Assessing the Effects of Nitrification Inhibitor DMPP on Acidification and Inorganic N Leaching Loss from Tea (<i>Camellia sinensis</i> L.) Cultivated Soils with Increasing Urea–N Rates

The effects of nitrification inhibitor in tea gardens with different urea–N rates have rarely been assessed. For eight months, a glasshouse experiment was conducted to investigate the effects of a nitrification inhibitor (3, 4–dimethylpyrazole phosphate, DMPP) on the changes of soil pH and inorganic N loss. Urea (0, 300, 500, and 800 kg N ha−1) with or without DMPP (1% of urea–N applied) were added to pots that hosted six plants that were three years old. Next, three leaching events were conducted with 600 mL of water after 7, 35, and 71 days of intervention while soil samples were collected to determine pH and inorganic N. Averaged across sampling dates, urea–N application at an increasing rate reduced soil pH with the lowest values at 800 kg urea–N ha−1. Adding DMPP increased soil pH up to a rate of 500 kg ha−1. Irrespective of the addition of DMPP, gradient urea–N application increased the leaching loss of inorganic N. On overage, DMPP increased soil pH and decreased leaching losses of total inorganic N, suggesting a higher soil N retention. Therefore, we believe that this increase in soil pH is associated with a relatively lower proton release from the reduced nitrification in the DMPP–receiving pots. This nitrification reduction also contributed to the N loss reduction (NO3−–N). Altogether, our results suggest that DMPP can reduce N leaching loss while maintaining the pH of tea–cultivated soils. Therefore, DMPP application has a significant potential for the sustainable N management of tea gardens

Synthetic nitrogen fertilizers alter the soil chemistry, production and quality of tea. A meta-analysis

The intensive use of synthetic nitrogen fertilizers over the last century has both increased agricultural productivity and modified biogeochemical cycles in terrestrial ecosystems, causing severe negative environmental impacts. Tea (Camellia sinensis L.) plantations usually receive high levels of synthetic fertilizers, which strongly affect plant and soil properties. However, there is no quantitative study to assess how synthetic N additions affect soil chemistry and the production and quality of tea shoots. Here, we conducted a comprehensive meta-analysis to evaluate the effects of experimental synthetic N fertilizers. Our main findings are (1) N additions in tea plantations acidify soils (-0.41 pH unit in average) and produce soil nutrient imbalance. Soil acidification commonly exacerbates the accumulations of toxic aluminum ions. (2) Synthetic N fertilizer additions may strongly increase tea production by almost 70% but alter tea shoot quality by increasing the concentrations of free amino acids (+ 16%), caffeine (+ 14%), and water extracts (+ 5%) while decreasing those of soluble sugars (-8%) in the tea shoots. The responses of soil chemistry, tea production, and quality to N additions can vary among experimental conditions, tea tree species, and N fertilizer forms. Because there is statistical limitation in this meta-analysis, our findings recommend performing additional field studies to explore the potential mechanisms of nutrient cycling and ecosystem functioning under synthetic N additions. The development of a sustainable N management strategy in tea plantations is also urgently needed to enhance N use efficiency and reduce environmental risks

Synthetic nitrogen fertilizers alter the soil chemistry, production and quality of tea. A meta-analysis

This file is supplementary material for the literature which was titled with "Synthetic nitrogen fertilizers alter the soil chemistry, production and quality of tea. A meta-analysis". The details including: Table S1 Database structure: numbers of publication and observation of each variable; Table S2 Detail information of the database for this meta-analysis; Table S3 Between-group heterogeneity (Qb) and probability (P value) of soil and tea variables with different experimental factors; Figure S1 Dependences of soil pH responses to soil initial pH (a) and N fertilizer addition levels (b); and Figure S2 Dependences of responses of free amino acids (a) and PP: AA ratio (b) to synthetic N addition levels

Effects of Soil Temperature and Moisture on Soil Respiration on the Tibetan Plateau - Fig 1

<p><b>Effects of incubation temperature (A) and incubation day (B) on soil respiration.</b> Mean ±se is shown in the figures. Different letters and * indicate significant difference at 0.05 level.</p

Relationships between soil respiration and root biomass under different treatments.

<p>T1M1: 5°C with 30% water holding capacity (WHC); T1M2: 5°C with 60% WHC; T2M1: 15°C with 30% WHC; T2M2: 15°C with 60% WHC; T3M1: 25°C with 30% WHC; and T3M2: 25°C with 60% WHC.</p

Concentrations of total carbon (TC), total nitrogen (TN), microbial biomass carbon (MBC) and nitrogen (MBN) and root biomass in 0–10 cm soil depth under different treatments.

<p>Concentrations of total carbon (TC), total nitrogen (TN), microbial biomass carbon (MBC) and nitrogen (MBN) and root biomass in 0–10 cm soil depth under different treatments.</p

Summary of repeated-measure ANOVAs for soil respiration using original treatments, soil temperature and soil moisture incubated as main factors.

<p>Summary of repeated-measure ANOVAs for soil respiration using original treatments, soil temperature and soil moisture incubated as main factors.</p

Temperature sensitivity (Q₁₀) of soil respiration under different original field treatments.

<p>C: no-warming with no-grazing; G: no-warming with grazing; W: warming without grazing; WG: warming with grazing. Mean ±se is shown in the figures. Different letters indicate significant difference at 0.05 level.</p

Dynamics of soil respiration over the incubation period under different treatments.

<p>(A) Combination of incubation temperature and soil moisture. (B) combination of original warming treatment and incubation temperature. T1M1: 5°C with 30% water holding capacity (WHC); T1M2: 5°C with 60% WHC; T2M1: 15°C with 30% WHC; T2M2: 15°C with 60% WHC; T3M1: 25°C with 30% WHC; and T3M2: 25°C with 60% WHC. NWT1: no-warming with 5°C incubation; NWT2: no-warming with 15°C incubation; NWT3: no-warming with 25°C incubation; WT1: warming with 5°C incubation; WT2: warming with 15°C incubation; WT3: warming with 25°C incubation; Mean±se in the figures. Different letters indicate significant difference at 0.05 level.</p

Appendix B. Figures showing dynamics of rainfall and air temperature, mean soil temperature and soil moisture at 10 cm, mean frequency and coverage of different plant species during the 5-year experiment under warming and grazing treatments, and aboveground net primary production of natural alpine Kobresia meadow and an annual oat crop under nitrogen fertilization.

Figures showing dynamics of rainfall and air temperature, mean soil temperature and soil moisture at 10 cm, mean frequency and coverage of different plant species during the 5-year experiment under warming and grazing treatments, and aboveground net primary production of natural alpine Kobresia meadow and an annual oat crop under nitrogen fertilization