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In this study, the effectiveness of an inoculant containing a nitrogen (N)-fixing microorganism (Methylobacterium symbioticum) was evaluated on maize (Zea mays L.) grown both in the field (silage maize) and in pots over two years (2021 and 2022). The field trial included the following two treatments: with (Yes) and without (No) the inoculant. The pot experiment was designed as a factorial arrangement with two factors: the application of the inoculant (Yes and No) and N applied to the soil (0, 0.4, 0.8, and 1.6 g pot−1). In the field, total dry matter yield (DMY) did not differ significantly between treatments, although the average DMY was higher in the inoculant treatment. In pots, the total DMY varied significantly across all N rates but was only significantly affected by the inoculant application in 2022. N fixation estimates in the field were 58.8 and 14.5 kg ha−1 for 2021 and 2022, respectively, representing 23.7% and 9.1% of the N recovered in the aboveground plant parts. In pots, the estimated fixed N values were −49.2 and 199.2 mg pot−1 in 2021 and 2022, respectively, which corresponded to −5.2% and 18.5% of the N found in the aboveground plant parts. Considering the average values obtained across the four cultivation conditions, there was a positive outcome for the treated plants. However, these values cannot be considered significant when compared to nitrogen removal in maize crops. A commercial product should provide an unequivocal and quantitatively relevant contribution to plant nutrition, which did not appear to be the case. Thus, for this inoculant to provide reliable guarantees of positive outcomes for farmers and become a useful tool in promoting more sustainable agriculture, further studies appear necessary. These studies should aim to determine in which crops and under what cultivation conditions the application of the inoculant is truly effective in enhancing N fixation and improving crop productivity. [ABSTRACT FROM AUTHOR]

In this study, two commercial products based on the main groups of contemporary biostimulants—a commercial leonardite and a seaweed extract—were tested with the objective of assessing the conditions under which they can enhance lettuce (Lactuca sativa L.) performance, particularly to determine if synergies with conventional fertilization methods can be observed. The experimental protocol was arranged as a factorial design with two factors: organic or mineral fertilization × plant biostimulant. The organic or mineral fertilization factor included five levels: two rates of a nitrogen (N) fertilizer (40 (Nmin40) and 80 (Nmin80) kg ha−1 of N), the same N rates applied as an organic amendment (Norg40 and Norg80), and an unfertilized control (N0). The plant biostimulants used were a commercial leonardite (leonardite) for soil application before planting, a commercial seaweed extract (algae) for foliar application during the growing season, and a control without plant biostimulant. Leonardite significantly increased lettuce dry matter yield (DMY) compared to the control only in the first growing cycle (11.5 and 13.5 g plant−1) and showed no significant interaction with conventional fertilization. It also consistently increased phosphorus (P) levels in the plant tissues. The seaweed extract did not show any effect on the plant, nor did it have any interactions with conventional fertilization regarding DMY. In contrast, with mineral fertilization, lettuce DMY increased from 8.0 and 4.0 g plant−1 (N0) to 22.2 and 12.0 g plant−1 (Nmin80) in the first and second growing cycles, respectively. The response to organic fertilization was lower, yet DMY still increased from 4.0 to 8.1 g plant−1 in the second growing cycle. Generally, this type of plant biostimulant is tested under some form of environmental stress, where it often yields positive results. In this study, the optimal cultivation conditions maintained for the lettuce in the pots likely explain the limited response to the biostimulants. This study suggests that the product labels should more clearly indicate whether they are recommended for general cultivation conditions or specifically for situations where a particular environmental stress can be anticipated. [ABSTRACT FROM AUTHOR]

There is a need for alternatives or complements to synthetic fertilizers to enhance agricultural sustainability. Applying organic amendments can play a significant role in this. Insect droppings show high potential, though studies evaluating their agronomic value have only recently begun to emerge. This study compared black soldier fly (Hermetia illucens L.) and mealworm (Tenebrio molitor L.) larvae frass with another organic amendment (Nutrimais) derived from composting forestry, agro-industrial, and domestic waste. The experiment also included ammonium nitrate at two rates [the same as the organic amendments, 50 kg ha−1 nitrogen (N) (FullR), and half that rate (HalfR)] and an unfertilized control. The study spanned two growth cycles of lettuce (Lactuca sativa L.) grown in pots, followed by unfertilized oats (Avena sativa L.) to assess the residual effects of the fertilizing treatments. Mealworm larvae frass mineralized rapidly, with an apparent N recovery of 37.4% over the two lettuce growth cycles, indicating its high availability to soil heterotrophic microorganisms. The average dry matter yield (DMY) of lettuce was the highest among all treatments (12.8 and 9.8 g plant−1 in the first and second lettuce cycles), even compared to the FullR treatment (12.2 and 7.8 g plant−1), though without significant differences. Although mealworm larvae frass exhibited a high mineralization rate, the DMY cannot be attributed solely to N supply, as plants in the FullR treatment showed better N nutritional status. Mealworm larvae frass provided strong evidence of a plant biostimulant effect, not explained by the variables measured in this study. Black soldier fly larvae frass exhibited typical behavior of a moderately reactive organic amendment, while Nutrimais showed low reactivity, with a near-neutral mineralization/immobilization balance. The results suggest mealworm larvae frass is recommended for early maturing vegetable crops, whereas Nutrimais appears more suitable for perennial crops with low short-term nutrient requirements. [ABSTRACT FROM AUTHOR]

Sewage sludge can be used as an organic amendment as long as it is ensured that there is no risk of environmental contamination or risk to public health. In this study, sewage sludge from two wastewater treatment plants (WWTPs) subjected to two disinfection and stabilization treatments [40% (mass/mass), calcium oxide, and calcium hydroxide] and their respective untreated sewage sludge were used. Three control treatments were also added: conventional farmyard manure (FYM), a nitrogen (N) mineral fertilizer (ammonium nitrate 34.5% N) applied at a rate of 50 kg N ha−1 (N50) (the same rate of all organic amendments), and an unfertilized control (N0), totaling nine treatments. Lettuce (Lactuca sativa L.) was cultivated in pots for two growing cycles. The dry matter yield (DMY) was higher in the N50 treatment (13.5 and 10.6 g plant−1 in the first and second growing cycles, respectively), followed by sewage sludge (10.8 to 12.4 and 8.4 to 8.7 g plant−1), FYM (8.5 and 7.2 g plant−1), and the control (7.7 and 6.0 g plant−1). The DMY was related to the N provided by the different treatments, assessed by the N and nitrate concentrations in tissues, N uptake, and apparent N recovery (ANR). Sewage sludge, due to its high N concentration and low carbon (C)/N ratio, mineralized rapidly, providing a significant amount of N to plants, as well as other nutrients, such as phosphorus (P) and boron (B). FYM, with a higher C/N ratio, provided less N to plants, also due to the short duration of the lettuce growing cycle. Alkalized sewage sludge increased soil pH and calcium (Ca) availability for plants. Fertilizer treatments minimally influenced cationic micronutrients. Heavy metals in the initial sewage sludge were below the threshold values established in international legislation, and the levels in soil and lettuce tissues were generally not higher than those in other treatments. Both of the sewage sludges used in this study showed high fertilizing value and very reactive behavior, making nutrients available much more quickly than FYM. This information is relevant to consider in defining their agricultural use. [ABSTRACT FROM AUTHOR]

Sewage sludge should primarily find use in agriculture, reducing the quantity directed towards alternative disposal methods like incineration or deposition in municipal landfills. This study evaluated the agronomic value and the risk of soil and plant tissue contamination with heavy metals in sewage sludge obtained from two wastewater treatment plants (WWTP). The experiment was arranged as a 2 × 5 factorial (two sewage sludges, five sanitation treatments), involving lettuce cultivation in pots over two growing cycles. The two sewage sludges were sourced from the WWTPs of Gelfa and Viana do Castelo and underwent five sanitation and stabilization treatments (40% and 20% calcium oxide, 40% and 20% calcium hydroxide, and untreated sewage sludge). The Gelfa sewage sludge, characterized by a higher initial nitrogen (N) concentration, resulted in greater dry-matter yield (DMY) (12.4 and 8.6 g plant−1 for the first and second growing cycles, respectively) compared to that from Viana do Castelo (11.0 and 8.1 g plant−1), with N release likely being a major factor influencing crop productivity. The high N concentration and the low carbon (C)/N ratio of sewage sludge led to rapid mineralization of the organic substrate, which additionally led to a higher release of other important nutrients, such as phosphorus (P) and boron (B), making them available for plant uptake. Alkalizing treatments further stimulated sewage sludge mineralization, increasing soil pH and exchangeable calcium (Ca), thereby enhancing Ca availability for plants, and indicating a preference for use in acidic soils. Cationic micronutrients were minimally affected by the sewage sludge and their treatments. The concentrations of heavy metals in the sewage sludge, soils, and lettuce tissues were all below internationally established threshold limits. This study highlighted the high fertilizing value of these sewage sludges, supplying N, P, and B to plants, while demonstrating a low risk of environmental contamination with heavy metals. Nevertheless, the safe use of sewage sludge by farmers depends on monitoring other risks, such as toxic organic compounds, which were not evaluated in this study. [ABSTRACT FROM AUTHOR]

Olive orchards represent a key agricultural system in the Mediterranean Basin. Soil degradation processes associated with unsustainable agronomic practices and climate change could severely impact the sustainability of Mediterranean rainfed olive orchards. In this context, soil amendments are important tools that can be used to enhance soil fertility for sustained environmental quality and plant performance. In this study, a field trial was conducted for 4 years in olive tree (Olea europaea L.) to assess the effects of a mineral fertilizer compound and the combination with a single application of zeolites or biochar on the physiological and biochemical performance, tree nutritional status, crop yield and soil chemical and biological properties to gain knowledge towards more sustainable management. Our results showed that the addition of zeolites and biochar to mineral fertilizer ameliorated the physiological and biochemical performance, as evidenced by consistent increments of relative water content, stomatal conductance and net photosynthesis and by lower signs of oxidative stress during the periods of greater climate adversity. However, crop yield was not significantly different among soil treatments. On the other hand, soil chemical and biological traits at the surface layer (0–10 cm) have shown different and relevant responses after 4 years of soil amendment application. In fact, zeolite supply stood out as increased pH, extractable K, cation exchange capacity, microbial biomass carbon and microbial biomass quotient and reduced extractable Cu. Furthermore, zeolites induced positive changes in soil enzymatic activity, leading to increases in 10 enzymes involved in C, N and P cycles. In contrast, the effects of biochar on soil properties were much more reduced, given that it decreased the microbial biomass nitrogen and enhanced the activities of three P‐cycle enzymes. In summary, our data demonstrated that both soil amendments can be an interesting complement to mineral fertilization, in order to increase trees' resilience under rainfed conditions and to promote soil health, although the use of zeolites appears to be a more promising strategy because of the induction of higher soil sustainability. [ABSTRACT FROM AUTHOR]

Weeds reduce crop yields and require annual measures of control, although they can provide important ecological benefits. In this work, the efficacy was tested of an ecological fertilizer with herbicidal properties (Bioscrop Herbitec®) which in high concentrations (10-15%) can have a similar effect to a contact herbicide. The composition of the product is 6.0 % of water-soluble potassium oxide, 54.7 % of organic acids and 39.3 % of dispersants and diluents. The product was tested in six field trials during two years, which included two vineyards and two olive orchards and winter and spring vegetation. In each experiment three treatments were imposed, being the product applied at the concentrations of 10% and 15% and a non-treated control. In treated plots, the entire ground surface (rows and inter-rows) was sprayed. The evaluation of the effect of the treatments on vegetation was assessed by the pin point and grid methods which consisted of determining the percentage of damaged and not damaged vegetation and bare soil. The production of dry biomass of weeds was also evaluated as a measure of the persistence of the damage on vegetation. The floristic composition of the stands was also recorded to evaluate the specific susceptibility of the weeds to the different treatments. The results showed that the product severely damaged the vegetation, and the effect persisted for more than a month. The application of the product caused a severe reduction in the aboveground biomass while keeping the soil protected, showing a useful compromise between the reduction in weed competition and the maintenance of ground cover. Some species were severely damaged while others seemed to have benefited in relative terms, suggesting that the effectiveness of the product will be dependent on the weed species present.

In acid soils, when no‐tillage farmers intend to apply lime, the question arises as to whether it should be incorporated into the soil or whether it can be left on the soil surface. In this study, two types of limestone, calcitic (Lcal) and dolomitic (Lmag), were tested in two olive groves of cv. Cobrançosa, with an initial pH of 4.9 (S. Pedro) and 5.5 (Raparigas). In S. Pedro, limestone was incorporated into the soil (Lburied) and in Raparigas, it was left on the floor (Lfloor). The use of limestone significantly increased soil pH in the 0–0.10 m layer in both experiments. In the 0.10–0.20 m soil layer, only Lmag increased significantly the soil pH in comparison with the control. Lmag was more effective than Lcal in increasing cation exchange capacity (CEC) and reducing exchangeable acidity (EA) and aluminium (Al3+) in the Lfloor experiment. Both limes increased leaf calcium (Ca) concentration, and Lmag increased the leaf levels of magnesium (Mg). In Lfloor experiment (higher soil pH), soil microbial carbon (C) decreased, and microbial nitrogen (N) increased with liming, which may indicate an increase in bacteria in the soil and a decrease in fungi. In Lburied experiment (initial pH of 4.9), liming significantly increased accumulated (2018–2021) olive yield (56 and more than 67 kg tree−1, respectively, in the control and liming treatments). In Lfloor experiment (initial pH of 5.5), the accumulated olive yields did not differ significantly between treatments (average values between 105 and 115 kg tree−1). The results of this study provide evidence that liming may increase olive yield in very acid soils and that dolomitic limestone should preferably be used by no‐tillage farmers, due its higher solubility and faster effect on soil and trees. [ABSTRACT FROM AUTHOR]

The application of fertilizers as a topdressing in maize raises serious concerns because too much fertilizer is retained in the upper leaves, causing burning to the tissues. In this study, the use of a controlled-release and a stabilized fertilizer (with 3, 4-dimethylpyrazole phosphate) was compared with the application of a conventional fertilizer split into two equivalent applications in a forage maize-oats cropping system. In maize, 100 and 200 kg N ha−1 of different fertilizers were used in addition to an unfertilized control. The oat crop was not fertilized, since it served only as a winter catch crop. Maize dry matter (DM) yield increased significantly with N rate only in 2019, being the second growing season, with the control showing the lowest average value (7.1 t ha−1). The most fertilized treatments (200 kg N ha−1) gave the highest DM yields, ranging between 14.2 and 16.7 t ha−1, but with no significant differences between them. Oats had a relevant role as a catch crop recovering residual N that could have potentially been lost from the soil. Stalk nitrate concentration proved to be very sensitive to N fertilization (varying from 150.4 to 1945.6 mg kg−1 in 2018 and 494.9 to 1574.9 mg kg−1 in 2019), showing great potential as a tool of N management. These three fertilization strategies seem to be valid options that farmers can consider, after incorporating technical-economic information related to equipment suitability and the price of fertilizers. [ABSTRACT FROM AUTHOR]