Giacomo Tosti1*, Daniele Antichi2,Paolo Benincasa1, Simona Bosco3, Christian Frasconi2, Luigi Manfrini4, Andrea Onofri1,
Marcello Guiducci1
1 Dipartimento di Scienze Agrarie, Alimentari e Ambientali - Università degli Studi di Perugia, Borgo XX Giugno 74, 06121 Perugia, Italy
2 Dipartimento di Scienze Agrarie, Alimentari e Agro-ambientali – Università di Pisa, via del Borghetto 80, 56124 Pisa, Italy 3 Istituto di Scienze della Vita, Scuola Superiore Sant'Anna, via S. Cecilia, 3 56127 Pisa, Italy
4 Dipartimento di Scienze Agrarie, Università di Bologna, V.le Fanin 44, 40127 Bologna, Italy. *giacomo.tosti@gmail.com
Abstract
The SMOCA (Smart Management Organic Conservation Agriculture) project aims at integrating conservation agriculture and organic farming in three of the most representative scenarios in Italy: (i) arable field crops, (ii) field vegetables, (iii) tree fruit orchards. Maximising the advantages of organic and conservative systems has been pursued through the “intensification” of the “ecological efficiency” through smart and advanced techniques.
Innovative machines for cover crops (CC) termination, minimum tillage, direct seeding/transplanting and physical weed control have been made “ex-novo” on purpose or optimized for each scenario. Following a common scheme, three different cropping systems were compared by each research unit:
- Integrated control (INT): conventional integrated farming system (herbicides and agrochemicals allowed, ordinary soil tillage, no CC use);
- Traditional organic (ORG): organic farming system which includes reduced soil tillage, the use of CC, preventive and direct non-chemical weed control methods;
- Advanced organic (ORG+): deep integration between organic farming and conservative techniques. It includes a permanent green cover of the soil, no-tillage, physical weed control, the use of CC as living or dead mulches.
The study of the overall sustainability of the three systems included the following aspects: - agronomical (e.g. yield, N uptake, weed development, product quality, etc.);
- environmental and energetic (e.g. greenhouse gas emissions, C and N balance, LCA, etc.).
In the present contribution, the N balance and the relevant agronomic implications for the DSA3 research unit will be presented and discussed.
Keywords: processing tomato; durum wheat; vegetable production; horticulture; N use efficiency; leaching; sustainability. Parole chiave: pomodoro da industria, frumento duro, orticoltura; efficienza d’uso dell’N, lisciviazione; sostenibilità. Introduction
Organic farming systems are considered not compatible with conservation tillage mainly because of the reliance of conservative systems on herbicides, to control increasing weed pressure in absence of inversion tillage, and mineral fertilisers, in order to obtain satisfactory yields with a reduced mineralisation rate (Peigné et al., 2007). Consequently, the integration of organic and conservative systems can be achieved only if two major issues are addressed: the availability of specific versatile and efficient machines for non-chemical CC management, weed control and sod-seeding/planting (Sartori and Rota, 2007); and the optimisation of cropping systems in function of improved nutrient cycling and preventive weed control. Nitrogen management in low input and organic farming systems relies indeed to a great extent on preventive measures such as the introduction of legumes and CC in the crop rotation, and the adoption of conservative soil tillage techniques (Thorup-Kristensen et al., 2003). The high environmental and economic costs of N management only based on extra-farm fertilisers are not sustainable in the long term (Pimentel et al., 2005). Thus, several strategies are adopted in order to increase (i) N-self-sufficiency and (ii) N use efficiency at the plant, crop and whole rotation scales (Dresbøll and Thorup-Kristensen, 2014; Benincasa et al., 2017). The main objectives of this study were to test the performances of conservative crop production under organic farming conditions (ORG+), practiced with intensive use of CC and innovative machines and to assess the effect of such system on N leaching and soil N stock as compared to a traditional organic (ORG) and to a conventional integrated (INT) cropping system.
Materials and Methods
The field experiment was carried out in three consecutive years (2013/14, 2014/15 and 2015/16) at the experimental station of DSA3. Weather data were collected by an automatic meteorological station located inside the experimental site. The
crop rotation implemented in PG consisted of processing tomato, Lycopersicon esculentum Mill. cv. PS1296) followed by durum wheat (Triticum durum Desf. cv. Dylan). In each experimental year, both crop were grown alternately in two adiacent fields. In a randomized blocks design with two replications for each field, three cropping systems (treatments) at increasing ecological intensification were compared: (i) integrated system with no CC and conventional tillage technique (INT), (ii) organic system with green manures and conventional tillage (ORG), and (iii) innovative organic system with CC and conservation tillage techniques (ORG+). Processing tomato was preceded by bare soil in INT and by an autumn sown CC mixtures (barley 25%:field pea 75%) in ORG and ORG+. CC were terminated by cutting and incorporating the biomass into the soil (ORG) or by using a roller crimper and leaving the biomass as dead mulch (ORG+). Both crops were transplanted/sown after traditional (harrowing/spading) soil preparation (INT and ORG) or after strip tillage/no-tillage (ORG+). Wheat N fertility management was fully based on external inputs in INT (160 kg N ha-1 in two split applications)
and ORG (40 kg N ha-1 broadcasted at pre-sowing as poultry manure), while it was based on natural N-fixing process in
ORG+ by adopting a temporary intercropping (Tosti and Guiducci, 2010) wheat-faba bean (Vicia faba L sub minor ). N nutrition of processing tomato was managed by fertigation using synthetic input in INT (full dose of 150 kg N ha-1) and
organic fertiliser in ORG and ORG+ (variable rates calculated as the complement to 150 kg N ha-1 of the pea N
accumulation observed in the preceding CC). During the crop cycle N leaching was measured with porous lysimeter cups (details can be found in Tosti et al., 2014 and 2016). Biomass, yield and N% (Kjeldahl) of the plant material were recorded at harvest. A simple N apparent balance for each system, year and crop was calculated as follows:
NB = NI - NR - NL
where NB represents the positive or negative variation of total N in the soil (residues included) at the end of each cropping
cycle, NI is the N input (fertiliser + N derived from atmosphere), NR is the N removed with crop yield and NL is the N lost
with drainage water in the deep watershed. Data were anlysed by using a linear mixed model where the year, treatment and crop species were included as fixed effect and the plot was included as random effect to account for repeated measures. Data analisys was performed by using the lme() function within the nlme library (Pinheiro et al., 2017) in the statistical software R (R Core Team, 2017).
Fig. 1: Mean air temperatures (monthly values) and cumulated rainfalls recorded at the DSA3 experimental station during the 3-year experiment (2013-14, 2014-15 and 2015-16 comparing to the long-term mean over 1950–2015).
Figura 1: Temperatura media dell'aria (valori mensili) e precipitazioni cumulate registrate nella stazione sperimentale DSA3 durante l'esperimento triennale (2013-14, 2014-15 e 2015-16 rispetto alla media a lungo termine nel periodo 1950- 2015).
Results and Discussion
WEATHER CONDITIONS
During the three years, mean air temperature was generally higher than the long-term mean (Fig. 1). Autumn and winter temperatures were particularly high during 2014/15. The amount of precipitation was variable during the experiment: cumulated rainfall were much higher (2013/14), similar (2014/15) or lower (2015/16) than the long-term mean. Thus drainage volumes were particularly high in 2013/14 and, due to a short period of intense rainfall in February/March, in 2014/15. On the contrary, drainage was low in 2015/16 because the autumn-winter period was unusually dry.
N APPARENT BALANCE
The interaction Year x Crop x Treatment was significant for both NI (p = 0.0120) and NR (p = 0.0222), so results are
presented separately for each crop, year and treatment separated (Tab. 1). Considering wheat, NI was constant in INT and
ORG, while it varied in ORG+ depending on faba bean N accumulation. However, except for the third year, the N-fixing activity of the legumes supplied a low amount of N that was not different from the rate commonly supplied in ORG via
organic extra-farm source (poultry manure). NI of processing tomato was kept rather constant across treatments, as
fertigation technique allows an accurate management of the N dose with both organic or synthetic fertilizers. The main difference was that part of the total input was ensured in ORG and ORG+ by the N-fixing activity of the CC legume component (i.e. pea).
Tab. 1: N input (NI) and N removed with crop yield (NR) in the integrated (INT), traditional organic (ORG) and innovative
organic (ORG+) systems during the 3-year experiment. Percentage values represent the amount of N derived from the
atmosphere (via N-fixing activity of faba bean and pea) on NI.
Tab. 1: N ingresso (NI) e N rimosso con resa delle colture (NR) nei sistemi integrato (INT), biologico tradizionale (ORG) e
biologico innovativo (ORG +) durante i tre anni di sperimentazione. I valori percentuali rappresentano la quantità di N
derivata dall'atmosfera (tramite l'attività di azoto-fissazione di fagiolini e piselli) su NI.
Again, excepted for the third year, when both ORG and ORG+ performed quite bad, the N-fixing activity was better under ORG than ORG+ system, and that was mainly to be ascribed to the sod seeding that hampered the pea emergence. For both wheat and processing tomato, the NR rankings among treatments was constant (i.e. INT>ORG>ORG+) across years. The
higher NI (100% extra-farm and synthetic N) of INT promoted higher yields and, as a consequence, higher NR. The lower
NR of ORG+ was worsened by the higher presence of weeds compared to the other systems (data not shown).
Fig. 2: N lost by leaching (NL, kg N ha-1) in the integrated (INT), traditional organic (ORG) and innovative organic
(ORG+) systems during the 3-year experiment. SEM = 6.526.
Fig. 2: N persi per lisciviazione (NL, kg N ha-1) nei sistemi integrato (INT), biologico tradizionale (ORG) e biologico
innovativo (ORG +) durante i tre anni di sperimentazione. SEM = 6.526.
As expected, NL was greatly influenced by the Year x Treatment interaction (p = 0.0007) (Fig. 2). The presence/absence of
CC and the N rate were the most important factors that determined the NL amount (Tonitto et al., 2006). The use of CC has
strongly improved the ability of the agroecosystem to retain N and avoid that this resource is being lost by leaching. The biogeochemical cycles of carbon and N has been recoupled by the fertility building crop strategies (Gardner and Drinkwater, 2009), and, moreover, the conservation devitalization of the CC seemed to significantly decrease NL compared
to the traditional devitalization. However, a longer time span is needed in order to collect more reliable data on how this ecological service could be influenced. Concerning NB, the Crop x Treatment interaction was significant (p < 0.0001).
Wheat NB was negative in all the three systems, while it showed important differences amongst treatment for processing
tomato (Fig. 3). INT performance in terms of NB was dramatically influenced by the high NL in 2013/14 and the high NR in
NB was, in fact, negative in wheat and positive in processing tomato. As NI and NL were similar in ORG and ORG+, the
lower NB values in ORG have to be ascribed to the higher NR as compared to ORG+. Even if the low NR (i.e. yield)
represents a weak point of ORG+, such system confirmed to be the most sustainable in terms of soil N fertility improvement. Research of innovative tools for weed and crop management should be a primary objective for coupling organic and conservation agriculture.
Fig. 3: N balance (NB kg N ha-1) in the integrated (INT), traditional organic (ORG) and innovative organic (ORG+)
systems during the 3-year experiment. SEM = 9.615.
Fig. 3: Bilancio dell’azoto (NB kg N ha-1) nei sistemi integrato (INT), biologico tradizionale (ORG) e biologico innovativo
(ORG +) durante i tre anni di sperimentazione. SEM = 9.615.
Conclusions
N management could be improved strongly in organic systems by intensive use of fertility building crops, which also strongly reduced its losses to the environment. Conservation organic agriculture has proved to be an excellent system to build up the “N stock”, but further research is needed in order to understand and deal with the implications of such system on cash and cover crops performance.
Acknowledgements
Research funded by MIUR FIRB 2013 – Project SMOCA (2014-2017) (Smart Management of Organic Conservative Agriculture). Project coordinator Christian Frasconi.
We wish to thank Dr. Marco Fernando Manco and Dr. Paolo Mucci for their support with the field activities.
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