Laboratory Extractions of Soil Phosphorus Do Not Reflect the Fact That Liming Increases Rye Phosphorus Content and Yield in an Acidic Soil.

In addition to aluminum and other heavy metal toxicities, acidic soils also feature nutrient deficits that are not easily overcome by merely adding the required amounts of mineral fertilizers. One of the most critically scarce nutrients in acidic soils is phosphorus, which reacts with aluminum and iron to form phosphates that keep soil phosphorus availability significantly low. Liming ameliorates acidic soils by increasing pH and decreasing aluminum contents; however, it also increases the amount of calcium, which can react with phosphorus to form low-solubility phosphates. In the present work, three liming materials, namely, dolomitic limestone, limestone and sugar foam, were applied on a Typic Palexerult cropped with rye. The effects of these materials on soil properties, including soil available phosphorus extracted with the Olsen and Bray-1 methods, rye phosphorus content in stems and stem and spike harvested biomasses were monitored for nine years. According to the Olsen extraction, the amount of soil available phosphorus generally decreased following liming, with limestone presenting the lowest values; however, the amount of soil available phosphorus increased according to the Bray-1 extraction, though only to a significant extent with the sugar foam from the third year onward. Regardless, the phosphorus content in rye and the relative biomass yield in both stems and spikes generally increased as a consequence of liming. Since crop uptake and growth are the ultimate tests of soil nutrient availability, the inconsistent stem phosphorus content results following the Olsen and Bray-1 extraction methods suggest a lowered efficiency of both extractants regarding crops in soils rich in both aluminum and calcium ions. This decrease can lead to important interpretation errors in the specific conditions of these limed acidic soils, so other methods should be applied and/or researched to better mimic the crop roots' phosphorus extraction ability. Consequently, the effects of the liming of acidic soils on phosphorus availability and crop performance in the short and long term will be better understood.

Effects of Leonardite Amendments on Vineyard Calcareous Soil Fertility, Vine Nutrition and Grape Quality.

Vineyard calcareous soils are usually low in organic matter, which makes them prone to physical, chemical, and biological degradation. Besides, these soils are also usually poor in various nutrients in plant-available form, e.g., iron. To make up for this lack of soil fertility, on the one hand, manures, and on the other, iron chelates are usually used. However, the soil application of these materials is not free from problems, and other amendments based on leonardites could be advantageously used as an alternative. Therefore, two organic amendments, one leonardite alone (1 Mg/ha), and the other leonardite (1 Mg/ha) plus ferrous sulphate heptahydrate (0.5 Mg/ha), were tested for three years in a commercial vineyard calcareous plot under Mediterranean climate. The effects of these amendments on soil fertility, plant nutrient contents, and berry quality were studied against a control of bare soil by means of a fully randomized trial with three repetitions per treatment. Soil organic matter (SOM) increased as a consequence of both leonardite treatments, but much more than expected on the basis of a simple mass transfer from the amendments. With the ferrous-sulphate-heptahydrate-supplemented leonardite, the increase in SOM was noticeably higher. This is explained on the basis of nutrient quantity and intensity-pH-related effects, which increased soil nutrient plant-availability and presumably enhanced vine root growth. In response to the higher plant availability of nutrients, the petiole nutrient concentrations were observed to increase under the leonardite treatments. However, only a trend to increase potassium in petioles and in grape must, linked to a decrease of grape must pH, was observed in harvest quality under the leonardite treatments. Leonardite and adequately supplemented leonardite seem to have potential for increasing SOM contents and nutrient plant-availability, thus improving the soil fertility of vineyard calcareous soils.

The Importance of Liming with an Appropriate Liming Material: Long-Term Experience with a Typic Palexerult.

Aluminium phytotoxicity is considered the main limiting factor for crop productivity in agricultural acid soils. Liming is a common practice used to improve acidic soil properties, but an appropriate liming material is essential for both agricultural productivity and environmental sustainability. A long-term field experiment with two liming amendments (dolomitic limestone and limestone) was developed during 10 years to determine the changes in soil acidity and assess the effects on crop (rye) yields. Although the adverse effects of the soil acidity conditions were alleviated with both amendments tested, dolomitic limestone was the most effective in the short- and long-term period. In terms of the saturation of exchange complex, dolomitic limestone had a better efficiency, likely based on its rate of dissolution. No significant changes in soil organic matter and exchangeable potassium levels between the treatments tested were found. Both liming materials significantly increased the rye total biomass, but interestingly, significant correlations were showed between tissue levels of magnesium and biomass production, but not between the latter and calcium. The increases in rye biomass production compared with control soils at the end of the research were the following: dolomitic limestone, 47%, and limestone, 32%. A link between an increase in magnesium bioavailability and biomass production was found, as well as between magnesium rye content and total, spike and stem biomass. Hence, it could conceivably be hypothesized that since magnesium is crucial for the transport of assimilates from source leaves to sink organs, alleviating its deficiency leads to avoiding the reducing growth rate of sink organs. Although further investigations are needed to gain a better understanding of liming on the biological, chemical and physical soil properties in the long term, our research provides support for the conceptual premise that an appropriate selection of liming material is crucial for the productivity of acid soils.

Use of Endophytic and Rhizosphere Actinobacteria from Grapevine Plants To Reduce Nursery Fungal Graft Infections That Lead to Young Grapevine Decline.

Endophytic and rhizosphere actinobacteria isolated from the root system of 1-year-old grafted Vitis vinifera plants were evaluated for their activities against fungi that cause grapevine trunk diseases. A total of 58 endophytic and 94 rhizosphere isolates were tested. Based on an in vitro bioassay, 15.5% of the endophytic isolates and 30.8% of the rhizosphere isolates exhibited antifungal activity against the fungal pathogen Diplodia seriata, whereas 13.8% of the endophytic isolates and 16.0% of the rhizosphere isolates showed antifungal activity against Dactylonectria macrodidyma (formerly Ilyonectria macrodidyma). The strains which showed the greatest in vitro efficacy against both pathogens were further analyzed for their ability to inhibit the growth of Phaeomoniella chlamydospora and Phaeoacremonium minimum (formerly Phaeoacremonium aleophilum). Based on their antifungal activity, three rhizosphere isolates and three endophytic isolates were applied on grafts in an open-root field nursery in a 3-year trial. The field trial led to the identification of one endophytic strain, Streptomyces sp. VV/E1, and two rhizosphere isolates, Streptomyces sp. VV/R1 and Streptomyces sp. VV/R4, which significantly reduced the infection rates produced by the fungal pathogens Dactylonectria sp., Ilyonectria sp., P. chlamydospora, and P. minimum, all of which cause young grapevine decline. The VV/R1 and VV/R4 isolates also significantly reduced the mortality level of grafted plants in the nursery. This study shows that certain actinobacteria could represent a promising new tool for controlling fungal trunk pathogens that infect grapevine plants through the root system in nurseries.IMPORTANCE Grapevine trunk diseases are a major threat to the wine and grape industry worldwide. They cause a significant reduction in yields as well as in grape quality, and they can even cause plant death. Trunk diseases are caused by fungal pathogens that enter through pruning wounds and/or the root system. Although different strategies have recently been developed to protect pruning wounds using antifungal compounds (natural or synthetic) or biocontrol agents, no tools are yet available for controlling soil pathogens that infect plants through their root system. This study shows that different actinobacterial isolates, when applied to grafts in a nursery, can significantly reduce the infection rate caused by fungal pathogens that enter through the root system. This is a new, promising, and green alternative for preventing the decline of young grapevines in nurseries and vineyards.

Effectiveness of Natural Antifungal Compounds in Controlling Infection by Grapevine Trunk Disease Pathogens through Pruning Wounds.

Grapevine trunk fungal pathogens, such as Diplodia seriata and Phaeomoniella chlamydospora, can infect plants through pruning wounds. They cause grapevine trunk diseases and are involved in grapevine decline. Accordingly, the protection of pruning wounds is crucial for the management of grapevine trunk diseases. The efficacy of different natural antifungals in inhibiting the growth of several fungi causing grapevine trunk diseases was evaluated in vitro. The fungi showing greater in vitro efficacy were tested on autoclaved grape wood assays against D. seriata and P. chlamydospora. Based on results from these assays, chitosan oligosaccharide, vanillin, and garlic extract were selected for further evaluation on pruning wounds inoculated with D. seriata and P. chlamydospora in field trials. A significant decrease in plant mortality was observed after 2 years of growth in the plants treated with the different natural antifungals compared to the mortality rate observed in infected plants that were not treated with antifungals. Also, the infection rate for the inoculated pathogens was significantly reduced in plants treated with the selected natural antifungals. Therefore, natural antifungals represent a promising alternative for disease control and could provide significant economic benefits for the grape-growing industry.