Effects of Harvesting Mucuna bracteata on the Legume Biomass and Soil Properties under Mature Oil Palm

The under-utilized legume Mucuna bracteata is a potential biomass resource in Malaysia. A 24-month study was conducted under 10-year-old mature oil palm trees to determine the effects of several harvesting frequencies of M. bracteata on the legume biomass and soil properties. The experimental design was a randomized complete block design (RCBD) for the biomass and a two-factorial RCBD for the soil properties. The treatments were the harvesting frequencies, which were once every two, four, six, and twelve months. The control treatment was without harvest. There were significant effects on the legume’s cumulative biomass, standing biomass, leaf area, nutrient contents, and total nutrient harvested for N, Ca, Mg, and cellulose content. Generally, the more frequent the harvest, the more biomass was obtained, but the more legume standing biomass and leaf area were reduced. Despite the reduction in legume growth and leaf area in the field, harvesting the legume did not affect any of the soil physicochemical properties. The biomass N, Ca, and Mg contents and nutrient harvested were also affected by harvesting. This was due to the production of relatively more young shoots after harvesting, which would remove most of the aboveground plant parts. The cellulose content in the legume also increased for the same reasons. Results showed that harvesting M. bracteata once every six months was an acceptable compromise between collecting large amounts of legume biomass and having a reduced legume growth recovery and leaf area in the field, but yet not detrimentally affecting the soil properties.

The ACC-Deaminase Producing Bacterium Variovorax sp. CT7.15 as a Tool for Improving Calicotome villosa Nodulation and Growth in Arid Regions of Tunisia

Calicotome villosa is a spontaneous Mediterranean legume that can be a good candidate as pioneer plants to limit regression of vegetation cover and loss of biodiversity in Tunisian arid soils. In order to grow legumes in such soils, pairing rhizobia and nodule associated bacteria (NAB) might provide numerous advantages. In this work, cultivable biodiversity of rhizobial symbionts and NAB in nodules of C. villosa plants growing in five arid regions of south Tunisia was characterized. Phylogenetic analysis using 16S rDNA gene, dnak, recA and nodD sequences separated nodule-forming bacteria in six clades associated to genera Ensifer, Neorhizobium, Phyllobacterium and Rhizobium. Among NAB, the strain Variovorax sp. CT7.15 was selected due to its capacity to solubilise phosphate and, more interestingly, its high level of aminocyclopropane-1-carboxylate deaminase (ACC deaminase) activity. C. villosa plants were inoculated with representative rhizobia of each phylogenetic group and co-inoculated with the same rhizobia and strain CT7.15. Compared with single rhizobia inoculation, co-inoculation significantly improved plant growth and nodulation, ameliorated plant physiological state and increased nitrogen content in the plants, independently of the rhizobia used. These results support the benefits of pairing rhizobia and selected NAB to promote legume growth in arid or degraded soils.

Subsoil microbial community responses to air exposure and legume growth depend on soil properties across different depths

Anthropogenic disturbance, such as agricultural and architectural activities, can greatly influence belowground soil microbes, and thus soil formation and nutrient cycling. The objective of this study was to investigate microbial community variation in deep soils affected by strong disturbances. In present study, twelve soil samples were collected from different depths (0–300 cm) and placed onto the surface. We investigated the structure variation of the microbial community down through the soil profiles in response to disturbance originated by legume plants (robinia and clover) cultivation vs. plant-free controls. The high-throughput sequencing of 16S rRNA genes showed that microbial α-diversity decreased with depth, and that growing both plants significantly impacted the diversity in the topsoil. The soil profile was clustered into three layers: I (0–40 cm), II (40–120 cm), and III (120–300 cm); with significantly different taxa found among them. Soil properties explained a large amount of the variation (23.5%) in the microbial community, and distinct factors affected microbial assembly in the different layers, e.g., available potassium in layer I, pH and total nitrogen in layer II, pH and organic matter in layer III. The prediction of metabolic functions and oxygen requirements indicated that the number of aerobic bacteria increased with more air exposure, which may further accelerate the transformation of nitrogen, sulfur, carbon, and pesticides in the soil. The diversity of soil microorganisms followed a depth-decay pattern, but became higher following legume growth and air exposure, with notable abundance variation of several important bacterial species, mainly belonging to Nitrospira, Verrucomicrobia, and Planctomycetes, and soil properties occurring across the soil profiles.

Soil acidity and aluminium in South Island high and hill country: new data and future needs

Soil extractable aluminium (Al) concentrations can have a strong impact on the establishment, growth and persistence of pasture legumes. This has become clear in New Zealand high and hill-country, where legumes are scarce and failing to persist in acid soils with high Al levels. For the last decade a research programme has been conducted at Lincoln University focused on legume growth and persistence in acid, high Al concentration soils. Research has examined several aspects of soil acidity and Al toxicity and screened and evaluated a range of legume species, identifying several that show promise in their growth and persistence under acidic and high Al concentrations, in addition to harsh climatic environments. This paper summarises this extensive body of research and also suggests some future research topics for addressing the growing challenge of increasing soil acidity and soil Al faced by increasing numbers of producers.

Sustainable perennial pastures in Northland

In the northern half of Northland, perennial ryegrassbased pastures have exhibited poor persistence. Nineteen tall fescue and ryegrass pastures in the region infected with either MaxP or AR37 fungal endophytes, respectively, had high levels of endophyte-infected tillers and low levels of contamination from wild endophytes. On surveyed farms, MaxP-infected tall fescue pastures had good contents of sown grass, which were higher than sown grass contents in AR37-infected ryegrass pastures, but on two far-north monitor farms these temperate grasses failed to compete with summer active C4 grasses such as kikuyu and carpet grass. For tall fescue and perennial ryegrass to form productive pastures in this region, sown seed should have high levels of viable endophyte, soil fertility should be adequate for good grass and legume growth, and pastures should be well managed. Summer droughts may still be too severe in some years for these temperate grasses to persist in the face of C4 grass competition. Keywords: Endophyte, Epichloë, Neotyphodium, Lolium perenne, Festuca arundinacea, soil fertility