Effect of elevated tropospheric ozone on soil carbon and nitrogen: A meta-analysis

Elevated tropospheric ozone concentration ([O3]) may substantially influence the belowground processes of the terrestrial ecosystem. Nevertheless, a comprehensive and quantitative understanding of the responses of soil C and N dynamics to elevated [O3] remains elusive. In this study, the results of 41 peer-reviewed studies were synthesized using meta-analytic techniques, to quantify the impact of O3 on ten variables associated with soil C and N, i.e., total C (TC, including soil organic C), total N (TN), dissolved organic C (DOC), ammonia N (NH4 +), nitrate N (NO3 -), microbial biomass C (MBC) and N (MBN), rates of nitrification (NTF) and denitrification (DNF), as well as C/N ratio. The results depicted that all these variables showed significant changes (P < 0.05) with [O3] increased by 27.6 ± 18.7 nL/L (mean ± SD), including decreases in TC, DOC, TN, NH4 +, MBC, MBN and NTF, and increases in C/N, NO3 - and DNF. The effect sizes of TN, NTF, and DNF were significantly correlated with O3 fumigation level and experimental duration (P < 0.05). Soil pH and climate were essential in analyses of O3 impacts on soil C and N. However, the responses of most variables to elevated [O3] were generally independent of O3 fumigation method, terrestrial ecosystem type, and additional [CO2] exposure. The altered soil C and N dynamics under elevated [O3] may reduce its C sink capacity, and change soil N availability thus impact plant growth and enhance soil N losses.

Strong Interactive Effects of Warming and Insect Herbivory on Soil Carbon and Nitrogen Dynamics at Subarctic Tree Line

Warming will likely stimulate Arctic primary production, but also soil C and N mineralization, and it remains uncertain whether the Arctic will become a sink or a source for CO2. Increasing insect herbivory may also dampen the positive response of plant production and soil C input to warming. We conducted an open-air warming experiment with Subarctic field layer vegetation in North Finland to explore the effects of warming (+3°C) and reduced insect herbivory (67% reduction in leaf damage using an insecticide) on soil C and N dynamics. We found that plant root growth, soil C and N concentrations, microbial biomass C, microbial activity, and soil NH4+ availability were increased by both warming and reduced herbivory when applied alone, but not when combined. Soil NO3– availability increased by warming only and in-situ soil respiration by reduced herbivory only. Our results suggest that increasing C input from vegetation under climate warming increases soil C concentration, but also stimulates soil C turnover. On the other hand, it appears that insect herbivores can significantly reduce plant growth. If their abundance increases with warming as predicted, they may curtail the positive effect of warming on soil C concentration. Moreover, our results suggest that temperature and herbivory effects on root growth and soil variables interact strongly, which probably arises from a combination of N demand increasing under lower herbivory and soil mineral N supply increasing under higher temperature. This may further complicate the effects of rising temperatures on Subarctic soil C dynamics.

Toward greater sustainability: how investing in soil health may enhance maize productivity in Southern Africa

Climate change and soil fertility decline are major threats to smallholder farmers' food and nutrition security in southern Africa, and cropping systems that improve soil health are needed to address these challenges. Cropping systems that invest in soil organic matter, such as no-tillage (NT) with crop residue retention, have been proposed as potential solutions. However, a key challenge for assessing the sustainability of NT systems is that soil carbon (C) stocks develop over long timescales, and there is an urgent need to identify trajectory indicators of sustainability and crop productivity. Here we examined the effects of NT as compared with conventional tillage without residue retention on relationships between soil characteristics and maize (Zea mays L.) productivity in long-term on-farm and on-station trials in Zimbabwe. Our results show that relationships between soil characteristics and maize productivity, and the effects of management on these relationships, varied with soil type. Total soil nitrogen (N) and C were strong predictors of maize grain yield and above-ground biomass (i.e., stover) in the clayey soils, but not in the sandy soils, under both managements. This highlights context-specific benefits of management that fosters the accumulation of soil C and N stocks. Despite a strong effect of NT management on soil C and N in sandy soils, this accrual was not sufficient to support increased crop productivity in these soils. We suggest that sandy soils should be the priority target of NT with organic resource inputs interventions in southern Africa, as mineral fertilizer inputs alone will not halt the soil fertility decline. This will require a holistic management approach and input of C in various forms (e.g., biomass from cover crops and tree components, crop residues, in combination with mineral fertilizers). Clayey soils on the other hand have greater buffering capacity against detrimental effects of soil tillage and low C input.

Distribution and soil carbon stocks of agroforestry vegetation on dry land in Aceh Besar regency

Research to find out how big the potential of soil carbon in agroforestry vegetation in Aceh Besar regency. This research was conducted on agroforestry vegetation on dry land in the Aceh Besar regency. Content carbon on the type of agroforestry land-use, two samples were taken each composite soil on depth 0-5 cm, 5-10 cm, 10-20 cm, 20-30 cm, 30-70 cm and 70-100. For the analysis of carbon content, activities are carried out in the soil laboratory and plants of the Faculty of Agriculture, Syiah Kuala University. The carbon content in agroforestry vegetation is quite high, and this can be described in the percentage of carbon which has a classification from high to very low. Soil depth 0-5 cm has a carbon percentage with a high classification value of 3.40 and at a depth of 30-70 cm has the lowest % C value of 0.35% with a very low classification. tends to increase soil C and N through increased root complementarity, lower underground competition.

Soil carbon and nitrogen regulation using organic and inorganic fertilizers for leaf physiological activity, grain yield and nutritional quality improvements in rice

Organic fertilizers are widely used in agriculture production and change the soil carbon (C) and nitrogen (N) contents, thus improving crop production. The increased amount of soil C and N exhibit a greater potential to improve the leaf physiological activity, yields and grain quality of rice by improving soil fertility indices. To understand the relationship between soil C and N contents with leaf physiological activity and grain quality; organic fertilizers (i.e., cattle manure (CM) and poultry manure (PM)) coupled with chemical fertilizer (CF) was applied at the different proportion. The recommended rate of N 150 (kg ha−1) was provided from manure and CF using six treatments, i.e., T1— CF0; T2—100% CF; T3—60% CM + 40% CF; T4—30% CM + 70%CF; T5—60% PM + 40% CF, and T6—30% PM + 70% CF. Results showed that soil organic C (SOC), total N (TN), leaf net photosynthetic rate (Pn), SPAD values, grain yield and grain quality attributes were significantly increased with combined organic and inorganic fertilizer application. Averaged over the years, T6 treatment significantly improved SOC, TN, Pn, starch content (SC), amylose content (AC), and grain yield by 16%, 12%, 9%, 7%, 12%, and 24%, respectively, compared to CF-only. However, no significant differences among T4 and T6 were observed for studied parameters. In addition, the linear regression exhibited that SOC (R2= 0.70** & R2=0.50*) and TN (R2= 0.62* & R2=0.58*) were positively correlated with grain SC and AC, respectively. Likewise, Pn (R2= 0.51* & R2=0.62*) were also positively associated with SC and AC, respectively. The correlation analysis showed that improving SOC and TN played a key role in enhancing leaf physiological activity and grain nutritional quality. Thus, the combination of organic and inorganic fertilizers at a 30:70 ratio is a promising option for the improvement of soil fertility and grain yield of rice as well as grain nutritional traits.