Abstract
Site-specific crop management demands maps which present the content of the main macronutrients. Such maps are prepared based on optimized soil sampling within management zones, which should be quite homogenous according to nutrient content, especially the content of potassium and phosphorus. Delineation of management zones is very often conducted using soil apparent electrical conductivity (EC) or other variables related to soil condition, including satellite-derived vegetation indices. In this study conducted in North-Western Poland, relationships between soil electrical conductivity and the satellite-derived normalized difference vegetation index (NDVI) of various crops (wheat, barley, and rapeseed) with soil pH and content of P, K, and Mg were evaluated. Strong relationships were observed between NDVI of cereals with potassium content in soil. Correlation coefficients for wheat ranged from 0.37 to 0.60 for average potassium content for three years and from 0.05 to 0.63 for barley. Stronger relationships were observed for the years 2018 and 2019 when NDVI was based on Sentinel-2 data, while weaker for year 2017 when Landsat 8 NDVI was used. Relationships between EC and macronutrients content were similar to those observed with NDVI. Satellite-derived NDVI of cereals can be used as a variable for the delineation of within-field management zones. The same relationships were much weaker and not consistent for winter rapeseed.
Highlights
Evaluation of available nutrients content such as potassium, magnesium, and phosphorus as well soil pH is very important in crop production because it allows for the optimization of soil fertilization and liming
Soil reaction as well content of available forms of phosphorus, potassium, and magnesium in most of the studied area was favorable for crops because the content of available nutrients (P, K, and Mg) in the soil was sufficient for most of the area (Table 2)
In the case of magnesium, only 15 (3.4%) management zones showed low content and for the rest of the area the content of magnesium was from medium to very high according to the recommendations for Poland [47]
Summary
Evaluation of available nutrients content such as potassium, magnesium, and phosphorus as well soil pH is very important in crop production because it allows for the optimization of soil fertilization and liming. One composite soil sample represents each management zone Areas of such management zones should be homogenous according to the most important agronomical soil properties such as soil texture, content of soil organic carbon, pH, and content of the most important nutrients such as potassium, phosphorus, and magnesium. One of the most common spectral indices used for delineation of management zones is NDVI (Normalized Difference Vegetation Index) from satellite sensors of high or medium spatial resolutions such as, e.g., Sentinel-2 [1,2], Landsat 8 [3,4], or PlanetScope [5]
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