Crop rotation

The definition of Long-Term Agroecosystem Experiment (LTAE) encompasses two basic concepts: the inherent experimental nature of the system and the long-term duration. The first concept is relatively easy to be defined. An experiment should consider a planned manipulation of a system, designed to answer to some specific hypothesis. This marks a boundary between experimental (manipulated) and non-experimental (observational) studies, where the aim is to depict the evolution of a natural system, ideally without influences from the observator. The definition of long-term is, on the other hand, more challenging because it depends on the temporal dynamic of the phenomena under study. Empirical criteria have been considered to define an experiment as long-term and, generally, a LTAE should be at least 15–20 years old to be out from its initialisation phase.

 

Although the original purposes of LTAEs were to define the immediate effects of crop management on crop yield and other soil characteristics (SOM, P availability, N dynamics, etc.) (Karlen et al., 2013, Bhogal et al., 2015) in the last decades many other potential uses arose (Morari et al., 2006, Stockmann et al., 2013). As a general rule, LTAEs are essential when considering parameters characterised by a slow temporal dynamic. Indeed, in complex systems the initial response trajectories of monitored factors can be different from the long-term change. Short-term experiments are focused on these initial trajectories, while long-term experiments allow to depict which are the mechanisms involved in temporal dynamics and on the variation of trajectories in time (Knapp et al., 2012).

LTAEs, and the archived material from them, are essential for understanding many of the problems facing farmers, ecologists and policy makers (Richter et al., 2007), from SOM decline to acidification, to nutrient efficiency and leaching from soils to adaptation to climate changes, and so on (Dick, 1992, Giardini and Morari, 2004, Mazzoncini et al., 2011, Amato et al., 2013, Blanco-Moure et al., 2013, Buysse et al., 2013, Lehtinen et al., 2014, Migliorini et al., 2014, Lassaletta et al., 2014, Congreves et al., 2015).

Rasmussen et al. (1998) indicates that most of the main topics now developed within LTAEs, such as sustainability, environmental quality, species-adaptation impacts, were never envisioned by the founders of classical LTAEs (Fig. 1).


Fig. 1. Evolution of the main topics of agricultural long-term research. Redrawn from Rasmussen et al. (1998)

 

In the next future new questions will probably arise and the maintaining of proper designed long-term experiments seems to be the best way to cope with these new problems. In particular, Likens and Lindermayer (2011) identified the LTAEs as the best way to:
● Document and provide baselines against which changes, or extremes can be evaluated.
● Detect and evaluate changes in ecosystem pattern and function.
● Guide and evaluate evidence-based environmental legislation (e.g. laws to control air and water pollutants).
● Evaluate ecological responses to natural or experimental disturbance.
● Identify ecological surprises.
● Generate new and important questions about ecological dynamics.
● Provide empirical data for testing ecological theory and develop models.
● Provide information for data mining when exploring new environmental questions.

Methods

 

Four LTAEs are still undergoing at Lucio Toniolo Padova University experimental farm which started from early 60’s to 70’s. The local climate is sub-humid with a mean annual rainfall of 825 mm. The temperature reaches minimum values in January (2.3°C, on average) and maximum values in July and August (22.4°C, on average). Reference evapotranspiration (ET0) is 945 mm y−1, which exceeds the April to September rainfall (maximum peak in July, 5 mm day−1). The site has a shallow water table that ranges from about 0.5–1.5 m (from late winter to early spring) to 1–2 m (in summer).

Aims of establishing and still running LTAEs at the University of Padova

 

In the early ‘60s, LTAEs have been initially thought to provide an answer to the agronomic questions of the time such as the increase in productivity and quality of crops. They were mainly related to the developments in crop production factors such as the advent of mineral fertilizers or irrigation techniques. The way of farming as changed as well as the problems and needs of the civil society. Over the years, it has become fundamental to study agricultural practices while minimizing the environmental impact. Lastly, agricultural systems have been greatly re-evaluated for their capacity to deliver multiple ecosystem services, such that the LTAEs were used to identify the most promising cropping systems to mitigate climate change by removing CO2 from the air and store stably in the soil as organic carbon (SOC).

Experiment 1 – “Long-term rotation experiment”

 

The trial has been underway since 1962. The soil is a Fluvi-Calcaric Cambisol (FAO-UNESCO, 1990), silty or sandy loam, with a pH of 7.8. The main physical and chemical properties of the topsoil in 1962 are reported in Table 1 (Giardini and Morari, 2004). At the start of the trial the SOC in the 0–30 cm layer was 12 g kg−1 with a C:N ratio of 12. Prior management conditions included manure applications and ley cropping with alfalfa.
Rotations with different rates of fertilizer have been used to compare high- and low-input cropping systems (Giardini, 2004). The experimental layout is a split plot with three replications on 288 plots of 7.8 m × 6 m, with the intensification level as the split factor (Fig. 2).

Soil tillage is autumn ploughing at 40–45 cm, as usual in the area, followed by standard seedbed preparation operations at different times according to crop. Inside the “long-term rotation experiment”, four sub-experiments dealing with specific agronomic practice are compared, as follows.

 

 


Fig. 2. Experimental design of the long-term rotation experiment.

 

 

1.1 Crop rotations experiment (CR)
The treatments come from the factorial combination of four crop rotations (1-, 2-, 4- and 6-year), three inorganic fertilizer rates (I0, I1, I2) and two levels of management intensity (HI, high input; LI, low input).
The 6-year rotation was maize (Zea mays L.)–sugarbeet (Beta vulgaris L.)–maize–wheat (Triticum aestivum L.)–alfalfa (Medicago sativa L.)–alfalfa. The 4-year rotation is sugarbeet–maize–wheat–maize. In the period 1989–2001, soya bean (Glycine max (L.) Merr.) substituted maize after the sugarbeet. The 2-year rotation is maize–wheat. The 1-year rotation is maize monoculture.
All rotations end their cycles contemporaneously every 12 years. Before the beginning of each cycle an intermediate year was included (1963, 1976, 1989). Over the 50 years, the type of intensification has been modified at the end of each rotation cycle to respond to new agronomic problems, but always with the same rotations and fertilizer rates. In the first cycle (1964–1975), the intensification factor was irrigated versus non-irrigated crops (irrigation applied only on spring-summer crops); in the second (1977–1988) intensive inter-annual successions and farmyard manure (FYM) application versus main crop only and residue incorporation (R); in the third and fourth cycles (1990–today), slurry versus absence of organic fertilization. The low input 6-year rotation continued to receive FYM in the second, third and fourth cycles. All rotations receiving FYM had the crop residues removed for use as livestock litter.
Farmyard manure (average composition 20% dry matter, 0.5% N, 0.25% P2O5, 0.7% K2O) was applied at average doses of 20 t ha−1 per year prior to ploughing, generally in October. The slurry treatments (average composition 10% d.m., 0.4% N, 0.3% P2O5, 0.4% K2O) were applied every year at a rate of 40 t ha−1. FYM and slurry came from the cattle livestock on the experimental farm.
The three inorganic fertilizer rates were (a) zero (I0); (b) 70, 70, 90 kg ha−1 of N, P2O5, K2O, respectively (I1); (c) 140, 140, 180 kg ha−1 of N, P2O5, K2O, respectively (I2). No N was applied to soya bean or alfalfa. The crop rotation experiment includes 234 plots out of a total of 288 plots.

 

1.2 Grass experiment (G)
Permanent grassland was established in 1962. In the first cycle, the experimental layout was the same as CR, with two levels of intensity and three inorganic fertilizer rates (18 plots). In the second and third cycles, only the high-intensity level with the three inorganic fertilizer rates were continued (9 plots). Grassland was managed for hay.

 

1.3 Wheat monoculture experiment (WHM) and silage maize monoculture experiment (SMM)
These two monoculture experiments were introduced at the start of the second cycle (1977), substituting the low-intensity grass plots. The wheat monoculture experiment includes the same intensification levels as the CR experiment, but with only the I0 and I2 inorganic fertilizer rates (12 plots).
In the silage maize monoculture experiment, the FYM application in the second cycle of the high-intensity treatments was replaced by slurry (40 t ha−1 year−1). There were three inorganic fertilizer rates: I0, I1 and I2, giving a total of nine plots.

 

1.4 High-input maize monoculture experiment (HMM)
This experiment includes eight treatments with maize as main crop, for a total of 24 plots. In the last rotation cycle these have allowed a comparison of fertilization with only organic (F2 = farmyard manure; S2 = slurry), only inorganic fertilizer (I2) or mixed inputs (F1I1 = farmyard manure + inorganic input; S1I1 = slurry + inorganic input) and no fertilization (I0). Half of the treatments also include crop residue incorporation (+r). Details of all inputs are given in Supplementary Table 2.

 

Experiment 2 – “Nitrogen fertilization and crop residue in three types of soil”

 

A long-term field experiment was established in 1970 at the experimental farm ‘L. Toniolo’ of the University of Padova (45°21′N, 11°50′E; 6 m a.s.l.). Initially, 108 lysimeters (4 m2, 80-cm deep) and three types of soils (clay, sandy loam and sandy) were used to study the effects of high- and low-input cropping systems. The clay soil is classified as a Gleyic-Vertic Chernozem, the sandy loam soil as a Fluvi-Calcaric Cambisol and the sandy soil as a Calcaric Arenosol (FAO-UNESCO, 2008). Until 1988, the trial was conducted with a maize–wheat rotation, comparing 12 treatments as a factorial combination of three nitrogen applications (from 0 to 200 kg ha−1) and four crop residue managements (burial or removal of one or both crops). The trial was modified in 1988 to a 4-year rotation of wheat–maize–tomato or potato–sugarbeet. Crop residue management was simplified to compare two situations (burial or removal), whereas the nitrogen applications considered were increased to six (from 0 to 400 kg ha−1). These treatments were maintained until the end of the experiment in 2012. Further details are given in Pituello et al. (2016a).

 

In 2013, the experimental treatments were modified to evaluate the effects of different carbon sources on soil properties. The experimental design was a randomized block with three replicates. Treatments were defined by the factorial combination of four carbon management inputs and three nitrogen fertilization amounts, with maintenance of the 4-year rotation (Fig. 3). Carbon management included three types: (i) a control (NR) with no crop residue incorporation or biochar addition, (ii) incorporation of crop residues from the previous year (R), ranging in annual amounts (dry matter) from 4.69 to 9.09 Mg ha−1 in clay, 4.00 to 7.86 Mg ha−1 in sandy loam and 1.73 to 5.73 Mg ha−1 in sandy soil (Pituello et al., 2016b), and (iii) one-time biochar application of 20 Mg ha−1 (BC20) and one-time biochar application of 40 Mg ha−1 (BC40). Amounts of N fertilizer were 0, 100 and 300 kg N ha−1 year−1. Biochar was applied once in December 2013 and incorporated by shovel into the top 20-cm layer. The two rates corresponded to approximately 13.7 and 27.4 Mg C ha−1, which corresponded to about 44% and 88% of the native soil organic carbon (SOC) for the clay soil, 67% and 133% for the sandy loam soil, and seven- and 14-fold for the sandy soil, respectively. Maize (Zea mays L.) was cultivated in 2014 and 2015, and fertilized with an additional 150 kg ha−1 year−1 P2O5 and 200 kg ha−1 year−1 K2O during sowing.

 

 


Fig. 3. Experimental design of the Nitrogen fertilization and crop residue in three types of soil trial.

 

 

Experiment 3 – “Organic and mineral fertilization in three types of soil”

The experiment began in 1964 in 4-m2 open lysimeters, 80 cm deep, where three types of soil (hereinafter called clayey (CLY), sand (SND), and peaty (PTY), in relation to their dominant property) were factorially combined with six types of mineral, organic, or mixed fertilization, organized in two randomized blocks (36 lysimeters) (Fig. 4). The soils were brought from three locations in the Veneto region: clayey soil from the south-western plain, sandy soil from the central coastal area, and peaty soil from the southern plain. The original soil profiles were reconstructed in the lysimeters. The sandy soil (Calcaric Arenosols, Typic Ustipsamments, mixed, mesic—ARPAV, 2005) contains predominantly quartz and feldspar and a significant amount of dolomite (16 %). The clayey soil (Cumulic, Vertic, Endoaquoll fine, mixed, calcareous, mesic—ARPAV, 2005) has a higher amount of smectite/montmorillonite (16 %) than the other soils and a considerable presence of mica (19 %) and dolomite (15 %). The peaty soil (Typic Sulfisaprists, euic, mesic—ARPAV, 2005) is characterized by a higher mica content (25 %), whereas smectite/montmorillonite reaches 12 %. After 40 years of experimental conditions, some original properties have changed, as reported in Morari et al. (2008).

Fertilization treatments were as follows: no applications (O), farmyard manure (FYM) (40 t ha−1 year−1) and mineral fertilizer (Min) (200 kg ha−1 year−1 N–100 P2O5–240 K2O). The FYM applied almost the same amount of macroelements as Min, with about 3.5–4 t C ha−1 year−1. Until 1984, there was a 2-year maize (Zea mays L.)—wheat rotation (Triticum aestivum L.). Thereafter, a variable rotation was adopted between 1985 and 1992, with various horticultural crops. Since 1993, there has been a 3-year rotation of tomato (Lycopersicon esculentum Mill.)–sugarbeet (Beta vulgaris L.)–maize, followed by various horticultural crops, maize and sunflower (Helianthus annuus L.) from 2003 to 2007. Apart from fertilization, all plots were treated in the same way in terms of rotation and management (tillage, sowing, harvest, etc.). The top 15–20 cm was dug each autumn, and crop residues were removed.


Fig. 4. Experimental design of organic and mineral fertilization in three types of soil trial.

 

 

Experiment 4 – “Fertilization and crop residue incorporation in silty loam soil”

 

The trial, begun in 1966, has been conducted on 64 35 m2 (5.4 9 6.4 m2) plots in a Fluvi-Calcaric Cambisol (FAO-UNESCO 2008) with a clay loam texture. At the start of the experiment, the carbonate content was measured as 33.1%, with a soil pH of 7.8, bulk density of 1.44 g cm-3, organic matter content of 1.8%, and an 8.3 C:N ratio in the topsoil (0–30 cm). The experimental treatments were derived from the factorial combination of three crop residue managements (previous crop residue incorporation (RI), previous crop residue incorporation with 1 t ha-1 of dried poultry manure (RI + PM), and residues removed (RR)) with five levels of nitrogen fertilisation (0, 60, 120, 180, and 240 kg ha-1 y-1). The PM was applied by burying (ca. 15 cm) it during shallow disk harrowing immediately after harvest. It provided 60 kg organic N ha-1. Until 1981, mineral N was applied as ammonium-nitrate, after which urea was used. Mineral N was supplied in two top-dressing applications. In spring and summer crops, N distribution was followed by an inter-row cultivation (ca. 7 cm).

 

Residue incorporation occurred during soil tillage in a 40/45-cm autumn ploughing and subsequent seedbed preparation (e.g., 10-cm disk harrowing). All treatments received the same amounts of P (65.5 kg ha-1 y-1) and K (124.5 kg ha-1 y-1) at sowing by mineral fertilisers. The trial was designed as a split-plot of four blocks with residue management as the main plot; fertilisation levels and one unfertilised control plot were randomised inside the main plot (Fig. 5). Prior to 1984, the trial was conducted with maize (Zea mays L.) in monoculture. Thereafter a variable rotation scheme was used based mainly on maize, sugar beet (Beta vulgaris L.), winter wheat (Triticum aestivum L.), potato (Solanum tuberosum L.), soybean (Glycine max (L.) Merr.), and tomato (Solanum lycopersicum L.). For a single year sorghum (Sorghum vulgare Pers.) and sunflower (Helianthus annuus L.) were also grown.

Fig. 5. Experimental design of the fertilization and crop residue incorporation in silty loam soil trial.

Results Yields

Crop yields are affected by numerous external and agronomic factors. Crop production is obviously affected by the meteorological pattern and by the soil fertility, but the farmer can affect yields properly selecting the succession of the crops, regulating the timing of the agronomic operations, and integrating the limiting factors, such as nutrients (i.e. organic and/or mineral fertilisation) and water supply. The set of LTAEs considers the effects of crop rotation, of fertilisation, of the management of crop residues on the typical soil of the low Venetian plain and in interaction with different types of soils.

Fig. 6: Yields observed in relation to the complexity of the rotation – Long-term rotation experiment


The Long-term rotation experiment focuses on the effects of crop rotation depending on the level of intensification (Low or High input level). Considering the crops present in more than one rotation (Sugarbeet, present in the 4-year and 6-year rotations), Winter Wheat and Grain Maize (present in all the rotations), the effect of the simplification of the succession is evident (Fig. 6).

 

For all the crops the values reported are the averages of the three levels of mineral fertilisation: a clear increase on the yields is evident, particularly for the Low input system. Increasing the nutrient availability (high input) the effect of rotation is less evident, clearly indicating that the main effect involved is the over-exploitation of soil nutrient reserves when every year is sown the same crop or crops with similar requirements such as the cereals included in the 2-year rotation.

Fig. 7: Effects of N mineral input and of residue incorporation – fertilization and crop residue incorporation in silty loam soil experiment.


The effect of the mineral fertilisation and of the incorporation of crop residues is shown by the Experiment 4 – “fertilization and crop residue incorporation in silty loam soil”, conducted in the same type of soil as the Long-term rotation experiment (Piccoli et al., 2020). The average yields of the different crop tested shows a clear dependence on N input (Fig. 7). In spring-summer crops such as Maize and Sugarbeet (Fig. 7 a and c), there is both a clear effect of N input and of residues: the parallelism of the curves with and without residue incorporation, and so a positive effect of residues both at low and high N inputs, indicates that the incorporation of residues improve the overall fertility of the soil, independently from the level of external nutrition. This is probably due to an increase of soil organic matter, improving soil structure and, consequently, root penetration in soil and water retention during summer.

 

Sugarbeet evidence its inherent ability to valorise organic inputs, being the only crop beneficiating from the distribution of poultry manure. On the other hand, Winter wheat (Fig. 7 e) shows an effect of residues only at low N inputs; with this winter crop, growing in a period when water supply is generally sufficient, the positive effects on soil structure are less evident and the effect of residues is mainly due to their contribution to plant nutrition.

The two solanaceous crops tested (Potato – Fig. 7b and Tomato – Fig 7 d) are not affected by residue incorporation or poultry manure, showing only a response to N supply, very evident on Tomato and less pronounced in Potato, which shows a yield decrease at higher N inputs.

Figure 8: Effects of N mineral input and of residue incorporation in different soils – Nitrogen fertilization and crop residue in three types of soil experiment


The interaction between N supply and soil type are the main focus of Experiment 2 – “Nitrogen fertilization and crop residue in three types of soil” (Pituello et al., 2016a). The average yields for the different crops tested shows that cereals (Maize and Winter wheat) are less affected by the soil type, being able to reach relatively high yields also in the sandy soil, if the N supply is sufficient (Fig. 8).

 

Sugarbeet, on the contrary, gives good yields on the Clay and Sandy-loam soils, while is not able to reach high productions in the Sandy soil, evidencing a higher dependence on soil traits, and specifically on water availability in the first part of the crop cycle. Tomato and Potato evidenced an intermediate behaviour, with a reduction of the potential yield moving from the Clay to the Sandy soil, only partly compensated by N input.

Nitrogen use efficiency


Nitrogen use efficiency (NUE) is an established metric used to benchmark N management. There are several way of calculation NUE but the most slime, as suggested by the Nitrogen Expert Panel is the ratio between N output (N content in the harvested product) and N input (N arrived at soil with fertilization). Generally, higher levels of NUE are associated with greater system efficiency while lower NUE might highlight possible risks of N loose in the environment.


In this context, the 2015 EU Nitrogen Expert Panel drew attention to the Nitrogen Use Efficiency (NUE) concept and proposed an easily visualisable method for system sustainability evaluation based on minimum productivity levels and the range of NUE. The rationale for a reference value for N output is that some minimum yield level should be achieved, given the need to produce a desired amount of food, feed and biofuel, and for a farmer, region and country to be competitive. For European cropping system a target N output value equal to the EU average (80 kg N per ha per year) can be a reasonable limit. The rationale of three zones is that both a ‘too high’ and ‘too low’ NUE are undesirable, especially over long time periods.

 

A ‘too low’ NUE value indicates inefficient resource use and points to high N losses; a ‘too high’ NUE points to resource depletion, i.e., soil N depletion often termed ‘soil nutrient mining’. Mining N (and other nutrients) from soils is a common phenomenon that leads to soil degradation and erosion. On the other hand, mining of nutrients from highly fertile soils may be considered good practice, as it results in a high resource use, and it may decrease potential nutrient losses. For cropping systems reasonable upper and lower NUE limits might be 90% and 50%. From the graphical representation of these limits, a sustainability zone can be therefore drawn (yellow area in Fig. 9) allowing to identify which cropping systems can be considered more sustainable.

Fig. 9. Graphical presentation of nitrogen use efficiency (NUE) using the results of the input vs.
output diagram.

 

The lines corresponding to nutrient NUE = 0.90, NUE = 0.50, and desired minimum productivity create the “sustainability area” (in light yellow)
able to identify which cropping systems can be considered more sustainable according to EU Nitrogen Expert Panel (2015).

Fig. 10. Nitrogen use efficiency at LTAE.

 

A general trend of increasing output was observed at each rotation complexity increment, from the monoculture that occupied the lowest part of the graph to the 6-year crop rotation that occupied the highest part of the graph. The only exception was the permanent meadow that had an observed output similar to that of the 6-year crop rotation. Cropping system sustainability was first determined by the type of agronomic input (e.g., crop residue incorporation or residue + slurry incorporation).

 

Crop residue incorporation often fell in the soil mining area of the NUE graph, which highlighted the importance of combining residue with organic fertiliser (Piccoli et al., 2020). However, soil mining may only represent a real risk in the long term (e.g., 3–5 years). Organic fertilisation was associated with higher N surpluses compared to mineral fertilisation, which in contrast, showed a higher nutrient efficiency. A lower nutrient efficiency in organic fertiliser is well documented in the literature, although a nutrient surplus should not directly result in pollution of water bodies because the nutrients are partially stored as soil organic matter, potentially increasing C storage and, in turn, soil fertility (Quemada et al., 2020, Gattinger et al., 2014, Maillard & Angers, 2014, Grillo et al., 2021).

Storing carbon in agricultural soils to mitigate global warming


Soils are partly made of broken-down plant matter. This means that soils can contain a lot of organic matter –which is mainly composed of carbon– that those plants took in from the atmosphere as carbon dioxide (CO2) when they were alive. If not for soil, this carbon would return to the atmosphere as CO2. Scientists have estimated that agricultural systems can contribute significantly to mitigate climate change by removing atmospheric CO2 and sequestering it as organic carbon in the soil (SOC) in a stable organic matter form (Lal 2018, Georgiou 2020).


Scientific evidence come from LTAEs around the world, which have contributed to quantify over the years to what extent different agricultural practices can store more SOC in different climates and soil types (Poulton et al., 2018, Buysse et al., 2013).

Fig. 11.

Soil is a dynamic entity, which can form slowly, but degrade rapidly. Long-term experiments are the tools to identify agricultural management practices to maintain healthy soils following the principles of sustainability.

Fig. 12.
Results obtained by LTAEs experiments at the University of Padova (Berti et al., 2016) have demonstrated that the SOC content in the 0-30 cm layer remained almost constant in the permanent meadow over the years, while a steep decrease was observed in the first years after the beginning of the experiment in ploughed soils.

 

After that, a partial recovery was found in plots amended with farmyard manure with high humification coefficients. The replacement of farmyard manure with other organic inputs (e.g. slurries or crop residues) led to a further decrease in SOC. Only after further 10 years a new equilibrium was reached.

Fig. 13
The scatterplot was obtained by merging the results from all the LTAEs at the University of Padova (Dal Ferro et al., 2020). Results from the long term are very important because they test whether agriculture is sustainable in preserving the soil from degradation. In this specific context results tell us whether some agricultural practices should be adopted to mitigate climate change by sequestering SOC.


Regardless of soil type (different colors), additional SOC accumulation is nearly always possible along the soil profile by adopting specific practices. Especially those that strongly impact the rate of SOC stock change would mean conversion to permanent meadow and farmyard manure application. This would impact much more than using mineral fertilizers or other sources of organic inputs, such as crop residues or slurry. Moreover, the results suggest reducing tillage intensity such that the mineralization rate of SOC is strongly reduced.

References


Amato, G., Ruisi, P., Frenda, A.S., Di Miceli, G., Saia, S., Plaia, A., Giambalvo, D., 2013.Long-term tillage and crop sequence effects on wheat grain yield and quality. Agron. J. 105 (5), 1317–1327.
Berti, A., Morari, F., Dal Ferro, N., Simonetti, G., & Polese, R. (2016). Organic input quality is more important than its quantity: C turnover coefficients in different cropping systems. European Journal of Agronomy, 77, 138-145.
Bhogal, A., Taylor, M., Nicholson, F., Lewis, P., 2015. Importance of long-term field experiments for understanding the impact of management practices on soil organic carbon. In: Peacock, S., Smith, B.M., Stockdale, E.A., Watson, C. (Eds.), Valuing Long-Term Sites and Experiments for Agriculture and Ecology. AAB,pp. 125–131.
Blanco-Moure, N., Gracia, R., Bielsa, A.C., López, M.V., 2013. Long-term no-tillage effects on particulate and mineral-associated soil organic matter under rainfed Mediterranean conditions. Soil Use Manag. 29, 250–259.
Buysse, P., Schnepf-Kiss, A. C., Carnol, M., Malchair, S., Roisin, C., & Aubinet, M. (2013). Fifty years of crop residue management have a limited impact on soil heterotrophic respiration. Agricultural and forest meteorology, 180, 102-111.
Buysse, P., Schnepf-Kiss, A.C., Carnol, M., Malchair, S., Roisin, C., Aubinet, M., 2013.Fifty years of crop residue management have a limited impact on soil heterotrophic respiration. Agric. For. Meteorol. 180, 102–111.
Congreves, K.A., Hayes, A., Verhallen, E.A., Van Eerd, L.L., 2015. Long-term impact of tillage and crop rotation on soil health at four temperate agroecosystems. Soil Till. Res. 152, 17–28.
Dal Ferro, N., Piccoli, I., Berti, A., Polese, R., & Morari, F. (2020). Organic carbon storage potential in deep agricultural soil layers: Evidence from long-term experiments in northeast Italy. Agriculture, Ecosystems & Environment, 300, 106967.
Dick, R.P., 1992. A review: long-term effects of agricultural systems on soil biochemical and microbial parameters. Agric. Ecosyst. Environ. 40, 25–36.
Gattinger, A., Muller, A., Haeni, M., Skinner, C., Fliessbach, A., Buchmann, N., Mäder, P., Stolze, M., Smith, P., Scialabba, N.E.H., et al., 2012. Enhanced top soil carbon stocks under organic farming. Proc. Natl. Acad. Sci. USA, 109, 18226–18231.
Georgiou, K., Jackson, R. B., Vindušková, O., Abramoff, R. Z., Ahlström, A., Feng, W., … & Torn, M. S. (2022). Global stocks and capacity of mineral-associated soil organic carbon. Nature communications, 13(1), 1-12.
Giardini, L., Morari, F., 2004. Soil fertility parameters. In: Giardini, L. (Ed.), Productivity and Sustainability of Different Cropping Systems. 40 Years of Experiments in Veneto Region (Italy). Patron, Bologna, pp. 191–256.
Grillo, F., Piccoli, I., Furlanetto, I., Ragazzi, F., Obber, S., Bonato, T., Meneghetti, F., Morari, F., 2021. Agro-environmental sustainability of anaerobic digestate fractions in intensive cropping systems: Insights regarding the Nitrogen use efficiency and crop performance. Agronomy 11, 745.
Karlen, D.L., Kovar, J.L., Cambardella, C.A., Colvin, T.S., 2013. Thirty-year tillageeffects on crop yield and soil fertility indicators. Soil Till. Res. 130, 24–41.
Knapp, A.K., Smith, M.D., Hobbie, S.E., Collins, S.L., Fahey, T.J., Hansen, G.J.A., Landis, D.A., La Pierre, K.J., Melillo, J.M., Seasted, T.R., Shaver, G.R., Webster, J.R., 2012.Past, present, and future roles of long-term experiments in the LTER network. BioScience 62, 377–389.
Lal, R. (2018). Digging deeper: A holistic perspective of factors affecting soil organic carbon sequestration in agroecosystems. Global change biology, 24(8), 3285-3301.
Lassaletta, L., Billen, G., Grizzetti, B., Anglade, J., Garnier, J., 2014. 50 year trends in nitrogen use efficiency of world cropping systems: the relationship between yield and nitrogen input to cropland. Environ. Res. Lett. 9 (10), 105011.
Lehtinen, T., Schlatter, N., Baumgarten, A., Bechini, L., Krüger, J., Grignani, C.,Zavattaro, L., Costamagna, C., Spiegel, H., 2014. Effect of crop residue incorporation on soil organic carbon and greenhouse gas emissions in European agricultural soils. Soil Use Manag. 30, 524–538.
Likens, G.E., Lindermayer, D.B., 2011. A strategic plan for an Australian Long-Term Environmental Monitoring Network. Austral Ecol. 36, 1–8.
Maillard, É., Angers, D.A., 2014. Animal manure application and soil organic carbon stocks: A meta-analysis. Glob. Chang. Biol. 20, 666–679.
Mazzoncini, M., Sapkota, T.B., Bàrberi, P., Antichi, D., Risaliti, R., 2011. Long-term effect of tillage: nitrogen fertilization and cover crops on soil organic carbon and total nitrogen content. Soil Till. Res. 2, 165–174.
Migliorini, P., Moschini, V., Tittarelli, F., Ciaccia, C., Benedettelli, S., Vazzana, C., Canali, S., 2014. Agronomic performance, carbon storage and nitrogen utilisation of long-term organic and conventional stockless arable systems in Mediterranean area. Eur. J. Agron. 52, 138–145.
Morari, F., Lugato, E., Berti, A., Giardini, L., 2006. Long-term effects of recommended management practices on soil carbon changes and sequestration in north-eastern Italy. Soil Use Manag. 22, 71–81.
Piccoli, I., Sartori, F., Polese, R., Berti, A, 2020. Crop yield after 5 decades of contrasting residue management. Nutr. Cycl. Agroecosystems, 117, 231–241.
Pituello, C., Dal Ferro, N., Simonetti, G., Berti, A.&Morari, F. 2016b. Nano to macro pore structuree changes induced by long-term residue management in three different soils. Agriculture, Ecosystems & Environment, 217, 49–58.
Pituello, C., Polese, R., Morari, F. & Berti, A. 2016a. Outcomes from a long-term study on crop residue effects on plant yield and nitrogen use efficiency in contrasting soils. European Journal of Agronomy, 77, 179–187.
Poulton, P., Johnston, J., Macdonald, A., White, R., & Powlson, D. (2018). Major limitations to achieving “4 per 1000” increases in soil organic carbon stock in temperate regions: Evidence from long‐term experiments at Rothamsted Research, United Kingdom. Global Change Biology, 24(6), 2563-2584.
Quemada, M., Lassaletta, L., Jensen, L.S., Godinot, O., Brentrup, F., Buckley, C., Foray, S., Hvid, S.K., Oenema, J., Richards, K.G., et al., 2020. Exploring nitrogen indicators of farm performance among farm types across several European case studies. Agric. Syst. 177, 102689.
Richter, D. deB., Hofmockel, M., Callaham, M.A., Powlson, D.S., Smith, P., 2007.Long-term soil experiments: keys to managing earth’s rapidly changing ecosystems. Soil Sci. Soc. Am. J. 71 (2), 266–279.
Stockmann, U., Adams, M.A., Crawford, J.W., Field, D.J., Henakaarchchi, N., Jenkins,M., Minasny, B., McBratney, A.B., de Remy de Courcelles, V., Singh, K., Wheeler,I., Abbott, L., Angers, D., Baldock, J., Bird, M., Brookes, P.C., Chenu, C., Jastrow, J., Lal, R., Lehmann, C.J., O’Donnell, A.G., Parton, W.J., Whitehead, D., Zimmermann, M., 2013. The knowns: known unknowns and unknowns of sequestration of soil organic carbon. Agric. Ecosyst. Environ. 164, 80–99.

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Lugato, E., Berti, A., Giardini, L. (2006) Soil organic carbon (SOC) dynamics with and without residue incorporation in relation to different nitrogen fertilisation rates Geoderma, 135, pp. 315–321
Lugato, E., Morari, F., Nardi, S., Berti, A., Giardini, L. (2009) Relationship between aggregate pore size distribution and organic-humic carbon in contrasting soils Soil and Tillage Research, 103(1), pp. 153–157
Lugato, E., Simonetti, G., Morari, F., Nardi, S., Berti, A., Giardini, L. (2010) Distribution of organic and humic carbon in wet-sieved aggregates of different soils under long-term fertilization experiment Geoderma, 157(3-4), pp. 80–85
Marini, L., St-Martin, A.,Vico, G., Baldoni G., Berti A., Blecharczyk A., Malecka-Jankowiak I., Morari F., Sawinska, Z., Bommarco, R. (2020) Crop rotations sustain cereal yields under a changing climate Environmental Research Letters, 15(12), 124011
Morari, F., Lugato, E., Berti, A., & Giardini, L. (2006). Long‐term effects of recommended management practices on soil carbon changes and sequestration in north‐eastern Italy. Soil Use and Management, 22(1), 71-81.
Nardi, S., Morari, F., Berti, A., Tosoni, M., Giardini, L. (2004) Soil organic matter properties after 40 years of different use of organic and mineral fertilisers European Journal of Agronomy, 21(3), pp. 357–367
Piccoli, I., Sartori, F., Polese, R., Borin, M., Berti, A. (2021). Can long-term experiments predict real field n and p balance and system sustainability? Results from maize, winter wheat, and soybean trials using mineral and organic fertilisers. Agronomy, 11(8), 1472
Pituello, C., Dal Ferro, N., Francioso, O., G. Simonetti, A. Berti, I. Piccoli, Pisi, A., Morari, F. (2018) Effects of biochar on the dynamics of aggregate stability in clay and sandy loam soils European Journal of Soil Science, 69(5), pp. 827–842
Pizzeghello, D., Berti, A., Nardi, S., & Morari, F. (2014). Phosphorus-related properties in the profiles of three Italian soils after long-term mineral and manure applications. Agriculture, ecosystems & environment, 189, 216-228.
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Pizzeghello, D., Berti, A., Nardi, S., Morari, F. (2016) Relationship between soil test phosphorus and phosphorus release to solution in three soils after long-term mineral and manure application Agriculture, Ecosystems and Environment, 233, pp. 214–223
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