Soil Organic Carbon Mineralization and Its Temperature Sensitivity under Different Substrate Levels in the Mollisols of Northeast China

Effects on soil carbon storage from municipal biosolids application to agricultural fields

This study investigated the influence of biosolid applications on soil carbon storage and evaluated nutrient management strategies affecting soil carbon dynamics. The research assessed alterations in soil pH, soil carbon stock, and soil nitrogen content within short-term and long-term biosolids-amended soils in Bible Hill, Nova Scotia, Canada, extending to a depth of 0-60 cm. The findings indicated an increase in soil pH with alkaline treatment biosolids (ATB) applications across both study sites, with a legacy effect on soil pH noted in the long-term biosolids-amended soil following a single ATB application over 13 years. Both sites demonstrated significant increases in soil total carbon (STC) and soil organic carbon (SOC) within the 0-30 cm soil depth after biosolid application, and soil inorganic carbon (SIC) accounted for approximately 5-10% of STC, specifically in the surface soil layer (0-15 cm). In the long-term study site, annual 14, 28 and 42 Mg ATB ha-1 treatments resulted in a substantial rise in soil carbon stock (59.5, 60.1 and 68.0 Mg C ha-1), marking a 25% increase compared to control soil. The SOC content in biosolids-amended soil showed a declining trend with increasing soil depth at both study sites. Notably, the carbon stock in the short-term site was observed in composted biosolids (COMP) > ATB > liquid mesophilic anaerobically digested biosolids (LMAD) from the 0-60 cm soil depth. Approximately 79-80% of the variation in SOC response at both sites was concentrated within the top 30 cm soil. Soil total nitrogen (STN) showed no significant differences at the short-term site, and STN in biosolids-amended soil decreased with increasing soil depth at the long-term site. Biosolids-induced C retention coefficients (BCR) for ATB remained consistent at both sites, ranging from -13% to 31.4% with a mean of 11.12%. BCR values for COMP ranged from 1.9% to 34.4% with a mean of 18.73%, while those for LMAD exhibited variability, spanning from -6.2% to 106.3% with a mean of 53.9%.

Nitrates directive restriction: To change or not to change in terms of climate change, that is the question

The positive effect of nitrogen fertilization in agriculture inevitably increases residual nitrogen losses. Water pollution led to legal restrictions of some farm practices within the framework of the Nitrates Directive of the EU. Nevertheless, even several decades later, the situation has not improved significantly. We present a possible science-based explanation of such a state and provide it to farmers and government as a support for environmental management settings. This study aimed to compare an established approach to implementing the Nitrates Directive, specifically the climate-based zoning of nitrogen fertilization restrictions using data from the mid-20th century. We evaluated this approach by juxtaposing the initial climate data with more recent data spanning from 1991 to 2020. Subsequently, we examined this zoning framework from the perspective of the non-vegetative period, characterized by temperatures below 5 °C, which is widely acknowledged as a critical threshold for nitrogen intake by plants. We found out that i) the employed climate-born zoning does not correspond to recent climate data; ii) nonvegetation period is longer than nitrogen fertilization restrictions. Therefore, despite a noteworthy 22 day reduction in the nonvegetation period from 1961/1962 to 2019/2020, we cast doubt on the notion that the period limiting nitrogen fertilizer application should also be shortened, while admitting that there are other abiotic and biotic factors affecting nitrogen behaviour within the ecosystem.

Organic fertilizer type and dose affect growth, morphological and physiological parameters, and mineral nutrition of watermelon seedlings

Background

Organic agriculture has grown rapidly in recent years due to its environmental friendliness, sustainability, and improved farm profitability. Transplants are commonly used for fruits and vegetables to achieve consistent quality, uniformity, and easy field spacing control. The efficacy and optimal amounts of fertilizers for organic transplant production need to be investigated.

Methods

The effects of three organic fertilizers (Sustane 4-6-4, Nature Safe 7-7-7, and Dramatic 2-4-1) and one conventional fertilizer Peters Professional 20-20-20 (Conventional) with four doses (nitrogen (N) content was matched among fertilizers in each level, as 0.14 g/L, 0.28 g/L, 0.56 g/L, and 0.84 g/L N, respectively) on watermelon seedlings were compared in this study.

Results

The results showed that all organic fertilizer treatments were not significantly different from the Conventional group in terms of watermelon germination. The only exception was the highest dose of Sustane 4-6-4 (0.84 g/L N) which decreased the germination rate and relative emergence index. Generally, growth index, shoot fresh and dry weights, true leaf number, and stem diameter increased as the amount of N increased within each fertilizer type. The best shoot growth was observed in the highest doses of Conventional and Dramatic 2-4-1 treatments (0.84 g/L N). However, Dramatic 2-4-1 treatments resulted in the lowest root growth when compared to other fertilizers at the same N dose. The second highest fertilization dose (0.56 g/L N) of Sustane 4-6-4 had the best root growth according to root fresh weight, root volume, root area, total root length, as well as the numbers of root tip and crossing when compared to other treatments. For seedlings, a well-developed root system can ensure a good seedling establishment and high survival rate under stressful field conditions after transplanting. Thus, Sustane 4-6-4 at 14 g/L (0.56 g/L N) is recommended to produce high-quality organic watermelon seedlings among the treatments applied in this study.