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Rapid assessment tools are required for monitoring crop nutrient status and managing fertiliser applications in real time. Hyperspectral imaging has emerged as a promising assessment tool to manage crop nutrition. This study aimed to determine the potential of hyperspectral imaging for predicting foliar nutrient concentrations in avocado trees and establish whether imaging different sides of the leaves affects prediction accuracy. Hyperspectral images (400–1000 nm) were taken of both surfaces of leaves collected from Hass avocado trees 0, 6, 10 and 28 weeks after peak anthesis. Partial least squares regression (PLSR) models were developed to predict mineral nutrient concentrations using images from (a) abaxial surfaces, (b) adaxial surfaces and (c) combined images of both leaf surfaces. Modelling successfully predicted foliar nitrogen (RP2 = 0.60, RPD = 1.61), phosphorus (RP2 = 0.71, RPD = 1.90), aluminium (RP2 = 0.88, RPD = 2.91), boron (RP2 = 0.63, RPD = 1.67), calcium (RP2 = 0.88, RPD = 2.86), copper (RP2 = 0.86, RPD = 2.76), iron (RP2 = 0.81, RPD = 2.34), magnesium (RP2 = 0.87, RPD = 2.81), manganese (RP2 = 0.87, RPD = 2.76) and zinc (RP2 = 0.79, RPD = 2.21) concentrations from either the abaxial or adaxial surface. Foliar potassium concentrations were predicted successfully only from the adaxial surface (RP2 = 0.56, RPD = 1.54). Foliar sodium concentrations were predicted successfully (RP2 = 0.59, RPD = 1.58) only from the combined images of both surfaces. In conclusion, hyperspectral imaging showed great potential as a rapid assessment tool for monitoring the crop nutrition status of avocado trees, with adaxial surfaces being the most useful for predicting foliar nutrient concentrations.

This study aimed to explore the effects of biochar on pulse CO2 and N2O emissions and N cycling microbial functional genes after a short-term drought through a soil incubation experiment. Soil samples were collected in a macadamia orchard where biochar was applied 5 years prior to the incubation. Samples were wetted after being subjected to short-term (2-month) drought conditions. Samples were analysed for gas emissions (N2O and CO2), available NH4+-N, and NO3−-N, water soluble organic carbon (WSOC), water soluble total N (WSTN), and N cycling microbial gene abundance for a period of 21 days post-drought. Soil CO2 emissions were significantly higher in the drought-affected soil with no biochar than in the control soil with no biochar. No effect of biochar was detected on CO2 emissions for drought-affected soil. Available labile C (WSOC) in drought-affected soil was higher than in soils not subjected to drought, regardless of the presence of biochar. Therefore, C loss after adding water could be explained by the release of labile C accumulated during drought. Drought-affected soil with biochar did not influence N2O emissions compared with control soil subject to drought. In soils not subjected to drought, biochar had higher NO3−-N than the soil without biochar at day 7 post-drought, which could partly be explained by increased soil ammonia-oxidising bacteria (AOB) gene abundance. Our study suggested that a pulse C loss was more likely to occur post-drought whereas pulse N loss through N2O emission was not evident regardless of biochar application particularly within first day after being rewetted. Our study highlights the pulse effects of drought on GHG emissions from the soil after being wetted.

Replenishing soil nutrient particularly total nitrogen (TN) and available phosphorus (P) is important to sustain soil health for food production. Organic amendments such as compost and biochar are commonly applied to improve soil nutrient retention especially N and P. In farms, biochar is usually applied once followed by applying other organic amendment applied in their full rates. Both form and rate of organic amendments can affect soil nutrient concentrations particularly in short term. This study aimed to examine the effects of compost and mixture of compost with biochar (both at full rates) on soil nutrient concentrations in short term. A randomised complete block filed experiment with eight replicates was used for this study. The effects of biochar (5 t/ha) only, compost (at the rates of 10 t/ha, 25 t/ha and 35 t/ha) and biochar mixed with compost (5 t/ha and 10 t/ha, respectively) on soil nutrient concentrations compared with control were explored in a corn field. Compost treatment at the rate of 35 t/ha had significantly higher TN, available P, calcium (Ca) and iron (Fe) compared with other treatments and control. Soil potassium (K) levels remained unchanged among all treatments. Biochar only treatment had significantly higher available P and Ca concentrations compared with biochar mixed with compost treatment. Compost application at higher rate (35 t/ha) proved best practice to significantly increase TN and available P concentrations in short term. Significantly higher available P concentration in biochar only treatment compared with the biochar mixed with compost treatment could have been associated with stimulation of P immobilisation when biochar was mixed with compost. Our results indicated that the form and rate of organic amendments in short term cropping systems are important to be considered while applying to a volcanic soil to ensure N and P availability for plants are not compromised.

Biochar can improve soil nutrient retention and alleviate salinity; however, use is not widespread due to cost. Biochar is usually co-applied with a full-rate of supplementary fertiliser before planting. This study investigated co-application of bamboo biochar with organic fertiliser and amendments on nutrient cycling, plant growth, yield and commercial value of ginger. Four treatments were applied including no amendment, organic amendments and organic amendments co-applied with biochar at two applications rates of 10 t ha−1 and 30 t ha−1. Plant growth, biomass, foliar nutrient and water-extractable soil nutrients were examined. Co-applied high rate biochar increased available soil potassium (K) concentration (+ 89%) over 22 weeks and led to increased foliar K concentration (+ 25%) at harvest and after 30 weeks compared with organic amendments alone. Biochar high rate decreased soil sodium concentration (− 22%) over 22 weeks. Biochar high rate increased root mass fraction and plant height but decreased the number of stems, and therefore, did not increase aboveground biomass compared with all other treatments. In contrast, ginger rhizome yield, grade and commercial value were not affected by biochar treatments. Added biochar provided additional net K that improved foliar concentration late in the growing season following dissolution. The additional K supply then stimulated root growth and biomass re-allocation despite daily irrigation throughout the growing season. Therefore, we suggest biochar as a useful amendment to prevent nutrient loss and alleviate salinity for organic crops.

The use of biochar is changing, and the combined application of biochar with fertilizer is increasingly gaining acceptance. However, the yield gains results reported in the existing literature through the co-application of fertilizer with biochar are conflicting. To resolve this, we utilized a meta-analysis of 627 paired data points extracted from 57 published articles to assess the performance of the co-application of biochar and fertilizers on crop yield compared with the corresponding controls. We also studied the impact of biochar characteristics, experimental conditions, and soil properties on crop yield. Our analysis showed that individually, biochar and inorganic fertilizer increased crop yield by 25.3% ± 3.2 (Bootstrap CI 95%) and 21.9% ± 4.4, respectively. The co-application of biochar with both inorganic and organic fertilizers increased crop yield by 179.6% ± 18.7, however, this data needs to be treated with caution due to the limited dataset. The highest yield increase was observed with amendments to very acidic soils (pH ≤5), but the benefits of biochar were not affected by the rate and the time after the application. In addition, the effects of biochar are enhanced when it is produced at 401–500 °C with a C:N ratio of 31–100. Our results suggest that the co-application of biochar with either inorganic and/or organic fertilizers in acidic soils increase crop productivity compared to amendment with either fertilizer or biochar. Our meta-analysis supports the utilization of biochar to enhance the efficiency and profitability of fertilizers.

Fast and real-time prediction of leaf nutrient concentrations can facilitate decision-making for fertilisation regimes on farms and address issues raised with over-fertilisation. Cacao (Theobroma cacao L.) is an important cash crop and requires nutrient supply to maintain yield. This project aimed to use chemometric analysis and wavelength selection to improve the accuracy of foliar nutrient prediction. We used a visible-near infrared (400–1000 nm) hyperspectral imaging (HSI) system to predict foliar calcium (Ca), potassium (K), phosphorus (P) and nitrogen (N) of cacao trees. Images were captured from 95 leaf samples. Partial least square regression (PLSR) models were developed to predict leaf nutrient concentrations and wavelength selection was undertaken. Using all wavelengths, Ca (R2CV = 0.76, RMSECV = 0.28), K (R2CV = 0.35, RMSECV = 0.46), P (R2CV = 0.75, RMSECV = 0.019) and N (R2CV = 0.73, RMSECV = 0.17) were predicted. Wavelength selection increased the prediction accuracy of Ca (R2CV = 0.79, RMSECV = 0.27) and N (R2CV = 0.74, RMSECV = 0.16), while did not affect prediction accuracy of foliar K (R2CV = 0.35, RMSECV = 0.46) and P (R2CV = 0.75, RMSECV = 0.019). Visible-near infrared HSI has a good potential to predict Ca, P and N concentrations in cacao leaf samples, but K concentrations could not be predicted reliably. Wavelength selection increased the prediction accuracy of foliar Ca and N leading to a reduced number of wavelengths involved in developed models.

Hyperspectral image analysis in laboratory-based settings has the potential to estimate soil elements. This study aimed to explore the effects of soil particle size on element estimation using visible-near infrared (400–1000 nm) hyperspectral imaging. Images were captured from 116 sieved and ground soil samples. Data acquired from hyperspectral images (HSI) were used to develop partial least square regression (PLSR) models to predict soil available aluminum (Al), boron (B), calcium (Ca), copper (Cu), iron (Fe), potassium (K), magnesium (Mg), manganese (Mn), sodium (Na), phosphorus (P) and zinc (Zn). The soil available Al, Fe, K, Mn, Na and P were not predicted with high precision. However, the developed PLSR models predicted B (R2CV = 0.62 and RMSECV = 0.15), Ca (R2CV = 0.81 and RMSECV = 260.97), Cu (R2CV = 0.74 and RMSECV = 0.27), Mg (R2CV = 0.80 and RMSECV = 43.71) and Zn (R2CV = 0.76 and RMSECV = 0.97) in sieved soils. The PLSR models using reflectance of ground soil were also developed for B (R2CV = 0.53 and RMSECV = 0.16), Ca (R2CV = 0.81 and RMSECV = 260.79), Cu (R2CV = 0.73 and RMSECV = 0.29), Mg (R2CV = 0.79 and RMSECV = 45.45) and Zn (R2CV = 0.76 and RMSECV = 0.97). RMSE of different PLSR models, developed from sieved and ground soils for the corresponding elements did not significantly differ based on the Levene's test. Therefore, this study indicated that it was not necessary to grind soil samples to predict elements using HSI.

Biochar compound fertilisers (BCFs) are an emerging technology that combine biochar with nutrients, clays and minerals and can be formulated to address specific issues in soil-plant systems. However, knowledge of BCF performance over consecutive crops and without re-application is limited. This study aims to assess the residual effect of organic BCFs soil-plant nutrient cycling 2 years after application and without additional fertiliser inputs. We applied BCFs and biochar with organic fertiliser amendments and established a crop of ginger and a second crop of turmeric (Curcuma longa) without re-application or additional fertilisation. All treatment formulations included bamboo-biochar and organic fertiliser amendments; however, two novel BCFs were formulated to promote agronomic response in an intensive cropping system. We report here on the effect of treatments on soil and plant macronutrient and micronutrient cycling and turmeric growth, biomass and yield at harvest. Both BCFs (enriched (10 t ha-1) and organo-mineral biochar (8.6 t ha-1) increased foliar K (+155% and +120%) and decreased foliar Mg (-20% and -19%) concentration compared with all other treatments, suggesting antagonism between K and Mg. Plants were limited for K, P and B at harvest but not N, Ca or Mg. Foliar K was dependent on the biochar formulation rather than the rate of application. Biochar-clay aggregates increased K retention and cycling in the soil solution 2 years after application. Clay blended BCFs reduced K limitation in turmeric compared to biochar co-applied with organic amendments, suggesting these blends can be used to manage organic K nutrition. All formulations and rates of biochar increased leaf biomass and shoot-to-root ratio. Novel BCFs should be considered as an alternative to co-applying biochar with organic fertiliser amendments to decrease application rates and increase economic feasibility for farmers. Applying BCFs without re-application or supplementary fertiliser did not provide sufficient K or P reserves in the second year for consecutive cropping. Therefore, supplementary fertilisation is recommended to avoid nutrient deficiency and reduced yield for consecutive organic rhizome crops.

Replenishing soil nutrient particularly total nitrogen (TN) and available phosphorus (P) is important to sustain soil health for food production. Organic amendments such as compost and biochar are commonly applied to improve soil nutrient retention especially N and P. In farms, biochar is usually applied once followed by applying other organic amendment applied in their full rates. Both form and rate of organic amendments can affect soil nutrient concentrations particularly in short term. This study aimed to examine the effects of compost and mixture of compost with biochar (both at full rates) on soil nutrient concentrations in short term. A randomised complete block filed experiment with eight replicates was used for this study. The effects of biochar (5 t/ha) only, compost (at the rates of 10 t/ha, 25 t/ha and 35 t/ha) and biochar mixed with compost (5 t/ha and 10 t/ha, respectively) on soil nutrient concentrations compared with control were explored in a corn field. Compost treatment at the rate of 35 t/ha had significantly higher TN, available P, calcium (Ca) and iron (Fe) compared with other treatments and control. Soil potassium (K) levels remained unchanged among all treatments. Biochar only treatment had significantly higher available P and Ca concentrations compared with biochar mixed with compost treatment. Compost application at higher rate (35 t/ha) proved best practice to significantly increase TN and available P concentrations in short term. Significantly higher available P concentration in biochar only treatment compared with the biochar mixed with compost treatment could have been associated with stimulation of P immobilisation when biochar was mixed with compost. Our results indicated that the form and rate of organic amendments in short term cropping systems are important to be considered while applying to a volcanic soil to ensure N and P availability for plants are not compromised.

Biochar has agronomic potential but currently is too expensive for widespread adoption. New methodologies are emerging to reduce the cost such as enriching biochar with nutrients that match crops and soil requirements. However, the effects of biochar-based fertilisers on plant yield and soil nutrient availability have not been widely examined. This study investigated the effects of a novel organo-mineral biochar fertiliser in comparison to organic and commercial biochar fertiliser on ginger (Zingiber officinale Canton). There were four treatments: (1) commercial organic fertiliser (5 t ha−1), as the control; (2) commercial biochar-based fertiliser (5 t ha−1); (3) organo-mineral biochar fertiliser at low rate (3 t ha−1); and (4) organo-mineral biochar fertiliser at high rate (7.5 t ha−1). A replicated pot trial was established with black dermosol soil and ten replicate pots for each treatment. Ginger was planted and grown for 30 weeks. Plant growth, biomass, foliar nutrients and water extractable soil nutrients including phosphorus (P), potassium (K) and calcium (Ca) were examined. High rate organo-mineral biochar fertiliser increased soil P and K availability at week 30 (harvest) after planting, compared to all other treatments and low rate organo-mineral biochar fertiliser performed similarly to the organic control for P and K. High rate organo-mineral biochar fertiliser increased total foliar nutrient content at week 30 in P, K and Ca compared to commercial biochar fertiliser. High rate organo-mineral biochar fertiliser improved the commercial value of ginger (+ 36%) due to a shift in the proportion of higher grade rhizomes. Low rate organo-mineral biochar fertiliser plants displayed similar yield, total dry and aboveground biomass to commercial organic fertiliser. Commercial biochar fertiliser had significantly lower biomass measures compared with other treatments as the rate applied had lower nutrient concentrations. Our results show organo-mineral biochar fertilisers could be substituted for commercial organic fertilisers at low rates to maintain similar yield or applied at high rates to increase commercial value where economically feasible.

Prescribed fire is a management tool in many Australian and international ecosystems, where it can benefit biodiversity conservation and potentially reduce the risk of extreme wildfires threatening highly valued assets. However, the economic efficiency of prescribed fire is poorly understood. The aim of this study was to progress this understanding by improving estimates of prescribed fire costs. A generalized linear prescribed fire cost model for south-east Queensland has been developed from a dataset of 527 prescribed fire on public land over the period 2004 to 2015, to estimate prescribed fire costs per hectare as a function of environmental predictors. The best model explained 88% of the variance, and significant predictor variables were prescribed fire burned area, fire vegetation group (FVG), forest fire danger index (FFDI), fuel quantity, distance to the nearest building, distance to the nearest Queensland Parks and Wildlife Service and Partnerships (QPWS&P) base, and distance to the nearest freshwater body. Prescribed fire costs per hectare were negatively related to prescribed fire burned area, distances to the nearest building and nearest freshwater body and the FFDI, but positively related to fuel quantity and distance to nearest QPWS&P base. Prescribed fire costs also varied significantly between some FVGs. Prescribed fire burned area had the strongest influence on prescribed fire costs (83% of variation in cost explained). Prescribed fire cost for riparian, foredune and beach ridge vegetation was significantly higher than for heath, while prescribed fire cost for melaleuca vegetation was significantly lower than heath. Higher costs were associated with prescribed fires within 500 m of the nearest building. The model can support the estimation and justification of annual operational budgets for prescribed fire.

The six recommendations made by the Guidelines for Assessment and Instruction in Statistics Education (GAISE) committee were first communicated in 2005 and more formally in 2010. In this article, 25 introductory statistics textbooks are examined to assess how well these textbooks have incorporated the three GAISE recommendations most relevant to implementation in textbooks (statistical literacy and thinking; use of real data; stress concepts over procedures). The implementation of another recommendation (using technology) is described but not assessed. In general, most textbooks appear to be adopting the GAISE recommendations reasonably well in both exposition and exercises. The textbooks are particularly adept at using real data, using real data well, and promoting statistical literacy. Textbooks are less adept—but still rated reasonably well, in general—at explaining concepts over procedures and promoting statistical thinking. In contrast, few textbooks have easy-usable glossaries of statistical...

Organo-mineral biochar fertiliser has the potential to replace conventional biochar and organic fertiliser to improve soil quality and increase plant photosynthesis. This study explored mechanisms involved in nitrogen (N) cycling in both soil and ginger plants (Zingiber officinale: Zingiberaceae) following different treatments including organic fertiliser, commercial bamboo biochar fertiliser, and organo-mineral biochar fertiliser. Soil received four treatments including (1) commercial organic fertiliser (5 t ha−1) as the control, (2) commercial bamboo biochar fertiliser (5 t ha−1), (3) organo-mineral biochar fertiliser at a low rate (3 t ha−1), and (4) organo-mineral biochar fertiliser at a high rate (7.5 t ha−1). C and N fractions of soil and plant, and gas exchange measurements were analysed. Initially, organo-mineral biochar fertiliser applied at the low rate increased leaf N. Organo-mineral biochar fertiliser applied at the high rate significantly increased N use efficiency (NUE) of the aboveground biomass compared with other treatments and improved photosynthesis compared with the control. There was N fractionation during plant N uptake and assimilation since the 15N enrichment between the root, leaf, and stem were significantly different from zero; however, treatments did not affect this N fractionation. Organo-mineral biochar fertiliser has agronomic advantages over inorganic and raw organic (manure-based) N fertiliser because it allows farmer to put high concentrations of nutrients into soil without restricting N availability, N uptake, and plant photosynthesis. We recommend applying the low rate of organo-mineral biochar fertiliser as a substitute for commercial organic fertiliser.

Application of synthetic herbicides is currently the most widely used and cost-effective methods to assist with revegetation programs. However, the effects of short-term application of herbicides such as Roundup®, acetic acid, BioWeed™ and Slasher® as compared with mulch, on soil microbial biomass and microbial diversity remain unknown. This study examined the effects of short-term herbicide application on soil microbial biomass, C:N ratio, and fungal and bacterial communities at months 2 and 8 following initiation of treatment application. No effects of treatments on soil pH, C:N and microbial biomass were found. No segregation among treatments in the community structure of bacteria and fungi was observed. However, the fungal phylum Basiodiomycota had one unidentified class, which was only found in the mulch treatment, suggesting the C quality in the mulch treatment may differ compared with the other treatments. The dry and hot conditions experienced throughout the study period may have resulted in fast degradation of the herbicides and may have minimised the impacts of the herbicides on microbial diversity and community structure. Given that the research was undertaken at a single site and over only a short time frame, the results should be extrapolated with caution. Herbicides may have greater impact with long-term use. Future research will need to assess the revegetation success of each treatment and determine if the observed change in Basidiomycota profile and C quality identified in this study becomes significant over the long-term. We hypothesise that mulching may be a preferred treatment to facilitate weed control in riparian zone revegetation.

Hyperspectral image (HSI) analysis has the potential to estimate organic compounds in plants and foods. Curcumin is an important compound used to treat a range of medical conditions. Therefore, a method to rapidly determine rhizomes with high curcumin content on-farm would be of significant advantage for farmers. Curcumin content of rhizomes varies within, and between varieties but current chemical analysis methods are expensive and time consuming. This study compared curcumin in three turmeric (Curcuma longa) varieties and examined the potential for laboratory-based HSI to rapidly predict curcumin using the visible–near infrared (400–1000 nm) spectrum. Hyperspectral images (n = 152) of the fresh rhizome outer-skin and flesh were captured, using three local varieties (yellow, orange, and red). Distribution of curcuminoids and total curcumin was analysed. Partial least squares regression (PLSR) models were developed to predict total curcumin concentrations. Total curcumin and the proportion of three curcuminoids differed significantly among all varieties. Red turmeric had the highest total curcumin concentration (0.83 ± 0.21%) compared with orange (0.37 ± 0.12%) and yellow (0.02 ± 0.02%). PLSR models predicted curcumin using raw spectra of rhizome flesh and pooled data for all three varieties (R2c = 0.83, R2p = 0.55, ratio of prediction to deviation (RPD) = 1.51) and was slightly improved by using images of a single variety (orange) only (R2c = 0.85, R2p = 0.62, RPD = 1.65). However, prediction of curcumin using outer-skin of rhizomes was poor (R2c = 0.64, R2p = 0.37, RPD = 1.28). These models can discriminate between ‘low’ and ‘high’ values and so may be adapted into a two-level grading system. HSI has the potential to help identify turmeric rhizomes with high curcumin concentrations and allow for more efficient refinement into curcumin for medicinal purposes.