New AG International NOV/DEC 2020
Cobalt is found in most soils at low concentrations Cobalt incidence depends on soil's parent material, soil's texture and its contents of organic matter. Sorption by mineral surfaces and organic matter decreases with rising pH, in a similar way to that of zinc (Zn) and nickel (Ni). Weathered, coarse-textured soils are generally low in cobalt (Co) because they don't resist its leaching. Finer-textured soils, and soils containing higher levels of organic matter, tend to have greater Co concentrations. And soils developed from minerals such as olivine and pyroxene have ample Co. It is largely present as Co2+. Its highest masses are required in trace amounts by atmospheric nitrogen fixing microorganisms.
Cobalt is essential for leguminous plants Cobalt is an essential component of several enzymes and co-enzymes that can affect the growth and metabolism of plants. Under low Co containing soils, a small increase in Co stimulates growth of both algae and higher plants. However, high Co concentrations can become toxic to plants.
Some plants appear to benefit from trace amounts of Co, but their preferences vary widely at 4-600 µg/kg (ppb), depending upon plant species and soil content. In general, broadleaf (dicot) plants, especially legumes, take up and accumulate more Co than grasses and grain crops. Cobalt concentrations in forage dry matter typically range between 10-500ppb, which corresponds well with 100ppb Co that meets animal nutritional requirements. When soil is comparatively low in Co, mixing legumes with grasses often improves the Co supply to grazing livestock.
Cobalt is actively absorbed by roots as Co2+, and it can be moderately mobile within plants when complexed with organic compounds. But inorganic Co2+ movement from roots to stems and leaves is poorly mobile in plants. There is insufficient understanding of the role of Co in plant nutrition.
Some beneficial effects of Co include retardation of leaf senescence, increased drought resistance in seeds, regulation of alkaloid accumulation in medicinal plants, and blocking synthesis of ethylene, the plant stress hormone. Cobalt is not found at the active site of any respiratory chain enzyme but is involved in mitochondrial respiration. Non-legume plant species can grow on soils with very low Co availability, without presenting any Co deficiency symptoms. But legumes (e.g. soybean, alfalfa, clover, beans) that require it for nitrogen (N) fixation exhibit Co deficit by N-deficiency symptoms, namely uniform chlorosis, or reddening of leaves, and stunting. Also, smaller than usual root nodules, retardation of seed production and reduced seed germination under dry conditions. Co phytotoxicity can be severe when plants' Co is above 50-100ppm in dry matter. The direct symptoms of Co toxicity often appear as stunted plants, with chlorotic young leaves and discolored veins. It may also result in iron deficiency symptoms.
Cobalt is essential for animals to synthesize vitamin B12. Vitamin B12, also known as cobalamin, is a cofactor in DNA synthesis and in the metabolism of fatty acids and amino acids. It is particularly important in the normal functioning of the nervous system via its role in the synthesis of myelin, and in the maturation of red blood cells in the bone marrow. Predators can source their B12 vitamin from their vegetarian prey, but vegetarians depend on their forage to satisfy their requirement for this essential vitamin. Too low Co concentrations in plant forage provoke Co deficiency disease on grazing animals.
Ruminants, however, rely on their rumen flora which, if supplied with sufficient Co, can synthesize vitamin B12, which is finally consumed by the hosting animal. Non-ruminant farm animals need higher Co, that can be obtained by Co fertilization of the forage, or by mineral Co supplements, directly administered to the animals.
Cobalt application is simple Cobalt deficiency in plants can be corrected by mixing Co salts with a fertilizer or with a sand carrier, and spreading over the grazing pastures. Co application rates for improving legume growth are very low, at 45-140 g/ha of actual Co, as Co-nitrate or Co-sulphate. Other methods to boost plant Co concentrations include seed treatment or foliar sprays. The critical soil concentration of Co to meet the plant requirement is very low and varies significantly between crop species.
Most crops show remarkable responses A clear-cut positive response to Co fertilization of peanuts was shown by Gad, 2012. Fertigated Co at 8ppm significantly increased the tissue concentrations of N, phosphorus (P), potassium (K), manganese (Mn) and Zn, and markedly enhanced nitrogen-use efficiency. Additionally, plant's growth was improved by 34 percent compared with non-Co-treated plants. This positive response was attributed to improved N-fixation.
Farooq et al., 2012, reported enhanced crop growth of common bean (leguminous), oat and squash (non-leguminous) following seed treatment with diluted Co solutions (see Table 1). The squash responded by increased plant dry matter, number of female flowers and fruit yields. The oat responded with increased panicle length, number of seeds/panicle and grain yield. The latter authors also mentioned excessively high Co accumulation was manifested as interveinal chlorosis in new leaves, followed by white leaf margins and tips.
These results and other ones suggest that cobalt is not only an essential nutrient for N-fixing bacteria, but is also beneficial and almost essential to numerous non-legume plants.
An N-deficient bean plant; similar symptoms take place under Co deficiency. Photo: IPNI
Table 1. Positive responses to seed treatment by different Co application rates (Source: Farooq et al., 2012)
Co fertilizer
Solution concentration (mg/L)
Crop treated
Yield increase
(%)
Co(NO3)2
1
Common bean
53
CoSO4
0.5
Summer squash
41
10
Oat
11
New AG International NOV/DEC2020
Portuguese biotech company Asfertglobal has released field-trial results on the application of biofertilizers on apple production.
This is the first study of biofertilizer application on the Gala Redlum variety in Portugal, the company told New AG International. “In general, the study of the effect of biofertilizers in fruit trees is almost done in laboratory conditions and without long-term field assessments to prove the results in uncontrolled conditions,” Asfertglobal told New Ag International. “But this study evaluated the use of biofertilizers in commercial real conditions, reinforcing agronomic and physiological assessments that are not made in laboratory conditions,” the company said. Asfertglobal established the experimental protocol with the Institute of Agricultural and Veterinary Research of Portugal (Instituto Nacional de Investigação Agrária e Veterinária – INIAV, I.P.). The trial, which is on-going, began in May 2018 and the results shared by the company are for the 2018 and 2019 crop seasons. The crop was the Gala Redlum variety of apples. ‘Gala’ is the main variety of apple in Portugal and ‘Redlum’ is a recent clone of ‘Gala’ with a more intensive red colour of the fruits than the standard clones, Asfertglobal told New AG International. “It is the first study made with this variety and in these conditions in Portugal, not common because it is time consuming and the number of years needed for conclusions, and can not only prove to be an important tool in orchards development but also in the possibility of reducing fertilizers applications, concerning recent environmental challenges,” said Miguel Leão, PhD, who was conducting the trial, and is a researcher with INIAV. The study was carried out using three of Asfertglobal’s biofertilizers, applied in different doses: Mycoshell, whose mycorrhizae improve the transport of nutrients and gives plants greater resistance to pathogenic organisms; Kiplant All-Grip, a biofertilizer composed of phosphorus-solubilising microorganisms, and finally Kiplant iNmass a biofertilizer that increases the production of phytohormones such as Indole-3-acetic Acid (IAA), which aids the formation of lateral roots, in the stimulation of cell division and in the elongation of the roots and stem. In terms of the results and biometrics, Asfertglobal told New Ag International: “During the period in which the analysis has been carried out, the trees treated with biofertilizers have revealed more favourable values, with some of them with higher accumulated trunk growth and total vegetative growth, as well as thicker leaves than the control lines with the same amount of fertilizers.”
Trunk cross-sectional area (TSCA) is also an important factor to analyse tree relations between vegetative growth and production, and can help to understand more deeply the differences involved in response to biofertilizer application,” said Leão.
Regarding yield, results from the trials showed increased productivity levels against the control. The application of Kiplant All-Grip was the most productive of all, and it surpassed the control lines of 70% and 100% standard input without biofertilization by 16.2%.
The effects of the biofertilizers on root growth and development were also highlighted. “Modern orchards are planted with branched trees, since it means higher and earlier potential productions. These trees can be more susceptible to plantation stress which means that a better initial root development can help to overcome this problem and minimize involved risks,” explained Leão.
Asfertglobal has published full details of the results, and is working with INIAV to publish the study in a peer-review academic journal in future.
‘Gala’ is the main variety of apple in Portugal and ‘Redlum’ is a recent clone of ‘Gala’ with a more intensive red colour