Soil nitrogen activation (Nact) is pivotal for the global N cycle, influencing crop N availability and environmental N losses. However, it remains unclear how climate and fertilization individually, or jointly, affect soil Nact over multiple decades. Here, we examined the dynamic shifts in Nact between the first decade and later period in soils treated with non-fertilizer, mineral fertilizer with/without manure, mineral fertilizer with stover return, in 1982 and 1990, in six typical agricultural zones. Results revealed that soil total N (TN) and available N (AN) increased at rates of 10.1–58.2 and 1.41–4.13 mg kg–1 yr–1, respectively, by manure application at five sites, suggesting that manure enhanced both soil N storage and availability. The GZL site exhibited the highest annual change rate (ACR) in TN (48.3–58.2 mg kg–1 yr–1), while the ZY site had the lowest (10.1 mg kg–1 yr–1). Conversely, the YL site showed the highest ACR in AN (3.65–4.13 mg kg–1 yr–1), whereas the ZZ site exhibited the lowest (1.41–2.23 mg kg–1 yr–1). Notably, the Nact rates with manure application were higher in the first decade (42–181 mg g–1) than in the later period (33–92 mg g–1) at all sites. Overall, the average Nact of all treatments in the first decade (79–105 mg g–1) across six study sites was higher than in the later period (30–78 mg g–1). Variance portioning analysis indicated that soil properties’ contribution to Nact increased from 35% to 45% over time, while climatic conditions’ effect decreased from 19% to 8%. Structural equation modeling confirmed a direct impact of annual temperature on Nact, with path coefficients of 0.86 in the first decade and 0.45 in the later period. These results show that the impacts of climate on soil Nact were attenuated under long-term fertilizer application, while the interactions between climate and soil had an enhanced impact on Nact in the later period of fertilization. This context-specific insight can guide soil management strategies to enhance N availability, modulate the effects of climate change on agricultural production, and minimize environmental N losses.
- Article type
- Year
- Co-author
Open Access
Research Article
Issue
Straw and manure are the main sources of organic materials in China, and rotary tillage is the main way of returning farmland. In this study, the characteristics and driving factors of their decomposition process in typical farmland soils in China were investigated to provide a scientific basis for better utilization of straw resources and rational application of manure.
The landfill experiment of field organic material mixed with soil was carried out on a typical black soil, fluvo-aquic soil, and red soil in China. Four treatments were set up: wheat straw plus soil (WS+Soil), maize straw plus soil (MS+Soil), pig manure plus soil (PM+Soil), and cow manure plus soil (CM+Soil). All the organic materials (8 g carbon) were mixed with 200 g of soil in a nylon mesh bag buried in soil, six samples were taken within one year after landfilling, once from 2 to 2.5 years after landfilling, and once in 3 years, then a total of eight samples were taken. The decomposition differences of organic materials in different mixtures were analyzed. The double exponential equation was used to clarify the proportion and decomposition rate of easy-to-decompose carbon pool and refractory organic carbon pool, and to clarify the fast decomposition rate, slow decomposition rate and accumulated temperature turning point of organic materials in each soil. The random forest model was used to quantify the relative contribution of material composition and environmental factors to the decomposition rate.
The humification coefficient of straw pluil was ranged from 22% to 43%, and that of manure plus soil was ranged from 45% to 58%. The decomposition rate of manure plus soil was slower than straw plus soil, and there was little difference between regions. Besides, the decomposition of organic materials was accelerated from north to south, and the decomposition of straw was faster than that of organic fertilizers. The proportion of decomposable organic carbon poor of straw (70%-87%) was higher than that of organic fertilizer (57%-83%), and the decomposition rate of straw decomposable carbon pool k1 (1.0%·a-1-4.9%·a-1) was higher than that of organic fertilizer k1 (0.7%·a-1-1.1%·a-1). There was little difference in the turning point of accumulated temperature of straw in the three types of soil. Before 3 700℃, it was the stage of rapid decomposition, and then it was the stage of slow decomposition. On the other hand, the difference in accumulated temperature at the turning point of rapid decomposition and slow decomposition of organic fertilizer gradually increased from north to south, and the accumulated temperature at the turning point of organic fertilizer was 2-5 times higher that of straw. Soil accumulated temperature and soil organic carbon content were the main driving factors of mixed soil straw and organic fertilizer, contributing about 17% and 13% of the decomposition rate, respectively. In addition, the main driving factor for mixed soil straw was the ratio of soil carbon to nitrogen, but the main driving factor for mixed soil organic fertilizer was the time.
Straw returning to the field decomposed faster than organic fertilizer, and the high proportion of easily decomposable organic carbon pool with fast decomposition rate of straw was one of the main reasons for the difference. For straw, the ratio of carbon to nitrogen was the main factor affecting its decomposition, and for organic fertilizer, it was time. Therefore, the ratio of carbon to nitrogen of soil and material should be considered to regulate the decomposition of straw, and the long-term effect of organic fertilizer should be fully considered.
The purpose of this study was to explore the differences in the content and properties of different types of iron oxide bound organic carbon in different dryland soils and their responses to long-term straw returning.
Based on the long-term fertilization experiments of black soil and fluvo-aquic soil in Gongzhuling, Jilin Province and Zhengzhou, Henan Province since 1990, soil samples under no fertilization (CK), single application of chemical fertilizer (NPK) and chemical fertilizer +straw returning (NPKS) for 29 years were collected, and the complex iron (FePP), amorphous iron oxides (FeHH) and crystalline iron oxides (FeDH) were obtained through continuous extraction method. The differences in the content of different forms of iron oxides and their bound organic carbons were explored. Combined with ultraviolet-visible spectroscopy, the differences in the properties of iron oxide-bound organic carbon were also accessed.
Compared with CK and NPK treatments, the soil organic carbon content under NPKS treatment in black soil was significantly increased by 18.1% and 14.9%, respectively, and fluvo-aquic soil was significantly increased by 46.1% and 13.3%, respectively. The content of FePP in the two soils were lower than those under FeHH and FeDH, but the content of complexed iron-bound organic carbon (OCPP) were significantly higher than those of amorphous iron oxide-bound organic carbon (OCHH) and crystalline iron oxide-bound organic carbon (OCDH), accounting for 71.4%-93.2% of the total iron oxide-bound organic carbon content, indicating that OCPP was the main form of iron oxide-bound organic carbon. Compared with NPK treatment, the FePP content in black soil was significantly reduced by 65.6%. FeHH content was significantly reduced by 17.8%, and FeDH content was not significantly changed under NPKS treatment, while the FePP content in fluvo-aquic soil was significantly increased by 15.9%. FeHH content was not significantly changed, and FeDH content was significantly increased by 24.6%. Compared with NPK treatment, NPKS treatment significantly reduced the content of total iron oxide bound organic carbon in black soil, among which OCPP decreased by 11.3%, while OCDH increased by 53.7%, and OCHH did not change significantly, but had no significant effect on the content of total iron oxide bound organic carbon in fluvo-aquic soil. Further analysis of the binding organic carbon content per gram of iron oxides showed that compared with NPK treatment, NPKS treatment significantly increased the binding capacity of three iron oxides in black soil, but had no significant effect in the fluvo-aquic soil. FePP was mainly combined with macromolecular organic carbon with strong hydrophobicity and weak aromaticity while FeHH was mainly combined with small molecule organic carbon with strong hydrophobicity and aromaticity, and FeDH was mainly combined with some macromolecular compounds with poor hydrophobicity and aromaticity.
Comparing with the single application of chemical fertilizer, the content of crystalline and amorphous iron oxide bound organic carbon in black soil and fluvo-aquic soil increased significantly after long-term straw returning to the field, while the content of complexed iron bound organic carbon in black soil decreased significantly and did not change in fluvo-aquic soil. This was one of the important mechanisms for the different increases of soil organic carbon levels in different soil types after straw returning.
京公网安备11010802044758号