Data from: Carbon and Water Balances in a Watermelon Crop Mulched with Biodegradable Films in Mediterranean Conditions at Extended Growth Season Scale

Abstract

The uploaded data are relative to the investigation around (i) the carbon source/sink nature and, further, (ii) the water and carbon balances, of a drip-irrigated and mulched watermelon. The crop was cultivated under the semi-arid climate of the Apulia region, in south Italy.

The used mulching films were biodegradable as indicate by the producer; plants and some non-standard fruits were left on the soil as green manure after harvesting, thus, the experiment spanned from planting to the subsequent crop (6 months of continuous measurement from June to November 2023).

The results detailed in the original publication indicate that mulching films contribute to carbon sequestration in the soil (+19.3 gC m−2). However, this mulched watermelon represents a net carbon source, with a net biome exchange, as loss from ecosystems, equal to +230 gC m−2. This is primarily due to the substantial amount of carbon exported through marketable fruits. Fixed water scheduling led to water waste through deep percolation (approximately 1/6 of the water supplied), which also contributed to the loss of organic carbon via leaching (−4.3 gC m−2).

Methods

Site and crop

The field site was at the CREA-AA Research Unit experimental farm located in southern Italy (Rutigliano–Bari, 41 01’ N, 17°01’ E, altitude 147 m a.s.l.)., characterized by a Mediterranean semi-arid climate (average annual rainfall of 535 mm). The soil is classified as Lithic Rhodoxeralf, with a clay texture, stable structure, shallow profile (0.6–1.1 m) and rapid drainage due to an underlying cracked limestone subsoil. The SOC content averages around 12.0 g kg−1. The field capacity and the permanent wilting point volumetric water contents are 0.36 and 0.21 m3 m−3, respectively; with a bulk density of 1.15 Mg m−3, the available soil water ranges from 80 to 140 mm.

The studied watermelon crop (seedless var. Lion king), followed a broccoli cabbage crop harvested in April and partially incorporated (0.81 kg m−2 of fresh biomass in a soil layer depth of 0.30 m, corresponding to 0.69 kgH2O m−2) as green manure on 25 May 2023. Main tillage at medium depth ploughing (0.30 m) and seedbed preparation were performed between 25 and 30 May 2023; the biodegradable film mulch (model PC 100 d8, BASF, Italy, 1 m width) was applied on 1 June 2023. On the same day, driplines (2.1 Lh−1 emitters, 0.60 m apart) and the main organic fertilization (Orga-Kem 6.11.8 + 11CaO, 300 kg ha−1) were also applied. The watermelon plants were transplanted on 9 June at a spacing of 2.70 m between rows and 1 m between plants, covering an area of about 4.0 ha, with a density of approximately 3200 plants ha−1. Every 6 rows, the inter-row distance was 5 m to facilitate machinery passage. The first irrigation was performed the day before planting. Crop management adhered to the usual treatments in the area including mechanical weed removal every 4 weeks, irrigation around three times per week to maintain optimal soil water conditions and monthly fertigation (ammonium sulphate 50 kg ha−1, magnesium nitrate 30 kg ha−1, calcium nitrate 60 kg ha−1, mycorrhizae 20 kg ha−1). The scalar harvest of marketable fruits occurred between 28 and 31 August 2023. After harvesting, on 25 September 2023, the fresh plant residues (0.6 kg m−2 of fresh biomass, corresponding to 0.49 kgH2O m−2), unharvested fruits (4.0 kg m−2 of fresh material, corresponding to 3.7 kgH2O m−2) and the mulching film were chopped by a tractor shredder and ploughed in two steps, on 2 and 13 October 2023, to a soil depth of 0.30 m. Measurements concluded at the end of November 2023, when tillage for the new winter crop commenced.

Measurements of H2O and CO2 fluxes; partitioning in evaporation, transpiration, photosynthesis and respiration

The eddy covariance technique was employed to monitor water vapor (H2O) and carbon dioxide (CO2) fluxes. The equipment comprised a three-dimensional sonic anemometer (uSonic 3 Scientific, Metek GmbH, 25337 Elmshorn, Germany) and a fast response open-path infrared gas analyzer (LI-7500, Li-COR Inc., Lincoln, NE, USA). The three wind components, sonic temperature and atmospheric concentrations of CO2 and H2O were continuously measured at 1.5 m above the crop canopy, with the sensor height adjusted to follow crop growth, reaching a maximum of 1.75 m.

Data were recorded at a frequency of 10 Hz on a dedicated computer using the MeteoFlux software (Servizi Territorio, S.n.c., Cinisello Balsamo, Italy) and were stored on an hourly scale. Post-processing and computation of hourly fluxes of H2O (mmol m−2 s−1) and CO2 (μmol m−2 s−1) were conducted using EddyPro software, v7.0.9 (http://www.licor.com/eddypro), applying 60 min block averaging, double coordinate rotation, the statistical test, the maximum cross-covariance method, and the WPL density correction.

H2O and CO2 fluxes were partitioned into transpiration, evaporation, photosynthesis and respiration, respectively, using the flux variance similarity method. This method utilizes the Monin–Obukhov similarity theory to separate stomatal (photosynthesis, Fp, and transpiration, Ft) from non-stomatal (respiration, Fr, and evaporation, Fe) processes (Palatella et al., 2014). the H2O and CO2 EC fluxes were partitioned using an adaptation of the code in Phyton provided by (Skaggs et al., 2018) and downloaded from  https://github.com/usda-arsussl/fluxpart (V0.2.10).

摘要

本上传数据集围绕覆膜滴灌西瓜开展两项研究：一是探究其碳源/汇属性，二是分析其水分与碳平衡。该试验于意大利南部普利亚（Apulia）大区的半干旱气候区开展。

所用覆膜为厂商标注的可降解地膜；收获后将植株与部分次品果留于田中作为绿肥。本试验周期涵盖从播种至下一茬作物种植，2023年6月至11月间开展了为期6个月的连续监测。

已发表文献中的详细结果表明，覆膜可促进土壤碳固存（固碳量+19.3 gC m⁻²）。但该覆膜西瓜田整体为净碳源，生态系统净碳交换量为+230 gC m⁻²，即生态系统向外排放碳。这主要归因于商品果带走了大量碳。固定灌溉制度导致约1/6的供水量通过深层渗漏产生水资源浪费，同时也造成有机碳随淋溶损失（损失量−4.3 gC m⁻²）。

## 研究方法

### 试验地点与供试作物
试验地点位于意大利南部的CREA-AA研究单元试验农场（鲁蒂利亚诺-巴里，北纬41°01′，东经17°01′，海拔147 m），该区域属地中海半干旱气候，年平均降雨量535 mm。

土壤类型为石质温性暗色湿润老成土（Lithic Rhodoxeralf），质地为黏土，结构稳定，土层较浅（0.6~1.1 m），下层为裂隙石灰岩母质，排水迅速。土壤有机碳（Soil Organic Carbon, SOC）平均含量约12.0 g kg⁻¹。田间持水量和永久萎蔫点的体积含水量分别为0.36 m³ m⁻³和0.21 m³ m⁻³；土壤容重为1.15 Mg m⁻³，有效土壤水量范围为80~140 mm。

供试作物为无籽西瓜品种“Lion king”，前茬为青花菜，于2023年4月收获，2023年5月25日将部分鲜生物量（0.81 kg m⁻²，施入0.30 m土层，对应含水量0.69 kgH₂O m⁻²）作为绿肥翻埋入土。

2023年5月25日至30日进行了中等深度翻耕（0.30 m）和苗床准备；2023年6月1日铺设可降解地膜（型号PC 100 d8，巴斯夫BASF，意大利，宽度1 m）。当日同时安装滴灌带（滴头流量2.1 L h⁻¹，间距0.60 m）并施用基础有机肥（Orga-Kem 6.11.8 + 11CaO，施用量300 kg ha⁻¹）。2023年6月9日进行西瓜移栽，行间距2.70 m，株距1 m，种植面积约4.0 ha，种植密度约3200株 ha⁻¹；每6行设置5 m宽的行间通道以方便农机通行。移栽前一天进行第一次灌溉。田间管理遵循当地常规措施：每4周进行一次机械除草，每周灌溉约3次以维持最优土壤水分条件，每月进行一次追肥灌溉（施用硫酸铵50 kg ha⁻¹、硝酸镁30 kg ha⁻¹、硝酸钙60 kg ha⁻¹、菌根菌剂20 kg ha⁻¹）。商品果分批采收于2023年8月28日至31日。收获后，2023年9月25日将新鲜植株残体（鲜生物量0.6 kg m⁻²，对应含水量0.49 kgH₂O m⁻²）、未采收果实（鲜重4.0 kg m⁻²，对应含水量3.7 kgH₂O m⁻²）连同地膜一同用拖拉机粉碎机粉碎，分别于2023年10月2日和13日分两步翻耕入土，翻耕深度0.30 m。2023年11月底，即下一茬冬作物翻耕开始时，本试验监测工作结束。

### 水汽与二氧化碳通量测定及通量分配：蒸发、蒸腾、光合作用与呼吸作用
本研究采用涡度协方差技术（Eddy Covariance Technique）监测水汽（H₂O）与二氧化碳（CO₂）通量。观测设备包括三维超声风速仪（uSonic 3 Scientific，Metek GmbH，德国埃尔姆肖恩25337）和快速响应开放式红外气体分析仪（LI-7500，Li-COR Inc.，美国内布拉斯加州林肯市）。在作物冠层上方1.5 m处连续测定三维风速分量、超声温度以及大气中CO₂和H₂O浓度，传感器高度随作物生长进行调整，最大高度达1.75 m。

数据由专用计算机以10 Hz的频率采集，采用MeteoFlux软件（Servizi Territorio, S.n.c.，意大利奇尼塞洛巴尔萨莫）记录，并以小时为单位存储。采用EddyPro软件v7.0.9（http://www.licor.com/eddypro）对小时尺度的H₂O通量（单位：mmol m⁻² s⁻¹）和CO₂通量（单位：μmol m⁻² s⁻¹）进行后处理与计算，处理流程包括60 min块平均、双坐标旋转、统计检验、最大互协方差法以及WPL密度校正。

本研究采用通量方差相似性方法将H₂O和CO₂通量分别划分为蒸腾、蒸发、光合作用和呼吸作用分量。该方法基于莫宁-奥布霍夫相似性理论，将气孔相关过程（光合作用Fp和蒸腾作用Ft）与非气孔相关过程（呼吸作用Fr和蒸发作用Fe）区分开来（Palatella等，2014）。H₂O和CO₂涡度协方差通量的分配采用Skaggs等（2018）提供的Python代码改编版，该代码从https://github.com/usda-arsussl/fluxpart（V0.2.10）下载获取。