Junxiang Peng
Research Scientist
(+47) 403 40 352
junxiang.peng@nibio.no
Place
Særheim
Visiting address
Postvegen 213, NO-4353 Klepp stasjon
Abstract
Potato field management in Europe is already optimized for high production and tuber quality; however, numerous environmental challenges remain if the industry is to achieve “green economy” targets, such as less resources utilized, and less nitrate leached to the environment. Strategic co-scheduling irrigation and nitrogen (N) fertilization might increase resource use efficiency while minimizing reactive losses such as nitrate leaching. This study aimed to quantify the combined effect of irrigation and N fertilization on potato production, growth, and resource use efficiencies. A field experiment was conducted from 2017 to 2019 on a coarse sandy soil in Denmark, with a drought event occurring in 2018. Full (Ifull, maximized), deficit (Idef, 70–80 % of Ifull) and low irrigation treatments (Ilow, minimized amount to keep crop survival), each under full (Nfull, maximized) and variable (Nvar, variable amount according to the crops’ needs) N fertilization were applied. The analyses results show that Ilow limited potato growth under a drought-heat event; otherwise, potato growth was comparable between Ifull and Idef treatments, with 31–32 % higher irrigation efficiency (IE) under Idef than under Ifull. Nitrate leaching was variable and not significantly different among the treatments, being in general 9–13 % lower under Idef in absolute terms than under Ifull. Unexpectedly, outcomes from Nvar were statistically lower compared to those from Nfull. Radiation use efficiencies (RUEs) from Ilow and Nvar were significantly lower than from Ifull and Idef (14–19 %), and from Nfull (9–11 %). N use efficiencies (NUE) were comparable between N fertilization treatments but significantly different among different irrigation treatments. Overall, this study confirms that Idef is the best irrigation strategy. Future efforts should focus on developing improved approaches for detecting in-season crop N status and further quantifying N requirements, as well as promoting the co-scheduled management of irrigation and N fertilization. Remote sensing approaches have great potential to assist with this.
Abstract
Nitrogen (N) management is one of the main factors enhancing potato productivity and promoting sustainable agricultural practices. The Nitrogen Nutrition Index (NNI, obtained as the ratio of actual plant N, to the critical plant N concentration) is widely applied to assess the N status of various crops. Traditionally, NNI is calculated using field data, but remote sensing (RS) technologies can offer more rapidly and timely assessment of the spatiotemporal (within field) variability of this index. This study employs multispectral data acquired via Unmanned Aerial Vehicle (UAV) and machine learning (ML) models to estimate potato NNI. A Bayesian hierarchical partially pooled method was fitted to a three-year f ield experiment in Denmark and extensive ground-based potato datasets to model the critical nitrogen dilution curve (CNDC) and calculate the NNI. Multispectral UAV data were processed to extract four spectral bands and calculate several vegetation indices, which were used as predictors to train and test six ML models: Linear regression, support vector machines, gaussian process regression, stepwise linear regression, ensemble trees and neural networks. Among the compared models, gaussian process regression outperformed, showing R 2 equal to 0.83 and a RMSE of 0.10 and providing accurate NNI predictions, comparable to ground-based Bayesian estimates. The variability of the NNI was analyzed over the seasons using 28 NNI maps derived from UAV surveys at spatial resolution of 0.04–0.09 m/pixel, capturing spatial variations in crop N status over time. The proposed framework, designed for NNI prediction at the intra-field scale, has the potential to be adapted to different environments and crops. The framework can support practical decisions for precision N management, reducing the environmental impact of potato cultivations and enhancing sustainability.
Authors
Shaohui Zhang Poul Erik Lærke Mathias Neumann Andersen Junxiang Peng Esben Øster Mortensen Johannes Wilhelmus Maria Pullens Sheng Wang Klaus Steenberg Larsen Davide Cammarano Uffe Jørgensen Kiril ManevskiAbstract
Under optimal growth conditions, net primary productivity (NPP) is a product of intercepted photosynthetic active radiation (Ipar) and maximum radiation use efficiency (RUEmax; conversion of Ipar to biomass). The objective of this study was to improve and validate the RUEmax-based Carnegie-Ames-Stanford Approach (CASA) for the determination of grassland NPP by canopy multispectral reflectance collected at field (handheld sensor) and airborne (UAV) scale considering environmental constraints. The analysis was based on multi-year field experiments on sandy loam soil in Denmark, measured shoot and estimated root biomass to calculate NPP, long-term meteorological data, and daily NPP estimated from CO2 flux chamber measurements for deriving environmental constraints. The results derived from CO2 flux data showed that NPP and plant respiration were higher in the middle of the season before the second harvest when temperature was also high. The daily maximum air temperature optimal for grass biomass production was 16.5 °C. The improved CASA model built in this study was accurate for modeling NPP at both daily (nRMSE decrease of 9 %) and seasonal (nRMSE decrease of 8–34 %) scales when considering the best environmental constraints such as maximum air temperature, vapor pressure deficit, cloudiness, and water stress, compared to no constraints. Maximum air temperature and water stress were the most important environmental constraints to the grass RUEmax. Seasonal RUEmax for modeling NPP after considering best environmental constraints was 1.9–2.7 g C MJ−1 for ryegrass and 1.9–2.2 g C MJ−1 for grass-legume mixture using the two remote sensors for measuring spectral reflectance. Over the whole growing season, tall fescue (3.1 g C MJ−1) and festulolium (2.9 g C MJ−1) obtained higher RUEmax than perennial ryegrass (2.3 g C MJ−1). This study highlights the practical implications of using the CASA model improved by maximum temperature and water stress functions for real-time, remote sensing-based assessments of grassland productivity.