The pattern of nitrogen net change (ΔN) in potato tops during the period extending from BBCH 33 to BBCH 40 is crucial for tuber yield (TY). This hypothesis was verified based on data from field experiments (2006–2008) with sequentially added nutrients (0, NP, NPK, NPKS, NPKSMg) to potato. The water shortage in June/July 2006 and in June 2008 significantly affected N content, and in turn TY. The TY was reduced by 38% in 2006 and by 23% in 2008, as compared to 2007 (53.7 t/ha). The N content in potato tops at BBCH 40 of 2.5% indicated the lowest TY, whereas 4.3% the maximum TY. The ΔN of +0.4% within the period from BBCH 33 to BBCH 40 determined the optimal range of the N content for the maximum TY (3.9–4.3%). The ΔN trend depended on the change of phosphorus and potassium contents. The key reason of N inefficiency was the shortage of potassium (K), resulting in its negligible change within this period. The pattern of zinc content at BBCH 40 reflected fairly well disturbances in N as well as K supply to potato. A good supply of K and Zn to potato can improve N management just before tuber initiation.

The Soil Fertility Clock (SFC) concept is based on the assumption that the critical content (range) of essential nutrients in the soil is adapted to the requirements of the most sensitive plant in the cropping sequence (CS). This provides a key way to effectively control the productivity of fertilizer nitrogen (Nf). The production goals of a farm are set for the maximum crop yield, which is defined by the environmental conditions of the production process. This target can be achieved, provided that the efficiency of Nf approaches 1.0. Nitrogen (in fact, nitrate) is the determining yield-forming factor, but only when it is balanced with the supply of other nutrients (nitrogen-supporting nutrients; N-SNs). The condition for achieving this level of Nf efficiency is the effectiveness of other production factors, including N-SNs, which should be set at ≤1.0. A key source of N-SNs for a plant is the soil zone occupied by the roots. N-SNs should be applied in order to restore their content in the topsoil to the level required by the most sensitive crop in a given CS. Other plants in the CS provide the timeframe for active controlling the distance of the N-SNs from their critical range.

Yields of oilseed rape harvested by farmers in Poland are usually much below the attainable potential of currently cultivated varieties, mainly because of the insufficient supply of nutrients during the yield foundation period, which determines the final number of secondary branches. This situation is typical of whole Poland, but may take place even on farms where high yields are harvested, for example in 2007. In 2006, 2007 and 2008, the year effect of multi-micronutrient fertilizers on yield of seeds, elements of yield structure and macronutrient content was studied. Multi-micronutrient fertilizers were applied twice over oilseed rape foliage during its pre-anthesis growth (BBCH45 and 53). In 2007, due to a drought in April, the harvested yields of seeds were below the country's average. However, in each year of the study, a significant increase in the seed yield owing to the foliar application of multi-micronutrient fertilizers was found. The increase in the yield of seeds, averaged for the three years, reached 0.486 t ha-1 for the NPK+MiMo treatment (full set of micronutrients) and 0.36 t ha-1 for the NPK + Mi treatment (without molybdenum). The increments of the oilseed rape yield resulted from an increased number of developed secondary branches. This yield-forming element was an indirect result of the application of multi-micronutrient fertilizers, which affected the nitrogen economy by oilseed rape plants during the foundation period of their growth. At the same time, the increase in seed yield was significantly modified by the total number of developed pods, which is shaped during the yield-forming period of oilseed rape crop growth. Under conditions of the study, the magnesium content in secondary branches was found to be an element significantly correcting their number, thus increasing the yield of seeds.

The actual yields of sugar beets harvested by farmers in Poland are much below the yielding potential of currently cultivated varieties, even when grown on fertile soils. Deficiency of micronutrients can be considered as a factor which prohibits reaching a state of nutrient balance, especially in nitrogen, by a crop. The aim of the study was to assess the effect of foliar application of multi-microelement fertilizers on a sugar beet nutritional status in early stages of canopy growth and, in turn, on yields of taproots and recoverable sugar. For this purpose, in two growing seasons, 2005 and 2006, eight field trials were set up in the region of Wielkopolska on fertile soils originated from sandy loam. A simple experimental design comprised three treatments: (1) control (a plot fertilized only with NPK), and (2) multi-microelement fertilizer composed of cations (Mi), (3) cations plus boron (MiB). It has been found that the applied micronutrient fertilizers had a significant effect, irrespectively of the field location and seasonal yield variability, on the sugar beet nutritional status, especially in terms of nitrogen. Yields of taproots have increased by 31.6% and 22.1% for the NPK+Mi and NPK+MiB treatments, respectively. Almost the same degree of increase was noted for yields of recoverable sugar. The achieved nitrogen balance at the stage of harvestable part development, as measured at BBCH43, was probably the main reason for high positive response of sugar beet crop to external supply of micronutrients. All the analyzed standards of sugar beet nutritional status, DRIS indices, responded to the investigated experimental factor, i.e., foliar application of multi-microelement fertilizer, but only those for nitrogen underwent a change from negative to positive values, thus enabling us to make a reliable yield prognosis.

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