Gabrijel Ondrasek

Increase in the concentration of atmospheric greenhouse gases significantly contributes to global warming, representing a substantial challenge for crop production. The study was conducted to determine the growth competition between rice (Oryza sativa) and barnyardgrass (Echinochloa oryzicola) under (i) different cropping patterns and (ii) elevated air temperatures in phytotrons under field condition, at two plant densities (4 and 16 plants per pot). Rice and barnyardgrass were planted with varying cropping patterns (rice: barnyardgrass mixture proportions); 100:0, 75:25, 50:50, 25:75 and 0:100. Air temperatures were maintained in phytotrons as follows: Ambient–A (Control), A +0.8 °C, A +1.9 °C and A +3.4 °C. Plant attributes such as plant height, number of effective tillers, shoot dry weight and grain yield of rice were recorded in this study in the rice/barnyardgrass mixture proportions in the order of 100:0 > 75:25 > 50:50 > 25:75. The highest rice grain yield (37.7 g/pot) was recorded in the monoculture (100:0 rice/barnyardgrass) under ambient temperature, whereas the lowest rice grain yield (0.3 g/pot) was recorded at the 25:75 rice/barnyardgrass mixture proportion under ambient +3.4 °C. The increase in temperature had a significant impact on growth, number of tillers and shoot dry weight of both rice and barnyardgrass plants and followed the order of ambient +3.4 °C > ambient +1.9 °C > ambient +0.8 °C > ambient. However, higher temperature negatively affected the yield of rice and resulted in a substantial decrease in the grain yield. Barnyardgrass showed the highest plant characteristics when grown alongside rice compared to the growth in monoculture. This indicates that barnyardgrass was highly competitive when grown under interspecific competition compared to an intraspecific competition. In contrast, rice grew better in monoculture than in mixture with barnyardgrass.

In polder-type land, water dynamics are heavily influenced by the artificial maintenance of water levels. Polders are low-lying areas of land that have been reclaimed from the sea or from freshwater bodies and are protected from flooding by dikes or other types of flood-protection structures. The water regime in polders is typically managed using a system of canals, pumps, and sluices to control the flow of water in and out of the area. In this study, the temporal changes in water salinity in the polder-type agricultural floodplain within the Neretva River Delta (NRD), Croatia, were analyzed by applying multivariate statistics and forecast modelling. The main aim of the study was to test the model that can be used in practice to forecast, primarily, water suitability for irrigation in a coastal low-lying agricultural catchment. The specific aim of this study was to use hydrochemistry data series to explain processes in water salinity dynamics and to test the model which may provide accurate salinity prediction, or finally select the conditions in which the model can be applied. We considered the accuracy of the model, and it was validated using independent data sets. To describe different patterns of chemical changes in different water classes due to their complex hydrological connectivity, multivariate statistics (PCA) were coupled with time-series analysis and Vector Autoregression (VAR) model forecasting. The multivariate statistics applied here did not indicate a clear connection between water salinity of the surface-water bodies and groundwater. The lack of correlation lies in the complex hydrological dynamics and interconnectivity of the water bodies highly affected by the artificial maintenance of the groundwater level within the polder area, as well as interventions in the temporal release of freshwater into the drainage canal network. Not all individual water classes contributed equally to the dominant patterns of ionic species identified by PCA. Apparently, land use and agricultural management practices in the different polders lead to uneven water chemistry and the predominant contributions of specific ions, especially nutrients. After applying the Granger causality test to reveal the causal information and explain hidden relationships among the variables, only two surface-water and two groundwater monitoring locations displayed a strong causal relationship between water electrical conductivity (ECw) as an effect and sea level as a possible cause. The developed models can be used to evaluate and emphasize the unique characteristics and phenomena of low-lying land and to communicate their importance and influence to management authorities and agricultural producers in managing and planning irrigation management in the wider Mediterranean area.

Recently, nanomaterials have received considerable attention in the agricultural sector, due to their distinctive characteristics such as small size, high surface area to volume ratio, and charged surface. These properties allow nanomaterials to be utilized as nanofertilizers, that can improve crop nutrient management and reduce environmental nutrient losses. However, after soil application, metallic nanoparticles have been shown to be toxic to soil biota and their associated ecosystem services. The organic nature of nanobiochar (nanoB) may help to overcome this toxicity while maintaining all the beneficial effects of nanomaterials. We aimed to synthesize nanoB from goat manure and utilize it with CuO nanoparticles (nanoCu) to influence soil microbes, nutrient content, and wheat productivity. An X-ray diffractogram (XRD) confirmed nanoB synthesis (crystal size = 20 nm). The XRD spectrum showed a distinct carbon peak at 2θ = 42.9°. Fourier-transform spectroscopy of nanoB’s surface indicated the presence of C=O, C≡N–R, and C=C bonds, and other functional groups. The electron microscopic micrographs of nanoB showed cubical, pentagonal, needle, and spherical shapes. NanoB and nanoCu were applied alone and as a mixture at the rate of 1000 mg kg−1 soil, to pots where wheat crop was grown. NanoCu did not influence any soil or plant parameters except soil Cu content and plant Cu uptake. The soil and wheat Cu content in the nanoCu treatment were 146 and 91% higher, respectively, than in the control. NanoB increased microbial biomass N, mineral N, and plant available P by 57, 28, and 64%, respectively, compared to the control. The mixture of nanoB and nanoCu further increased these parameters, by 61, 18, and 38%, compared to nanoB or nanoCu alone. Consequently, wheat biological, grain yields, and N uptake were 35, 62 and 80% higher in the nanoB+nanoCu treatment compared to the control. NanoB further increased wheat Cu uptake by 37% in the nanoB+nanoCu treatment compared to the nanoCu alone. Hence, nanoB alone, or in a mixture with nanoCu, enhanced soil microbial activity, nutrient content, and wheat production. NanoB also increased wheat Cu uptake when mixed with nanoCu, a micronutrient essential for seed and chlorophyll production. Therefore, a mixture of nanobiochar and nanoCu would be recommended to farmers for improving their clayey loam soil quality and increasing Cu uptake and crop productivity in such agroecosystems.