Dwarf nettle (Urtica urens) is an annual herbaceous plant, native to Mediterranean Europe, that grows between 10 and 75 cm in height. Figure 1 Life stages, from germination to floweringLeaves are up to 6 cm in length but often 1-3 cm, oval to elliptical in shape, deeply toothed or serrated on the edges, green to dark green, and covered with scattered stinging hairs. Clusters of small, greenish-white flowers form where the leaves join the stems.Dwarf nettle is also known in Australia as small nettle, lesser nettle, or stinging nettle. Vegetable farmers are likely to be very familiar with it where it is found on their farm, and to be well aware of how to identify it. However depending on its stage of growth, it may be possible to mis-identify it as tall nettle (Urtica dioica), native scrub nettle (Urtica incisa) or potentially deadnettle (Lamium amplexicaule), particularly where the plants are recently germinated.

There is considerable global interest in using recycled organic materials because of perceived benefits to soil health and environment. However, information on the effects of organic waste products and their optimal application rates on the quality of heavy clay soils such as Vertisols is sparse. An incubation experiment was therefore conducted using five organic amendments at various rates to identify their optimal application rates, which could improve the quality of the Vertisol. Cotton gin trash, cattle manure, biosolids (dry weight basis 7.5-120 t/ha), chicken manure (dry weight basis 2.25-36 t/ha) and a liquefied vermicast (60-960 L/ha, volumetric basis) changed the soil chemical, physical and microbiological properties compared with a control where no amendments were applied, viz. higher light fraction of organic matter, nutrient content (N and P) and soil microbial activity. Higher application of chicken manure resulted in an increase in dry-sieved mean weight diameter. Increasing rates of cattle manure increased exchangeable Na concentration and ESP. Although vermicast itself did not contribute a significant amount of N into the soil, when applied at higher rates (60-960 L/ha), its application resulted in increased concentration of NO₃-N in soil by amounts ranging from 43 to 429%. Optimal application rates for cattle manure and cotton gin trash were 30 t/ha, whereas for biosolids and chicken manure, the optimum rate was 60-18 t/ha, respectively.

Marshmallow (also sometimes called ‘small-flowered mallow’ or ‘little mallow’) is an annual sprawling herb, native to the Mediterranean region, with a single long taproot. It can grow up to 1.2 m in height and 2.1 m in width.The plant is woody at the base. Leaves are dull dark green and surrounded with scalloped lobes and radiating veins. They are variable in size, at 2 to 12 cm wide and 1 to7 cm long. Flowers emerge in clusters, with five notched petals white to pale pink, around 5 mm in length. Fruit is a round capsule approximately 1 cm in diameter, containing between 8 and 12 non-hairy seeds. When ripe, these change colour from green to dark brown. There are several other Malva and related species present in Australia, many of which are also weeds of disturbed sites such as cultivation, gardens, drains and roadsides but less prevalent than marshmallow. These include: Tree mallow, Malva arborea; Musk mallow, Malva moschate; Dwarf mallow, Malva neglecta; Mallow-of-Nice, Malva nicaeensis; Cretan mallow, Malva pseudolavatera; Tall mallow, Malva sylvestris; Spiked malvastrum, Malvastrum americanum; Red-flowered mallow, Modiola caroliniana.

Macadamia ('Macadamia integrifolia' Maiden and Betche, 'M. tetraphylla' Johnson and hybrids) orchards in Australia are typically hedged around anthesis (September). Such hedging reduces yields, largely through competition for carbohydrates between early fruit set and the post-pruning vegetative flush, but also through a reduction in photosynthetic capacity caused by the loss of canopy. We examined whether hedging at other times might mitigate yield losses. Hedging time was found to affect yields across four cultivars: 'A4', 'A38', '344' and '816'. Yield losses were lower for trees hedged in November-December than for trees hedged in September. Yields for trees hedged in June were higher than for trees hedged in September in one experiment, but were similar in a second experiment. Yield losses for September and October hedging were similar. Hedging time changed the pattern of fluctuations in stem water-soluble carbohydrates (WSC). WSC declined shortly after hedging in September, October or November, and the declines preceded increases in fruit abscission relative to unpruned control trees. The increase in fruit abscission was less pronounced for the trees hedged in November, consistent with the idea that fruit become less sensitive to carbon limitation as they mature.

Concerns about declining soil organic carbon (SOC) and increased greenhouse gas emissions due to practices such as intensive tillage and bare fallows have encouraged the adoption of practices such as no-tillage, crop rotations and residue retention. However, whilst no-till farming is suited for broadacre crops, it has not been widely adapted for most vegetable production systems. Vegetable production systems, especially organic ones, routinely use tillage to prepare beds and manage weeds. These tillage operations break soil structure and aggregates, which is known to accelerate losses of SOC stocks. Despite requiring multiple tillage operations, the vegetable systems are also characterised by little or no crop residue input, potentially further reducing SOC stocks. The effect of sweet corn ('Zea mays L. var. rugosa') residue management (RM; i.e. incorporation or removal) in a corn-cabbage ('Brassica oleracea' L.) rotation on SOC parameters in two soil management systems (SMS; i.e. organic and conventional) was examined because crop residue incorporation and application of organic fertilisers could be ways to counteract loss of SOC due to tillage in vegetable systems. The principal aim of this thesis was to examine the effect of RM in the two SMS on soil total carbon (TOC) concentrations and stock, soil carbon fractions and microbial biomass carbon (MBC) through a field experiment of a corn/cabbage rotation over two years. A laboratory experiment was performed to separate the confounding factors of SMS in the field experiment, i.e. herbicide and mineral fertilisers in the conventional SMS, and cultivation and organic fertilisers in the organic SMS. To supplement the field experiment, another laboratory experiment focused on how two potentially opposing determinants of TOC, residue incorporation and simulated tillage (sieving), influence the emission of CO₂-C. Although, the research objectives of this thesis are focused on SOC, agronomic and fertility parameters, the essential components of a crop production system, were also considered.

This is the second report the Biological Farmers of Australia has commissioned to help industry bench mark the growth and health of its sectors. This report - another significant milestone in the two decade plus history of the rapidly developing Australian certified organic sector - builds the information base for industry to benchmark production and market value against past and current claims and estimates and will enable monitoring of future growth of the certified organic market in Australia and its farming and production base. In an industry characterised by operational diversity, this report allows for performance assessment by sector. The next publication in this series is planned in 2012 (biennial since the inaugural report in 2008) as a means of providing the wider industry with invaluable and realistic market information.

Intercropping may increase and stabilise crop yield in heavy Vertosol soils and may assist in the uptake of phosphorus (P) nutrient. Phosphorus niche complementarity is the supposition that there is decreased competition due to complementary use of available P and niche distinction among intercropped species in the form of a given P, in space or in time. Phosphorus deficiency and its unavailability for crops commonly limits crop yield in these soils. Thus, intercropping may be an appropriate means to improve the productivity of low input cropping systems in these soils.

This study quantifies biomass yield performance and competition effects, and the capture and utilisation of resources by summer cereals and legumes as sole and intercrops. The principal novelty of this research work reported in this thesis was to investigate the effect of intercropped species (i.e. legumes and cereals) and how phosphorus fertilisers controlled the growth and P uptake (e.g. by sorghum and soybean) of these fertilisers. Thus, both P acquisitions and growth performance processes were evaluated under the interactions with the level of moisture content changes in black vertosol. To address this aim, a one field experiment and two glasshouses experiments assessed P fertiliser and water content on intercrops and corresponding sole crops of soybean and sorghum in irrigated black Vertosol soil. Several methods were used to analyse and present the results of each crop performance, such as univariate analyses, bivariate analysis, indices and graphical methods.

The study covered three aspects of P fertiliser in cropping systems. Firstly, in the field two rates of P fertiliser, 0 kg ha^-1 (P0) and 20 kg ha^-1 (P20), were studied, and intercropped sorghum with soybean was compared to sole crops in irrigated black Vertosol soil. Biomass yield (BY), P yield (PY) and nitrogen yield (NY), which are the measure of competition and complementary efficiency, were used for comparison of the relative performance of sorghum and soybean as sole crops and intercropped. The BY, PY and NY were higher by 39%, 48% and 47%, respectively, in intercropped soybean with sorghum than in sole soybean for both P rates, but their value was higher in P20. However, soybean was not aggressive to sorghum; the BY and NY of sole sorghum and mixed sorghum were still on par, while PY was higher by 77% at P0 and 86% at P20 in intercropped sorghum with soybean than sole sorghum. When these results were combined with waterlogged conditions, there were indications of low competition between intercropped species and sorghum appeared to facilitated nitrogen (N) and P uptake by soybean in these conditions.

The second phase of the study examined P utilisation and plant growth in a sorghum/soybean intercropping system compared to individual soybean and sorghum plants in a moist Vertosol soil. Soybean was either inoculated with Rhizobium or N fertiliser, and sorghum was N fertilised at 50 kg/ha. One glasshouse experiment was conducted in root boxes (two plants per box). Phosphorus fertiliser was applied between the plants for the sole treatments and half of the mixed treatments and under each plant for the other half of them. Phosphorus fertiliser was tracked using ³²P and ³³P isotope methods. Generally, the water depletion in sorghum was higher and faster than soybean in moist conditions. Intercropping soybean with sorghum in moist Vertosol soil increased its biomass yield and P content in the green parts, thereby improving its performance. Sorghum was more competitive for P fertiliser than soybean when the P fertiliser was added between plants. However, soybean with N fertiliser was unaffected by sorghum competition on P fertiliser when it was applied under the plants. Overall, water uptake by mixed sorghum/soybean roots in moist Vertosol soil appeared to affect the water status of soybean roots, thus increasing their growth and nutrient uptake.

Phosphorus utilisation and plant growth in sorghum/soybean combined in pots were compared to separate individual soybean and sorghum plants with different irrigation patterns in the third phase, a single glasshouse study. Three watering patterns were dry, wet and fluctuation from wet to dry (DW). Here, it was demonstrated that biomass yield and P parameters for sole soybean were similar to soybean planted with sorghum in three irrigation patterns. Similarly, the biomass yield and P parameters of sorghum were unaffected by planting pattern in dry and DW irrigation patterns. However, the biomass, P content and P utilisation of mixed sorghum exceeded that of sole sorghum in wet irrigation treatment. Attributes of mixed sorghum were higher than mixed soybean in all treatments. Overall, wet treatment conditions had increased growth and P utilisation of mixed sorghum. In contrast to the previous two experiments, wet and DW conditions had no effect on mixed soybean. It is possible that soybean and sorghum were competing for nutrients in the limited soil of the small pots compared to field and root boxes. In addition, the soil did not flood in the pots because of the high infiltration rates of short pots compared to the other two experimental methods.

The findings of these studies indicate the potential for higher productivity and P utilisation of mixed soybean with sorghum in moist black Vertosol by utilising carefully planned water management. Further research is needed in multiple years or locations, and repeated glasshouse studies.

Soil organic carbon (SOC) is the part of carbon (C) in the soil that is derived from living organisms and plays an important role in the C cycle (Paustian et al. 1997). Soil is a major reservoir of soil C, at 3.3 times the size of the atmospheric pool of 760 pentagrams (Pg) and 4.5 times the size of the biotic pool of 560 Pg (Lal 2004). Soils act as a reservoir of SOC and the level of storage within an ecosystem is mainly dependent on the soil type, climate, land use history, and current management practices. The quantity of SOC stored in a particular soil is dependent on the quantity and quality of organic matter returned to the soil matrix, the soil's ability to retain SOC (a function of texture and cation exchange capacity), and abiotic influences of both temperature and precipitation (Grace et al. 2005). SOC is essential for maintaining fertility, water retention, and plant production in terrestrial ecosystems with different land uses (Grace et al. 2006). Soil organic matter (SOM) maintains soil structure and productivity in agroecosystems (Lal 2010). Maintaining high levels of SOM is beneficial for all agriculture and crucial in improving soil quality. SOM has been widely used as an effective indicator of the functional response of soils to land use intensification (Dalal et al. 2003).

Yields of macadamia ('Macadamia integrifolia', 'M. tetraphylla', and hybrids) orchards tend to increase with increasing tree size up to ≈94% light interception. Beyond this, there is some indication that crowding leads to yield decline, but the evidence is limited to one site. Increasing tree size and orchard crowding also present numerous management problems, including soil erosion, harvest delays, and increased pest and disease pressure. The aim of this study was to better characterize long-term yield trends in mature orchards and to assess the effects of manual and mechanical pruning strategies on yield, nut characteristics, tree size, and economics. We monitored yield at four sites in mature '344' and '246' orchards for up to seven years and confirmed a decline in yield with crowding for three of the sites. There was a small increase in yield over time at the fourth site, which may reflect the lower initial level of crowding and shorter monitoring period compared with the other sites, and highlights the need for long-term records to establish yield trends. Pruning to remove several large limbs from '246' trees to improve light penetration into the canopy increased yield relative to control trees but the effect was short-lived and not cost-effective. Removal of a codominant leader from '344' trees reduced yield by 21%. Annual side-hedging of '246' trees reduced yield by 12% and mechanical topping of '344' trees caused a substantial reduction in yield of up to 50%. Removal of limbs in the upper canopy to reduce the height of '344' trees had less effect on yield than topping but re-pruning was not practical because of the extensive regrowth around the pruning cuts. Tree size control is necessary for efficient orchard management, but in this study, pruning strategies that controlled tree size also reduced yield. Research into the physiological response to pruning in macadamia is required to improve outcomes.

In Australia, the surface and subsurface soils of the majority of cotton ('Gossypium hirsutum' L.)-growing regions are sodic. Application of organic amendments can be an option to stabilize the structure of sodic Vertisols due to their potential positive effect on soil physical properties. An incubation experiment was conducted for 4 wk in a temperature-controlled (30°C) growth chamber to study the effect of organic amendments on the properties of two Vertisols with different sodicity levels. The exchangeable Na percentages (ESPs) in these Vertisol soils collected from the Australian Cotton Research Institute (ACRI) near Narrabri, New South Wales, and a commercial cotton farm near Dalby, Queensland, were modified such that three different sodicity levels resulted, i.e., nonsodic (ESP<6), moderately sodic (ESP 6-15), and strongly sodic (ESP>15). The organic amendments used were cotton gin trash (60 Mg ha⁻¹), cattle manure (60 Mg ha⁻¹), and composted chicken manure (18 Mg ha⁻¹), as well as an unamended control. The organic amendments improved the physical properties of both Vertisols by decreasing clay dispersion. In the Dalby soil, cotton gin trash produced the largest decrease (29%) in the dispersion index over the control at the moderate sodicity level, whereas in the strongly sodic soil, the lowest dispersion index resulted from the application of chicken manure. Nutrient availability (N, P, and K) was also increased significantly at higher sodicity levels for both the ACRI and Dalby soils by using organic amendments. These results indicate that using organic amendments can be beneficial for the amelioration of sodic vertisols and also to sustain soil quality.