Antonio Vallejo

Effects of fertiliser type and the presence or absence of plants on nitrous oxide emissions from irrigated soils

Nitrous oxide (N2O) emissions and denitrification losses from an irrigated sandy loam soil amended with composted municipal solid waste (MSW), sheep manure (SM), surface applied pig slurry (SPS), incorporated pig slurry (IPS) or urea (U) were studied under Mediterranean conditions. We quantified emissions, in both the presence and absence of maize and N2O production, via denitrification and nitrification pathways using varying concentrations of acetylene. Discounting the N2O lost in the Control, the percentages of N2O lost in relation to the total N applied were greater for urea (1.80%) than for MSW (0.50%), SM (0.46%), SPS (1.02%) or IPS (1.27%). In general, plots treated with organic fertilisers emitted higher amounts of N2O when under maize than bare soil plots. On the other hand, greater denitrification losses were also recorded for plots in the absence of plants (between 9.7 and 29.3xa0kg N2O-Nxa0ha−1) than for areas with plants (between 7.1 and 24.1xa0kg N2O-Nxa0ha−1). The proportion of N2O produced via denitrification was greater from fertiliser treatments than for the controls and also greater without plants (between 66 and 91 % of the N2O emitted) than with plants (between 48 and 81%).

Role of maize stover incorporation on nitrogen oxide emissions in a non-irrigated Mediterranean barley field

AimsAgricultural soils in semiarid Mediterranean areas are characterized by low organic matter contents and low fertility levels. Application of crop residues and/or manures as amendments is a cost-effective and sustainable alternative to overcome this problem. However, these management practices may induce important changes in the nitrogen oxide emissions from these agroecosystems, with additional impacts on carbon dioxide emissions. In this context, a field experiment was carried out with a barley (Hordeum vulgare L.) crop under Mediterranean conditions to evaluate the effect of combining maize (Zea mays L.) residues and N fertilizer inputs (organic and/or mineral) on these emissions.MethodsCrop yield and N uptake, soil mineral N concentrations, dissolved organic carbon (DOC), denitrification capacity, N2O, NO and CO2 fluxes were measured during the growing season.ResultsThe incorporation of maize stover increased N2O emissions during the experimental period by c. 105xa0%. Conversely, NO emissions were significantly reduced in the plots amended with crop residues. The partial substitution of urea by pig slurry reduced net N2O emissions by 46 and 39xa0%, with and without the incorporation of crop residues respectively. Net emissions of NO were reduced 38 and 17xa0% for the same treatments. Molar DOC:NO3− ratio was found to be a robust predictor of N2O and NO fluxes.ConclusionsThe main effect of the interaction between crop residue and N fertilizer application occurred in the medium term (4–6xa0month after application), enhancing N2O emissions and decreasing NO emissions as consequence of residue incorporation. The substitution of urea by pig slurry can be considered a good management strategy since N2O and NO emissions were reduced by the use of the organic residue.

Effectiveness of urease inhibition on the abatement of ammonia, nitrous oxide and nitric oxide emissions in a non-irrigated Mediterranean barley field

Urea is considered the cheapest and most commonly used form of inorganic N fertilizer worldwide. However, its use is associated with emissions of ammonia (NH(3)), nitrous oxide (N(2)O) and nitric oxide (NO), which have both economic and environmental impact. Urease activity inhibitors have been proposed as a means to reduce NH(3) emissions, although limited information exists about their effect on N(2)O and NO emissions. In this context, a field experiment was carried out with a barley crop (Hordeum vulgare L.) under Mediterranean conditions to test the effectiveness of the urease inhibitor N-(n-butyl) thiophosphoric triamide (NBPT) on reducing these gaseous N losses from surface applied urea. Crop yield, soil mineral N concentrations, dissolved organic carbon (DOC), denitrification potential, NH(3), N(2)O and NO fluxes were measured during the growing season. The inclusion of the inhibitor reduced NH(3) emissions in the 30 d following urea application by 58% and net N(2)O and NO emissions in the 95 d following urea application by 86% and 88%, respectively. NBPT addition also increased grain yield by 5% and N uptake by 6%, although neither increase was statistically significant. Under the experimental conditions presented here, these results demonstrate the potential of the urease inhibitor NBPT in abating NH(3), N(2)O and NO emissions from arable soils fertilized with urea, slowing urea hydrolysis and releasing lower concentrations of NH(4)(+) to the upper soil layer.

Management of irrigation frequency and nitrogen fertilization to mitigate GHG and NO emissions from drip-fertigated crops

Drip irrigation combined with split application of fertilizer nitrogen (N) dissolved in the irrigation water (i.e. drip fertigation) is commonly considered best management practice for water and nutrient efficiency. As a consequence, its use is becoming widespread. Some of the main factors (water-filled pore space, NH4(+) and NO3(-)) regulating the emissions of greenhouse gases (i.e. N2O, CO2 and CH4) and NO from agroecosystems can easily be manipulated by drip fertigation without yield penalties. In this study, we tested management options to reduce these emissions in a field experiment with a melon (Cucumis melo L.) crop. Treatments included drip irrigation frequency (weekly/daily) and type of N fertilizer (urea/calcium nitrate) applied by fertigation. Crop yield, environmental parameters, soil mineral N concentrations and fluxes of N2O, NO, CH4 and CO2 were measured during 85 days. Fertigation with urea instead of calcium nitrate increased N2O and NO emissions by a factor of 2.4 and 2.9, respectively (P<0.005). Daily irrigation reduced NO emissions by 42% (P<0.005) but increased CO2 emissions by 21% (P<0.05) compared with weekly irrigation. We found no relation between irrigation frequency and N2O emissions. Based on yield-scaled Global Warming Potential as well as NO cumulative emissions, we conclude that weekly fertigation with a NO3(-)-based fertilizer is the best option to combine agronomic productivity with environmental sustainability. Our study shows that adequate management of drip fertigation, while contributing to the attainment of water and food security, may provide an opportunity for climate change mitigation.

Yield-scaled mitigation of ammonia emission from N fertilization: the Spanish case

Synthetic nitrogen (N) fertilizer and field application of livestock manure are the major sources of ammonia (NH3) volatilization. This N loss may decrease crop productivity and subsequent deposition promotes environmental problems associated with soil acidification and eutrophication. Mitigation measures may have associated side effects such as decreased crop productivity (e.g. if N fertilizer application is reduced), or the release of other reactive N compounds (e.g. N2O emissions if manure is incorporated). Here, we present a novel methodology to provide an integrated assessment of the best strategies to abate NH3 from N applications to crops. Using scenario analyses, we assessed the potential of 11 mitigation measures to reduce NH3 volatilization while accounting for their side effects on crop productivity, N use efficiency (NUE) and N surplus (used as an indicator of potential N losses by denitrification/nitrification and NO3− leaching/run-off). Spain, including its 48 provinces, was selected as a case study as it is the third major producer of agricultural goods in Europe, and also the European country with the highest increase in NH3 emissions from 1990 to 2011. Mitigation scenarios comprised of individual measures and combinations of strategies were evaluated at a country- and regional level. Compared to the reference situation of standard practices for the year 2008, implementation of the most effective region-specific mitigation strategy led to 63% NH3 mitigation at the country level. Implementation of a single strategy for all regions reduced NH3 by 57% at the highest. Strategies that involved combining mitigation measures produced the largest NH3 abatement in all cases, with an 80% reduction in some regions. Among the strategies analyzed, only suppression of urea application combined with manure incorporation and incorporation of N synthetic fertilizers other than urea showed a fully beneficial situation: yield-scaled NH3 emissions were reduced by 82%, N surplus was reduced by 9%, NUE was increased by 19% and yield was around 98% that of the reference situation. This study shows that the adoption of viable measures may provide an opportunity for countries like Spain to meet the international agreements on NH3 mitigation, while maintaining crop yields and increasing NUE.

Pre-plant slow-release fertilization of strawberry plants before fertigation

The advantages of pre-plant fertilization were studied by using a slow-release fertilizer (nitrophoska permanent) with strawberry plants (Fragaria ananassa, cv Chandler) before fertigation. A sandy soil was used in the experiment in conditions of abundant rain. When the slow-release NPK was mixed with soil, the leachate analysis of a glasshouse crop showed a lower loss of N and therefore a lower degree of ground water contamination compared with the traditional NPK fertilizer. However, when the fertilizer in question was placed at 10 cm from the surface, as in the case of ornamental plants, the results were less favourable. Consequently, the slow-release fertilizer mixed with the soil not only increases the N uptake by the plant as well as the leaf and root weight, but it also produces higher yields.ResumenSe estudian las ventajas de una fertilización de fondo del cultivo de fresón, con un fertilizante de liberación lenta (nitrophoska permanent), previa a la fertilización. Se utilizó un suelo arenoso y se reprodujo una alta pluviosidad en los ensayos. En cultivo de invernadero se comprobó, mediante el análisis de drenajes, una menor pérdida de N y por lo tanto menor contaminación de acuíferos, para el NPK de liberación lenta mezclado con el suelo. Sin embargo, cuando este fertilizante se localiza a 10 cm de la superficie como en el caso de plantas ornamentales los resultados son menos positivos. Por tanto, el fertilizante de liberación lenta, mezclado con el suelo, proporciona mayor exportación de N por la planta y mayor peso de hoja y raiz, así como mejores rendimientos.

Controlling phosphorus fixation in calcareous soils by using coated diammonium phosphate

In this paper, phosphorus fixation in calcareous soils is controlled by means of rosin-coated diammonium phosphate pellets, with several rates of phosphorus release. Four soils from arid regions in the Spanish south-east were chosen and separately treated with one of the following fertilizers: superphosphate (SP) or diammonium phosphate (DAP) coated with 0, 10 or 22% rosin with a dosage of 1000 Kg P/ha. After treatment, the soils were incubated for 8 months, in the course of which samples were taken to evaluate the evolution of P availability by means of the electroultrafiltration (EUF) technique.The results obtained show that the use of DAP with a 22% coating enables phosphorus fixation in calcareous soils to be controlled. The coating was sufficiently stable to last for the time it takes the crop to grow.

Nitrogen availability of soluble and slow release nitrogen fertilizers as assessed by electroultrafiltration

The efficiency of different nitrogenous fertilizers under forced leaching conditions was determined in pot experiments using ryegrass as an indicator plant in a sandy loam soil. Treatments were: ON (unfertilized), AN (ammonium nitrate), U (urea), DAP (diammonium phosphate), T (Triabon), FK (Floranid Komplett) and CDU (crotonylidendiurea).N source effects on N uptake, and N leached (as % of N applied) were evaluated. Results show that the fertilizers which behaved best with regard to N uptake were FK followed by Triabon and AN. The most soluble fertilizers, AN and urea, gave the highest N leaching losses.Significant correlations between EUF-NI (rapidly soluble fraction) and leaching, as well as between EUF-N (I + II) and N uptake by the plant (where EUF-N II relates to the slowly soluble fraction) were obtained.