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1.9 g N kg-1; pH 8.0) was applied to a clay-loam soil (sand 45%; silt 25%; clay 30%; organic C 1.16%; total N 0.14%; pH 6.8). Manure-amended soil (MAN) and unamended soil (CON) were incubated. We adopted a fully randomised experimental design with three replicates and we followed the “nursery” method by Thuriès et al. (2000). In order to provide enough experimental units (mix of soil + manure or water) for a total of 35 destructive measurements over time, we set up 210 experimental units (2 treatments × 4 manure applications × 3 replicates × 35 sampling dates). Each experimental unit contained an amount of preincubated soil corresponding to 100 g dry soil. Preincubation was carried out for 1-week to allow mineralisation of labile pools present in the soil after air desiccation, sieving (at 2 mm) and remoistening. Experimental units were divided in four groups; the first group received manure once, the second group twice, the third three times, and the last group four times. Repeated applications were made every 85 days at a rate of 100 mg N kg-1 soil (corresponding to 360 kg N ha-1, considering a plough depth of 0.3 m and a soil bulk density of
1.2 g cm-3) for each addition. After the last manure application, 3 replicates of MAN and CON were analyzed for respired C and soil mineral N concentration on Day 0, 1, 7, 15, 29, 41 and 85; in addition, experimental units receiving 1 and 4 manure applications, were analyzed on Day 21 and, only experimental units receiving manure once, were analyzed on Day 10.
The incubation was carried out at a soil water potential of -50 kPa, and a temperature of 25°C.
Experimental units were periodically watered to compensate for water loss by evaporation.
Measurements of respired C were carried out by the alkali trap method (Stotzky, 1965) while concentrations of 1M KCl extractable ammonium and nitrate were determined by flow injection analysis and spectrometric detection. For each incubation interval, the net respiration of manure C was determined by subtracting the CO2-C of CON from that of MAN (assuming no priming effect from the manure). These values were summed for all the intervals to obtain the accumulated respiration. For each incubation interval net soil mineral nitrogen concentration (SMN = NH4–N + NO3–N) was calculated as the SMN in MAN minus the SMN in CON. Manure C residual effect (CRE) due to one, two or three manure applications was calculated as the difference between the net accumulated CO2–C at day 85 measured during application 4 and the net accumulated CO2–C
Nitrogen Workshop 2012
measured at day 85 during applications 3, 2 or 1. We hypothesised that increments in the respiration of manure C after repeated applications could be ascribed to the mineralisation of the recalcitrant components of the manure applied to the soil. Manure N residual effect (NRE) due to one, two or three manure applications was calculated as the difference between the net SMN at day 85 measured during application 4 and the net SMN measured at day 85 during applications 3, 2 or 1.
Figure 1. Carbon (a) and nitrogen (b) residual effects of a liquid dairy cow manure applied to a clay-loam soil.
4. Conclusions These preliminary results show that after repeated manure applications of liquid dairy manure to a clay-loam soil, part of the added organic matter is slowly mineralised, contributing to a progressive release of ammonium into the soil. The results of these incubation studies are useful to better understand the residual effect of carbon and nitrogen in the field and to improve simulation models.
References Bechini, L. and Marino, P. 2009. Short-term nitrogen fertilizing value of liquid dairy manures is mainly due to ammonium. Soil Sci. Soc. Am. J. 73, 2159-2169.
Schröder, J., Uenk, D. and Hilhorst, G. 2007. Long-term nitrogen fertilizer replacement value of cattle manures applied to cut grassland. Plant and Soil 299, 83-99.
Sørensen, P. 1998. Effects of storage time and straw content of cattle slurry on the mineralization of nitrogen and carbon in soil. Biol. Fert. Soils 27, 85-91.
Sørensen, P. 2004. Immobilisation, remineralisation and residual effects in subsequent crops of dairy cattle slurry nitrogen compared to mineral fertiliser nitrogen. Plant and Soil 267, 285-296.
Stotzky, G. 1965. Microbial respiration, In C.A. Black et al. (ed.) Methods of soil analysis. Agron. Monogr. 9. ASA, Madison, WI pp. 1150–1572.
Thuriès, L., Larrè-Larrouy, M.C. and Pansu, M. 2000. Evaluation of three incubation designs for mineralization kinetics of organic materials in soil. Comm. Soil Sci. Plant Anal. 31, 289-304.
Van Kessel, J.S., Reeves III, J.B. and Meisinger, J.J. 2000. Nitrogen and carbon mineralization of potential manure Components. J. Environ. Qual 29, 1669-1677.
Nitrogen Workshop 2012
Comparing N recovery from legumes grown as green manures in olive orchards Arrobas, M.a, Ferreira, I.Q.a, Claro, M.a, Correia, C.M.b, Moutinho-Pereira, J.M.b, Bacelar, E.b, Fernandes-Silva, A.A.b, Rodrigues, M.Aa.
a CIMO – Mountain Research Centre, Polytecnic Institute of Bragança, Portugal b CITAB – Centre for the Research and Technology of Agro-Environmental and Biological Sciences, UTAD, Portugal
1. Background & Objectives Green manuring is probably the only option for extending on a great scale the acreage of organic farming in the perennial crops of the Mediterranean basin such as olive groves. Olive growers, in general, do not have animals so the availability of organic manures is not sufficient to maintain soil fertility. In addition, the organic composts approved for organic farming on the market have high prices and are sometimes speculative, in relation to their fertiliser value (Rodrigues et al., 2006). In NE Portugal there is a long tradition in the cultivation of white lupin (Lupinus albus) as a means of improving soil fertility. However, little is known about the dry matter yield and N fixation potential of lupin in these agrosystems, and also of the transfer of fixed N to the trees. In this work the results of dry matter yield and N recovery by lupin, vetch (Vicia villosa) and a mixture of self-reseeding annual legumes are presented. The trial also included plots of oats (Avena sativa) and natural vegetation.
2. Materials & Methods Two field trials were carried out on Carrascal farm (Vila Flor) and Suçães (Mirandela) in NE Portugal. On Carrascal farm the treatments of the experimental design were: white lupin, vetch, a mixture of self-reseeding annual legumes, oats and natural vegetation as control. The species/varieties of the mixture were: Ornithopus compressus cv. Charano, Ornithopus sativus cvs.
Erica and Margurita, Trifolium subterraneum cvs. Dalkeith, Seaton Park, Denmark and Nungarin, Trifolium resupinatum cv. Prolific, Trifolium incarnatum cv. Contea, Trifolium michelianum cv.
Frontier and Biserrula pelecinus cv. Mauro. On Suçães, the treatments were: white lupin, the same mixture of self-reseeding annual legumes, oats and natural vegetation fertilised with N (60 kg N haand not fertilised. Dry matter yield and N recovery were determined from field samples of the above-ground biomass. Nitrogen concentration in plant tissues was determined by a Kjeldahl procedure.
3. Results & Discussion White lupin produced 6.9 and 8.2 Mg DM ha-1 and accumulated 138 and 195 kg N ha-1 in the above-ground biomass at Carrascal and Suçães, respectively (Figures 1 and 2). The values may be considered high if compared with others reported in the literature (Carranca et al., 2009). In Carrascal, vetch showed slightly lower DM yield than white lupin, but its tissues presented higher N concentration. As a result, N recovered was slightly higher in vetch (156 kg N ha-1) in comparison to lupin. Annual legumes produced 5.6 and 6.4 Mg DM ha-1 and recovered 105 and 110 kg N ha-1.
Oats showed fair DM yields (4.7 and 3.0 Mg ha-1), but N concentrations in tissues were very low (5.4 and 5.2 g kg-1), recovering only 25.6 and 15.7 kg N ha-1. The dry matter yields recorded from the natural vegetation not fertilized were low (1.1 and 0.7 Mg ha-1) and N recoveries very low (11 and 7 kg N ha-1), revealing that these soils presented very low levels of N availability. Applying N, only a small increase in DM yield was found (1.1 Mg N ha-1), but N concentration in tissues increased markedly (20.8 g kg-1). The reduced stimulus in DM yield of natural vegetation by N application in spring is explained by reduced nitrophily, a short growing season, and the small size
of several dominant species in the infertile soils where the orchards are established, such as Mibora minima, Crassula tillaea and Spergula arvensis (Rodrigues et al., 2009).
Figure 2. Dry matter yield, N concentration and N recovery in above-ground biomass in Suçães, Mirandela.
4. Conclusion The legume species included in these experiments were particularly well adapted to the agroecological conditions of the region. They showed high potential for DM yield and N fixation in soils with very low natural fertility. White lupin and vetch might accumulate more than 150 kg N ha-1 yr-1, values that seem high enough to ensure the N nutrition of the trees without additional fertilisers. However, further studies are necessary to evaluate the efficiency of N transfer to the trees.
Acknowledgement Funded by FCT (Portugal) through the project PTDC/AGR-AAM/098326/2008.
References Rodrigues, M.A., Pereira, A., Cabanas, J. E., Dias, L. Pires, J. and Arrobas, M. 2006. Crops use-efficiency of nitrogen from manures permitted in organic farming. European Journal of Agronomy 25, 328-335.
Rodrigues, M.A., Cabanas, J.E., Lopes, J.I., Pavão, F., Aguiar, C. and Arrobas, M. 2009. Grau de cobertura do solo e dinâmica da vegetação em olivais de sequeiro com a introdução de herbicidas. Ver. Ciências Agrárias XXXII, 30-42.
Carranca, C., Torres, M.O. and Baeta, J. 2009. White lupine as a beneficial crop in Southern Europe. I. Potential for N mineralization in lupine amended soil and yield and N2 fixation by white lupine. Europ. J. Agron. 31, 183-189.
Nitrogen Workshop 2012
Comparing strategies for implementing soil organic matter and nitrogen use in two contrasting soils Fiorentino N.a Bertora C.b, Alluvione F.b, Zavattaro L.b, Fagnano M.a, Quaglietta Chiarandà F.a, Grignani C.b a Department of Agricultural Engineering and Agronomy, University of Naples Federico II, Italy b Department of Agronomy, Forest, and Land Management, University of Turin, Italy
1. Background & Objectives In the last decades, wide scientific debate has highlighted the need to preserve and restore soil organic matter and to improve soil ecosystemic functions. A field experiment was designed to assess the applicability of alternative C sequestration strategies: either adoption of minimum tillage or addition of stabilized organic matter in the form of compost. Strategy success was evaluated by the ability of each tool to effectively enhance soil organic carbon (SOC) and support maize yield.
2. Materials & Methods Tested treatment were compost distribution (COM) or minimum tillage (MT) compared to conventional management (CONV), under contrasting soil conditions (high fertility-coarse texture at Turin site – NW Italy- and low fertility-fine texture at Naples site- southern Italy). Field trials lasted from 2006 to 2008. N input was 130 kg N ha-1 for all the treatments except a non-N-fertilized ploughed control (0N). N sources were urban waste compost (COM) and urea (MT, CONV).
Treatment effect was evaluated through yield and medium-term variation of soil fertility, as indicated by SOC and total N. Variables were analysed through ANOVA considering the treatment as the main factor; for yield, year effect was analysed as a repeated measure. Site was not included as factor in order to preserve homogeneity of variance (sites were analysed separately).
3. Results & Discussion Soil properties influenced the different maize responses to treatments between the two study sites.
Naples was characterized by a lower fertility than Turin, which resulted in a marked reduction of COM agronomic performance with respect to CONV in all years. Different results occurred at Turin, where its higher fertility buffered any treatment effect (Table 1). It is likely that compost released a fraction of its organic N after soil incorporation where it acted as a slow-release fertilizer (Erhart et al., 2007), with labile N representing a small portion of total N. Thus, complete substitution of mineral fertilizers with compost is usually possible in coarse but fertile soils, while higher amounts of total N with respect to mineral fertilizers are needed in fine-textured low-fertile soils (Fagnano et al., 2011). Lower initial soil fertility at Naples resulted in higher soil C sequestration (Figure 1); even though maize yield was lower. Reduction of tillage intensity was effective in sequestering C in the Naples clayey soil, likely because maize root mineralization was mitigated by anoxic conditions, while coarse textured soil at Turin always favoured crop residue oxidation. Still it is possible that C sequestration at Turin could occur in the medium- to long-term.
Results suggested that SOC preservation could be agronomically sustainable in the fine-textured soils near Naples only with MT. In fact SOC increased with either using compost or MT, but compost strongly reduced maize yield since anoxic soil conditions hindered organic matter mineralization and favoured plant-available N immobilization. SOC preservation in the fertile and coarse-textured soils near Turin was achieved only with compost addition (55.1 % of added C), probably because soil aeration fostered root oxidation in MT.
-0,8 Figure 1. Soil organic C and total N concentration variations of the different treatments at Naples and Turin at the end of treatment application (harvest in 2008) relative to pre-treatment conditions (pre-fertilization in 2006).