean-type environment: I. Yield potential and quality

AbstractWheat grain yields, grain protein and grain size are often variable in a Mediterranean-type environment due to large rainfall variability. Grain yields are often low due to low N inputs as a result of large uncertainties of rainfall, particularly during the latter part of the season. Larger amounts of N fertiliser might increase yields and also grain protein in such environments but could have negative effects on grain size. A systems analysis approach was taken, using the APSIM-Nwheat crop model, to assess potential yield, grain protein concentration and grain size of wheat across a range of conditions. Rainfall and temperature varied with location. Soil type, different amounts of initial stored water and a range of management options, including varying sowing dates and N fertiliser applications, were also considered. In Australia, penalties for small grain size are based on ‘screenings’: the percentage of grain to pass through a 2 mm sieve. A new routine was developed for the model describing the relationship between screenings percentage and average simulated grain size.At low rainfall locations, 30 mm of plant-available soil water at seeding gave a significant increase in grain yield (>20%) above that for no soil water. At high rainfall locations there was little effect (<7%). Three typical coarse textured soils had similar yields at low N supplies but soils with higher plant-available water-holding capacity responded more to N applications and thus at high N applications achieved higher grain yields. Above average rainfall from May to September in combination with below average temperatures resulted in the highest simulated yields. However, seasons with an average amount of in-seasonal rainfall but with rainfall well distributed throughout the season also had above average yields. Applications of small amounts of N (30 kg N/ha) caused a slight reduction in grain protein concentration, but higher N applications (>30 kg N/ha) resulted in increased protein and screenings. Nevertheless, with moderate N (60 kg N/ha) applications and early sowing, the proportion of years with low grain protein (<10%) and low screenings (<2%) was still more than two-thirds.Simulated average yields of a location increased with average rainfall but declined with increasing average temperature of a location. This allowed the development of a simple rule of thumb in which average grain yields can be related to the rainfall/temperature index of a location. The simulation analysis showed that there is potential to increase current farmer yields through higher and split N applications on light soils in Mediterranean-type environments without increasing average screenings above 3%. However, grain protein concentrations are likely to be low in most seasons on low water-holding soils.

Physiological determinants of high yielding ultra-narrow row cotton: Biomass accumulation and partitioning

AbstractUltra-narrow row (UNR) cotton, may have the potential for increased yields in high yielding, high-input production systems. Attaining higher yields in UNR cotton relative to conventionally spaced crops must depend on either increased biomass production or partitioning to fruit. We compared biomass production and partitioning in UNR treatments (25 cm spaced rows) to that of treatments with conventionally spaced rows (100 cm) in high yielding, high-input production systems (where lint yield was greater than 1800 kg ha−1). Early biomass accumulation was faster in the UNR crop (36 plants m−2) compared to the conventionally spaced treatments (12 plants m−2) but slowed later in the season. Despite a three fold increase in plant density in the UNR treatments total dry matter production per unit area was not different to the conventionally spaced treatments. On a per plant basis dry matter accumulation was slower and total biomass production was significantly lower in the UNR crops. This was accompanied by a decrease in boll size, suggesting that competition for resources was limiting crop growth. These differences were significant across three seasons. However, the increase in yield in the UNR crops was obtained through increased partitioning of dry matter to fruit compared to the conventionally spaced crops, resulting in higher boll numbers and increased lint yield in high-input UNR production systems. As there were no differences between row spacings in total water use or nitrogen uptake, investigations are continuing to determining the key determinants limiting crop growth and biomass production in high-input UNR production systems.

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