Percorrer por autor "Sawimbo, Almeida"
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- Assessing the Role of Phosphorus, Starter Nitrogen and Boron in Subterranean Clover and Annual Ryegrass Grown in Acidic Soils Under Mediterranean Conditions in PortugalPublication . Sawimbo, Almeida; Aguiar, Peltier; Arrobas, Margarida; Aguiar, Carlos; Rodrigues, Nuno; Jongen, Marjan; Teixeira, Ricardo F. M.; Domingos, Tiago; Rodrigues, Manuel ÂngeloIn Mediterranean pasture systems, maintaining legume persistence and productivity is often constrained by phosphorus (P) deficiency in acidic soils. Although small doses of starter nitrogen (N) are commonly used in pulse crops to support early growth before N fixation begins, this practice has not been widely tested in legume-grass mixtures. In addition, boron (B), a micronutrient particularly important for dicot species, may also influence legume performance under these conditions. Thus, this study investigated the effects of P application on dry matter yield (DMY) and nutrient uptake in subterranean clover (Trifolium subterraneum L., cv. Denmark), annual ryegrass (Lolium multiflorum Lam., cv. Falladino) and their mixture, using a pot experiment with acidic soils from two distinct locations in Portugal. The study also evaluated the impact of a small N starter dose and B application. Although Soil 2 had higher acidity (pH 5.0) than Soil 1 (pH 5.4), it supported greater biomass production, likely due to its higher organic carbon (C) content (50.8 g kg-1), which may have buffered soil acidity. P application significantly increased P uptake, DMY and N accumulation in legumes, suggesting a critical role in nodulation and/or nodule function. The N starter had no significant effect, likely because sufficient N was released from soil organic matter prior to the onset of biological N fixation. While the B application increased tissue B concentrations, it did not affect DMY, possibly because B was adequately available from organic matter. These findings highlight the importance of P in legume management in pasture systems and suggest that, in soils with sufficient organic matter, the application of starter N and B may not be necessary.
- Evaluating soil phosphorus tests and nutrient limitations in Mediterranean pasturesPublication . Arrobas, Margarida; Raimundo, Soraia; Sawimbo, Almeida; Rodrigues, Nuno; Jongen, Marjan; Teixeira, Ricardo F.M.; Domingos, Tiago; Rodrigues, Manuel ÂngeloReliable phosphorus (P) fertilization guidelines for Mediterranean pastures remain uncertain due to inconsistent soil testing methods, the complexity of mixed-species systems, and the neglect of other limiting nutrients. This study primarily aimed to identify reliable soil P tests and secondarily to explore potential nutrient limitations by assessing seven acidic Portuguese soils under Mediterranean conditions using subterranean clover (Trifolium subterraneum) and ryegrass (Lolium multiflorum) as model species. Five P extraction methods (Egner-Riehm, Olsen, Bray II, Mehlich I, and anion exchange resin) were compared alongside a pot experiment with clover, ryegrass, and their mixture. Biomass production, plant nutritional status, and soil-plant relationships were used to assess nutrient availability and plant response. The Egner-Riehm method proved the most reliable, showing linear correlation with the resin method (R2 = 0.89), widely regarded as the best indicator of soil P bioavailability. P availability was therefore not a limiting factor for biomass production. The lowest soil P content (54 mg kg-1 P2O5, Egner-Riehm) was close to the medium threshold (50-100 mg kg-1), yet plant growth indicated adequacy. In contrast, nitrogen (N) emerged as the main growth constraint, and boron (B) deficiency further restricted clover performance, confirming additional nutritional imbalances. A linear relationship between soil and tissue B supported its association with DMY, and tissue B levels were below sufficiency thresholds. Overall, in acidic Portuguese soils under Mediterranean conditions, soil P was adequate, whereas N and B acted as key constraints to productivity. These findings support more accurate and efficient fertilization strategies for Mediterranean pastures.
- Sewage Sludge Increased Lettuce Yields by Releasing Valuable Nutrients While Keeping Heavy Metals in Soil and Plants at Levels Well below International Legislative LimitsPublication . Rodrigues, M.A.; Sawimbo, Almeida; Silva, Julieta Moreira da; Correia, Carlos M.; Arrobas, MargaridaSewage 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.