{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2025,10,27]],"date-time":"2025-10-27T05:04:44Z","timestamp":1761541484468,"version":"build-2065373602"},"reference-count":58,"publisher":"MDPI AG","issue":"4","license":[{"start":{"date-parts":[[2019,2,25]],"date-time":"2019-02-25T00:00:00Z","timestamp":1551052800000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"name":"Seventh Framework Programme","award":["606983"],"award-info":[{"award-number":["606983"]}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Sensors"],"abstract":"<jats:p>Accurate nitrogen (N) management is crucial for the economic and environmental sustainability of cropping systems. Different methods have been developed to increase the efficiency of N fertilizations. However, their costs and\/or low usability have often prevented their adoption in operational contexts. We developed a diagnostic system to support topdressing N fertilization based on the use of smart apps to derive a N nutritional index (NNI; actual\/critical plant N content). The system was tested on paddy rice via dedicated field experiments, where the smart apps PocketLAI and PocketN were used to estimate, respectively, critical (from leaf area index) and actual plant N content. Results highlighted the system\u2019s capability to correctly detect the conditions of N stress (NNI &lt; 1) and N surplus (NNI &gt; 1), thereby effectively supporting topdressing fertilizations. A resource-efficient methodology to derive PocketN calibration curves for different varieties\u2014needed to extend the system to new contexts\u2014was also developed and successfully evaluated on 43 widely grown European varieties. The widespread availability of smartphones and the possibility to integrate NNI and remote sensing technologies to derive variable rate fertilization maps generate new opportunities for supporting N management under real farming conditions.<\/jats:p>","DOI":"10.3390\/s19040981","type":"journal-article","created":{"date-parts":[[2019,2,26]],"date-time":"2019-02-26T11:00:44Z","timestamp":1551178844000},"page":"981","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":18,"title":["Estimating Crop Nutritional Status Using Smart Apps to Support Nitrogen Fertilization. A Case Study on Paddy Rice"],"prefix":"10.3390","volume":"19","author":[{"given":"Livia","family":"Paleari","sequence":"first","affiliation":[{"name":"Department of Environmental Science and Policy, Universit\u00e0 degli Studi di Milano, Cassandra lab, via Celoria 2, 20133 Milan, Italy"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Ermes","family":"Movedi","sequence":"additional","affiliation":[{"name":"Department of Environmental Science and Policy, Universit\u00e0 degli Studi di Milano, Cassandra lab, via Celoria 2, 20133 Milan, Italy"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Fosco M.","family":"Vesely","sequence":"additional","affiliation":[{"name":"Department of Environmental Science and Policy, Universit\u00e0 degli Studi di Milano, Cassandra lab, via Celoria 2, 20133 Milan, Italy"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"William","family":"Thoelke","sequence":"additional","affiliation":[{"name":"Department of Environmental Science and Policy, Universit\u00e0 degli Studi di Milano, Cassandra lab, via Celoria 2, 20133 Milan, Italy"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Sofia","family":"Tartarini","sequence":"additional","affiliation":[{"name":"Department of Environmental Science and Policy, Universit\u00e0 degli Studi di Milano, Cassandra lab, via Celoria 2, 20133 Milan, Italy"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Marco","family":"Foi","sequence":"additional","affiliation":[{"name":"Department of Environmental Science and Policy, Universit\u00e0 degli Studi di Milano, Cassandra lab, via Celoria 2, 20133 Milan, Italy"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-2156-4166","authenticated-orcid":false,"given":"Mirco","family":"Boschetti","sequence":"additional","affiliation":[{"name":"Italian National Research Council, Institute on Remote Sensing of Environment (CNR-IREA), via Bassini 15, 20133 Milan, Italy"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Francesco","family":"Nutini","sequence":"additional","affiliation":[{"name":"Italian National Research Council, Institute on Remote Sensing of Environment (CNR-IREA), via Bassini 15, 20133 Milan, Italy"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Roberto","family":"Confalonieri","sequence":"additional","affiliation":[{"name":"Department of Environmental Science and Policy, Universit\u00e0 degli Studi di Milano, Cassandra lab, via Celoria 2, 20133 Milan, Italy"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"1968","published-online":{"date-parts":[[2019,2,25]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"20260","DOI":"10.1073\/pnas.1116437108","article-title":"Global food demand and the sustainable intensification of agriculture","volume":"108","author":"Tilman","year":"2011","journal-title":"Proc. Natl. Acad. Sci USA"},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"254","DOI":"10.1038\/nature11420","article-title":"Closing yield gaps through nutrient and water management","volume":"490","author":"Mueller","year":"2012","journal-title":"Nature"},{"key":"ref_3","doi-asserted-by":"crossref","first-page":"667","DOI":"10.1098\/rstb.2007.2177","article-title":"Optimizing nutrient management for farm systems","volume":"363","author":"Goulding","year":"2008","journal-title":"Philos. Trans. R. Soc. Lond. B Biol. Sci."},{"key":"ref_4","doi-asserted-by":"crossref","first-page":"168","DOI":"10.1016\/j.agsy.2017.03.016","article-title":"Agricultural household effects of fertilizer price changes for smallholder farmers in central Malawi","volume":"154","author":"Komarek","year":"2017","journal-title":"Agric. Syst."},{"key":"ref_5","first-page":"265","article-title":"Increase of fungal pathogenicity and role of plant glutamine in nitrogen-induced susceptibility (NIS) to rice blast","volume":"8","author":"Huang","year":"2017","journal-title":"Front. Plant Sci."},{"key":"ref_6","doi-asserted-by":"crossref","first-page":"859","DOI":"10.1007\/s10265-017-0943-3","article-title":"Nitrogen fertilizer application affects lodging resistance by altering secondary cell wall synthesis in japonica rice (Oryza sativa)","volume":"130","author":"Zhang","year":"2017","journal-title":"J. Plant Res."},{"key":"ref_7","doi-asserted-by":"crossref","first-page":"47","DOI":"10.1016\/j.fcr.2015.02.007","article-title":"Roots and shoots traits for rice varieties with higher grain yield and higher nitrogen use efficiency at lower nitrogen rates applications","volume":"175","author":"Ju","year":"2015","journal-title":"Field Crop. Res."},{"key":"ref_8","doi-asserted-by":"crossref","first-page":"50","DOI":"10.1007\/s13593-017-0457-3","article-title":"Diverse concepts of breeding for nitrogen use efficiency. A review","volume":"37","author":"Struik","year":"2017","journal-title":"Agron. Sustain. Dev."},{"key":"ref_9","unstructured":"Robert, P.C., Rush, R.H., and Larson, W.E. (1999). Using Yield Maps to Regionalize Fields into Potential Management Units. Precision Agriculture, ASA\/CSSA\/SSSA."},{"key":"ref_10","doi-asserted-by":"crossref","first-page":"1572","DOI":"10.2134\/agronj2004.1572","article-title":"Site specific management: Economic feasibility of variable-rate nitrogen application utilizing site-specific management zones","volume":"96","author":"Koch","year":"2004","journal-title":"Agron. J."},{"key":"ref_11","doi-asserted-by":"crossref","first-page":"2759","DOI":"10.1080\/00103620500303988","article-title":"Optical sensor-based algorithm for crop nitrogen fertilization","volume":"36","author":"Raun","year":"2005","journal-title":"Commun. Soil Sci. Plan."},{"key":"ref_12","doi-asserted-by":"crossref","first-page":"227","DOI":"10.1016\/j.scitotenv.2015.12.104","article-title":"Environmental and economic benefits of variable rate nitrogen fertilization in a nitrate vulnerable zone","volume":"545\u2013546","author":"Basso","year":"2016","journal-title":"Sci. Total Environ."},{"key":"ref_13","doi-asserted-by":"crossref","first-page":"288","DOI":"10.1017\/S2040470017000103","article-title":"Early stage variable rate nitrogen fertilization of silage maize driven by multi-temporal clustering of archive satellite data","volume":"8","author":"Casa","year":"2017","journal-title":"Adv. Anim. Biosci."},{"key":"ref_14","doi-asserted-by":"crossref","first-page":"56","DOI":"10.1007\/s11119-018-9581-6","article-title":"Fine-tuning of wheat (Triticum aestivum, L.) variable nitrogen rate by combining crop sensing and management zones approaches in southern Brazil","volume":"20","author":"Schwalbert","year":"2019","journal-title":"Precis. Agric."},{"key":"ref_15","unstructured":"Salette, J., and Lemaire, G. (1981). Sur la Variation de la Teneur en Azote des Gramin\u00e9es Fourrag\u00e8res Pendant Leur Croissance: Formulation D\u2019une Loi de Diluition, Compte Rendus de l\u2019acad\u00e9mie des Sciences. [S\u00e9rie III. ed.]."},{"key":"ref_16","doi-asserted-by":"crossref","first-page":"42679","DOI":"10.1038\/srep42679","article-title":"Comparison of different critical nitrogen curves for nitrogen diagnosis in rice","volume":"7","author":"Zhu","year":"2017","journal-title":"Sci. Rep."},{"key":"ref_17","doi-asserted-by":"crossref","first-page":"397","DOI":"10.1006\/anbo.1994.1133","article-title":"Determination of a critical nitrogen dilution curve for winter wheat crops","volume":"74","author":"Justes","year":"1994","journal-title":"Ann. Bot."},{"key":"ref_18","doi-asserted-by":"crossref","first-page":"614","DOI":"10.1016\/j.eja.2008.01.005","article-title":"Diagnosis tool for plant and crop N status in vegetative stage. Theory and practices for crop N management","volume":"28","author":"Lemaire","year":"2008","journal-title":"Eur. J. Agron."},{"key":"ref_19","doi-asserted-by":"crossref","first-page":"4527","DOI":"10.3390\/rs70404527","article-title":"A comparison of two approaches for estimating the wheat nitrogen nutrition index using remote sensing","volume":"7","author":"Chen","year":"2015","journal-title":"Remote Sens."},{"key":"ref_20","doi-asserted-by":"crossref","first-page":"10646","DOI":"10.3390\/rs70810646","article-title":"Satellite remote sensing-based in-season diagnosis of rice nitrogen status in Northeast China","volume":"7","author":"Huang","year":"2015","journal-title":"Remote Sens."},{"key":"ref_21","doi-asserted-by":"crossref","first-page":"1804","DOI":"10.1109\/TGRS.2006.872529","article-title":"Validation of global moderate-resolution LAI products: A framework proposed within the CEOS land product validation subgroup","volume":"44","author":"Morisette","year":"2006","journal-title":"IEEE Trans. Geosci. Remote"},{"key":"ref_22","doi-asserted-by":"crossref","first-page":"10823","DOI":"10.3390\/s130810823","article-title":"A review of methods for sensing the nitrogen status in plants: Advantages, disadvantages and recent advances","volume":"13","year":"2013","journal-title":"Sensors"},{"key":"ref_23","doi-asserted-by":"crossref","unstructured":"Orlando, F., Movedi, E., Coduto, D., Parisi, S., Brancadoro, L., Pagani, V., Guarneri, T., and Confalonieri, R. (2016). Estimating LAI in vineyard using the PocketLAI smart-app. Sensors, 16.","DOI":"10.3390\/s16122004"},{"key":"ref_24","doi-asserted-by":"crossref","first-page":"80","DOI":"10.1016\/j.compag.2018.08.008","article-title":"An operational workflow to assess rice nutritional status based on satellite imagery and smartphone apps","volume":"154","author":"Nutini","year":"2018","journal-title":"Comput. Electron. Agric."},{"key":"ref_25","doi-asserted-by":"crossref","first-page":"949","DOI":"10.2134\/agronj2004.0206","article-title":"Leaf color chart for managing nitrogen fertilizer in lowland rice in Bangladesh","volume":"97","author":"Alam","year":"2005","journal-title":"Agron. J."},{"key":"ref_26","doi-asserted-by":"crossref","first-page":"633","DOI":"10.1017\/S0021859611000177","article-title":"A new approach for determining rice critical nitrogen concentration","volume":"149","author":"Confalonieri","year":"2011","journal-title":"J. Agric. Sci."},{"key":"ref_27","doi-asserted-by":"crossref","first-page":"243","DOI":"10.1016\/0378-4290(96)00018-4","article-title":"Increased N-use efficiency using a chlorophyll meter on high-yielding irrigated rice","volume":"47","author":"Peng","year":"1996","journal-title":"Field Crop. Res."},{"key":"ref_28","doi-asserted-by":"crossref","first-page":"19","DOI":"10.1016\/j.agrformet.2003.08.027","article-title":"Review of methods for in situ leaf area index determination. Part I. Theories, sensors and hemispherical photography","volume":"121","author":"Jonckheere","year":"2004","journal-title":"Agric. For. Meteorol."},{"key":"ref_29","doi-asserted-by":"crossref","first-page":"167","DOI":"10.1016\/j.fcr.2006.04.002","article-title":"Evaluation of LAI-2000 for leaf area index monitoring in paddy rice","volume":"99","author":"Stroppiana","year":"2006","journal-title":"Field Crop. Res."},{"key":"ref_30","doi-asserted-by":"crossref","first-page":"251","DOI":"10.1111\/j.1399-3054.2012.01639.x","article-title":"A new optical leaf-clip meter for simultaneous nondestructive assessment of leaf chlorophyll and epidermal flavonoids","volume":"146","author":"Cerovic","year":"2012","journal-title":"Physiol. Plant."},{"key":"ref_31","doi-asserted-by":"crossref","first-page":"197","DOI":"10.1023\/A:1015878719389","article-title":"SPAD readings and associated leaf traits in durum wheat, barley and triticale cultivars","volume":"125","author":"Giunta","year":"2002","journal-title":"Euphytica"},{"key":"ref_32","doi-asserted-by":"crossref","first-page":"190","DOI":"10.1016\/S2095-3119(14)60925-4","article-title":"Establishing dynamic thresholds for potato nitrogen status diagnosis with the SPAD chlorophyll meter","volume":"14","author":"Zheng","year":"2015","journal-title":"J. Integr. Agr."},{"key":"ref_33","doi-asserted-by":"crossref","first-page":"73","DOI":"10.1016\/j.fcr.2017.08.023","article-title":"Use of a chlorophyll meter to assess nitrogen nutrition index during the growth cycle in winter wheat","volume":"214","author":"Ravier","year":"2016","journal-title":"Field Crop. Res."},{"key":"ref_34","first-page":"1829","article-title":"Non-destructive assessment of plant nitrogen parameters using leaf chlorophyll measurements in rice","volume":"7","author":"Cao","year":"2016","journal-title":"Front. Plant Sci."},{"key":"ref_35","doi-asserted-by":"crossref","first-page":"67","DOI":"10.1016\/j.compag.2013.04.019","article-title":"Development of an app for estimating leaf area index using a smartphone. Trueness and precision determination and comparison with other indirect methods","volume":"96","author":"Confalonieri","year":"2013","journal-title":"Comput. Electron. Agric."},{"key":"ref_36","doi-asserted-by":"crossref","first-page":"21","DOI":"10.1016\/j.biosystemseng.2015.04.013","article-title":"Improving in vivo plant nitrogen content estimates from digital images: Trueness and precision of a new approach as compared to other methods and commercial devices","volume":"135","author":"Confalonieri","year":"2015","journal-title":"Biosyst. Eng."},{"key":"ref_37","unstructured":"Baruth, B., Van den Berg, M., and Niemeyer, S. (2019, February 23). MARS Bulletin, 2014, Volume 22, n.13. Available online: publications.jrc.ec.europa.eu\/repository\/bitstream\/JRC88391\/marsbulletin_vol22_no13.pdf."},{"key":"ref_38","unstructured":"Baruth, B., Van den Berg, M., and Niemeyer, S. (2019, February 23). MARS Bulletin, 2015, Volume 23, n.8. Available online: publications.jrc.ec.europa.eu\/repository\/bitstream\/JRC98793\/lb-am-15-008-en-n.pdf."},{"key":"ref_39","doi-asserted-by":"crossref","first-page":"195","DOI":"10.1007\/s12892-009-0133-5","article-title":"Assessment of N topdressing rate at panicle initiation stage with chlorophyll meter-based diagnosis in rice","volume":"12","author":"Lee","year":"2009","journal-title":"J. Crop Sci. Biotechnol."},{"key":"ref_40","doi-asserted-by":"crossref","first-page":"943","DOI":"10.2135\/cropsci2003.9430","article-title":"Quantifying turfgrass color using digital image analysis","volume":"43","author":"Karcher","year":"2003","journal-title":"Crop Sci."},{"key":"ref_41","doi-asserted-by":"crossref","first-page":"95","DOI":"10.1071\/BT9630095","article-title":"Estimation of foliage denseness and foliage angle by inclined point quadrats","volume":"11","year":"1963","journal-title":"Aust. J. Bot."},{"key":"ref_42","doi-asserted-by":"crossref","first-page":"1393","DOI":"10.1016\/j.agrformet.2010.04.011","article-title":"GAI estimates of row crops from downward looking digital photos taken perpendicular to rows at 57.5\u00b0 zenith angle: Theoretical considerations based on 3D architecture models and application to wheat crops","volume":"150","author":"Baret","year":"2010","journal-title":"Agric. For. Meteorol."},{"key":"ref_43","unstructured":"Gomez, K.A. (1972). Techniques for Field Experiments with Rice: Layout, Sampling, Sources of Error, International Rice Research Institute."},{"key":"ref_44","doi-asserted-by":"crossref","first-page":"135","DOI":"10.1016\/j.fcr.2005.09.008","article-title":"Analysis of rice sample size variability due to development stage, nitrogen fertilization, sowing technique and variety using the visual jackknife","volume":"97","author":"Confalonieri","year":"2006","journal-title":"Field Crop. Res."},{"key":"ref_45","doi-asserted-by":"crossref","first-page":"497","DOI":"10.13031\/2013.31032","article-title":"The EPIC crop growth model","volume":"32","author":"Williams","year":"1989","journal-title":"Trans. ASAE"},{"key":"ref_46","doi-asserted-by":"crossref","first-page":"425","DOI":"10.1093\/oxfordjournals.aob.a088044","article-title":"Decline in percentage N of C3 and C4 crops with increasing plant mass","volume":"66","author":"Greenwood","year":"1990","journal-title":"Ann. Bot."},{"key":"ref_47","first-page":"281","article-title":"Some Methods for Classification and Analysis of Multivariate Observations","volume":"Volume 1","author":"MacQueen","year":"1967","journal-title":"Proceedings of the 5th Berkeley Symposium on Mathematical Statistics and Probability"},{"key":"ref_48","doi-asserted-by":"crossref","first-page":"59","DOI":"10.1016\/j.fcr.2015.10.021","article-title":"Rapid and nondestructive estimation of the nitrogen nutrition index in winter barley using chlorophyll measurements","volume":"185","author":"Zhao","year":"2016","journal-title":"Field Crop. Res."},{"key":"ref_49","doi-asserted-by":"crossref","first-page":"271","DOI":"10.2134\/agronj2007.0059","article-title":"Critical nitrogen curve and nitrogen nutrition index for corn in eastern Canada","volume":"100","author":"Ziadi","year":"2008","journal-title":"Agron. J."},{"key":"ref_50","doi-asserted-by":"crossref","first-page":"1","DOI":"10.1016\/j.fcr.2016.04.027","article-title":"In-season estimation of rice grain yield using critical nitrogen dilution curve","volume":"195","author":"Liu","year":"2016","journal-title":"Field Crop. Res."},{"key":"ref_51","doi-asserted-by":"crossref","first-page":"2561","DOI":"10.1080\/00103629409369207","article-title":"Soil texture effect on nitrate leaching in soil percolates","volume":"25","author":"Gaines","year":"2008","journal-title":"Commun. Soil Sci. Plant Anal."},{"key":"ref_52","doi-asserted-by":"crossref","first-page":"252","DOI":"10.1016\/j.soilbio.2013.10.004","article-title":"Soil enzyme activities, microbial communities, and carbon and nitrogen availability in organic agroecosystems across an intensively-managed agricultural landscape","volume":"68","author":"Bowles","year":"2014","journal-title":"Soil Biol. Biochem."},{"key":"ref_53","unstructured":"Davis, J.G., Malzer, G.L., Copeland, P.J., Lamb, J.A., Robert, P.C., and Bruulsema, T.W. (1996, January 23\u201326). Using yield variability to characterize spatial crop response to applied N. Proceedings of the 3rd International Conference Precision Agriculture, Minneapolis, MN, USA."},{"key":"ref_54","doi-asserted-by":"crossref","first-page":"66","DOI":"10.1626\/pps.17.66","article-title":"Comparison of five different nitrogen dressing methods to optimize rice growth","volume":"17","author":"Chen","year":"2014","journal-title":"Plant Prod. Sci."},{"key":"ref_55","doi-asserted-by":"crossref","first-page":"337","DOI":"10.1016\/j.fcr.2004.02.019","article-title":"Temporal origin of nitrogen in the grain of irrigated rice in the dry season: The outcome or recycling, cycling, senescence and competition studied using a 15N-point placement technique","volume":"89","author":"Sheehy","year":"2004","journal-title":"Field Crop. Res."},{"key":"ref_56","doi-asserted-by":"crossref","first-page":"467","DOI":"10.1007\/BF00032301","article-title":"Calibration of the Minolta SPAD-502 leaf chlorophyll meter","volume":"46","author":"Markwell","year":"1995","journal-title":"Photosynth. Res."},{"key":"ref_57","doi-asserted-by":"crossref","first-page":"822","DOI":"10.2134\/agronj2015.0258","article-title":"Assessment of leaf color chart observations for estimating maize chlorophyll content by analysis of digital photographs","volume":"108","author":"Friedman","year":"2014","journal-title":"Agron. J."},{"key":"ref_58","doi-asserted-by":"crossref","first-page":"53","DOI":"10.1626\/pps.13.53","article-title":"Varietal differences in photosynthetic rates in rice plants, with special reference to nitrogen content of leaves","volume":"13","author":"Hirasawa","year":"2010","journal-title":"Plant Prod. Sci."}],"container-title":["Sensors"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/1424-8220\/19\/4\/981\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2025,10,11]],"date-time":"2025-10-11T12:34:41Z","timestamp":1760186081000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/1424-8220\/19\/4\/981"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2019,2,25]]},"references-count":58,"journal-issue":{"issue":"4","published-online":{"date-parts":[[2019,2]]}},"alternative-id":["s19040981"],"URL":"https:\/\/doi.org\/10.3390\/s19040981","relation":{},"ISSN":["1424-8220"],"issn-type":[{"type":"electronic","value":"1424-8220"}],"subject":[],"published":{"date-parts":[[2019,2,25]]}}}