Jaume Lloveras

Analysis of Vegetation Indices to Determine Nitrogen Application and Yield Prediction in Maize (Zea mays L.) from a Standard UAV Service

The growing use of commercial unmanned aerial vehicles (UAV) and the need to adjust N fertilization rates in maize (Zea mays L.) currently constitute a key research issue. In this study, different multispectral vegetation indices (green-band and red-band based indices), SPAD and crop height (derived from a multispectral compact camera mounted on a UAV) were analysed to predict grain yield and determine whether an additional sidedress application of N fertilizer was required just before flowering. Seven different inorganic N rates (0, 100, 150, 200, 250, 300, 400 kg·N·ha−1), two different pig slurry manure rates (Ps) (150 or 250 kg·N·ha−1) and four different inorganic-organic N combinations (N100Ps150, N100Ps250, N200Ps150, N200Ps250) were applied to maize experimental plots. The spectral index that best explained final grain yield for the N treatments was the Wide Dynamic Range Vegetation Index (WDRVI). It identified a key threshold above/below 250–300 kg·N·ha−1. WDRVI, NDVI and crop height showed no significant response to extra N application at the economic optimum rate of fertilization (239.8 kg·N·ha−1), for which a grain yield of 16.12 Mg·ha−1 was obtained. This demonstrates their potential as yield predictors at V12 stage. Finally, a ranking of different vegetation indices and crop height is proposed to overcome the uncertainty associated with basing decisions on a single index.

Current Status of Hemp Production and Transformation in Spain

Abstract Hemp has long been a traditional crop in Spain, although it almost disappeared in 1972. In that year the paper industry started using hemp as a raw material, and as a consequence, there was a renewed interest in the crop. At present, hemp is mainly grown in northeast Spain (800 ha). Farmers appreciate its agronomic and economic advantages but the future of the crop depends on the effect of the recent EU regulations and the ability of the industry to develop new hemp based products. The objective of this paper is to describe the hemp cropping practices, fibre processing and uses in Spain.

Hemp and Flax Biomass and Fiber Production and Linseed Yield in Irrigated Mediterranean Conditions

Abstract Field trials were conducted in the irrigated areas of the Ebro valley, one of the most important irrigated areas in Spain, in order to study the feasibility of flax and hemp as possible alternative crops. Field experiments were established in 2000 and 2001, and three varieties of hemp and five of flax (two fiber types and three oilseed types) were compared under irrigation. Stem dry matter yields for hemp averaged 9,118 kg ha−1 and 7,635 kg ha−1, with average bark contents of 32.2% and 22.5%, in 2000 and 2001, respectively. Straw yields and bark contents for flax averaged 4,790 and 4,259 kg ha−1 and 27.0 and 20.1%, in 2000 and 2001, respectively, whereas average linseed yields were of 1,741 and 468 kg ha−1, in 2000 and in 2001, respectively. The results suggest that in the irrigated conditions of the Ebro valley hemp seems a more appropriate crop than flax for the pulp paper industry, although in order to obtain higher yields earlier sowing and longer cycle varieties should be studied.

Use of Multispectral Airborne Images to Improve In-Season Nitrogen Management, Predict Grain Yield and Estimate Economic Return of Maize in Irrigated High Yielding Environments

Vegetation indices (VIs) derived from active or passive sensors have been used for maize growth monitoring and real-time nitrogen (N) management at field scale. In the present multilocation two-year study, multispectral VIs (green- and red-based), chlorophyll meter (SPAD) and plant height (PltH) measured at V12–VT stage of maize development, were used to distinguish among the N status of maize, to predict grain yield and economic return in high yielding environments. Moreover, linear plateau-models were performed with VIs, SPAD and PltH measurements to determine the amount of N needed to achieve maximum maize grain yields and economic return. The available N in the topsoil (0–30 cm) was measured, and its relationship with VIs, maize yield and maize N requirements was analyzed. Green-based VIs were the most accurate indices to predict grain yield and to estimate the grain yield optimum N rate (GYONr) (216.8 kg N ha−1), but underestimated the grain yield optimum N available (GYONa) (248.6 kg N ha−1). Red-based VIs slightly overestimated the GYONr and GYONa, while SPAD highly underestimated both of them. The determination of the available N did not improve the accuracy of the VIs to determine the grain yield. The green chlorophyll index (GCI) distinguished maize that would yield less than 84% of the maximum yield, showing a high potential to detect and correct maize N deficiencies at V12 stage. The economic optimum nitrogen rate (EONr) and economic optimum nitrogen available (EONa) were determined below the GYONr and the GYONa, demonstrating that maximum grain yield strategies in maize are not normally the most profitable for farmers. Further research is needed to fine-tune the response of maize to N applications when deficiencies are detected at V12 stage, but airborne imagery could be useful for practical farming implementation in irrigated high yielding environments.

Erratum: Maresma, A., et al. Analysis of Vegetation Indices to Determine Nitrogen Application and Yield Prediction in Maize (Zea mays L.) from a Standard UAV Service. Remote Sens. 2017, 9, 648

After publication of the research paper [1], the authors noticed an error and wish to make the following correction.[...]