Anne Falk Øgaard

Plant availability of inorganic and organic selenium fertiliser as influenced by soil organic matter content and pH

The objective of the present study was to investigate the influence of soil organic matter content and pH on plant availability of both inorganic and organic selenium (Se) fertilisers. Further, the risk of Se leaching after application of inorganic Se fertiliser was evaluated. A new interpretation of an older field study at different sites in Southern Norway showed that organic C was correlated with grain Se concentration in wheat, barley and oats, explaining up to 60% of the variation in Se concentration. Pot experiments with a peat soil, a loam soil and a peat/loam soil mixture were conducted for the present study at a range of pH values between pH 5 and 7. Below pH 6, Se uptake from added Se fertiliser was higher in the soil types with high organic matter content than in the loam. The opposite occurred at a soil pH above 6, where Se uptake was higher in the loam than in the peat soil. A simple leaching experiment after one growing season confirmed the findings of the pot experiments that Se availability in the loam soil with a relatively low organic matter content increased with increasing pH, whereas it decreased in the peat soil. Neither Se yeast, nor pure Se methionine, used as organic Se fertiliser, resulted in any significant uptake of Se when added at concentrations similar to the inorganic Se applications.

Contrasting responses of root morphology and root-exuded organic acids to low phosphorus availability in three important food crops with divergent root traits.

Available phosphorus (P) is one of the most important factors affecting crop production worldwide. Study on improving plant P uptake is hence of global importance. We have investigated the responses of root morphology and root-exuded organic acids to low P availability in three important food crops (barley, canola and potato) with divergent root traits using a hydroponic culture system. Results showed that plants evolved divergent adaptations of root morphology and exudation as a response to low P availability. These results could underpin future efforts to improve P uptake of the three crops which are important for future sustainable crop production.

Effect of cattle manure on selenate and selenite retention in soil

The aim of the present investigation was to study the effect of manure on retention of selenium (Se) in soil. Addition of cattle manure in combination with selenite and selenate reduced the adsorption of both anions to a loam soil in a batch experiment. The results were explained by the content of low-molecular-weight organic acids in the manure which compete with Se for the sorption sites. In a pot experiment with loam and peat soils and with two pH levels within each soil, cattle slurry added together with selenate was found to increase the Se concentration in grain at the highest pH level (6.1 and 6.8 for the loam and peat, respectively). At a lower pH (5.4 and 6.0 for the loam and peat, respectively) there was no significant effect of slurry on Se concentration in grain. Application of slurry also increased the residual effect of Se applied to the loam soil in the preceding growing season. In the peat soil, no residual effect of Se was found either with or without the addition of slurry.

Use of Diffusive Gradients in Thin Films to Predict Potentially Bioavailable Selenium in Soil

Abstract In this study, diffusive gradients in thin films (DGT) were used for determination of anionic selenium (Se) species. First, a laboratory experiment was carried out to investigate ferrihydrite (the anionic sorbent in the DGT) complexation of anionic Se in an aqueous solution. A conditional DGT effective diffusion coefficient (DDGT) for Se was estimated to be 5.0×10−6 and 5.3×10−6 cm2 s−1 at pH 5.1 and pH 6.3, respectively. Second, DGT units were placed in pastes of soil that were sampled from a field experiment with mineral Se fertilization at two soil pH levels. Based on the DGT measurements, an effective concentration (CE) for Se in soil was calculated. A CE(Se) value significantly higher than the control was estimated at the highest Se dose and the lower pH (5.5). Refinement of the method is needed, but this investigation indicates that the DGT technique can be used to determine potentially bioavailable Se fractions in soil.

Rhizosphere Organic Anions Play a Minor Role in Improving Crop Species' Ability to Take Up Residual Phosphorus (P) in Agricultural Soils Low in P Availability

Many arable lands have accumulated large reserves of residual phosphorus (P) and a relatively large proportion of soil P is less available for uptake by plants. Root released organic anions are widely documented as a key physiological strategy to enhance P availability, while limited information has been generated on the contribution of rhizosphere organic anions to P utilization by crops grown in agricultural soils that are low in available P and high in extractable Ca, Al, and Fe. We studied the role of rhizosphere organic anions in P uptake from residual P in four common crops Triticum aestivum, Avena sativa, Solanum tuberosum, and Brassica napus in low- and high-P availability agricultural soils from long-term fertilization field trials in a mini-rhizotron experiment with four replications. Malate was generally the dominant organic anion. More rhizosphere citrate was detected in low P soils than in high P soil. B. napus showed 74–103% increase of malate in low P loam, compared with clay loam. A. sativa had the greatest rhizosphere citrate concentration in all soils (5.3–15.2 μmol g−1 root DW). A. sativa also showed the highest level of root colonization by arbuscular mycorrhizal fungi (AMF; 36 and 40%), the greatest root mass ratio (0.51 and 0.66) in the low-P clay loam and loam respectively, and the greatest total P uptake (5.92 mg P/mini-rhizotron) in the low-P loam. B. napus had 15–44% more rhizosphere acid phosphatase (APase) activity, ~0.1–0.4 units lower rhizosphere pH than other species, the greatest increase in rhizosphere water-soluble P in the low-P soils, and the greatest total P uptake in the low-P clay loam. Shoot P content was mainly explained by rhizosphere APase activity, water-soluble P and pH within low P soils across species. Within species, P uptake was mainly linked to rhizosphere water soluble P, APase, and pH in low P soils. The effects of rhizosphere organic anions varied among species and they appeared to play minor roles in improving P availability and uptake.

Efficient Phosphorus Cycling in Food Production: Predicting the Phosphorus Fertilization Effect of Sludge from Chemical Wastewater Treatment

This study examined the P fertilization effects of 11 sewage sludges obtained from sewage treated with Al and/or Fe salts to remove P by a pot experiment with ryegrass (Lolium multiflorum) and a nutrient-deficient sand-peat mixture. Also it investigated whether fertilization effects could be predicted by chemical sludge characteristics and/or by P extraction. The mineral fertilizer equivalent (MFE) value varied significantly but was low for all sludges. MFE was best predicted by a negative correlation with ox-Al and ox-Fe in sludge, or by a positive correlation with P extracted with 2% citric acid. Ox-Al had a greater negative impact on MFE than ox-Fe, indicating that Fe salts are preferable as a coagulant when aiming to increase the plant availability of P in sludge. The results also indicate that sludge liming after chemical wastewater treatment with Al and/or Fe salts increases the P fertilization effect.

Concentrations of Soil Potassium after Long-Term Organic Dairy Production

On five long-term organic dairy farms aiming at self-sufficiency with nutrients, soil concentrations of ammonium-acetate lactate extractable potassium (K-AL) and acid-soluble K was measured twice in topsoil (0–20 cm) and subsoil (20–40 cm) over periods of 6–14 years. Organic management had occurred for >9 years at the second sampling. On average there were most probably field level K-deficits. Even so, topsoil K-AL concentrations were medium high (65–155 mg K kg–1 soil), and did not decrease during the study period. However, for three farms, topsoil K-AL was approaching a minimum level determined by soil texture, where further decrease is slow. Subsoil K-AL concentrations were generally low (<65). The soils were mostly light-textured, and reserves of K-releasing soil minerals (illite) were low, never exceeding 6% of the mineral particles <2 mm diameter. Topsoil acid-soluble K concentrations were low (<300 mg K kg–1 soil) on two farms, medium (300–800) on three farms and decreased significantly on one farm. Cation-exchange capacity increased on two farms. This may indicate increased amount of expanded clay minerals caused by K-depletion. On self-sufficient organic dairy farms, purchased nutrients will be required by low soil nutrient reserves to avoid seriously decreased yields and quality of crops.

Drivers of Phosphorus Uptake by Barley Following Secondary Resource Application.

Minable rock phosphate is a finite resource. Replacing mineral phosphorus (P) fertilizer with P-rich secondary resources is one way to manage P more efficiently, but the importance of physicochemical and microbial soil processes induced by secondary resources for plant P uptake is still poorly understood. Using radioactive-labeling techniques, the fertilization effects of dairy manure, fish sludge, meat bone meal, and wood ash were studied as P uptake by barley after 44 days and compared with those of water-soluble mineral P (MinP) and an unfertilized control (NoP) in a pot experiment with an agricultural soil containing little available P at two soil pH levels, approximately pH 5.3 (unlimed soil) and pH 6.2 (limed soil). In a parallel incubation experiment, the effects of the secondary resources on physicochemical and microbial soil processes were studied. The results showed that the relative agronomic efficiency compared with MinP decreased in the order: manure ≥fish sludge ≥wood ash ≥meat bone meal. The solubility of inorganic P in secondary resources was the main driver for P uptake by barley (Hordeum vulgare). The effects of secondary resources on physicochemical and microbial soil processes were of little overall importance. Application of organic carbon with manure resulted in microbial P immobilization and decreased uptake by barley of P derived from the soil. On both soils, P uptake by barley was best explained by a positive linear relationship with the H2O + NaHCO3-soluble inorganic P fraction in fertilizers or by a linear negative relationship with the HCl-soluble inorganic P fraction in fertilizers.

Freezing and thawing effects on phosphorus release from grass and cover crop species

Cover crops, grassed buffer zones along watercourses and grassed waterways are recommended for mitigating erosion and phosphorus (P) losses from fields with arable crop production. There are, however, concerns that plant covers may release dissolved P and contribute to P loss after plant freezing. The objective of this study was to evaluate P release after freezing from different plant species of interest for use either as cover crops or in grassed buffer zones/waterways. In the laboratory, seven plant species (red clover (Trifolium pratense L.), timothy (Phleum pratense L.), annual ryegrass (Lolium multiflorum Lam.), hairy vetch (Vicia villosa Roth.), rye (Secale cereale L.) oil radish (Raphanus sativus L. var. oleiferus) and winter rapeseed (Brassica napus L. var. oleifera f. biennis)) were subjected to daily freeze–thaw cycles (FTCs; −10°C/+5°C) for one week. In a two-year outdoor experiment located under a roof to protect the plants from rain and snow, eight plant species (white clover (Trifolium repens L.), timothy, meadow fescue (Festuca pratensis L.), smooth meadow grass (Poa pratensis L.), annual ryegrass, perennial ryegrass (Lolium perenne L.), rye and hairy vetch) were subjected to winter temperatures. The plants were sampled in winter and spring. The results showed that after seven FTCs in the laboratory, less than 15% of the total phosphorus (TP) was water-extractable P for all species except oilseed radish for which 32% of the TP was water extractable. In the outdoor experiment, the plants were exposed to temperatures below −20°C during both winters. Depending on the plant species, 18–42% and 17–48% of the TP was water extractable in the spring of the first and second year, respectively. The minimum temperatures and the plant growth conditions were important for the ranking of different plant species with respect to the risk of off-season P leaching.

Nitrogen balance and nitrogen use efficiency in cereal production in Norway

Nitrogen (N) is usually the main nutrient affecting grain yields and is, therefore, applied in large quantities to maintain optimal yields. Economically, optimal fertilization may imply higher N application than the amount of N removed in grain, thereby causing high risk for N losses. The aims of this paper were to study the fertilization practice for cereals and the relationship between N application and yield, N balance, and N use efficiency for barley and oats in three of the catchments included in the Norwegian Agricultural Monitoring Programme (JOVA). The results showed that the average amount of applied N to cereals in these three catchments was higher, and sometimes considerably so, than the recommended N application. Within the range of N application in these catchments, there was no relationship between N application and yield for oats, whereas a tendency of increased yield with increased N application was found for barley in two of the catchments. The average N surplus in cereal production was significantly higher than that expected if fertilization recommendations had been followed. The average N surplus for the different cereals varied from 36 to 60 kg N ha−1 in two of the catchments and from 22 to 40 kg N ha−1 in the third catchment. The average N use efficiency (calculated as N removed in grain divided by the amount of applied N) ranged from 61 to 71% for barley and from 67 to 82% for oat. The JOVA data clearly demonstrate the importance of using moderate N applications in order to reduce N surplus, and thereby reduce N losses. N application for higher yield levels than those normally obtained, results in low N use efficiency and high N surplus in most years.