GROWTH, YIELD COMPONENTS AND CHEMICAL CONSTITUENTS OF Stevia rebaudiana Bert. AS AFFECTED BY HUMIC ACID AND NPK FERTILIZATION RATES

Stimulating growth, root quality, and yield of carrots cultivated under full and limited irrigation levels by humic and potassium applications

Water stress poses a significant challenge for carrot cultivation, leading to decreased yield and inefficient water use efficiency. Therefore, it is crucial to provide plants with suitable supplements that enhance their stress resistance. In this study, we investigated the effectiveness of humic and potassium applications on carrot growth, yield characteristics, root quality, and water use efficiency under varying irrigation levels. A split-split plot experiment was conducted, with two levels of gross water requirements (GWR) (100% and 80%) assigned to the main plots. The subplots were treated with humic acid through foliar application (Hsp) or soil drenching (Hgd). The sub-subplots were further divided to assess the impact of foliar potassium sources (potassium humate, Kh) and mineral applications (potassium sulfate, K2SO4). The results revealed a substantial reduction in carrot yield under limited irrigation, reaching about 32.2% lower than under GWR100%. Therefore, under limited irrigation conditions, the combined application of Hgd and K2SO4 resulted in a significant yield increase of 78.9% compared to the control under GWR80%. Conversely, under GWR100%, the highest average yield was achieved by applying either Hsp and Kh or Hsp and K2SO4, resulting in yields of 35,833 kg ha-1 and 40,183 kg ha-1, respectively. However, the combination of Hgd and Kh negatively affected the yield under both GWR100% and GWR80%. Nonetheless, applying Kh in combination with Hgd under GWR80% led to improved nitrogen, phosphorus, potassium, potassium/sodium ratio, and total sugar concentrations, while reducing sodium content in carrot roots. Based on this study, it is recommended to adopt GWR80% and treat plants with a combination of Hgd and foliar K2SO4. This approach can help plants overcome the negative effects of water stress, improve yield and root quality, and achieve optimal water use efficiency.

Effect of phosphorus-loaded biochar and nitrogen-fertilization on release kinetic of toxic heavy metals and tomato growth

In this study, we investigate the effect of nitrogen fertilizer application rates with and without phosphorus-loaded biochar (BCP) on the productivity of tomato (Solanum lycopersicum cv GS) planted on a contaminated soil based on pot and incubation experiments. The release kinetic of toxic metals as affected by BCP was also investigated. BCP at rate of 2% (w/w) and nitrogen levels (250 and 500 mg N kg^-1) were added to sandy loam soil polluted with Cd, Pb, Zn, and Cu. The experiment consisted of five treatments including: Control (C), nitrogen a rate of 250 (N₂₅₀), or 500 mg kg (N₅₀₀), BCP + N₂₅₀, and BCP + N₅₀₀. Maximum tomato growth was achieved in the soil that was treated with BCP + N₅₀₀, followed by BCP + N₂₅₀, while lowest one was observed in the control. Tomato yield as affected by the BCP and N-fertilization was in the descending order: BCP + N₅₀₀ > BCP + N₂₅₀ > N_{500 =} N₂₅₀ > C. The addition of N₂₅₀, N₅₀₀, BCP + N₂₅₀, and BCP + N₅₀₀ increased the fruit yield by 24, 31, 35, 58% in comparison with the control. Levels of Zn, Cu, and Pb in tomato fruit was in the descending order: N₅₀₀> N₂₅₀ > C > BCP + N₅₀₀ > BCP + N₂₅₀. The combined application of BCP and N-fertilization augmented the availability and uptake of essential nutrients and effectively reduced those of toxic ones. The addition of BCP + N₂₅₀ decreased Zn, Cu, Cd, and Pb content in fruit of tomato by 16, 10, 54, 54, and 58%, respectively, compared to the control soil, while these decreases were 13, 16, 60, 60, and 72% in the case of BCP + N₅₀₀. BCP succeeded significantly in reducing the release of toxic chemicals, which ultimately may restrict the transfer of toxic chemical to the food chain solution. Novelty statement Tomato grown on metal-contaminated soils contains high levels of toxic metals. Phosphorus-loaded biochar (BCP) reduced the negative effects of high inorganic-N rates by reducing the release of toxic metals to the soil solution. BCP enhanced the soil quality indicators and increased the soil microbe's activity.

Biochar and compost enhance soil quality and growth of roselle (Hibiscus sabdariffa L.) under saline conditions

Soil amendments may increase the slate tolerance of plants consequently; it may increase the opportunity of using saline water in agricultural production. In the present pot trial, the effects of biochar (BIC) and compost (COM) on roselle (Hibiscus sabdariffa L.) irrigated with saline water (EC = 7.50 dS m^-1) was studied. Roselle plants were amended with biochar (BIC₁ and BIC₂) or compost (COM₁ and COM₂) at rates of 1 and 2% (w/w), as well as by a mixture of the two amendments (BIC₁+). The experiment included a control soil without any amendments. Biochar and compost significantly enhanced the soil quality and nutrients availability under saline irrigation. Compost and biochar improved the degree of soil aggregation, total soil porosity and soil microbial biomass. BIC₁ + COM₁ increased the soil microbial biomass carbon and nitrogen over the individual application of each amendments and control soil. BIC₁ + COM₁ increased the activity of dehydrogenase and phosphatase enzymes. Growth of roselle plants including: plant height, shoot fresh and dry weight, and chlorophyll were significantly responded to the added amendments. The maximum sepal's yield was achieved from the combined application of compost and biochar. All the investigated treatments caused remarkable increases in the total flavonol and anthocyanin. BIC₁ + COM₁ increased the total anthocyanin and flavonol by 29 and 17% above the control. Despite the notable improvement in soil and roselle quality as a result of the single addition of compost or biochar, there is a clear superiority due to mixing the two amendments. It can be concluded that mixing of biochar and compost is recommended for roselle plants irrigated with saline water.