Soil Research最新文献

Soil nutrient limitations characterise savanna soils globally and are one of several constraints to establishing productive tree plantations and enhancing economic opportunities in tropical regions. Fertilisation offers an approach to overcome soil nutrient limitations to maximise tree growth and health, but requires research on nutrient contents, composition, rates and methods of delivery in the context of soil characteristics.

To determine the optimal contents, rates and methods of application of fertiliser to maximise the growth and health of the plantation timber species Pinus caribaea on low fertility savanna soils.

Factorial field experiments tested growth responses to applications of phosphorus (P), nitrogen (N) and sulfur (S) on three soils near Darwin, Australia. Further experiments tested effects of zinc (Zn), copper (Cu) and potassium (K) application and small-scale variation in soil characteristics on tree performance.

Positive growth responses to P, N and S were recorded, yet unhealthy trees developed, particularly in better-performing treatments. Second phase experiments addressing potential causes of ill health confirmed Zn limitations. Intense spatial soil sampling demonstrated substantial variation in cation exchange capacity and composition over short distances.

Nutrient additions to enhance plantation tree growth will need to encompass minor and trace elements in addition to N, P and S, specifically Zn, and consider the mechanism of application.

Small-scale variability in cation exchange capacity and composition indicates that optimal fertilisation rates will vary spatially, and that soil sampling for site characterisation would be more accurate with replicated dispersed samples.

Agricultural land use is intensifying globally. Irrigation and other farm practices associated with intensification, such as cultivation, grazing, and fertiliser application, can increase nutrient losses. Variable rate irrigation (VRI) systems manage irrigation to spatially variable soils and different crops (zones). We lack knowledge on nutrient losses under zone-specific irrigation for mixed-cropping systems (combined crop and livestock grazing).

This study evaluated drainage, nitrogen, and phosphorus leaching losses under zone-specific irrigation for a temperate mixed-cropping system.

The study site had sheep grazing and crops including peas, beans, wheat, turnips, plantain, and ryegrass-white clover pasture. It had a variable-rate centre-pivot irrigator for two soil zones (free draining Zone 1; poorly drained Zone 2). Drainage flux meters (DFMs) collected drainage leachate, and samples for measurement of nitrogen (N) and phosphorus (P) concentrations. Soil water balance data and statistical modelling evaluated nutrient leaching losses over 5 years.

The mean leaching load of NO_x-N (nitrate + nitrite) across 5 years was 133 (s.d. 77) and 121 (s.d. 97) kg N/ha/year for Zone 1 and Zone 2, respectively. Similarly, the mean leaching load of reactive P across all years was 0.17 (s.d. 0.30) and 0.14 (s.d. 0.14) kg P/ha/year for Zone 1 and Zone 2, respectively. The nitrogen concentrations and loads generally had greater uncertainty in Zone 2.

The DFMs worked well for the free draining sandy soil. However, fewer samples were collected in the silt soil, requiring the statistical modelling developed in this study. This study gave a reasonable estimate of annual leaching load means, but the indicators of their within-year variation were not reliable, partly due to differences in sampling frequency. With some exceptions, there was generally more NO_x-N leaching from the free draining Zone 1. VRI provided a system to control irrigation-related drainage and leaching in these soil zones.

Drainage flux meters are more reliable in well-drained than in poorly drained soil. Given the lack of published studies, this study has improved knowledge of nutrient losses under zone-specific irrigated mixed-cropping systems in a temperate climate.

More than 830 million ha of soils are salt affected, representing around 9% of the world’s land surface. Groundwater high in salt already covers some 16% of the land area. Saline water can be used effectively for irrigation by salt leaching to despatch the accumulated salts, but this can pose a risk of salinisation of groundwater. It is important that the efficacy of salt leaching is confirmed, and the impacts of salt loading below the rootzone can be assessed.

We examine the efficiency and impact of salt leaching to remove salt from the rootzone.

Our soil, a Typic Torripsamment, is the dominant soil across the Arabian Peninsula. We carried out detailed laboratory experiments of salt leaching dynamics via salt breakthrough curves, analytical modelling, and through the field monitoring of impacts.

Analytical solutions well predicted the salt breakthrough curves from repacked soil columns in the laboratory and we were able to confirm that all of the soil’s water was actively involved in transport, and that salt behaved as an inert tracer. The breakthrough curves were well predicted using a small solute dispersivity, so piston displacement was found to be a good assumption. Salt was easily flushed from the columns. To back this up in the field, soil sampling was carried out down to 1 m across 36 profiles after the harvest of a halophytic crop irrigated with saline water. Salt storage was only 1.8 kg m⁻², even though 80 kg m⁻² had been applied. This is a positive result for managing irrigation.

Salt leaching can maintain equable salinity in the rootzone. However, this leaching carried salt back to groundwater at 2–3 times the concentration of the applied water. We confirmed that the amount of salt leaching back to groundwater can be significant.

This salt dilemma will require careful management to achieve crop yields and protect the environment.

Gully erosion is a significant socioeconomic and environmental issue that affects agricultural productivity, infrastructure, and water quality of receiving waters. Despite a variety of interventions to prevent gully formation and rehabilitate existing gullies, cost-effective interventions are specific to individual gullies.

The aim of this study was to assess the performance of a suite of gully management interventions across three different classical gullies.

A one-dimensional process-based model, MERGE (modelling erosion resistance for gully erosion), was used to quantify the sediment yield exiting the gullies, in response to various management interventions.

The net decrease in sediment yield was 2.5–57.4% for each of four interventions applied in isolation and 51.2–78.7% in combination. Reductions in sediment yield for each intervention varied markedly among sites, by a factor of 2.6–78.3 in absolute terms. This resulted in a unique ranking of the interventions by their effectiveness for a given site. Overall, interventions applied in combination were most effective, outperforming those applied in isolation by a factor of 1.24–1.37, but the effect of applying interventions in combination was not additive.

This study demonstrates the ability of the gully erosion model MERGE to be a useful tool to identify and tailor effective intervention strategies for individual gullies, and be a useful guide for decision making for erosion management.

Analysis of expected benefits of gully remediation using tools such as MERGE is important for assessing options at gully sites due to their widely varying response.

The spreading of olive mill waste waters (OMWW) could offer an appropriate management option to add value to this agricultural by-product, such as to increase soil fertility and plant productivity.

The main objective of this work was to evaluate the effects of the application of OMWW (at a fixed dose of 50 m³ ha⁻¹), in the long term (20 years) on the soil rhizospheric properties and on old olive trees (80 years old) growth and productivity.

The experimental site consists of four plots treated with OMWW (T₁, T₂, T₃ and T₄) and four ‘control’ plots (C₁, C₂, C₃ and C₄), without any treatment. The treated plots have received each a fixed dose of 50 m³ ha⁻¹ of OMWW in February of each year since 2004.

The results obtained showed that the addition of OMWW increased the soil water retention capacity (SWRC) and its organic matter content (OMC), as well as the augment of phosphorus (P) and potassium (K) levels. The activity of the soil rhizospheric microflora was significantly enhanced.

OMWW application to the soil surface in an olive orchard at 50 m³ ha⁻¹, since 2004, had no negative effects on the tree’s vegetative growth and satisfied plant P, K and N requirement.

Our study showed that OMWW can enhance the soil properties and enrich the soil with necessary minerals.