Effect of continuous compost application on water-stable soil macroaggregation in a field subjected to double cropping

The influence of continuous application of compost and fertilizer on soil macroaggregation in a field subjected to long-term (ca. 20 years) double cropping (rice and barley) was investigated. Soil samples were collected from 4 different plots: a) No-NF, fertilizer containing P and K but no N; b) F, fertilizer containing N, P, and K; c) F+ LC, fertilizer plus low rate of compost; and d) F+ HC, fertilizer plus high rate of compost. The application of compost and fertilizer increased the degree of macroaggregation (>0.25 mm), the contents of organic C, total N, hydrolyzable carbohydrates, and dithionitecitrate-bicarbonate (DCB) soluble Al, and the hyphal length in the order of No-NF<F<F+LC<F+HC plots. The degree of macroaggregation showed high correlation coefficients (r ≥ 0.95) with the contents of organic and inorganic components or the hyphal length. Most of these properties were strongly intercorrelated among themselves. The results obtained in this study suggest that organic matter including polysaccharides, active Al, and hyphae play an important role together in soil macro aggregation in the field subjected to double cropping under study.     

Incorporation of nitrogen from urea fertilizer into soil organic matter in rice paddy and cassava upland fields in Indonesia

Incorporation of newly-immobilized N into major soil organic matter fractions during a cropping period under paddy and upland cropping systems in the tropics was investigated in Jawa paddy fields with and without fish cultivation and a Sumatra cassava field in Indonesia. ¹⁵N-labelled urea (¹⁵N urea) was applied as basal fertilizer, and the soil samples were collected after harvest. The percentage of distribution of the residual N in soil from ¹⁵N urea into the humic acids, fulvic acid fraction, and humin were 13.1–13.9, 19.0–20.5, and 53.4–54.3%, respectively, for the Jawa paddy soils, and 14.9, 27.4, and 52.4%, respectively, for the Sumatra cassava soil. These values were comparable to the reported ones for other climatic zones. The percentage of distribution of ¹⁵N urea-derived N into humic acids was larger than that of total N into the same fraction in all the soils. The distribution into the fulvic acid fraction was also larger for ¹⁵N urea-derived N than for total N in the Jawa soils. Humic and non-humic substances in the fulvic acid fraction were separated using insoluble polyvinylpyrrolidone (PVP) into the adsorbed and non-adsorbed fractions, respectively. Less than 5% of the ¹⁵N urea-derived N in fulvic acid fraction was detected in the PVP-adsorbed fraction (generic fulvic acids). The proportion of non-hydrolyzable N remained after boiling with 6 M HCl in the ¹⁵N urea-derived N was 9.4–13.5%, 17.3–26.7%, and 8.4–16.6% for the humic acids, generic fulvic acids, and humin, respectively. The significantly low resistance to acid hydrolysis suggested that the ¹⁵N urea-derived N was less stable than the total N in soil regardless of the fractions of humus.     

不同施肥措施对白土腐殖质组成的影响

以白土稻区4年大田定位试验为基础,设置2种翻耕深度(10 cm、20 cm,分别标记为T10、T20)和4种施肥措施(单施化肥、化肥+畜禽粪肥、化肥+秸秆还田、化肥+绿肥,分别标记为F、F+M、F+S、F+G),通过腐殖质组成修改法分别提取表层土壤水溶性物质、胡敏酸、富里酸和胡敏素,研究不同施肥措施对白土腐殖质各组分碳含量的影响。结果表明:单施化肥措施下,翻耕20 cm处理(T20+F)土壤总有机碳和腐殖质各组分碳含量均低于翻耕10 cm处理(T10+F),但差异未达显著水平。在翻耕20 cm的基础上增施有机肥能显著提高土壤总有机碳和腐殖质各组分碳含量,增施畜禽粪(T20+F+M)、秸秆还田(T20+F+S)和增施绿肥(T20+F+G)3处理的土壤总有机碳、胡敏酸、富里酸和水溶性物质碳含量较T20+F处理分别提高14.57%~30.64%、10.36%~30.57%、0.74%~12.31%和14.25%~26.80%。增施有机肥显著提高胡敏素碳含量,T20+F+M、T20+F+S和T20+F+G处理较T20+F处理提高18.87%~35.78%。4年不同翻耕与施肥措施对白土腐殖质性质未产生显著影响。增施有机肥能一定程度上提高土壤PQ值、胡富比、E4/E6值和色调系数。相关性分析表明,胡敏素、胡敏酸、富里酸碳含量与总有机碳含量间均存在显著或极显著正相关,与水溶性物质碳含量间无明显相关性。     

Cultivation-Induced Effects on the Organic Matter in Degraded Southern African Soils

We studied quantitative and qualitative changes in soil organic matter (SOM) due to different land uses (reference woodland versus cultivated) on six soils from Tanzania (Mkindo and Mafiga), Zimbabwe (Domboshawa and Chickwaka), and South Africa (Hertzog and Guquka). Structural characteristics of the humic acids (HAs) were measured by Curie-point pyrolysis–gas chromatography/mass spectrometry (P_y–GC/MS) and solid-state ¹³C nuclear magnetic resonance (CPMAS ¹³C NMR) spectroscopy. Significant changes in concentration and composition of SOM were observed between land uses. Losses of organic carbon after cultivation ranged from 35% to 50%. Virgin soils showed large proportions of colloidal humus fractions: humic acids (HAs) and fulvic acids (FAs) but negligible amounts of not-yet decomposed organic residues. The change in land use produced a contrasting effect on the composition of the HAs: a noteworthy “alkyl enhancement” in Mkindo soil and “alkyl depletion” in Chikwaka and to a lesser extent in Domwoshawa. The remaining soils displayed only minor alterations.     

Effect of humic amendments on inorganic N, dehydrogenase and alkaline phosphatase activities of a Mediterranean soil

Dehydrogenase activity, alkaline phosphatase activity and NH₄ ⁺, NO₂ ⁻ and NO₃ ⁻ concentrations were monitored in an aridisol treated with three commercially available humic amendments. The materials were of plant residue, lignite and peat origins. The humus plant residues, fulvic acids, with a high content of Kjeldahl-N, sustained high enzyme activities and highest levels of NH₄ ⁺, NO₂ ⁻ and NO₃ ⁻. Humus lignite (mainly humic acids) produced the highest dehydrogenase activity, whereas the alkaline phosphatase activity was not as high as that amendment with humus plant residues. The lower activity of alkaline phosphatase could not be attributed to the higher P content of humus lignite. Nitrification was also low, probably due to the low N content of this fertilizer. The amendment of humus peat origin (only humic acids) did not increase enzyme activity or inorganic N concentrations of soil. Our results show that although these materials are widely utilized and recommended as microbial and plant activators, they all behave very differently, and the effects on soil microbiological activity cannot be predicted solely on the basis of their humic and/or fulvic acid contents.     

The role of amino acids and nucleic bases in turnover of nitrogen and carbon in soil humic fractions

Incorporation of labelled ¹⁵N and ¹⁴C amino acids and nucleic bases into soil humus fractions as well as humus turnover was investigated under field conditions. The dynamics of ¹⁵N and ¹⁴C incorporation into organic matter was characterized by the following main steps: rapid incorporation of the labelled substance prevailing for the first 1–3 weeks, and decomposition of included labelled fragments prevailing beyond one month after substance addition. The annual turnover rates of N and C in humus fractions due to incorporation of amino acids and nucleic bases were calculated. The turnover rate of N in humus is two to three times that of C. The contribution of amino acids to organic matter generation is about twice as great as that of nucleic bases and other N-containing organic substances. This indicates the important role of amino acids in the humification process and humus turnover. Turnovers of humic acids (0·002 year^?1 for C and 0·02 for N) are the most rapid of humic fractions investigated, and humin is characterized by the slowest turnover (0·0002 year^?1 for C and 0·007 for N). There are no significant differences in the turnover rates of fulvic acid fractions (0·0002 year^?1 for C) with different molecular weight.     

长期施肥对小麦-玉米作物系统土壤腐殖质组分碳和氮的影响

通过对华北平原小麦–玉米轮作农田生态系统18年田间施肥试验,研究了长期不同施肥处理对耕层（0—20 cm）土壤腐殖质及活性腐殖质组分碳和氮的影响。试验设化肥NPK不同组合（NPK、NP、NK、PK）,全部施用有机肥（OM）,一半有机肥+化肥NPK（1/2OMN）及不施肥（CK）共7个处理。结果表明,各施肥处理均能在不同程度上增加土壤腐殖质（胡敏酸、富里酸和胡敏素）及活性腐殖质（活性胡敏酸和活性富里酸）组分碳和氮含量,提高可浸提腐殖质（胡敏酸和富里酸）及活性腐殖质组分碳和氮分配比例;但施肥对土壤活性腐殖质组分碳和氮含量的增加率均分别高于腐殖质组分碳和氮。各处理土壤腐殖质及活性腐殖质组分碳和氮含量均为OM处理最高,且有机肥与化肥NPK配施高于单施化肥各处理;而化肥处理中NPK均衡施用效果最好。说明施用有机肥、有机肥与化肥NPK配施及化肥NPK均衡施用是增加土壤腐殖质及活性腐殖质组分碳和氮的关键;活性腐殖质组分碳和氮较腐殖质组分碳和氮对施肥措施的响应更灵敏。     

Radiocarbon ages of humic substances in chernozems

Data on radiocarbon ages of different fractions of humus (humic acids, fulvic acids, and humin) in the profiles of chernozems are analyzed. A chronoecological grouping of humus in modern and buried (fossil) soils is suggested. An increase in the radiocarbon age of humic substances down the soil profile has a stepwise character. It is shown that the ¹⁴C content in chernozems decreases down the soil profile more somewhat slower than the ¹²C content. The dependence of a decrease in the humus content of buried soils on the age of burying is traced for a time span of 800 ka.     

Natural 15N and 13C abundance in Andisols influenced by long-term fertilization management in Japan

Two field experiments were conducted on Andisols in Japan to evaluate the changes in the natural ¹⁵N and ¹³C abundance in the soil profile and to determine whether the values of δ¹⁵N could be used as an indicator of fertilizer sources or fertilizer fate. The 6-year experiment conducted at the National Agricultural Research Center (NARC) consisted of the following treatments: application of swine compost (COMPOST), slow-release nitrogen fertilizer (SRNF), readily available nitrogen fertilizer (RANF), and absence of fertilization (CONTROL). Experimental plots located at the Nippon Agricultural Research Institute (NARI) received cattle compost at different rates for 12 years; a forest soil at this site was sampled for comparison. Swine compost application led to a considerable change in the δ¹⁵N distribution pattern in the soil profile, with the highest δ¹⁵N values recorded in the top 20 cm layers of the COMPOST plot, decreasing in the sequence of CONTROL >- RANF > SRNF, mainly due to the relatively high δ¹⁵N value of swine compost and its subsequent decomposition. In contrast, SRNF application resulted in the lowest δ¹⁵N values in soil, indicating the presence of negligible nitrogen losses relative to input and low nitrogen cycling rates. Values of δ¹⁵N increased with compost application rates at NARI. In the leachate collected at 1-m depth, the δ¹⁵N values decreased in the sequence of COMPOST > RANF ≥ CONTROL > SRNF. The δ¹³C values in soil peaked in the 40–60 cm layers for all the fertilizers. The δ¹³C value was lowest in forest soil due to the presence of plant residues in soil organic matter. These results indicated that the δ¹⁵N values in the upper soil layers or leachate may enable to detect pollution sources of organic or inorganic nitrogen qualitatively in Andisols.     

Assessment of degradation and generation of humus in a coffee soil affected by weed cover by means of a stable carbon isotopic ratio

We evaluated the effect of soil conservation by weeds on the degradation and generation of humic acids, fulvic acids, and water‐soluble non‐humic substances (WS‐NHS) in a red‐acid soil (Vertic Dystrudept) (Indonesia) from the changes in humus composition and stable carbon isotopic ratio (δ¹³C). Three plots, a weeded plot (T‐1; the common practice), a plot covered with Paspalum conjugatum Berg., a C₄ plant (T‐2), and a plot in which native weeds were allowed to grow (T‐3), were prepared. An incubation experiment determined the δ¹³C values of the humus fractions generated from Paspalum in soil. Based on the increase in δ¹³C value, the proportion of total C that originated from Paspalum C after 4 years under coffee was 16 ± 4% in the T‐2 topsoil (0–10 cm). Humic and fulvic acids in the T‐1 topsoil decreased to 46 and 84%, respectively, whilst both increased or remained constant in the T‐2 and T‐3 soils. The WS‐NHS content varied little and was independent of land management. The preferential loss of the humic acids with a smaller degree of humification as assessed by their darkness in colour was shown in T‐1. The decrease in the degree of humification suggested the accumulation of the weed‐derived humic acids in T‐2 and T‐3. In the T‐2 topsoil, 36 ± 2%, 13 ± 3% and 15 ± 2% of C in the humic acids, fulvic acids and WS‐NHS, respectively, were estimated to be Paspalum‐derived after 4 years. The estimated initial C loss during the same period was 17 ± 3%, 14 ± 2% and 7 ± 2%, respectively, for those fractions, which suggests the fastest turnover rate for the humic acids and significant retardation of their degradation in soil colonized by weeds.