Search Results (5)

In tropical regions, maintaining crop residues in the soil is challenging. Silicon (Si) may increase the persistence of these residues in the soil, as it is a precursor to lignin, providing a gradual release of nutrients for subsequent crops. Therefore, the objective of this study was to evaluate the influence of different doses of calcium silicate (Ca₂SiO₄) (0, 1, 2, and 3 Mg ha⁻¹) and limestone (0, 1, 2, and 3 Mg ha⁻¹) on the lignin content, residue decomposition, and nutrient release of four cover crops—Pennisetum glaucum, Urochloa ruziziensis, Crotalaria spectabilis, and Cajanus cajan—at various decomposition stages following cover crop management (0, 30, 60, 90, and 120 days). The experiment was conducted in the field at the experimental area of the Faculty of Engineering at Ilha Solteira-UNESP, located in the municipality of Selvíria, state of Mato Grosso do Sul, on Ferralsol. The decomposition rate of the residues was assessed using the decomposition bag method, which was installed after cover crop management. The concentrations of nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), sulfur (S), Si, lignin, and cellulose were determined. Silicate application did not affect the accumulation of nutrients by cover crops and their release into the soil. There was no relationship between the remaining Si in the dry matter of plants and more persistent residues. The most persistent plants had higher final dry matter lignin content. Using pearl millet and pigeon peas resulted in more persistent residues in the soil. Full article

The use of cover crops (CCs) based on tropical legumes, including Crotalaria ochroleuca, Crotalaria juncea, Crotalaria spectabilis, and Cajanus cajan, represents a pivotal aspect of agricultural rotations. These crops facilitate the incorporation of nitrogen through biological nitrogen fixation (BNF), thereby reducing the necessity for synthetic nitrogen fertilizers. Nevertheless, the capacity for the BNF of these species in Uruguay is relatively modest. To address this limitation, an approach is proposed that involves the immobilization of nitrogen in the soil using a highly energetic material, such as sucrose. The objective of this study was to examine the impact of incorporating sucrose into typical Uruguayan soil on aboveground dry matter production, nitrogen accumulation, and nitrogen fixation by legumes utilized as CCs. The experiments involved the planting of C. ochroleuca, C. juncea, C. spectabilis, and C. cajan in pots containing either soil alone or soil mixed with sucrose and the subsequent maintenance of these in a plant growth chamber for a period of 90 days. The addition of sucrose had a positive impact, with nearly double the aboveground dry matter production and nitrogen content observed. The percentage of nitrogen derived from the atmosphere (%Ndfa) increased significantly in all species, rising from an average of 83% to 96% in the sucrose-amended soil compared to the control. In the case of C. juncea, there was a notable threefold increase in aboveground dry matter and nitrogen accumulation across different treatments, accompanied by a 26% rise in %Ndfa and a fourfold increase in nitrogen fixation amounts. These findings indicate that C. juncea has the potential to significantly enhance performance and ecosystem services in typical Uruguayan soil. Full article

Brazilian soils are predominantly rich in aluminum, which becomes mobile at pH < 5, affecting sensitive plants; however, some species have developed aluminum tolerance mechanisms. The purpose of this study was to compare the physiological responses of Crotalaria genus species, family Fabaceae, which have the ability to associate with nitrogen-fixing bacteria under the influence of Al³⁺ in the soil. The soil used was Oxisol; the experimental design was in randomized blocks in a factorial scheme (2 × 3): soil factor (available toxic aluminum content; correction of dolomitic limestone—MgCO₃) and species factor (C. juncea; C. spectabilis; C. ochroleuca); cultivated within 43, 53, and 53 days, respectively, with five replications; 30 experimental samples. Mass and length, pigments, gas exchange, and changes in nitrogen metabolism were evaluated. C. juncea showed a higher concentration of amino acids in the leaves, internal carbon, and stomatal conductance in soil with Al³⁺, as well as higher production of ureides, allantoinic acid, allantoic acid, proteins, and amino acids in the nodules, with 78% of the Al³⁺ accumulation occurring in the roots. C. ochroleuca demonstrated greater shoot length and nodule number production in limed soil; in soil with Al³⁺, it showed a 91% increase in chlorophyll a content and 93% in carotenoids. C. spectabilis showed a 93% increase in ureide production in the leaves in soil with Al³⁺. Full article

Summer legume cover crops (CC) such as Crotalaria juncea, Crotalaria spectabilis, Crotalaria ochroleuca, and Cajanus cajan could offer diverse advantages for the environment and productive cropping systems. A low transpiration efficiency (TE) of CC can induce soil water content to levels that present a challenge for the subsequent crop. In a 75-day growth chamber experiment, using the natural abundance of ¹³C, ¹⁸O, and ¹⁵N we evaluated the TE and BNF under two soil water conditions. Our results showed that the four species tested are good candidates for their use as CC because they showed good results in terms of productivity parameters, TE, and BFN. Cajanus cajan had the highest TE, a high shoot dry matter production, and accumulated more N from BFN in the shoot than C. spectabilis, C. juncea, and C. ochroleuca. ∆¹⁸O increased under moderate water deficit and showed an inversely proportional relationship with the amount of transpired water, supporting the use of this isotopic indicator as a proxy for transpiration and stomatal conductance. For the isotopic parameters no interaction between the factors water regimen and species were found. We propose the mass ratio of nitrogen fixed by the volume of transpired water and the isotopic discrimination of ¹³C as useful indicators of drought fixing legumes tolerance. Full article

Crotalaria spectabilis and Crotalaria juncea are cover crops (CC) that are used in many different regions. Among the main attributes of these species are their high potential for biomass production and biological fixation of nitrogen (BNF). Attempting to maximize these attributes, while minimizing water consumption through high transpiration efficiency (TE), is a challenge in the design of sustainable agricultural rotations. In this study, the relationship between biomass productivity, BNF, and TE in C. spectabilis and C. juncea was evaluated. For this purpose, an experiment was carried out under controlled conditions without water limitations and using non-inoculated soil. BNF was determined by the natural abundance of ¹⁵N, while TE was estimated by several different methods, such as gravimetric or isotopic method (¹³C). C. juncea produced 42% less dry matter, fixed 28% less nitrogen from the air, and had 20% less TE than C. spectabilis. TE results in both species were consistent across methodologies. Under simulated environmental conditions of high temperature and non-limiting soil water content, C. spectabilis was a relatively more promising species than C. juncea to be used as CC. Full article