Ernesto Vasconcelos

The development of sustainable application practices, which do not demand incorporation into the soil, is necessary to encourage slurry use in conservation agriculture (CA). Incorporation is the most common practice to reduce nitrogen losses from the applied slurry. However, in CA, soil disturbance must be avoided. Two experiments were conducted to evaluate strategies to reduce gaseous emissions from dairy slurry applied to stubble-covered soil without incorporation. We evaluated (1) effects on ammonia (NH₃) emissions of pretreatment by acidification (ADS), irrigation (IR) and placement under the stubble (US); and (2) effects of ADS, IR, US and delayed fertilization (RDS T16) on greenhouse gases (GHG). The results of the evaluated strategies were compared to raw slurry (RDS) and ammonium sulphate (MS). Additionally, in experiment 2, the results were compared to ammonium sulphate (MB) and slurry injection (IN), both in bare soil. ADS, US and IR decreased NH₃ emissions by 66%, 60% and 32.5%, respectively, with total N emissions NH₃ emissions accounting for more than 79% of N losses in slurry-based treatments. Late application reduced N₂O emissions by 48%. GHG emissions from ADS, US and IR were similar to those from MS, MB and IN. ADS, US and IR are the most suitable strategies for slurry application in CA.

Acidification of animal slurry is recommended in order to reduce NH₃ emissions, but relatively little is known about the effect of such treatment on C and N dynamics during acidification, storage, and after soil application. A laboratory study was performed, and the CO₂ emissions from a high–dry matter slurry (HDM), a low–dry matter slurry (LDM), and the same respective acidified slurries (AHDM and ALDM) were followed during a storage period and after soil incorporation. The N‐mineralization and nitrification processes, as well as microbial‐biomass activity were also estimated in soil receiving both the acidified and nonacidified materials. We observed a strong CO₂ emission during the acidification process, and acidification led to a small increase in CO₂ emissions (≈ 11%) during storage of AHDM relative to HDM. No effect of LDM acidification on CO₂ emissions during storage was observed. About 30% of C released during storage of AHDM was inorganic C, and for ALDM the C release was exclusively inorganic. Soil application of AHDM and ALDM led to a decrease in soil respiration, nitrification, and microbial‐biomass‐C values, relative to soil application of HDM and LDM, respectively. Furthermore, it was shown that this effect was more pronounced in ALDM‐ than AHDM‐treated soil. Considering both steps (storage and soil application), acidification led to a significant decrease of C losses and lower C losses were observed from LDM slurries than from HDM slurries.

In a pot experiment with corn (Zea mays L. cv. Moncada) and an incubation study, ash from co-combustion of sugarcane bagasse and eucalyptus wood was evaluated for use as a potential alternative to conventional agricultural limestone. Ash was effective as liming agent. Soil pH increased from 5.1 to 5.9 in a Haplic Arenosol and from 5.3 to 6.0 in a Haplic Cambisol. pH of the ash-amended soils were similar to those amended with calcitic and dolomitic limestone. Soil extractable P and K increased by 254% and 869% in the Haplic Cambisol and by 183% and 208% in the Haplic Arenosol. Application of ash to soil was associated with an increase in corn yield of 32% in the Haplic Cambisol and 11% in the Haplic Arenosol relative to the unamended treatments. The uptake of K by corn was greatly enhanced after ash application, increasing from 319 to 1079 mg K pot⁻¹ in the Haplic Cambisol and from 397 to 729 mg K pot⁻¹ in the Haplic Arenosol. Results supported the view that ash is a by-product that can become an increasingly valuable amendment as it acts both as a liming material and as a P and K fertilizer.

The objective of the present work was to assess the short term potential of treated wastewater and sewage sludge for ornamental lawn fertilization and irrigation. A field experiment was performed and the following treatments were considered: sewage sludge application + irrigation with public water; sewage sludge application + irrigation with treated wastewater; irrigation with public water; irrigation with treated wastewater (TW). Irrigation with treated wastewater showed a positive effect on lawn installation through higher growth of grass (1,667 cm) and higher dry matter yield (18,147 g m⁻²). These results represent a significant increase in the grass yield compared with public water irrigation. The grass height (2,606 cm) and dry matter yield (23,177 g m⁻²) increased even more, when sewage sludge produced in the wastewater treatment plant (WWTP) was applied to soil, which proves once more its benefits as an organic fertilizer. At the end of the experiment, an increase of some soil parameters (pH, electrical conductivity, organic matter, Ca²⁺, Na⁺, K⁺, Mg²⁺ and NH₄⁺) was observed, indicating that treated wastewater irrigation can cause a soil sodization. This short term study indicated that use of treated wastewater and sewage sludge for ornamental lawn fertilization and irrigation is an environmentally sustainable option for re-use of the WWTP by-products.

The potential of an organically managed Cambic Arenosol to supply nitrogen (N) from either an applied commercial organic fertilizer (granulated hen manure), a compost produced on‐farm, or four different mixtures of both fertilizers was studied in a laboratory incubation and a pot experiment with lettuce. In the incubation experiment, a significant higher apparent N mineralization occurred after hen‐manure application (53.4% of the organic N applied) compared to compost (4.5%) or mixed‐fertilizer application (8.7% to 16.7%). The apparent N mineralization in a mixed treatment consisting of compost and half rate of hen manure (15.4% of the organic N applied) was significantly higher than that estimated based on the N mineralization for compost and hen‐manure treatments (7.6%), proving that a combined application of both fertilizers enhanced organic‐N mineralization when compared to separate fertilizer supply. In the pot experiment, a higher lettuce fresh‐matter yield was obtained with hen manure (1.9 kg m^–2) than with compost (1.7 kg m^–2) or unfertilized control treatment (1.3 kg m^–2). Combined application of compost with only a half rate of hen manure led to yields (2.0 kg m^–2) equal to those obtained with only hen manure. A good correlation was observed between the N‐mineralization incubation data and the N accumulated by lettuce plants in the pot experiment (r = 0.983). Hence, in the organic production of baby‐leaf lettuce, a mixture of compost and hen manure appears to be a good fertilization alternative, since it allows a reduction by half of the typical amount of commercial fertilizer usually applied (granulated hen manure), cutting fertilization costs, and providing an amount of available N that allows maintaining lettuce yields.