Seth Laurenson

Microorganisms in soils are responsible for many ecosystem services. However, in degraded soils microbial abundance and function are limited which compromises several biologically facilitated processes. Inoculating soils with desirable microbes can help to re-instate or initiate a viable functioning microbial community. However, establishment success is reliant on the survival of the microorganism in an adverse environment. In this proof-of-concept study, artificial microbial refugia have been developed using resin and light-emitting diode array (LED) 3D printing technology. We assessed whether the artificial refugia, termed a Rhiome, would support better microbial growth in degraded soils. Soil compaction, a form of soil degradation, and Rhizobium, an important microorganism for global agriculture, were both selected as the use case application for this assessment. Different materials together with resin were assessed for their suitability as a 3D printing material and for supporting rhizobial growth. The best result was found in materials constructed with a combination of polylactic acid (PLA) resin, yeast extract and mannitol. In a soil compaction experiment with inoculation of rhizobia, the addition of Rhiome significantly increased bacterium survival in the compacted soil to a level similar to, or higher than, the rhizobial loading in non-compacted soils. Augmentation of the resin with yeast extract and mannitol increased Rhizobium growth significantly compared with the Rhiome constructed only with resin. These results indicate that the Rhiome was highly beneficial for instigating and maintaining significant rhizobia survival and growth in compacted soils. Further work, including near-to-field assessments, are required to assess Rhiome performance in a range of applications and to refine material properties relative to important context-specific performance metrics such as degradation rate. We propose the Rhiome concept as a promising asset in the toolbox for soil ecological restoration as a means of improving soil resiliency.

BACKGROUND: Faecal contamination from dairy farm effluent is a major risk to water quality in New Zealand. In this experiment we have tested the efficacy of Kombucha SCOBY (symbiotic culture of bacteria and yeast), to reduce the concentration of Escherichia coli in dairy shed effluent (DSE).RESULTS: Kombucha SCOBY was highly effective in lowering the number of E. coli colony forming units (CFUs) to levels that were undetectable. The decrease in CFUs occurred rapidly within 48 h of Kombucha SCOBY being inoculated to the effluent matrix and was accompanied by a corresponding decline in pH.CONCLUSION: We conclude that Kombucha SCOBY was effective in reducing the abundance of E. coli in DSE due to its effect on solution pH. Further work is required to assess the practicality of treating DSE with Kombucha SCOBY within a farm environment where effluent management and climatic complexities are important. © 2021 Society of Chemical Industry.

Irrigation is a useful crop enhancement procedure up to the point where free surface water appears. However, over-irrigation can lead to an accumulation of free water on the soil surface, which in turn results in overland flow and a high risk of contaminant loss. The current work addresses the problem of measuring free water on the surface of agricultural soils by a real-time acoustic remote sensing method. Directional acoustic transmitter and receiver arrays are used to define a “footprint” on the ground from which changes in reflectance are sensed. These arrays are mounted on a moving irrigator. Chirp signals are used to provide along-path resolution and to ensure robustness against unwanted acoustic background noise from farm machinery and the irrigator. Field measurements have been conducted above a well-defined “quadrat” with controlled and measured water content and also with the instrument mounted on an operational irrigator. A structured light camera mounted above the footprint is used to validate surface water fraction. It is found that the areal fraction of free water on the soil surface can be reliably estimated from changes in the amplitude of the reflected sound waves. The mechanism giving rise to the observed acoustic reflectivity changes is discussed and a model is developed which agrees with normalized intensity observations with a coefficient of determination R² between 0.65 and 0.83. The rms error between model predictions and observations is comparable to the rms variation of the measurements, indicating that there is insignificant error due to the choice of model.

To meet the water quality outcomes sought by catchment communities and regulators, the losses of nitrogen (N), phosphorus (P) and sediment from dairy and sheep/beef farms must be reduced across many catchments. We conducted a high‐level desktop analysis of farm typologies and established that if mitigation actions were fully implemented across dairy and sheep/beef farms, losses of N and P could have been decreased by up to 16 and 23%, respectively, compared to the estimated losses for 2015 (where established actions were only partially implemented). Potential decreases were greater for dairy land (34% N and 26% P) because of its greater per hectare yield and number of mitigation actions available before land use change is required. If established and developing mitigation actions were fully implemented by 2035, potential N, P and sediment losses may decrease by up to 34, 39 and 66%, respectively, compared to actual 2015 losses. These results can inform investment and planning by the rural sector as part of an assessment of the potential for on‐farm actions to mitigate losses from existing land use.

This paper reviews the effects of irrigation on soil physical properties, particularly soil water movement and storage, under predominantly pastoral systems. Few studies address how irrigation impacts these in temperate climates, with very few studies under modern spray irrigation and intensive pastoral farming. Irrigation generally means intensive land use will occur. It is difficult to uncouple factors affecting physical conditions such nutrient cycling, land use, stock class, grazing management and animal treading. Irrigation (with associated increased land use intensity) tends to alter soil physical properties, changing them to be like soils formed under higher rainfall particularly in arid and semi‐arid climates. Changes in physical properties under irrigation in temperate and sub‐humid climates were more variable. Some studies showed increased available water capacity, while others showed no change. Knowledge gaps include effects of irrigation intensification on soil physical properties under modern farm systems to improve process, management, spatial and temporal information.

(2018). Preface from the editors. New Zealand Journal of Agricultural Research: Vol. 61, Special Issue: Soil, a Balancing Act Down Under: Selected papers from the combined NZSSS / ASSS conference, Queenstown, New Zealand. Guest Editors: Seth Laurenson, Jim Moir and Tony van der Weerden, pp. 313-314.

Dairy cow effluent collected over winter from a loose‐housed barn was applied to a series of large infield plots (400 m ² ) using low rate and low depth (LRLD) application methods. Applications were confined to the winter period, at a time when soil moisture content was often at or very near to field capacity and was applied over two seasons. Cows were confined to the housing facility during winter only, and outside of this period they remained on pasture. Losses of nitrogen (N), phosphorus (P) and the faecal indicator bacterium Escherichia coli ( E. coli ) in surface runoff and subsurface drainage from the LRLD treatment were compared with losses from effluent applications that occurred during spring to autumn, at an application depth not exceeding the soil water deficit, i.e. a standard practice treatment (SP, typically 10–15 mm per application). The annual quantities of nutrients applied by the treatments and the grazing managements imposed were similar. Although winter losses of N were significantly greater for the LRLD treatment (15 vs. 8 kg N ha ⁻¹ for the SP treatment), on an annual basis fluxes were similar between treatments (approximately 20 kg N ha ⁻¹ year ⁻¹ ). Effluent management had no significant effect on the annual fluxes of P and E. coli although the latter varied considerably. Average contaminant fluxes over a 2‐year period indicated that the LRLD management system did not lead to a significantly greater risk to water quality compared with standard practices.

This study used the DairyNZ Whole Farm Model to assess the cost–benefit of duration‐controlled grazing (DCG) to reduce the time dairy cows spend on pastures with high soil water content. Within the model, grazing duration was reduced from 21 hours down to 17, 13 or 0 hours when soil moisture was above a critical water content. Scenario farms encompassed four climatic regions of New Zealand and two soil types. Regardless of region, soil type or grazing duration, implementation of DCG was not profitable except in one single instance. Furthermore, increased pasture production in response to DCG was minimal due to poor pasture management. Farms located on poorly drained soils experienced more wet days per year, thereby increasing the frequency of standoff pad use and higher operational costs. Results indicate that any financial benefit that was gained from protecting imperfectly drained and poorly drained soils through DCG was diminished by a high capital repayment and operational cost associated with the off‐paddock facility.