Nitrous oxide fluxes and soil nitrogen contents over eight years in four cropping systems designed to meet both environmental and production goals: A French field nitrogen data set

With the development of agroecosystem approaches, new cropping systems have to be designed to deliver multiple ecosystem services. In this context, we assessed four innovative cropping systems, designed to reach multiple environmental and production goals, in a long-term field experiment (2009–2020) at Grignon (France, N 48.84°, E 1.95°). A wide range of measurements were made, for nutrient cycles and organic matter in particular, for an analysis of interactions occurring during the emissions of greenhouse gases. We focus here on nitrogen (N) data collected over eight years (2009–2016). The data include: nitrous oxide fluxes (N2O), soil N contents (NO3− and NH4+), aboveground plant N content and biomass at maturity, yield, agricultural practices including N spreading, and climate. The four systems differ in terms of tillage practices, N inputs, and species, which is likely to affect soil N. Field data were collected and N2O fluxes were calculated. These original new cropping systems are innovating, resulting in new combinations of agricultural practices. The data obtained could be used to improve models for parameterization and validation, and to increase the predictive accuracy of models of N losses in original conditions.


a b s t r a c t
With the development of agroecosystem approaches, new cropping systems have to be designed to deliver multiple ecosystem services. In this context, we assessed four innovative cropping systems, designed to reach multiple environmental and production goals, in a long-term field experiment (2009)(2010)(2011)(2012)(2013)(2014)(2015)(2016)(2017)(2018)(2019)(2020) at Grignon (France, N 48.84 °, E 1.95 °). A wide range of measurements were made, for nutrient cycles and organic matter in particular, for an analysis of interactions occurring during the emissions of greenhouse gases. We focus here on nitrogen (N) data collected over eight years (2009)(2010)(2011)(2012)(2013)(2014)(2015)(2016). The data include: nitrous oxide fluxes (N 2 O), soil N contents (NO 3 − and NH 4 + ), aboveground plant N content and biomass at maturity, yield, agricultural practices including N spreading, and climate. The four systems differ in terms of tillage practices, N inputs, and species, which is likely to affect soil N. Field data were collected and N 2 O fluxes were calculated. These original new cropping systems are innovating, resulting in new combinations of agricultural practices. The data obtained could be used to improve models for parameterization and validation, and to increase the predictive accuracy of models of N losses in original conditions.
© 2021 Published by Elsevier Inc. This is an open access article under the CC BY license ( http://creativecommons.org/licenses/by/4.0/ ) Specification Table   Subject Agronomy and Crop Science More specific subject area Nitrous oxide (N 2 O) fluxes, soil nitrogen contents (nitrate NO 3 − and ammonia NH 4 + ), aboveground plant nitrogen (N) content, long-term assessment of innovative cropping systems, agricultural practices. Type of data Tables and figure How data were acquired N 2 O fluxes: calculations based on gas samples collected from static chambers in the field trial. Soil NO 3 − and NH 4 + contents: soil samples collected manually from the field trial; soil N contents determined according to the international standard

Value of the Data
• These data were obtained from one of the first long-term field trial (2009-2020) carried out in France, at the AgroParisTech experimental farm at Grignon (France, N 48.84 °, E 1.95 °). The experiment was focused on the assessment of innovative cropping systems with multiple environmental and production objectives designed to deliver an entire package of ecosystem services. Here, the data were collected for the first eight years of the field assessment. • These data have already been used to assess the environmental and production performances of the innovative cropping systems [ 1 , 2 ]. • These data can be used as a benchmark for future studies aiming to design new cropping systems to decrease nitrogen (N) losses and improve N management in northern Europe cropping systems. • These data could be used to improve parameterization and validation, to increase the predictive accuracy of models of N fluxes. • These data can be used to calculate new indicators based on the measurements of N fluxes.

Data Set
The open-access research data set is organized into five files of nitrogen (N) data (soil, plant and atmosphere). The raw, descriptive and computed data were collected over the first eightyear period for the four innovative cropping systems assessed in a long-term (2009--2020) field trial at AgroParisTech experimental farm at Grignon (France, N 48.84 °, E 1.95 °) [1] . These cropping systems were designed to reach multiple environmental and production objectives and to provide ecosystem services. Practices differ considerably between these four systems, in terms of tillage, N inputs (date and amount), species, potentially modifying soil N content (nitrate NO 3 − , ammonia NH 4 + ), nitrous oxide (N 2 O) fluxes, crop N uptake and yield [2] . The following data are available: (i) N 2 O fluxes, (ii) soil N contents (NO 3 − and NH 4 + ), (iii) aboveground plant biomass and N content at maturity, and yield, (iv) agricultural practices and (v) climate data. N 2 O fluxes were calculated for the 2010-2016 period in two cropping systems: the PHEP (productive and high environmental performance) system and the L-GHG (less greenhouse gas emissions) system. All the other data were measured over the 2009-2016 period in all four cropping systems: the PHEP system, the L-GHG system, the No-Pest (no pesticide use) system and the L-EN (less energy consumption) system.

Field experiment site
The experiment took place at the AgroParisTech experimental farm at Grignon, in the Ile-de-France region (N 48.84 °, E 1.95 °: France). The field was characterized by a deep and homogeneous loamy clay soil (haplic luvisol according to the FAO classification [6] ). The mean soil characteristics of the plowed layer (0-25 cm) in 2009 were as follows: clay content = 20.6 g.kg −1 , silt content = 71.9 g.kg −1 , sand content = 7.4 g.kg −1 , bulk density = 1.4, CEC = 11.5 cmol + .kg −1 and carbon content = 15.9 g.kg −1 . The C/N ratio was 12.4 and the pH was 6.9 (further details are provided for each plot, in Table 1 ). The experimental field was flat, with a water table more than 2 m below the surface and an available water storage capacity of about 175 mm. The trial took place in an area with an oceanic climate. Over a period of 20 years, mean rainfall was 650 mm per year and mean daily temperature was 12.5 °C. The previous crop, in 2008, was winter barley. The field was plowed to a depth of 30 cm after the barley harvest. After six years of the experiment, various tillage practices in the different systems ( i.e. no-till practices in both the L-EN and L-GHG systems; four plowings over six years in the No-Pest system) had induced changes in bulk density requiring a second measurement in 2014.

Experimental design
The trial covered a total area of 6.2 ha, divided into three replicates ( Fig. 1 ). Each replicate was split into four wide plots, each dedicated to one of the four cropping systems. In the three replicates of each cropping system, three different crops from the crop sequence were sown in each year (e.g. in 2009, winter wheat, winter rapeseed and maize were sown in the three replicates of the L-GHG system; see [2] for more details). The three replicates were managed according to similar decision rules, resulting in different practices ( e.g. date and amount of N fertilizer applications) due to environmental factors and working organization constraints [7] . Farm machinery was used, as the area devoted to this experiment was almost 40 0 0 m ² per replicate.

Innovative cropping systems
The PHEP system was designed to minimize environmental impact: (i) cover crops were sown before each spring species to decrease nitrate losses; (ii) pesticide uses were lessened by increasing crop diversity, lengthening the crop sequence and sowing highly resistant varieties; (iii) energy consumption was reduced by allowing plowing only once in the crop sequence, and N fertilizer amounts spread were decreased by the incorporation of legumes into the crop sequence. This cropping system was also designed to reach the maximum yield given the environmental targets, as described in [1] . This cropping system, designed without major environmental constraint, was used as the reference system for comparisons with the other systems.
In the L-GHG system, greenhouse gas emissions were limited by increasing carbon sequestration in the soil (i.e. producing large amounts of residues from both the main crop and catch crops without tillage) and N 2 O emissions were decreased by using appropriate decision rules to prevent N fertilizer application in climatic conditions favoring N 2 O emissions.
The L-EN system was designed to reduce both direct and indirect energy consumption. Plowing was prohibited, direct sowing was implemented, the amount of N fertilizer applied was decreased by sowing many legumes and species with high N use efficiency, and target yield were decreased. Table 1 Physicochemical properties of the soil for each plot (layer = 0-25 cm, in 2009). Sampling method: plots were divided into four subplots. For each subplot, we collected, pooled and analyzed seven samples (clay (g.kg −1 ), silt (g.kg −1 ) and sand (g.kg    For the No-Pest cropping system, the no-pesticide constraint was satisfied by including a wide range of species ( e.g. hemp), the use of highly resistant varieties or species mixtures, a wide diversity of sowing dates, regular tillage and mechanical weeding to control weeds.
These three cropping systems, each designed with a major environmental constraint, were also required to meet the same environmental and yield goals as achieved by the PHEP system. During the design step, the constraints and targets were prioritized as follows: the environmental constraint had to be satisfied first, the set of other environmental targets then had to be reached and, finally, yield had to be maximized.

N 2 O fluxes
N 2 O fluxes were calculated for each of the three replicates of the PHEP and L-GHG systems. Data were collected monthly, except during the winter (from November to March) and August. Additional measurements were carried out during specific periods: four measurements were performed over a two-week period after each N fertilizer application; two measurements were made after the faba bean harvest if a significant rainfall event occurred ( > 10 mm). For each plot, N 2 O emissions were measured manually, with three static chambers inserted into the soil at a depth of 10 cm after sowing and left in place until harvest. Each chamber covered a surface area of 0.25 m 2 and the top of the chamber was 0.2 m above the soil surface. N 2 O emissions were measured between 10 a.m. and 3 p.m. (local time) at each sampling date, with the same order used for monitoring on each plot. The chambers were closed for 45 min, during which the headspace air was sampled four times (0, 15, 30 and 45 min after closure). Gas samples (20 mL) were collected in a syringe and immediately injected into pre-evacuated 12 mL glass vials (Exetainers, Labco, UK). These vials were stored in the dark at room temperature until laboratory analyses. N 2 O concentrations were analyzed with a gas chromatograph equipped with an electron capture detector (GC-ECD; Model 3800, Varian Inc., CA, USA; see more details in [8] ). N 2 O fluxes were calculated with the HMR model (i.e. R statistical core software [9] ), from four successive measurements of the N 2 O content of gas samples.

Soil N contents (NO 3 − and NH 4 + )
Two sets of soil N content data were managed and are provided in two different files: Set 1: measurements performed at the same time as those for N 2 O fluxes. Three randomized soil samples were collected close to the static chambers, at the depth either 0-25 cm or 0-30 cm, and pooled (data provided in file 21_06_30_N2O_2010_2016, columns 9, 10, 12 and 13). Set 2: measurements performed at three different periods over the year (i.e. at the beginning of winter (BW) around November 15, after winter (AW) around February 15, and about eight days post harvesting (PH) of the main crop). Six samples were collected from five layers (0-30 cm, 30-60 cm, 60-90 cm, 90-120 cm, and 120-150 cm) in each plot. Three samples from each layer were pooled to generate two soil samples per layer for each plot (data are in file 21_06_30_Soil_N_2009_2016, columns 11, 12, 14 and 15).
These two groups of measurements were managed in the same way. Soil samples were collected manually with an auger and stored in a cold box (4 °C) until analysis. Water content was measured gravimetrically, according to the international standard method (NF ISO 11-465). From a soil sample (50 g), soil inorganic N was extracted in potassium chloride solution (77 g.l −1 ) with the aid of a magnetic stirrer for 30 min. After 30 min of decantation, the suspended matter has settled and the supernatant was collected. Supernatant aliquots were sent to the analytical laboratory. NO 3 − was determined by reaction with N-(1-naphthyl) dichloride diamine ethylene, and NH 4 + was determined by reaction with sodium dichloro-isocyanurate and sodium salicylate. NO 3 − and NH 4 + contents were analyzed in an aliquot of the extracts obtained, by colorimetry (absorbance measured at 550 nm and at 630 nm, respectively; international standard method: NF ISO 14-255). Results were expressed both in kgN per hectare and in mgN per liter.

Aboveground biomass and N content at maturity
Depending on species, we collected nine to twelve samples (i.e. 1 m ² per sample) per plot at maturity, except for winter rapeseed, for which samples were collected at stage 8.0 [5] . Due to the high aboveground biomass for maize, we divided each sample into two subsamples ( A and B ) in all years except in 2009. Seeds were separated from the vegetative parts of the plant (straw and pod walls for legumes, straw and rachis for cereals, straw and panicles for oat, stalk and cobs for maize), except for winter rapeseed, for which all aboveground parts (stems, pods and green seeds) were pooled. All samples were oven-dried at 80 °C for 48 h. For analyses of N content, we pooled two or three samples, depending on species, which were then ground and analyzed by the Dumas combustion method [10] .

Yield
Yield (mean and standard deviation) were calculated on the basis of six samples (i.e. an area of about 140 m ² per sample, depending on the length of the plot harvested) collected at maturity, with a combine harvester, from each plot. Yield unit was tonne of dry matter per hectare.

Agricultural practices in the innovative cropping systems
The management of the four cropping systems has been described in detail in [2] . The crop sequences included five crops for the PHEP and L-EN systems, and six crops for the No-Pest and L-GHG systems. The species sown in each replicate of each system over the 2009-2016 period are detailed in Table 2 . All agricultural practices were recorded continuously and only those linked to N fluxes are reported in the file: (i) date and density of sowing, (ii) date and depth of tillage, (iii) date and amount of mineral N fertilizer applied, (iv) date and type of mechanical weeding, and (v) date and type of crop residue management.

Climatic data
Mean daily temperatures ( °C) and daily rainfalls (mm) data were collected from an automated INRAE meteorological station (no. 78615002: latitude 48.838 °N, longitude 1.953 °E, elevation: 125 m) located 150 m from the trial. Table 2 Crop sequences of the four cropping systems over the 2009-2016 period. PHEP: productive with high environmental performance; L-GHG: low greenhouse gas emissions; L-EN: low energy consumption; No-Pest: no pesticide use. Rep = replicate. W and S indicate winter and spring crops, respectively. W wheat * and W rapeseed * : intercropping of a legume with winter wheat and winter rapeseed, respectively. For crop sequences including two W wheat crops, W wheat1 indicates a W wheat crop sown after a legume species, W wheat2 indicates a W wheat crop sown after a non-legume species.

Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that have or could be perceived to have influenced the work reported in this article.