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1.
The organic forms of phosphorus in the soil appear to be changing as rice growing intensifies and the soil is flooded for longer in tropical Asia. To examine these changes, we extracted the labile mobile humic acid (MHA) and more recalcitrant calcium humate (CaHA) fractions from soils supporting long‐term field trials in the Philippines and analysed them by solution 31P‐nuclear magnetic resonance (NMR) spectroscopy. Diester P and sugar‐diester P accumulated moderately with increasing intensity of irrigated rice cropping, reaching a combined 42% of all MHA‐P for a triple‐cropped irrigated field compared with 28% for fully aerated fields growing dryland crops. The mono‐ to diester P ratio decreased by 43% for the MHA and CaHA from the aerated fields to the triple‐cropped field. Smaller effects on forms of P were noted for the rates and type of N, P and K fertilizer and site effects. The effects of treatment and site were more noticeable in the MHA than in the CaHA. The proportions in the NMR spectra were tightly correlated with visible light absorption, concentrations of organic free radicals and H, and 15N‐NMR spectral proportions, which indicate the degree of humification. The MHA and CaHA accounted for only 0.6–8.3% and 0.9–5.7%, respectively, of total P; most of the P is inorganic. 相似文献
2.
This review summarizes independent reports of yield decreases in several agricultural systems that are associated with repeated cropping under wet or submerged soil conditions. Crop and soil data from most of these agroecosystems have led researchers to attribute yield decreases to a reduction in crop uptake of N mineralized from soil organic matter (SOM). These trends are most evident in several long-term field experiments on continuous lowland rice systems in the Philippines, but similar trends are evident in a continuous rice rotation in Arkansas, USA and with no-till cropping systems in North American regions with cool, wet climatic conditions in Spring. Soil analyses from some of these systems have found an accumulation of phenolic lignin compounds in SOM. Phenolic compounds covalently bind nitrogenous compounds into recalcitrant forms in laboratory conditions and occurrence of this chemical immobilization under field conditions would be consistent with field observations of reduced soil N supply. However, technological shortcomings have precluded its demonstration for naturally formed SOM. Through recent advances in nuclear magnetic resonance spectroscopy, agronomically significant quantities of lignin-bound N were found in a triple-cropped rice soil in the Philippines. A major research challenge is to demonstrate in the anaerobic agroecosystems that these lignin residues bind sufficient quantities of soil N to cause the observed yield decreases. A key objective will be to elucidate the cycling dynamics of lignin-bound N relative to the seasonal pattern of crop N demand. Anaerobic decomposition of crop residues may be the key feature of anaerobic cropping systems that promotes the accumulation of phenolic lignin residues and hence the covalent binding of soil N. Potential mitigation options include improved timing of applied N fertilizer, which has already been shown to reverse yield decreases in tropical rice, and aerobic decomposition of crop residues, which can be accomplished through field drainage or timing of tillage operations. Future research will evaluate whether aerobic decomposition promotes the formation of phenol-depleted SOM and greater in-season N mineralization, even when the soil is otherwise maintained under flooded conditions during the growing season. 相似文献
3.
Olk Daniel C. Dinnes Dana L. Rene Scoresby J. Callaway Chad R. Darlington Jerald W. 《Journal of Soils and Sediments》2018,18(8):2881-2891
Journal of Soils and Sediments - Humic products have been used in cropland agriculture for several decades, but lack of widespread credibility has restricted their use to small proportions of... 相似文献
4.
Field observations indicate a long‐term decrease in crop uptake of N derived from soil organic matter under continuous production of irrigated lowland rice (Oryza sativa L.). Decreased availability has been associated with an accumulation of phenolic lignin residues in soil organic matter, which can chemically bind N. To evaluate the hypothesis that the decrease in N availability results primarily from anaerobic decomposition of incorporated crop residues, 15N‐labelled fertilizer was applied three times during one growing season in a field study that compared anaerobic decomposition with aerobic decomposition for annual rotations of rice (Oryza sativa L.)–rice and rice–maize (Zea mays L.). Contents of 15N and total N during the growing season were measured in humic fractions and total soil organic matter. Results indicated an inhibition of N mineralization for the rice–rice rotation with anaerobic decomposition of crop residues, both for 15N that was immobilized after application and for total N. The inhibition was strongest for 15N that was applied at planting. It became more evident as the season progressed and reached significant levels during mid‐season stages of plant growth when crop demand for N peaks. These results were clearest for a young, phenolic‐rich humic fraction that was active in 15N immobilization and remineralization. Comparable but less significant trends were evident for a more recalcitrant humic fraction and for soil organic matter. Trends in crop‐N uptake associated the combination of rice–rice rotation and anaerobic decomposition with inhibited uptake of soil organic N but uninhibited uptake of fertilizer N. Increased aeration of rice soils through aerobic decomposition of crop residues or crop rotation is a promising management technique for improving soil N supply in lowland rice cropping. 相似文献
5.
Dandan?Li Lin?Chen Jisheng?Xu Lei?Ma Dan?C.?Olk Bingzi?ZhaoEmail author Jiabao?Zhang Xiuli?Xin 《Biology and Fertility of Soils》2018,54(8):999-1012
Fertilization is an important factor influencing the chemical structure of soil organic carbon (SOC) and soil microbial communities; however, whether any connection exists between the two under different fertilization regimes remains unclear. Soils from a 27-year field experiment were used to explore potential associations between SOC functional groups and specific bacterial taxa, using quantitative multiple cross-polarization magic-angle spinning 13C nuclear magnetic resonance and 16S rRNA gene sequencing. Treatments included balanced fertilization with organic materials (OM) and with nitrogen (N), phosphorus (P), and potassium (K) mineral fertilizers (NPK); unbalanced fertilization without one of the major elements (NP, PK, or NK); and an unamended control. These treatments were divided into four distinct groups, namely OM, NPK, NP plus PK, and NK plus control, according to their bacterial community composition and SOC chemical structure. Soil total P, available P, and SOC contents were the major determinants of bacterial community composition after long-term fertilization. Compared to NPK, the OM treatment generated a higher aromatic C–O and OCH3 and lower alkyl C and OCH abundance, which were associated with the enhanced abundance of members of the Acidobacteria subgroups 6 and 5, Cytophagaceae, Chitinophagaceae, and Bacillus sp.; NP plus PK treatments resulted in a higher OCH and lower aromatic C–C abundance, which showed a close association with the enrichment of unclassified Chloracidobacteria, Syntrophobacteraceae, and Anaerolineae and depletion of Bacillales; and NK plus control treatments resulted in a higher abundance of aromatic C–C, which was associated with the enhanced abundance of Bacillales. Our results indicate that different fertilization regimes changed the SOC chemical structure and bacterial community composition in different patterns. The results also suggest that fertilization-induced variations in SOC chemical structure were strongly associated with shifts in specific microbial taxa which, in turn, may be affected by changes in soil properties. 相似文献
6.
Zhigao Zhou Xiaoyan Cao Klaus Schmidt-Rohr Daniel C. Olk Shunyao Zhuang Jing Zhou Zhihong Cao Jingdong Mao 《Biology and Fertility of Soils》2014,50(4):571-581
This study examined the chemical composition of soil organic matter (SOM) along a 2,000-year paddy soil chronosequence in eastern China by use of advanced solid-state nuclear magnetic resonance (NMR) spectroscopy as well as Fourier transform infrared spectroscopy (FTIR), aiming to identify changes in the chemical composition of SOM over a millennium timescale. The results showed that soil organic carbon concentration in the surface soil reached a steady state after 100 years of rice (Oryza sativa L.)–wheat (Triticum sp.) cropping on coastal tidal flats. The 13C NMR spectra and fractions of structural groups or components of the whole SOM samples differed little along the chronosequence, suggesting a similar chemical composition in SOM samples regardless of the duration of rice cultivation. The FTIR spectral pattern and relative intensities of some resolved functional groups or components of whole SOM were also similar along the soil chronosequence. The similarities in chemical composition of SOM can be attributed to the rice–wheat cropping system, in which SOM has undergone ongoing turnover under periodical fresh plant material input and wet–dry cropping alternation, leading to a similar chemical composition of bulk SOM. 相似文献
7.
Hamada M. Abdelrahman Dan C. Olk Dana Dinnes Domenico Ventrella Teodoro Miano Claudio Cocozza 《Journal of Soils and Sediments》2016,16(10):2375-2384
Purpose
The study aimed to describe the carbohydrates and amino compounds content in soil, the light fraction (LF), the >53 μm particulate organic matter (POM), and the mobile humic acid (MHA) fraction and to find out whether the carbohydrates and amino compounds can be used to explain the origin of SOM fractions.Materials and methods
Soil samples were collected from two agricultural fields managed under organic farming in southern Italy. The LF, the POM, and the MHA were sequentially extracted from each soil sample then characterized. Seven neutral sugars and 19 amino compounds (amino acids and amino sugars) were determined in each soil sample and its correspondent fractions.Results and discussion
The MHA contained less carbohydrate than the LF or the POM but its carbohydrates, although dominated by arabinose, were relatively with larger microbial contribution as revealed by the mannose/xylose ratio. The amino compounds were generally less in the LF or the POM than in the MHA, while the fungal (aspartic and serine) and bacterial (alanine and glycine) amino acids were larger in the MHA than in the LF or the POM, underlining the microbial contribution to the MHA. Results from both sites indicated that total carbohydrates content decreased moving from the LF (younger fraction) to the MHA (older fraction), which seems to follow a decomposition continuum of organic matter in the soil-plant system.Conclusions
The study showed that the MHA is a labile humified fraction of soil C due to its content of carbohydrates and concluded that the content of carbohydrates and amino compounds in the LF, the POM and the MHA can depict the nature of these fractions and their cycling pattern and response to land management.8.
9.
J. L. Gaunt H. -U. Neue K. G. Cassman D. C. Olk J. R. M. Arah C. Witt J. C. G. Ottow I. F. Grant 《Biology and Fertility of Soils》1995,19(4):333-342
A decline in rice yields has been associated with intensification of rice production. In continuously irrigated systems this has been attributed to a decline in soil N supply. Nutrient mineralisation and immobilisation is constrained by the quantity and nature of the organic substrates and the physico-chemical environment of the soil system itself. A flooded soil is very different from an aerobic one; electron acceptors other than oxygen have to be used. The transition to continuously anaerobic conditions associated with the intensification of wetland rice systems affects their organic matter turnover and may adversely affect their productivity. 相似文献
10.
Spin counting on solid‐state 13C cross‐polarization (CP) nuclear magnetic resonance (NMR) spectra of two humic fractions isolated from tropical lowland soils showed that only 32–81% of potential 13C NMR signal was detected. The observability of 13C NMR signal (Cobs) was higher in the mobile humic acid (MHA) than in the calcium humate (CaHA) fraction, and increased with increasing intensity of irrigated rice cropping. NMR observability appeared to be related to the nature of the organic carbon, with phenol‐ and methoxyl‐rich samples having the higher values of Cobs. The Bloch decay (BD) technique provided more quantitatively reliable 13C NMR spectra, as evidenced by values of Cobs in the range 91–100% for seven of the eight humic fractions studied. The BD spectra contained considerably more aryl and carbonyl signal, and less O–alkyl and alkyl signal, with the greatest differences between CP and BD spectra observed for the samples with low Cobs(CP). The causes of low CP observability were investigated using the spectral editing technique RESTORE ( RE storation of S pectra via T CH and T O ne R ho (T1ρH) E diting). Rapid T1ρH relaxation was found to be primarily responsible for the under‐representation of carbonyl carbon, whereas inefficient cross‐polarization was primarily responsible for the under‐representation of aryl carbon in CP spectra. Proton NMR relaxation rates T1H and T1ρH were found to correlate with other NMR properties and also with cropping management. Non‐uniform rates of T1H relaxation in two of the CaHA fractions enabled the generation of proton spin relaxation editing subspectra. 相似文献