Yield and texture-based management zones in a heterogeneous old morainic landscape

Urheber: 14th ECPA 2023, Bologna, Italy, 02-06 Jul 2023 (conference contribution
Ort: BOLOGNIA, ITALY
Jahr: 2023

Einordung:
Institut: Professur Geodäsie und Geoinformatik

Abstract:
Introduction (For the section titles, please use the style “Title 2”.)
While economic and environmental pressures still increase rapidly on farming, site-specific crop
and soil management provides efficient and cost-effective methods by delineating sub-field
productivity zones - so-called management zones (MZ). To apply inputs, common approaches
determine the MZ through decreasing variability of a single site condition solely that represents either
the nutrient storage potential or the nutrient withdrawal potential. However, MZs should be
determined on a combination of both.
The measurement of above ground biomass is a crucial factor in determining crop yields or net
primary productivity. In recent times, there has been a growing interest in utilizing vegetation indices
instead of productivity maps. The NDVI (Normalized Difference Vegetation Index), which is
calculated from satellite imagery [1], has gained widespread use globally due to its strong correlation
with crop productivity [2,3]. Moreover, high-resolution satellite images can be obtained
inexpensively, enabling the mapping of large areas with minimal investments.
In practice, farmers often use class based soil texture systems in order to determine fertilizer
amounts. As was shown by [4,5], the soil clay, silt and sand content can now be determined very
accurately and with a high degree of spatial accuracy using on-the-go soil sensors and digital soil
mapping techniques. However, when using class-based systems with these highly accurate input
data for fertilizer determination, much of the input information is lost because the classes of this
system are rather coarse. To consider the clay, silt and sand content equally, this study uses,
moreover, the mean particle size diameter (MPD) according to [6] and applied by [7].
Objectives
Therefore, this study tests the delineation of soil MZs based on a combination of soil texture (as
for the storage potential) and relative yields (as for the nutrient withdrawal) on a 62 ha field in a
heterogeneous old morainic landscape in northeast Germany.
Materials and methods
Level-2A data of Sentinel-2/MSI (10m resolution) of the study area and for the harvest periods
of the years 2016 to 2020 were obtained and NDVI values calculated from the reflectance in band 4
(red; center wavelength: 665 nm; bandwidth: 30 nm) and band 8 (NIR; 842 nm; 115 nm) after
excluding cloud pixels. NDVIs were averaged over the observation period and expressed as relative
yields with a mean yield set as 100. Clay, silt and sand content maps were derived from combining
spatially high-resolution soil electrical resistivity and gamma data and point reference samples as
described by [4,5] and the MPD derived [6,7]. Management zones were obtained by applying fuzzy
k-mean clustering on the MPD and relative yield maps of 2x2 m resolution. The number of cluster
zones were set fix to 6.
As the soil pH is a central element in soil fertility and therefore an indicator for nutrient availability,
MZs determined in this study were evaluated by the variability (variance, coefficient of variation
CV%) of the soil pH from a calibrated pH sensor map. The pH map was generated using a mobile
in-situ pH soil sensor before the crop cycle.
Results
Both maps (MPD and relative yields) showed similar spatial patterns. In the centre of the field,
lower MPD values indicate a higher clay content while higher MPDs to the field border indicate higher
silt and sand contents. Relative yields were highest in the field centre, but lower in the south and the
northeast. Correlation between MPD and relative yields was lower than 0.65 (Fig.1).
The clustering showed MZ in accordance with the both co-variates with zones of lower MPDs
and higher yields in the field centre and zones of lower yields and higher MPDs to the northeast and
the south.

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