Rita Kremper

Phosphogypsum (PG) is a high-volume industrial by-product that is receiving increasing attention as an alternative soil amendment. This study presents a two-year pot experiment evaluating the effects of PG on spring wheat (Triticum aestivum L.) grown on two contrasting soils: an acidic, sulfur-deficient Arenosol and a sodium-affected Solonetz. Treatments comprised an untreated control and PG applications at 2 and 10 t ha⁻¹, applied once in year 1 and repeated at the same rates in year 2. In the Solonetz, PG increased grain yield by 48–73% in year 2 and 31–40% in year 1, with the lower dose (2 t ha⁻¹) providing sufficient agronomic benefits. In contrast, no yield response was observed in the Arenosol. In both soils, PG acted as a slow-release sulfur source, increasing straw sulfur concentrations in the second year. Even the repeated application of the highest PG dose (10 t ha⁻¹) did not increase Al, Cd, Cr, or Sr accumulation in wheat grain, indicating no treatment-related increase in trace-element accumulation. PG also increased soil microbial biomass and altered the microbial community structure in the Solonetz, including higher relative abundances of arbuscular mycorrhizal fungi and actinomycetes. Overall, these results demonstrate the dual agronomic function of PG in improving sodic soil productivity and supplying sulfur to nutrient-deficient sandy soils without increasing treatment-related trace-element accumulation, thus highlighting its potential as a soil amendment in sustainable nutrient management systems.

Soil microbial communities are crucial for ecosystem services, soil fertility, and the resilience of agroecosystems. This study investigated how long-term (31 years) agronomic practices—tillage, NPK fertilization, and cropping system—along with measured environmental variables influence the microbial biomass and its community composition in Chernozem soil under corn cultivation. The polyfactorial field experiment included three tillage treatments ((moldboard (MT), ripped (RT), strip (ST)), two fertilization regimes (NPK (N: 160; P: 26; K: 74 kg/ha), and unfertilized control) and two cropping systems (corn monoculture and corn–wheat biculture). The soil samples (0–30 cm) were collected in June and September 2023. Microbial biomass and community structure were quantified using phospholipid fatty acid (PLFA) analysis, which allowed the estimation of total microbial biomass and community composition (arbuscular mycorrhizal (AM) fungi, fungi, Gram-negative (GN) and Gram-positive (GP) bacteria, actinomycetes). Our results showed that microbial biomass increased from June to September, rising by 270% in unfertilized plots and by 135% in NPK-fertilized plots, due to higher soil moisture. Reduced tillage, especially ST, promoted significantly higher microbial biomass, with biomass reaching 290% and 182% of that in MT plots in June and September, respectively. MT had a higher ratio of bacteria-to-fungi compared to RT and ST, indicating a greater sensitivity of fungi to disturbance. NPK fertilization lowered soil pH by about one unit (to 4.1–4.8) and reduced microbial biomass—by 2% in June and 48% in September—compared to the control, with the particular suppression of AM fungi. The cropping system had a smaller overall effect on microbial biomass.

The development of critical levels for sap nitrate and chlorophyll meter reading (SPAD test) in the case of various crops is of great importance for growers in characterizing a plant’s N status. A field experiment with spring oat (Avena sativa L.) was carried out on loamy soil in Debrecen, Hungary, using a small-plot design. Ammonium nitrate was broadcast at rates of 0, 30, 60, and 90 kg N/ha in three replicates. The total N content of the plant, sap nitrate content, and SPAD values were measured at jointing when the first node appeared above the soil surface (Feekes 6) and at boot stage (Feekes 10). Regression analysis between total N content and sap nitrate showed cubic and linear relationships with r² = 0.7982 (Feekes 6, whole plant) and 0.9625 (Feekes 10, upper developed leaves), respectively. Optimal grain yield was obtained when sap nitrate exceeded 650 mg/L and 540 mg/L at Feekes 6 and Feekes 10, respectively. There were linear and logarithmic relationships between total N content and SPAD values with r² = 0.8058 and 0.6258 at Feekes 6 and 10. Optimal grain yield occurred over SPAD values of 43 and 48 at Feekes 6 and 10, respectively. Optimal N rate was 60 kg N/ha on the experimental site.

In this study the fertilizing effect of ZnEDTA (zinc ethylenediaminetetraacetate), and ZnSO4ּ 7H2O (ZnSO4ּ) (zinc sulphate heptahydrate) was compared on calcareous loam soil. A pot experiment was set up with maize (Zea mays L. var. ‘P37N01’). Plants were treated with basic NPK doses and with Zn at increasing rates: 0, 2.5, 5.0 and 10 mg kg-1 Zn in ZnEDTA and in ZnSO4 form, respectively. The ZnEDTA and ZnSO4 treatments increased the dry matter production compared to control by an average of 16%. Applying 2.5 mg kg-1 Zn, shoot Zn uptake was 1.3-fold greater by plants treated with ZnEDTA, than that of treated with ZnSO4. In the case of higher rates (5.0 mg kg-1 Zn and 10 mg kg-1 Zn), Zn uptake from ZnEDTA was approximately twice as much as that of ZnSO4. This result confirms that ZnEDTA as Zn complex is more effective than ZnSO4 on calcareous soil. The increasing ZnEDTA and ZnSO4 doses enhanced the soil’s initial diethylenetriaminepentaacetic acid (DTPA) Zn concentration to 1.8, 3.0, 6.3 mg kg-1 and 1.9, 3.5, and 6.5 mg kg-1, respectively. Contrary to our expectations, DTPA soil extractant was not able to indicate the difference in Zn availability between soils treated with ZnEDTA and ZnSO4. During the experiment, 0.6-1.7% of the added Zn doses were absorbed by the plants, and 48-59% of it could be measured back in the form of DTPA-Zn for both Zn fertilizers, the other half of the added Zn presumably converted to less available Zn forms.

The combined effects of increasing sulfur (S) fertilization rates and drought stress on the yield and compositional parameters of spring wheat on Chernozem soil were studied. In a greenhouse pot experiment, increasing S doses (22.4, 28, 56 kg S/ha) were used with a constant nitrogen (N) dose (112 kg N/ha), resulting in different N:S ratios (1:0.2; 1:0.25; 1:0.5). Water supply treatments included optimal irrigation, maintaining 60% of field capacity, and a water stress treatment where irrigation was withheld until wilting symptoms appeared, followed by irrigation to 40% of field capacity. By measuring the dry biomass production; plant N and S%; and inorganic sulfate-S content, the N/S ratio; harvest index (HI); and organic S, N and S uptake were determined. Our findings indicate that, under water stress, S incorporation into plants is limited, as it tends to remain in an inorganic form. Furthermore, results showed an increase in the N/S ratio under drought conditions, suggesting that drought stress impedes S uptake more significantly than N uptake. In this experiment, fertilization with 112 kg N/ha and 56 kg S/ha (N:S = 1:0.5) proved to be most effective under adequate water supply. In this treatment, grain N and S% were 1.80% and 0.18%, respectively.

The effects of intensive and reduced tillage, fertilization, and irrigation on soil chemical and microbiological parameters were studied in a long-term field experiment in Hungary. The treatments were plowing tillage, ripper tillage, strip tillage; control (without fertilization), NPK fertilization (N: 160 kg/ha; P: 26 kg/ha; K: 74 kg/ha); and non-irrigation and irrigation. Soil samples were collected through maize monoculture in the fall of 2021 in the 30th year of the experiment. The soil organic carbon, total nitrogen, soil microbial biomass (based on PLFA analysis), and soil enzyme activity were observed to be significantly high in the strip tillage plots, but were lower in the ripper tillage plots, and even lower in the plowing tillage plots. The fungal, arbuscular mycorrhiza fungal, and bacterial biomasses were significantly higher in the strip tillage and ripper tillage plots compared to the plowing tillage plots. The strip tillage treatment was found to be the most favorable cultivation method for improving the microbial biomass and activity of Chernozem soil, followed by the ripper tillage and plowing tillage treatments. The long-term use of chemical fertilizers greatly reduced the soil microbial biomass and negatively impacted the soil microbial community, leading to a decrease in fungi and Gram-negative bacteria. The ratio of cyclopropyl PLFA precursors to cyclopropyl PLFAs, as a “stress factor”, indicated the most stressful bacterial environment was that found in the fertilized, non-irrigated plowed soil.

The traditional Hungarian method for determining soil phosphorus (P) status is ammonium-lactate acetic acid (AL) extraction. AL is an acidic solution (buffered at pH 3.75), which is also able to dissolve P reserves, so there is a need for extraction methods that also characterize the mobile P pool. 0.01 M CaCl₂-P is considered to directly describe available P forms, because the dilute salt solution has more or less the same ionic strength as the average salt concentration in many soil solutions. The amount of AL-P may be two orders of magnitude greater than that of CaCl₂-P. Previous studies suggested that the relationship between AL-P and CaCl₂-P was influenced by soil parameters. Regression analysis between AL-P and CaCl₂-P showed medium or strong correlations when using soils with homogeneous soil properties, while there was a weak correlation between them for soils with heterogeneous properties. The objective of this study was to increase the accuracy of the conversion between AL-P and CaCl₂-P, by constructing universal equations that also take soil properties into consideration. The AL-P and CaCl₂-P contents were measured in arable soils (n=622) originating from the Hungarian Soil Information and Monitoring System (SIMS). These soils covered a wide range of soil properties. A weak correlation was found between AL-P and CaCl₂-P in SIMS soils. The amounts and ratio of AL-P and CaCl₂-P depended on soil properties such as CaCO₃ content and texture. The ratio of AL-P to CaCl₂-P changed from 37 in noncalcareous soils to 141 on highly calcareous soils. CaCl₂-P decreased as a function of K_A (plasticity index according to Arany), which is related to the clay content, while the highest AL-P content was found on loam soils, probably due to the fact that a high proportion of them were calcareous. The relationships between AL-P, CaCl₂-P and soil properties in the SIMS dataset were evaluated using multiple linear regression analysis. In order to select the best model the Akaike Information Criterion (AIC) was used to compare different models. The soil factors included in the models were pHKCl, humus and CaCO₃ content to describe AL-P, and K_A, CaCO₃ content and pH_KCl to describe CaCl₂-P. AL-P was directly proportional to pH_KCl, humus and CaCO₃ content, while CaCl₂-P was inversely proportional to K_A, CaCO₃ content and pH_KCl. The explanatory power of the models increased when soil properties were included. The percentage of the explained variance in the AL-P and CaCl₂-P regression models was 56 and 51%, so the accuracy of the conversion between the two extraction methods was still not satisfactory and it does not seem to be possible to prepare a universally applicable equation. Further research is needed to obtain different regression equations for soils with different soil properties, and CaCl₂-P should also be calibrated in long-term P fertilization trials.

The effect of wheat straw ash as a fertlizizer was studied in a pot experiment with an acidic sandy loam soil (pHKCl=4.9) with weak K and P supply. The test plant was ryegrass (Lolium perenne). The treatments were the following: 1. control untreated soil, 2. NPK fertilizer, 3. small dose of ash (1.4 g kg-1), 4 large dose of ash (2.8 g kg-1), 5. small dose ash completed with NP fertilizers. Soil parameters (pHH2O, pHKCl, ammoinum-lactate soluble P, K, 0.01 M CaCl2 soluble PO43--P, K, Mn, Cu, Zn ) and plant parameters (yield, P, K, Ca, Mg, Zn, Mn uptake) were investigated. Based on the analysis of the straw ash sample and the results of pot experiment it can be stated that the wheat straw ash is suitable for the fertilization of the studied soil. The small dose ash completed with NP resulted in the largest yield increment (43%). In order of the treatments the pHKCl changes to: 4.9, 4.8, 5.2, 5.8, 5.1. As the N : P2O5 : K2O ratio is 0 : 1: 3.5 in the wheat straw ash sample, to reach optimal yield ash should be completed with N and P.

The effects of nitrogen (N), phosphorus (P), and zinc (Zn) fertilization on the yield of ryegrass was studied in a greenhouse experiment. The treatment combination was set according to the Box–Wilson method. By performing multiple regression analysis, the yield was described as a function of fertilizer doses by a polynomial of the second degree. The R² value of the regression was 0.863. Based on the regression equation, we calculated the optimal fertilizer doses and evaluated the effects of fertilizers by means of three-dimensional graphs. According to the graphs, it can be stated that the yield-increasing effect of N is dominant, but P and Zn doses also influenced yield. The optimum concentrations of the doses were N, 120; P₂O₅, 89; and Zn, 2.8 mg kg⁻¹. Optimal dry matter (12–14 g pot⁻¹) can be produced with a large range of Zn and P concentrations and a relatively large N range. At doses more than the optimal dose for each element, a slight depression can be observed.

The effect of Zn fertilization on the yield and Zn, N, P, K, Mg and Mn content of ryegrass was studied in a greenhouse experiment for 8 chernozem soils with three replicates under uniform NPK supply and irrigation. The applied Zn rates were 0, 2.5 and 5 mg/kg Zn. Due to Zn doses the yield incrased significantly. Zn fertilization increased the plant Zn content and decreased the plant P and Mn content significantly. For N, K and Mg there was no significant effect.