Search

ABSTRACT Boron (B) is readily leached from the soil, depending on the soil texture, soil organic matter (OM) content, and the fertilizer source used. This can restrict B uptake by plants. Therefore, we investigated the most adequate B source for soybeans grown in soils with contrasting textures and OM contents. The plants were cultivated for 55 days in columns filled with clayey or sandy Oxisols with low or high OM contents. The clay contents (%) in the soils were as follows: clayey soil with low OM = 64; clayey soil with high OM = 67; sandy soil with low OM = 4; and sandy soil with high OM = 15. The B sources tested comprised the control (no B supply), ulexite, zinc borate, boric acid, and B-monoethanolamine (B-MEA), with the equivalent of 6 kg B ha–1 applied. Boron leaching from ulexite was lower than other B fertilizers in the sandy soil with high OM content. Boron leaching was higher in sandy than in clayey soils. Boron accumulation in shoots was lower when boric acid was applied to the sandy soil with low OM content than the other B fertilizers. In this same soil, the agronomic efficiency and recovery of B applied by plants supplied with ulexite and zinc borate were higher compared to boric acid and B-MEA. In conclusion, the use of ulexite and zinc borate is more appropriate for soybean fertilization in sandy soils with low OM content, while B-MEA is more suitable for sandy soils with high OM content.

Abstract Experiments were conducted to evaluate the stability and degradation of NBPT under storage conditions and to quantify urease activity, ammonia losses by volatilization, and agronomic efficiency of urea treated with different urease inhibitors, measured in the field. Experiments included urea treated with 530 mg NBPT kg−1 (UNBPT) in contact with six P-sources (monoammonium phosphate-MAP; single superphosphate; triple superphosphate; P-Agrocote; P-Phusion; P-Policote), with two P-concentrations (30; 70%); the monitoring four N-technologies (SoILC; Limus; Nitrain; Anvol); and the application of conventional urea (UGRAN) or urea treated with urease inhibitors as topdressing in three maize fields, at three N rates. It is concluded that: the mixture of UNBPT and P-fertilizers is incompatible. When MAP granules were coated to control P-release (P-Agrocote), the degradation of NBPT was moderate (approximately 400 mg kg−1 at the end of the storage test). SoILC and Limus solvent technologies extended the NBPT half-life by up to 3.7 and 4.7 months, respectively. Under field, each inhibition technology reduced urease activity, and lowered the intensity of ammonia emission compared to UGRAN by 50–62%. Our results show that the concentration of NBPT is reduced by up to 53.7% for mixing with phosphates. In addition, even with coatings, the storage of mixtures of urea with NBPT and phosphates should be for a time that does not reduce the efficiency of the inhibitor after application, and this time under laboratory conditions was 168 h. The reduction of NBPT concentration in urea is reduced even in isolated storage, our results showed that the half-life time is variable according to the formulation used, being 4.7, 3.7, 2.8 and 2.7 days for Limus, SoILC, Nitrain and Anvol, respectively. The results of these NBPT formulations in the field showed that the average losses by volatilization in the three areas were: 15%, 16%, 17%, 19% and 39% of the N applied, for SoILC, Anvol, Nitrain, Limus and urea, respectively. The rate of nitrogen application affected all agronomic variables, with varied effects in Ingaí. Even without N, yields were higher than 9200 kg ha−1 of grains. The increase in nitrogen rates resulted in linear increases in production and N removal in Luminárias and Ingaí, but in Lavras, production decreased above 95.6 kg ha−1 of N. The highest production in Lavras (13,772 kg ha−1 of grains) occurred with 100 kg ha−1 of N. The application of Anvol reduced the removal of N in Ingaí.

We aimed to quantify the N losses through volatilization of the main conventional and stabilized N fertilizers applied in coffee plantations. Additionally, we also assessed microbiological attributes of the soil (microbial biomass carbon (MBC); microbial biomass nitrogen (MBN); microbial basal respiration (MBR); metabolic quotient (qCO2); urease, β-glucosidase, acid phosphatase, and arylsulfatase activities) and agronomic aspects of the crop (N content in the leaves and beans, yield, and N exportation by the beans). Treatments consisted of the combination of three fertilizers (ammonium nitrate - AN, conventional urea - U, and urea with N- (n-butyl) thiophosphoric triamide (NBPT) - UNBPT, and five doses of N (0, 150, 275, 400, and 525 kg ha-1 year-1 of N), with four replicates, totalling 60 experimental plots. In the two crop seasons evaluated, daily and cumulative losses of N-NH3 from the split fertilizer applications were influenced by the N fertilizer technologies. The application of U resulted in losses of 22.0% and 22.8% for the doses of 150 and 400 kg ha-1 year-1 of N. This means that 66 and 182 kg ha-1 of N-NH3 were lost, respectively, at the end of six fertilizations with U. UNBPT reduced urease activity and N-NH3 losses compared to conventional urea, avoiding the volatilization of 15.9 and 24.3 kg ha-1 of N. As for AN, N-NH3 losses did not exceed 1% of the applied dose, regardless of the weather conditions during the fertilization. Urease activity was higher on days of maximum NH3 volatilization. There was an effect of the N sources (NS), soil sampling time (ST), and their interaction (NS × ST) on the MBN and arylsulfatase activity. The N sources also influenced the MBC and the qCO2. A substantial amount of N was removed from the system by the beans and husks of the harvested fruits. Our study showed that N fertilizer technologies are interesting options to reduce N-NH3 losses by volatilization, increase N retention in the soil, and improve microbiological attributes and the sustainability of coffee production systems.

The paper consolidates the role of conventional and stabilized N fertilizers used in coffee crop production in Brazil and their N2O emissions in tropical systems. The experiment consisted of the combination of three fertilizers and five doses with four repetitions, totalling 60 experimental plots. The factors of the experiment were conventional urea (U), ammonium nitrate (AN), and urea + NBPT (UNBPT), while the doses were 0, 150, 275, 400, and 525 kg ha−1 year−1 of N. The municipality is located in a region at 1100 m of altitude, 20°53′26.04″ S and 44°52′04.14″ W. A randomized block design with a 3 × 5 factorial scheme was used. This region, traditional in coffee production, has a tropical humid climate, classified as Cwa according to the Köppen scale, with temperate summer and dry winter. UNBPT and the ammonium nitrate mitigated the N2O emissions by 50.6% and 78.5%, respectively, in comparison to the conventional urea. High C stocks were found in the 1 m soil layer, from 117 to 162 t ha−1 of organic C, indicating the importance of the soil as a C sink in coffee plantations. N stocks varied from 33 to 17 t ha−1 of N but no differences among the treatments were found. Approximately 50% of soil C was in the 0–0.4 m layer as a consequence of the greater amount of plant biomass, nutrients, and biological activity. Soil C:N ratio in the entire layer varied from 4.2 to 9.2. Our results indicate that nitrification is the most predominant process of N2O emissions. The standard EF proposed by the IPCC overestimates the N2O emissions in the Brazilian coffee plantations and the emissions differ according to the N fertilizer technology. These coffee crop systems have an important ability to stock C and N in the soil.

Enhanced efficiency fertilizers, such as urea treated with a urease inhibitor, controlled-release fertilizers (CRFs), and fertilizer blends, compose important strategies for improving efficiency in nitrogen (N) use by plants and mitigating ammonia (N-NH3) emissions. The physical mixture of fertilizers in blends can favor synchronization of N-release from the fertilizers and N-uptake by coffee plants and also dilute the costs of acquiring a pure CRF, making fertilizer blends more accessible to growers. To investigate this, a field experiment was conducted over two consecutive crop years with Coffea arabica with the aim of evaluating nitrogen fertilizer technologies at application rates ranging from 0 to 450 kg N ha−1. The fertilizers were characterized, and analyses were performed to quantify N-release from the fertilizers, ammonia volatilization, and nutritional and yield aspects of the coffee plant. The fertilizers used were urea (UCon), urea treated with N-(n-butyl) thiophosphoric-triamide (UNBPT), urea-coated with polymer of the E-Max technology (with 41%N (EMax41) or 43%N (EMax43)), and blends of UNBPT with E-Max (Blend41–Blend43). The cumulative N-release for EMax41 always remained below that for EMax43, just as occurred for Blend41 in relation to Blend43. Over the two crop years, the greatest volatilization of N-NH3 occurred with UCon (~25%) and the least with EMax41 (9%). The results indicate that the technologies mitigated the N-NH3 emissions in relation to UCon [EMax41 (63% mitigation) > Blend41 (43%) > EMax43 (32%) > UNBPT (28%) > Blend43 (19%)]. Crop management affects coffee yield. The yield increase went from 20% in the first crop year to 75% in the second, with better results from fertilizers containing CRF. We present information that can assist fertilizer producers and coffee growers, and, above all, we seek to contribute to environmental action for the reduction of agricultural NH3, clarifying potential strategies for mitigation of these emissions and strategies that generate advances in research on technologies for coffee growing.

The adoption of technologies for N fertilization has become essential for increasing the N use efficiency in no-till (NT) systems in Brazil. Thus, this study aimed to quantify ammonia losses, N removal in grains, and second crop season yield in no-till and conventional (T) areas that received the application of different N fertilizers and their technologies. Ammonia volatilization, N extraction in grains, and corn yield in response to the application of conventional fertilizers were compared to urea treated with urease inhibitors in NT and conventional systems. The treatments were: no-N (Control); Prilled urea (PU); urea + N-(n-Butyl) thiophosphoric triamide (UNBPT); urea + Cu + B (UCuB); ammonium nitrate (AN), and ammonium sulfate (AS). In the NT system, the N-NH3 losses were 49% higher than in the conventional; without differences in corn yield. The fertilizers AN and AS had the lowest N-NH3 losses, regardless of the tillage system. UNBPT reduced the mean N-NH3 loss by 33% compared to PU. UNBPT (1200 mg kg−1) and UNBPT (180 mg kg−1) reduced the N-NH3 losses by 72% and 22%, respectively, compared to PU in the NT system. We noticed that the NBPT concentration to be used in soils under NT should be adjusted, and a reduction of N-NH3 losses does not directly reflect an increase in yield and N extraction by corn.

The present study had the objective to evaluate the effect of blends of KCl and K2SO4 fertilizers and their influence on the yield and the nutritional state of coffee plants, as well as on the chemical composition and quality of the coffee beverage. The experimental design was in randomized blocks with four repetitions and six treatments (T1: 100% KCl; T2: 75% KCl + 25% K2SO4; T3: 50% KCl + 50% K2SO4; T4: 25% KCl + 75% K2SO4; T5: 100% K2SO4; and a control, without application of K). The following analyses were performed: K and Cl content in the leaves and the soil, stocks of Cl in soil, yield, removal of K and Cl with the beans, cup quality of the beverage, polyphenol oxidase activity (PPO), electric conductivity (EC), potassium leaching (KL), the content of phenolic compounds, the content of total sugars (TS), and total titratable acidity (TTA). The stocks of Cl in the soil decreased as the proportion of KCl in the fertilizer was reduced. The fertilization with KCl reduces the cup quality and the activity of the polyphenol oxidase, probably due to the ion Cl. The increase in the application of Cl directly relates to the increase in potassium leaching, electric conductivity, and titratable acidity. Indirectly, these variables indicate damages to the cells by the use of Cl in the fertilizer. The activity of the polyphenol oxidase enzyme and the cup quality indicate that the ion Cl- reduces the quality of the coffee beverage. K content in the leaves was not influenced by the application of blends of K fertilizer while Cl content increased linearly with KCl applied. The application of KCl and K2SO4 blends influenced coffee yield and the optimum proportion was 25% of KCl and 75% of K2SO4. The highest score in the cup quality test was observed with 100% K2SO4.

The aim of this study was to quantify NH3-N losses from conventional, stabilized, slow-release, and controlled-release N fertilizers in a coffee field. The N fertilizers analyzed were prilled urea, prilled urea dissolved in water, ammonium sulfate (AS), ammonium nitrate (AN), urea + Cu + B, urea + adhesive + CaCO3, and urea + NBPT (all with three split applications), as well as blended N fertilizer, urea + elastic resin, urea-formaldehyde, and urea + polyurethane (all applied only once). NH3-N losses (mean of two crop seasons) were statistically higher for urea + adhesive + CaCO3 (27.9% of applied N) in comparison with the other treatments. Loss from prilled urea (23.7%) was less than from urea + adhesive + CaCO3. Losses from urea + NBPT (14.5%) and urea + Cu + B (13.5%) were similar and lower than those from prilled urea. Urea dissolved in water (4.2%) had even lower losses than those treatments, and the lowest losses were observed for AS (0.6%) and AN (0.5%). For the single application fertilizers, higher losses occurred for urea + elastic resin (5.8%), blended N fertilizer (5.5%), and urea + polyurethane (5.2%); and urea-formaldehyde had a lower loss (0.5%). Except for urea + adhesive + CaCO3, all N-fertilizer technologies reduced NH3-N losses compared to prilled urea.