Accumulation In Soil Profile Research Articles

Shallow groundwater table fluctuations weaken nitrogen accumulation in the thin layer vadose zone of cropland around plateau lakes, Southwest China

Excessive accumulation of nitrogen (N) in the soil profile in the intensive agricultural region will seriously threaten groundwater quality and safety. However, the impact of shallow groundwater table (SGWT) fluctuations driven by seasonal variations on the N accumulation characterizations in the soil profiles has not been well quantified, particularly in the regions with thin layer vadose zone. Through in-situ monitoring and simulation experiments, the changes in the SGWT and N accumulation of soil profile in intensive cropland around 7 plateau lakes in Yunnan were studied during the rainy season (RS) and dry season (DS), and the N loss in soil profile of cropland driven by SGWT fluctuations was estimated. The results showed that the SGWT and N accumulation in soil profile of cropland around the plateau lakes had obvious seasonal variation characteristics. The proportion of N storage in different forms in 60–100 cm soil layer in the RS was greater than that in the DS, particularly the proportion of NH4+-N storage was as high as 55 %, while N accumulation in surface soil was obvious in the DS. Compared with the DS, due to the rising SGWT in the RS, the maximum storages of TN and NO3−-N in the 0–100 cm soil layer decreased by17% and 36 %, respectively. The TN loss intensities from the 0–100 cm soil profiles of cropland around Fuxian Lake, Yilong Lake, Qilu Lake, Dianchi Lake, Yangzong Lake, Erhai Lake, and Xingyun Lake were 74, 54, 127, 105, 93, 72 and 207 kg/ha, respectively. Moreover, if the SGWT was <30 cm, the average TN loss intensity and amount could reach 177 kg/ha and 1250 t, respectively. Therefore, the SGWT regulation was one of the key measures to reducing soil N loss from the thin layer vadose zone of cropland around plateau lakes and improving groundwater quality.

Effect of Fallow on Nitrogen Accumulation in Soil Profile and Shallow Groundwater in Cropland Around Fuxian Lake

Soil nitrogen accumulation in cropland and groundwater nitrogen pollution can be effectively alleviated by reducing exogenous nitrogen input, and fallow is an important measure for reducing exogenous nitrogen input. To explore the effects of fallow on nitrogen accumulation in the soil profile and shallow groundwater, the soil profile and shallow groundwater in cropland around Fuxian Lake were selected as research objects. The changes in nitrogen accumulation in the 0-100 cm soil profile and nitrogen concentration in shallow groundwater before (December 2017) and after (August 2020 and April 2021) fallow and their relationships were analyzed. The results showed that the content and storage of nitrogen in soil profiles were significantly reduced by fallow, and the contents of TN, ON, DTN, NO3--N, and NH4+-N in 0-30, 30-60, and 60-100 cm soil profiles after fallow decreased by 18.4 %-36.5 %, 16.1 %-26.8 %, 54.0 %-130.2 %, 59.5 %-90.8 %, and 60.1 %-110.6 %, respectively. The storages of TN, ON, DTN, NO3--N, and NH4+-N in 0-100 cm soil profiles before fallow were (17.20 ±0.97) t·hm-2, (15.50 ±1.23) t·hm-2, (0.68 ±0.06) t·hm-2, (266.8 ±31.17) kg·hm-2, and (18.7 ±3.04) kg·hm-2, respectively. However, their storages after fallow decreased by 25.5 %, 23.3 %, 44.7 %, 80.1 %, and 59.9 %, respectively. Fallow also changed the concentration and composition of different forms of nitrogen in shallow groundwater. The concentrations of TN, ON, NO3--N, and NH4+-N in groundwater after fallow decreased by 88.4 %, 82.7 %, 92.1 %, and 65.8 %, respectively, and ON/TN and NH4+-N/TN increased from 26 % and 6 % before fallow to 39 % and 17 % after fallow, respectively, whereas NO3--N/TN decreased from 61 % before fallow to 41 % after fallow. Changes in nitrogen concentrations and their forms in groundwater were closely related to DTN, NO3--N, and NH4+-N in the soil profile and pH, ORP, and DO in groundwater before and after fallow. Our study highlights that fallow effectively reduced nitrogen accumulation in cropland soil profiles, further alleviating nitrogen pollution in shallow groundwater, and was conducive to preventing the deterioration of water quality in plateau lakes.

Alternate partial root-zone drip irrigation with nitrogen fertigation promoted tomato growth, water and fertilizer-nitrogen use efficiency

Irrigation and fertilization play key roles in crop production. Scarcity of available water resources and low nutrient use efficiency calls for a need to improve water and nitrogen (N) use efficiency. This study aimed to investigate the effects of different irrigation and nitrogen treatments on the growth, yield, irrigation water-use efficiency (IWUE) and fertilizer-N utilization of tomato plants by using pre-buried soil columns (100 cm in depth) in a field. The irrigation treatments included conventional drip irrigation (CDI) and alternate partial root-zone drip irrigation (ADI) with sufficient or deficient water supply. Nitrogen fertilizer was set as high and low N input (8.30 g or 4.15 g 15N-labeled urea per plant) supplied as drip fertigation. Compared with the CDI treatment at the same nitrogen drip fertigation level, ADI promoted tomato root growth, induced more 15N accumulation in the 0−100 cm soil profile, facilitated the absorption of fertilizer-15N as well as soil N by plants, thus increasing plant growth and yield as well as IWUE and fertilizer-N use efficiency, while decreased 15N loss. Low nitrogen supply decreased plant growth, yield, 15N absorption, 15N accumulation in soil profile and IWUE, but increased both the 15N-use efficiency and 15N loss percentage. Thus, ADI coupled with nitrogen fertigation has a potential to save irrigation water, increase use efficiencies of both water and nitrogen fertilizers with reduced loss of N to the environment.

Impact of drained and un-drained soil conditions on water table depths, soil salinity and crop yields

The purpose of this study was to determine the comparison of salt accumulation in soil profile and crop yields under drained and un-drained conditions. Current field conditions were used to represent poorly drained conditions where drainage system was not installed yet. Simulations were performed to illustrate well drained condition using the water management simulation model while controlling soil salinity in root zone. To put forward drainage system impacts; soil salinity and relative crop yields for well drained conditions were compared to poorly drained conditions. Soil, crop and site parameters were obtained from coordinated 40 soil sampling locations where dry bean, winter wheat and fallow crop rotations were applied. Results of the study showed that water table decreased rapidly after installing proper drainage system. Percentage of salt decreases in soil profile occurred by 24.1, 37.9 and 14.4% for wheat, bean and fallow locations respectively with adequate drainage conditions. On the drained soils, the relative yield of the winter wheat was higher by 11.2%, on the average, whereas that of bean was higher by 24.7%. Overall the net impact of yield enhancement due to drainage was about 36%. This shows the positive impact of drainage system on crop yields in this area.

Plant cover and epipedon SOM stability as factors affecting brown soil profile development and microbial activity

This study aimed to evaluate the role of different plant covers on brown soil profile development changing SOM stability in the epipedons. In particular, two brown soils (Eutric Cambisols), located in Monghidoro at the Italian Apennines, were analysed in order to test the hypothesis that plant cover affects the brown soil profile development under eutric qualifier changing SOM stability and soil pH. Also we verified if soil biochemical activities and microbial biomass size could be promoted by factors supporting Eutric Cambisols development. The two soil profiles were formed under coniferous (M con) and beech cover (M beech), respectively; both of them had similar lithology, morphology, exposition, slope and elevation. The development of soil profiles was evaluated by the determination of their physical, chemical and biochemical properties, while SOM stability of the epipedons was assessed through the determination of some properties of humic substances by thermal (TG-DSC) and spectroscopic (FTIR) analysis, humification indexes and eco-physiological indicators such as microbial quotient (C mic:C org) and metabolic quotient (qCO 2). The C org content decreased along both soil profiles. The epipedon of M beech soil was richer in SOM that in turn showed a higher level of humification than M con. The pH value, CEC and the concentrations of all earth-alkaline cations were also higher in M beech than in M con soil profile. Differences in soil reaction and SOM quality seemed to affect weathering process, since the content of all Al forms (amorphous—Alo, crystalline—Ald and linked to SOM—Alp) increased as the soil pH decreased, and the Fe forms increased as the humification level of SOM increased. Nevertheless, the active iron ratio (Feo/Fed) calculated in the two soil profiles did not highlight significant differences between them in terms of podzolitation intensity. The activity of hydrolytic enzymes (β-glucosidase, cellulase and chitinase) was higher in M beech soil than in M con soil profile. The activity of all enzymes, on mass basis, decreased along both soil profiles, while the specific activity (per unit of organic carbon), increased only in the endopedons of M beech. Although biochemical properties were not correlated with physical and chemical properties of soil profile, significant correlations were observed between enzyme activity and the soil organic carbon or nitrogen content. As far as the epipedons SOM quality is concerned, the content of humified C, the microbial biomass carbon (C mic), as well as the C mic:C org were higher in M beech than in M con, whereas the qCO 2 was lower in M beech than in M con. Also the FTIR and TG-DSC analysis showed differences on HAs and FAs hydrophilic character and thermal stability between epipedons of M beech and M con. The SOM quality of epipendon under coniferous resulted in a more recalcitrant and hydrophobic composition than that of epipedon under beech. In conclusion the type of plant cover (coniferous vs. beech-tree) affected the weathering of the pedogenetic substrate changing the SOM properties and soil pH. Even if the beech-tree cover promoted SOM accumulation in soil profile, which represented the organic substrates for microbial biochemical activities, the weathering of soil under coniferous appeared more marked than beech-trees covered soil. Consequently, soil biochemical activity of microbial biomass along soil profile was not promoted by factors supporting weathering processes.

Long-term effects of N fertilization on cropping and growth of olive trees and on N accumulation in soil profile

Two experiments were conducted for 13 years in two olive groves of southern Spain to study the long-term effect of nitrogen (N) fertilization on trees and soil. In the first experiment, 12-year-old ‘Picual’ olive trees were arranged in a split plot design with method of N application (soil versus a 50% soil:50% foliar combination) as the whole plot factor, and amount of N applied annually (0, 0.12, 0.25, 0.5 or 1.0 kg N tree −1) as the subplot factor. In the second experiment, N application to 50-year-old ‘Picual’ trees was based on the previous season's leaf N concentration. Urea was the source of N in both experiments. During the last 4 years, soil samples were taken at 0–20, 20–40, 40–60, 60–80, and 80–100 cm depth to evaluate the effect of N application on soil eutrophication. Fertilization with N had no significant effects on yield, fruit characteristics, and growth of olive trees for the 13 years of study, even when leaf N concentration increased with the amount of fertilizer N applied. Combining soil and foliar application may reduce the amount of fertilizer N necessary to correct a possible N deficiency because our experiments showed this practice to be more effective in increasing leaf N that applying N only to the soil. Our results question the established deficiency threshold of 1.4% of N in dried leaf because no reduction in yield or growth was observed for lower concentrations. However, leaf N concentration did not drop below 1.2% after 13 years with no N application, probably because of N inputs from rainfall and the mineralization of organic N. Whereas under natural conditions of the non-fertilized treatments NH 4 +–N represented the dominant fraction of mineral N in soil, accumulation of high amounts of NO 3 −–N in the soil profile occurred in the fertilized plots, which represents a high risk of N leaching from soil. All these results suggest that annual applications of fertilizer N are unnecessary to maintain high productivity and growth in olive. Applying N only when the previous season's leaf analysis indicates that leaf N concentration is below the deficiency threshold, is thus a recommended practice to optimize N fertilization in olive orchards and to reduce N losses by leaching.

Three methods to estimate N2O fluxes as impacted by agricultural management

This study examines three methods of evaluating N2O flux and accumulation in soil profile over a growing season under three soil management regimes (fallow, fallow with manure addition and cropped to alfalfa). Estimates of N2O flux were made based on measured soil atmosphere concentration gradients in the top 15 cm and compared to flux estimates based on ex situ cores and micro-meteorological measurements made in parallel studies. All methods indicated strong seasonal trends relating to precipitation events. The amounts of N2O accumulating the profile decreased in the order alfalfa &lt; fallow &lt; fallow/manure. The amounts of N2O accumulating in the profile ranged from ambient (0.35 µL L−1) to 490 µL L−1. Diffusion of N2O to the lower profile was shown to provide temporary storage of N2O and thereby provide the opportunity for further reduction to N2 prior to efflux from the surface. In comparing the estimates of surface flux, all three methods were of the same order of magnitude for the fallow site but profile-based estimates were much lower and much higher for fallow/manure and alfalfa sites, respectively. Differences were attributed to the location and timing of carbon addition in each system. Key words: Nitrous oxide, N2O, flux, measurement, soil, management

Nitrate distribution and accumulation in an Ustochrept soil profile in a long term fertilizer experiment

Distribution and accumulation of NO3—N, down to 210 cm depth, in the soil profile of a long term fertilizer experiment were studied after 16 cycles of cropping (maize-wheat-fodder cowpea). The application of fertilizer N without P and K or in combination with only P resulted in higher NO3—N concentration in the soil profile than the application of N with P and K. With an annual application of 320 kg N ha−1 alone, a peak in NO3—N accumulation occurred at 135 cm soil depth. However, with the application of NPK, no peak in NO3—N distribution was discernible and its content at most of the sampling depths was either less than or equal to N and NP treatments. The annual application of 10 tons farm yard manure (FYM) per ha along with NPK resulted in a relatively lower NO3—N content in the sub soil. The amount of NO3—N accumulation in the soil profile decreased as the cumulative N uptake by the crops increased. Application of fertilizer amounts greater than that of the recommended (100% NPK) resulted in low percent N recoveries in crops and greater NO3—N accumulation in the soil profile.