Land-use changes, especially the conversion of native forest vegetation to cropland and plantations in tropical region, can alter soil C and N pools and N availability for plant uptake. Deforestation, followed by shif...Land-use changes, especially the conversion of native forest vegetation to cropland and plantations in tropical region, can alter soil C and N pools and N availability for plant uptake. Deforestation, followed by shifting cultivation and establishment of rubber tree plantation, is a common land-use change in Xishuangbanna, southwest China. However the influence of this kind of land-use change on soil C and N dynamics in this region remains poorly understood. This study was conducted to assess the effects of land-use change on soil C and N pools. Soil samples were collected on five adjacent plots, which belong to three land-use types including secondary forest-an acuminate banana(Musa itinerans) secondary forest and a male bamboo(Dendrocalamus membranaceae) secondary forest, shifting cultivation, and rubber tree (Hevea brasiliensis (H.B.K.) Muell. Arg.) plantation(one plot is 3-year-old, and another is 7-year-old). We measured soil bulk density (BD), pH value, moisture content and concentrations of soil organic carbon(SOC), total soil nitrogen(TSN), and inorganic N(NO - 3-N and NH + 4-N ) at 0—3, 3—20, 20—40 and 40—60 cm depths, and calculated C and N pools in 0—20, 20—40, 40—60, and 0—60 cm soil layers. Compared with the adjacent secondary forests, shifting cultivation and establishment of rubber tree plantations resulted in significant decline in concentrations and stocks of SOC and TSN in 0—20 and 0—60 cm soil layers, and increase in pH and bulk density at 0—3, 3—20, and 20—40 cm depths. Soil moisture content decreased only in 0—20 cm surface soils in shifting cultivation and plantations. The dynamics of mineral N was much more complex, which had different trends among depths and ecosystems. Compared with the secondary forests, SOC stocks in 0—20 cm surface soils in shifting cultivation and rubber tree plantations(3-year-old plantation and 7-year-old plantation) decreased by 34.0%, 33%, and 23%; and TSN stocks decreased by 32 2%, 20.4%, and 20.4%, respectively, whereas the decreases of SOC and TSN stocks in 0—60 cm soil layers were much less. The results indicated that C and N losses were mainly occurred in 0—20 cm surface soil, followed by 20—40 cm layer.展开更多
Polarized spectra-hyperspectral data fusion technique was used to estimate the soluble sugar(SS),total nitrogen(N),and their ratio(SS/N),of greenhouse tomato leaves.Fresh tomato leaves of five different growth stages(...Polarized spectra-hyperspectral data fusion technique was used to estimate the soluble sugar(SS),total nitrogen(N),and their ratio(SS/N),of greenhouse tomato leaves.Fresh tomato leaves of five different growth stages(seedling,flowering,initial fruiting,mid-fruiting and picking stage)and five different nitrogen treatments(severe stress 25%,moderate stress 50%,mild stress 75%,normal 100%,and excess 150%)at every stage were collected for spectra acquisition and SS and N determination.Polarized reflectance spectra were acquired with a polarization reflectance spectrum spectro-goniophotometer system and four polarization degree features were extracted.Hyperspectral data were collected with a hyperspectral imaging system and four reflectance spectrum features and eight image features were extracted.Initially,models were built with polarization degree features,image features,and spectral features respectively.Linear and nonlinear fusion methods were comparatively used for modeling based on normalized data of the three sources.The results suggest that the performances of SS/N models are better than those of N and SS models,and the prediction capability of the Support Vector Machine(SVM)models of N and SS/N are superior to those obtained with single kind feature.This work indicates that the polarized spectrum-hyperspectral multidimensional information detecting method can feasibly judge the tomato nutrient stress conditions.Multi-features data fusion analysis technique can enhance the prediction accuracy of spectral diagnostics technology in precision agriculture.展开更多
Point and nonpoint sources of phosphorus (P) and nitrogen (N) can cause reductions in water quality, including eutrophication. Nonpoint pollution represents a special challenge because of dispersed not easily identifi...Point and nonpoint sources of phosphorus (P) and nitrogen (N) can cause reductions in water quality, including eutrophication. Nonpoint pollution represents a special challenge because of dispersed not easily identifiable sources such as the runoff from soil, nutrients, and other chemicals from agricultural fields and residential areas. Laguna Cartagena is a tropical freshwater wetland, situated in southwestern Puerto Rico. It is a eutrophic ecosystem, and its eutrophication is caused by both external nutrient loading and internal, mainly by phosphorus. This wetland has been affected by phosphorus loading from inorganic agricultural fertilizer in this historically oligotrophic wetland system until the end of subsidized fertilizer use and sugar cane cultivation in the late 1990s. This study identifies: 1) nonpoint sources of phosphorus (SRP, Soluble Reactive Phosphorus and TP, Total Phosphorus) and nitrogen (nitrate, nitrite, and ammonia) that enter Laguna Cartagena;and 2) the role of precipitation events on the contributions of phosphorus and nitrogen loading to ecosystems. Herein we assess water samples from five channelized external sources of P and N that enter Laguna Cartagena at two-week intervals from October 2013 through November 2014. Rainfall data were obtained weekly from a rain gauge. Standard methods were used for all chemical analyses. Results showed that the channelized waterways that carry water to the lagoon can be classified as hypereutrophic (>100 μg/L) for TP concentrations and oligotrophic (<200 μg/L) for nitrogen concentrations. Currently agriculture (rice and cattle) is the predominant land use at the nearby University of Puerto Rico (UPR) Lajas Agricultural Experiment Substation, the predominant nonpoint source of nutrient pollution (SRP, TP and ammonia) in the principal channelized water sources to the lagoon. Current nutrient loads are likely derived from fertilizers applied to the Substation’s rice fields, and a high density livestock. The second important cause of external surface water degradation (SRP, TP and ammonia) is the discharge from rural households in the drainage basin that discharge greywater directly to the environment, as indicated by the results from Cerro Alto hills immediately to the north of the lagoon. Precipitation also was associated with SRP, TP and ammonia loads.展开更多
文摘Land-use changes, especially the conversion of native forest vegetation to cropland and plantations in tropical region, can alter soil C and N pools and N availability for plant uptake. Deforestation, followed by shifting cultivation and establishment of rubber tree plantation, is a common land-use change in Xishuangbanna, southwest China. However the influence of this kind of land-use change on soil C and N dynamics in this region remains poorly understood. This study was conducted to assess the effects of land-use change on soil C and N pools. Soil samples were collected on five adjacent plots, which belong to three land-use types including secondary forest-an acuminate banana(Musa itinerans) secondary forest and a male bamboo(Dendrocalamus membranaceae) secondary forest, shifting cultivation, and rubber tree (Hevea brasiliensis (H.B.K.) Muell. Arg.) plantation(one plot is 3-year-old, and another is 7-year-old). We measured soil bulk density (BD), pH value, moisture content and concentrations of soil organic carbon(SOC), total soil nitrogen(TSN), and inorganic N(NO - 3-N and NH + 4-N ) at 0—3, 3—20, 20—40 and 40—60 cm depths, and calculated C and N pools in 0—20, 20—40, 40—60, and 0—60 cm soil layers. Compared with the adjacent secondary forests, shifting cultivation and establishment of rubber tree plantations resulted in significant decline in concentrations and stocks of SOC and TSN in 0—20 and 0—60 cm soil layers, and increase in pH and bulk density at 0—3, 3—20, and 20—40 cm depths. Soil moisture content decreased only in 0—20 cm surface soils in shifting cultivation and plantations. The dynamics of mineral N was much more complex, which had different trends among depths and ecosystems. Compared with the secondary forests, SOC stocks in 0—20 cm surface soils in shifting cultivation and rubber tree plantations(3-year-old plantation and 7-year-old plantation) decreased by 34.0%, 33%, and 23%; and TSN stocks decreased by 32 2%, 20.4%, and 20.4%, respectively, whereas the decreases of SOC and TSN stocks in 0—60 cm soil layers were much less. The results indicated that C and N losses were mainly occurred in 0—20 cm surface soil, followed by 20—40 cm layer.
基金The authors are grateful to the financial support by China national key research and development plan(2017YFD0700504)China Postdoctoral Science Foundation(2016M601743)+3 种基金Senior talent research start-up fund of Jiangsu University(14JDG151)Natural Science Foundation of China Youth Fund(61901194)Natural Science Youth Foundation of Jiangsu Province(BK20180863,BK20180861)Priority Academic Program Development of Jiangsu Higher Education Institutions(PAPD-2018-87).
文摘Polarized spectra-hyperspectral data fusion technique was used to estimate the soluble sugar(SS),total nitrogen(N),and their ratio(SS/N),of greenhouse tomato leaves.Fresh tomato leaves of five different growth stages(seedling,flowering,initial fruiting,mid-fruiting and picking stage)and five different nitrogen treatments(severe stress 25%,moderate stress 50%,mild stress 75%,normal 100%,and excess 150%)at every stage were collected for spectra acquisition and SS and N determination.Polarized reflectance spectra were acquired with a polarization reflectance spectrum spectro-goniophotometer system and four polarization degree features were extracted.Hyperspectral data were collected with a hyperspectral imaging system and four reflectance spectrum features and eight image features were extracted.Initially,models were built with polarization degree features,image features,and spectral features respectively.Linear and nonlinear fusion methods were comparatively used for modeling based on normalized data of the three sources.The results suggest that the performances of SS/N models are better than those of N and SS models,and the prediction capability of the Support Vector Machine(SVM)models of N and SS/N are superior to those obtained with single kind feature.This work indicates that the polarized spectrum-hyperspectral multidimensional information detecting method can feasibly judge the tomato nutrient stress conditions.Multi-features data fusion analysis technique can enhance the prediction accuracy of spectral diagnostics technology in precision agriculture.
文摘Point and nonpoint sources of phosphorus (P) and nitrogen (N) can cause reductions in water quality, including eutrophication. Nonpoint pollution represents a special challenge because of dispersed not easily identifiable sources such as the runoff from soil, nutrients, and other chemicals from agricultural fields and residential areas. Laguna Cartagena is a tropical freshwater wetland, situated in southwestern Puerto Rico. It is a eutrophic ecosystem, and its eutrophication is caused by both external nutrient loading and internal, mainly by phosphorus. This wetland has been affected by phosphorus loading from inorganic agricultural fertilizer in this historically oligotrophic wetland system until the end of subsidized fertilizer use and sugar cane cultivation in the late 1990s. This study identifies: 1) nonpoint sources of phosphorus (SRP, Soluble Reactive Phosphorus and TP, Total Phosphorus) and nitrogen (nitrate, nitrite, and ammonia) that enter Laguna Cartagena;and 2) the role of precipitation events on the contributions of phosphorus and nitrogen loading to ecosystems. Herein we assess water samples from five channelized external sources of P and N that enter Laguna Cartagena at two-week intervals from October 2013 through November 2014. Rainfall data were obtained weekly from a rain gauge. Standard methods were used for all chemical analyses. Results showed that the channelized waterways that carry water to the lagoon can be classified as hypereutrophic (>100 μg/L) for TP concentrations and oligotrophic (<200 μg/L) for nitrogen concentrations. Currently agriculture (rice and cattle) is the predominant land use at the nearby University of Puerto Rico (UPR) Lajas Agricultural Experiment Substation, the predominant nonpoint source of nutrient pollution (SRP, TP and ammonia) in the principal channelized water sources to the lagoon. Current nutrient loads are likely derived from fertilizers applied to the Substation’s rice fields, and a high density livestock. The second important cause of external surface water degradation (SRP, TP and ammonia) is the discharge from rural households in the drainage basin that discharge greywater directly to the environment, as indicated by the results from Cerro Alto hills immediately to the north of the lagoon. Precipitation also was associated with SRP, TP and ammonia loads.
