The Operating Characteristics of Partial Nitrification by Controlling pH and Alkalinity

In many experiments, a partial nitrification device is initiated with the use of highly active nitrating sludge because of the large number of nitrifying bacteria. Ammonia-oxidizing bacteria (AOB) are more adaptable to low-dissolved oxygen environments than nitrite-oxidizing bacteria (NOB). NOB activity was inhibited when the dissolved oxygen (DO) levels were decreased, causing the nitrate-nitrogen concentration to gradually decrease in the effluent and the nitrite-nitrogen concentration to gradually increase, achieving the accumulation of nitrous nitrogen. In this experiment, a sequencing batch reactor (SBR) was used to suppress NOB activity at a given pH while maintaining DO at a very low level so that the ammonia–water reaction mainly occurred in the device, and then the mud and water separated. Compared with other experiments, this approach can occur in 25 days, and it runs stably for more than two months until the device closes when the ammonia-nitrogen concentration is about 170 mg/L. This experiment also compared the difference between the pH change at the beginning of the device operation and after the device was stable. In order to increase the efficiency of bacterial appreciation, supplementing NaHCO3 increased the HCO3− concentration by 300 mg/L on the 25th day. It was found that some nitrification reactions still occurred, but they were not enough to destabilize the device. The nitrosate accumulation efficiency still gradually increased, and the average nitrite accumulation efficiency was 87.25% after NaHCO3 supplementation.

Seedling growth, root development and nutrient use efficiency of Cypress clones in response to calcium fertilizer

Background: Cypress (Cupressus funebris Endl.) is an important tree species in the subtropics of China, it is also a major tree species for afforestation and forest land restoration under infertile site conditions. Cypress is considered to be a calcicolous tree, whose there are growth and development can be promoted significantly by exchangeable Calcium (Ca2+) in the soil. However, most of the subtropical regions have infertile acidic soils, in which Ca2+ gradually becomes a limiting element for cypress growth. Results: In this study, different concentrations of Ca2+ fertilizer were added under fertile and infertile soil conditions. Cypress clones responded differently to Ca2+ addition in different soil conditions. In the infertile soil, the addition of 3 g•kg− 1 Ca2+ advanced and prolonged the fast-growing period of seedling height growth, increased plant height and dry biomass, promoted the development of fine roots ≤ 1.5 mm in diameter, and improved accumulation efficiencies of nitrogen (N), phosphorous (P) and Ca by the roots in cypress clones; however, the addition of 6 g•kg− 1 Ca2+ inhibited height growth and root development of cypress. In the fertile soil, Ca2+ addition delayed and shortened the fast-growing period for cypress height growth, but plant height and dry biomass did not differ significantly between treatments; Ca2+ addition also inhibited the development of fine roots. The clone with fast height growth had a larger proportion of roots with a diameter ≤ 1.5 mm and achieved higher N accumulation efficiency, while Ca accumulation efficiency showed genotypic differences only in the fertile soil. Conclusions: An appropriate level of Ca2+ can be added to infertile soil to promote cypress seedling growth, and clones with fast height growth and developed fine roots can be selected for cultivation and promotion in the fertile soil without Ca2+ application.

The potential for full inversion tillage to increase soil carbon storage following pasture renewal in New Zealand

<p><span>The global atmospheric concentration of CO<sub>2</sub> and other greenhouse gases (GHG) is steadily increasing. It is estimated that, worldwide, soil C sequestration could offset GHG emissions by 400–1200 Mt C per year. Relative to 1990, New Zealand’s CH<sub>4</sub> and N<sub>2</sub>O emissions in 2013 had increased by 7% and 23% respectively, which translates to an annual emission increase of 1.09 Mt C that could be offset by a similar annual increase in soil C stock. Recent research has shown that some New Zealand pastoral soils are under-saturated in SOC. Subsurface soils (15–30 cm depth) typically have a greater soil C saturation deficit than topsoil (0-30 cm) because plant C inputs (roots) are lower. Using management practices that expose more of the under-saturated soil to higher C inputs could result in increased soil C storage and stabilisation.</span></p><p><span>Pasture renewal (destruction and re-establishment of pasture) is promoted to livestock farmers to improve pasture performance. This typically involves shallow cultivation or direct drilling to establish new grass. Whereas shallow cultivation of soil typically results in a loss of SOC, deeper full inversion tillage (FIT) of soil would result in the burial of C-rich topsoil in closer proximity to mineral material that has a higher stabilisation capacity.  Buried SOC is expected to have a slower decomposition rate owing to less variable temperatures and more anoxic conditions. Deep FIT would also bring under-saturated mineral soil to the surface, where the deposition of SOC from high producing pastures could increase the stabilisation of SOC.  Both the slower turnover of buried SOM and greater stabilisation of new carbon on under-saturated minerals at the soil surface are expected to result in increased SOC sequestration. </span></p><p><span>There is a lack of experimental data to directly address the effect of FIT on soil C stocks in pastoral soils. We applied a simple empirical model to predicting changes in soil C stocks following a one-off application of FIT (30 cm) during pasture renewal. The model accounts for the decomposition of SOC in buried topsoil and the accumulation of C in the new topsoil (inverted subsoil). The model was used to derive national estimates of soil C sequestration under different scenarios of C accumulation efficiency, farmer adoption of FIT and pasture renewal rates.</span></p><p>Our modelled estimates suggest that 32 Mt C could be sequestered over 20 years following a one-time application of FIT (0-30 cm) to 2 M ha of High Producing Grasslands on suitable New Zealand soils. This estimate is based on 100% accumulation efficiency (i.e. topsoil C stocks are returned to pre-inversion levels within 20 years) and a 10% annual rate of pasture renewal. In the absence of direct experimental evidence, a more conservative estimate is warranted, where topsoil C stocks are projected to return to 80% of pre-inversion levels, thus sequestering 20 Mt C. This paper will present our modelled estimates of SOC sequestration during FIT pasture renewal and discuss the potential benefits and adverse effects of deploying this management practice.</p>

Seedling growth, root development and nutrient use efficiency of Cypress clones in response to calcium fertilizer

Cypress (Cupressus funebris Endl.) is an important tree species in the subtropical regions of China; it is also a major tree species for afforestation and forest land restoration under low-fertility soil conditions. Cypress is considered a calcicolous tree, and its growth and development can be promoted significantly by exchangeable calcium (Ca2+) in the soil. However, most of the subtropical regions have low-fertility acidic soils, in which Ca2+ gradually becomes a limiting element for Cypress growth. In this study, different concentrations of Ca2+ fertilizer were added under fertile soil (3 g·kg-1 NPK fertilizer added) and low-fertility soil (0 g·kg-1 NPK fertilizer added) conditions. Cypress clones responded differently to Ca2+ addition in different soil conditions. The seedling height and dry matter quality of Cypress in fertile soil were significantly greater than those in low-fertility soil, but plant height and dry biomass did not differ significantly among Ca2+ treatments. The accumulation efficiencies of nitrogen (N), phosphorous (P) and Ca all differed significantly among the Ca2+ treatments. In low-fertility soil, the addition of 3 g·kg-1 Ca2+ significantly promoted development of roots 0.5–2 mm in diameter, and both the C1 and C2 clones achieved their highest N, P and Ca accumulation efficiencies. When the Ca2+ concentration increased to 6 g·kg-1, the seedling height, dry matter quality and root development were lower than those of the 3 g·kg-1 Ca2+ treatment. In the fertile soil, the addition of Ca2+ significantly inhibited development of roots 0.5–1 mm in diameter. The highest N accumulation efficiency was achieved under the 0 g·kg-1 Ca2+ treatment, and the highest Ca accumulation efficiency was achieved under the 6 g·kg-1 Ca2+ treatment. Seedling height, root dry weight, roots 0–1.5 mm in diameter and Ca accumulation showed a significant interaction effect between NPK fertilizer and Ca2+. Therefore, Ca accumulation was more efficient in low-fertility soils. Under low-fertility soil conditions, the addition of CaSO4 can promote the root development of seedlings and advance and prolong the fast growth period of seedling height. Cypress clones can be used as an important tree species for afforestation under low-fertility soil conditions, especially under calcareous soil conditions.

The species-specific responses of nutrient resorption and carbohydrate accumulation in leaves and roots to nitrogen addition in a subtropical mixed plantation

Ephemeral tissues such as leaves and fine roots are sensitive to nutrient alteration. Whether nutrient addition can influence the linkage between nutrient resorption and carbohydrate accumulation in leaves and roots is not clear. We measured nitrogen (N) and phosphorus (P) concentrations and nonstructural carbohydrates (NSC) of the <one- and >one-year-old leaves and absorptive and transportive roots in two species of a mixed plantation during the dormant and growing seasons within an N-addition experiment. Nitrogen addition decreased N and P resorption efficiencies (NRE and PRE, respectively) in leaves of Chinese fir and increased PRE in absorptive roots of Chinese fir but did not alter either efficiency in any tissues of Chinese sweetgum. Nitrogen addition increased starch accumulation efficiency (STAE) in >one-year-old leaves of Chinese fir but decreased soluble sugar accumulation efficiency (SSAE) in absorptive roots of Chinese sweetgum. Both NRE and PRE were negatively correlated with SSAE, STAE, and NSC accumulation efficiency (NSCAE) in >one-year-old leaves of Chinese fir, but this pattern was not found in leaves of Chinese sweetgum. Our study indicates that N addition can influence the linkage between nutrient resorption and NSC in leaves and roots, and this response to nutrient availability is species-dependent.