Beverley J. Gogel

Longevities and nitrogen, phosphorus, and potassium release patterns of polymer‐coated controlled‐release fertilizers at 30°C and 40°C

Abstract The weekly nitrogen (N), phosphorus (P), and potassium (K) release from 17 polymer‐coated controlled‐release fertilizer (CRF) formulations of Nutricote, Apex Gold, Osmocote, and a 9‐month Macrocote were measured at 30.6±0.8°C and 40.0±1.5°C. Five grams of each CRF were placed at a depth of 50 mm in 280x50 mm acid washed then rinsed silica sand columns which were leached with deionized water three times each week until nutrient recovery ceased. The volume of leachate was recorded each week and subsampled for ammonium‐N, nitrate‐N, phosphate‐P, and K analyses. Each CRF treatment was replicated three times at each temperature. Nutrient release profiles were determined. Longevities, measured as weeks to 90% nutrient recovery, were considerably shorter than the nominated release periods for all formulations. Within each CRF product group, the longevity of 9 and 12 month formulations were similar with Apex Gold 12–14 month high nitrate having the longest (38 weeks for N at 30°C) and Osmocote 8–9 month the shortest (23 weeks for N at 30°C). There were consistent trends in the nutrient release periods across all CRFs with P>K>N and with differences of around 10% in duration between nutrients. The P:N release ratio exceeded 0.10 for most CRFs during the early release period indicating an adequate P supply for most plant species. The mean reduction in longevity for Nutricote, Apex Gold, and Osmocote formulations for an increase in incubation temperature from 30°C to 40°C was 19–21 % for N, 13–14% for P, and 14–15% for K. All CRFs released nutrients unevenly with the highest rate occurring during the early part of the release period. This pattern was accentuated at 40°C and by the shorter term release formulations. The nutrient release rates of all CRFs declined steadily after their maxima.

An efficient computing strategy for prediction in mixed linear models

After estimation of effects from a linear mixed model, it is often useful to form predicted values for certain factor/variate combinations. This process has been well-defined for linear models, but the introduction of random effects means that a decision has to be made about the inclusion or exclusion of random model terms from the predictions, including the residual error. For spatially correlated data, kriging then becomes prediction from the fitted model. In many cases, the size of the matrices required to calculate predictions and their covariance matrix directly can be prohibitive. An efficient computational strategy for calculating predictions and their standard errors is given, which includes the ability to detect the invariance of predictions to the parameterisation used in the model.

A variance shift model for detection of outliers in the linear mixed model

A variance shift outlier model (VSOM), previously used for detecting outliers in the linear model, is extended to the variance components model. This VSOM accommodates outliers as observations with inflated variance, with the status of the ith observation as an outlier indicated by the size of the associated shift in the variance. Likelihood ratio and score test statistics are assessed as objective measures for determining whether the ith observation has inflated variance and is therefore an outlier. It is shown that standard asymptotic distributions do not apply to these tests for a VSOM, and a modified distribution is proposed. A parametric bootstrap procedure is proposed to account for multiple testing. The VSOM framework is extended to account for outliers in random effects and is shown to have an advantage over case-deletion approaches. A simulation study is presented to verify the performance of the proposed tests. Challenges associated with computation and extensions of the VSOM to the general linear mixed model with correlated errors are discussed.

Ginger (Zingiber officinale) autotetraploids with improved processing quality produced by an in vitro colchicine treatment

Ginger autotetraploids were produced by immersing shoot tips in a 0.5% w/v colchicine, 2% v/v dimethyl sulfoxide solution for 2 h. Stomatal measurements were used as an early indicator of ploidy differences in culture with mean stomata length of tetraploids (49.2 μm) being significantly larger than the diploid (38.8 µm). Of the 500 shoot tips treated, 2% were characterised as stable autotetraploid lines following field evaluation over several seasons. Results were confirmed with flow cytometry and, of the 7 lines evaluated for distinctness and uniformity, 6 were solid tetraploid mutants and 1 was a periclinal chimera. Significant differences were noted between individual tetraploid lines in terms of shoot length, leaf length, leaf width, size of rhizome sections (knob weight) and fibre content. The solid autotetraploid lines had significantly wider, greener leaves than the diploids, they had significantly fewer but thicker shoots and, although ‘Queensland’ (the diploid parent from which the tetraploids were derived) had a greater total rhizome mass at harvest, its knob size was significantly smaller. From the autotetraploid lines, one line was selected for commercial release as ‘Buderim Gold’. It compared the most favourably with ‘Queensland’ in terms of the aroma/flavour profile and fibre content at early harvest, and had consistently good rhizome yield. More importantly it produced large rhizome sections, resulting in a higher recovery of premium grade confectionery ginger and a more attractive fresh market product.

Quantitative trait loci for agronomic and physiological traits for a bread wheat population grown in environments with a range of salinity levels

Worldwide, salinity is a major environmental stress affecting agricultural production. Sodium (Na+) exclusion has long been recognised as a mechanism of salinity tolerance (ST) in cereals and several molecular markers have been suggested for breeding. However, there have been no empirical studies to show that selection for Na+ exclusion markers could improve grain yield in bread wheat under dryland salinity. In six field trials, a bread wheat mapping population was grown to validate Na+ exclusion quantitative trait loci (QTL) identified earlier in hydroponics, to determine the impact of Na+ exclusion on grain yield, and to identify QTL for yield-related traits. The traits included grain yield, grain number per m2, 1,000-grain weight, maturity, plant height, and leaf Na+ and K+ concentrations. The presence of numerous QTL with minor effects for most traits indicated the genetic complexity of these traits, and thus limited prospects for pyramiding at present. Considerable QTL-by-environment interactions were observed, with the stable QTL generally being co-located with maturity or early vigour/height genes, which demonstrates the importance of measuring major agronomic traits in order to discover genuine QTL for ST. Several QTL for seedling biomass and Na+ exclusion identified earlier in hydroponics were also detected in field trials but with marginal impact on grain yield. These results suggest that selection for Na+ exclusion and the use of hydroponics-based seedling assays may not necessarily result in improved ST. However, as this is the first report of its kind, there is an urgent need for testing other mapping populations in realistic environments to discover novel ST-QTL for breeding programs. In the meantime, grain yield QTL independent of maturity and height may offer potential to improve ST.

Leaf nitrogen and phosphorus levels in macadamias in response to canopy position and light exposure, their potential as leaf-based shading indicators, and implications for diagnostic leaf sampling protocols

The relationships between leaf nutrient content, leaf age, and within-canopy light exposure were studied in 10-11-year-old Macadamia integrifolia cvv. 660, 781, and 344 at Alstonville (28°59S, 149°E), New South Wales, during autumn and spring 1996. Quantum point sensors were placed at 16 positions in the canopy to give mean 24-hourly photosynthetic photon flux density (PFD) readings, which ranged from 13 to 540 µmol/m 2 .sec. At each of these positions, the youngest terminal leaf (YTL), the youngest fully expanded leaf (FEL) from a current flush, and a 6-7-month-old hardened off leaf (HOL) were sampled. In 1997, at 12 sites in the Alstonville district, leaves of cv. 344 were sampled (FEL and HOL) at 5 equidistant positions from the bottom, a height of 1.2 m (position 1), to the top (position 5), on the N-NE side of trees in late spring. The sites varied in canopy density from 50% to 95% ground cover, and PFD from the bottom shaded position to the top exposed position in the canopy across all sites increased by a factor of 1.3 to 17.9. At Alstonville, leaf parameters (N%, P%, specific leaf weight (SLW), N amount per unit leaf area (N area), and P area) increased (P FEL = YTL; and for P% and P area, YTL = FEL > HOL. Cultivar did not affect (P > 0.05) N%, N area or SLW; for P% and P area, cv. 660 > 781 > 344 (P < 0.05). At the Alstonville district sites, leaf parameters increased with PFD (P < 0.05). At each tree sampling position there was a weak negative correlation (P < 0.05) between the leaf parameters and percentage ground cover across all sites, which declined with height (and PFD). Nitrogen area and P area gave the highest R values (-0.60 and -0.40 at low canopy positions), and neither was a suitable replacement for percentage ground cover as a leaf-based shading indicator. The slope of the regression line (regression coefficient) between a leaf parameter and tree height for each macadamia site was determined. The regression coefficient for N area gave the best correlation with percentage ground cover (R 2 = 0.55, P < 0.01) and may be useful as a leaf-based shading indicator. At position 1, HOL N concentration ranged from 1.3% to 1.8% and P concentration from 0.06% to 0.11% across all sites. At each of the 5 tree positions, the N parameters were very poorly correlated with kernel yield, and for the HOL P parameters, there was a weak negative correlation (R = -0.521 to -0.673, P < 0.05) at tree positions 1 and 2 with kernel yield. Current recommendations to reduce macadamia leaf N concentrations because of detrimental effects of high leaf N on yield were not supported by the current study. Modification of the current diagnostic leaf sampling protocol is recommended to avoid the reduction in leaf N and P concentrations through shading and the cultivar effects on P concentration. We conclude that the current diagnostic leaf N and P standards cannot reliably diagnose the nutritional status of macadamia orchards. Additional keywords: photosynthetic, photon flux density, leaf age, canopy, shading. D. O. et elec .M A r AR 6 D. O. et Sh efee ad et

Macadamia nut size and maturity influenced by lime and nitrogen applications

A long-term study of the effects of lime and nitrogen on a young macadamia orchard included acidifying sulfate of ammonia treatments to separate pH and Ca effects of lime applications. Lime, per se, had no influence on yield, quality, or trunk girth growth. Annual nitrogen applications (with or without neutralising applications of lime), however, consistently depressed the size of nuts and kernels and the percentage of first grade kernels, but had no effect on yield or other quality characteristics. More nuts developed with N treatments but failed to fill effectively.

Comparison of a one- and two-stage mixed model analysis of Australia’s National Variety Trial Southern Region wheat data

A one-stage analysis of a series of variety trials involves a combined analysis of the individual plot data across trials. Together with prudent modelling of the genetic effects across trials, this is considered to be the gold standard analysis of multi-environment field trial data. An alternative is a two-stage approach in which the variety means from an analysis of the individual trials in stage one are combined into a weighted mixed model analysis in stage two to give the full set of predicted variety by environment effects and an estimate of their associated variance structure. The two-stage analysis will exactly reproduce the one-stage analysis if the full variance-covariance matrix of the means from stage one is known and is utilised in stage two. Typically the full matrix is not stored and a diagonal approximation is used. This introduces a compromise to the full analysis. The impacts of a diagonal approximation are greater in the presence of sophisticated models for the genetic effects. A second compromise is through a loss of information in estimating the non-genetic variance parameters using the two-stage approach. In this paper we draw a direct link between the one and two-stage analysis approaches for crop variety evaluation data in Australia. We now have the computing power to analyse large and complex multi-environment variety trial data sets using the one-stage approach without the need for a two-stage approximation. This should motivate a move away from the two-stage approach in a range of contexts.

The estimation of faeces output in penned cattle by controlled release of chromium oxide and the subsequent accuracy of predicting forage intake with in vitro digestibility.

The study examined the reliability of predicting faeces output of cattle from chromium oxide (Cr 2 O 3 ) released from a device (CRD) inserted in the rumen. Sixteen steers were selected from four genotypes and were offered a diet of low quality pasture hay with a protein meal supplement. The steers were placed in metabolism crates which allowed for total collection of faeces over two 5-day periods, days 6-9 (period 1), and days 13-16 (period 2), of a 20-day extrusion cycle of the CRD. Three faeces samples were taken from each steer per rectum; grab samples in the a.m. and p.m. and a daily subsample, that is, a sample of each daily total collected output. Cr 2 O 3 release rates were derived for each sampling regime (a.m., p.m. and daily from the Cr 2 O 3 content of faeces). These derived rates were compared with the release rate specified by the supplier to determine differences and any bias associated with the sampling regimes. Release rates were also derived from the predicted expiry date calculated from plunger travel in the CRD. Organic matter digestibility of the diet was determined from measurements of feed intake and faeces output over the 4 days for each steer and from an in vitro technique on diet samples. Predicted forage intakes were estimated using the mean faeces output collected over 4 days in combination with either the in vivo or in vitro digestibility estimates. Correlations between actual forage intake and predicted forage intake for each method were calculated and the bias in predicted forage intake between methods was compared. The daily data revealed significant effects of steer (and/or CRD) and sampling period on the estimated release rate of Cr 2 O 3 from the CRD. However, whilst there was only a period effect on the release rate with p.m. sampling there was a linear decline in release rate with the a.m. sampling. The correlation between predicted and actual forage intake was greatly reduced when in vivo digestibility was replaced by in vitro digestibility. The results of this study suggest that the CRD had release rates less than specified and therefore devices should be calibrated for both the animals and the pastures prior to use. Furthermore, faeces sampling should be restricted to < 13 days post-dosing to minimize bias.