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1.
Nitrogen (N) surpluses from fertilizer application can cause major environmental harm including pollution of surface water, groundwater, and air. To assess such negative externalities, N balances are a complex but useful tool to predict surpluses and to measure effects of nutrient optimization strategies in agriculture. The Yaqui Valley in north‐western Mexico is representative for thousands of square kilometres of intensive, irrigated wheat production under arid conditions worldwide and has been targeted for conservation agriculture in recent years. For these cropping systems, detailed N balances are scarce and often incomplete. To help fill this knowledge gap, data from a long‐term experiment were collected in 2013/14 on a Vertisol to examine the impact of three tillage‐straw management practices (CTB: conventionally tilled beds; PB‐straw: permanent raised beds with residue retention; PB‐burn: permanent raised beds with residue burning) on N dynamics. Tillage had significant effects on soil NO3‐N, NH4‐N, and total N contents across the cropping period. Soil total N content was at all sampling depths lowest in CTB. Soil NO3‐N in the 0–90 cm profile was highest in PB‐burn over the cropping period and ranged from 77 kg ha?1 in the bed before pre‐planting fertilizer application up to 269 kg ha?1 in the furrow after the second fertilizer application. Annual simple N balances were +59 kg N ha?1 in CTB, +39 kg N ha–1 in PB‐straw, and +46 kg N ha?1 in PB‐burn. Residual mineral soil N was significantly affected by tillage‐straw management and lowest for PB‐straw (+205 kg N ha?1) and highest for CTB, and for PB‐burn (+283 kg N ha?1 each) in the 0–90 cm soil profile. Soil NO3‐N moved out of the effective wheat root zone, as indicated by the high residual NO3‐N content at 30–90 cm depth, which is an important pathway of N leaching. Quantifiable N losses through leaching and volatilization averaged 100 kg N ha?1. Our findings suggest that there is potential for substantial reductions in N inputs in all tillage‐straw systems to decrease N losses and to reduce mineral residual soil N, but care should be taken to avoid reducing grain protein content, which in PB straw was already below the quality standard. A knowledge transfer of the European “Nmin” concept is advisable in this region to regulate N fertilizer over‐application.  相似文献   

2.
The effects of soil incorporation with cereal straw (nil, 2.5, 5 and 10 t straw ha?1) and direct drilling on the proportion and amount of pea N derived from biological N fixation were investigated in three field experiments. Fixed N was determined by15N dilution using barley as a reference plant. The three sites were on acidic, red clay-loams in the cropping zone of southeastern Australia. Seasonal plant available soil N, as determined by the N accumulated in barley, was 31, 56 and 158 kg N ha?1, for the three sites. Incorporated straw reduced soil nitrate at sowing by 10–50 kg N ha?1 (0–30 cm), and 5 or 10 t straw ha?1 reduced barley uptake of N by 10–38 kg N ha?1. However, reducing plant available soil N was generally ineffective for increasing the N fixed by pea. Fixed N increased only at the site with the least plant-available N, and only one-third of the increase could be attributed to lower soil N uptake by pea. There was no evidence that direct drilling pea increased fixed N by decreasing crop uptake of soil N. It is proposed that a lower requirement for soil N by pea as compared to barley, and availability of mineral N beneath the soil layer treated with straw, minimise the effectiveness of straw incorporation for increasing the N fixed by pea.  相似文献   

3.
ABSTRACT

Identification of the combination of tillage and N fertilization practices that reduce agricultural Nitrous oxide (N2O) emissions while maintaining productivity is strongly required in the Indian subcontinent. This study investigated the effects of tillage in combination with different levels of nitrogen fertilizer on N2O emissions from a rice paddy for two consecutive seasons (2013–2014 and 2014–2015). The experiment consisted of two tillage practices, i.e., conventional (CT) and reduced tillage (RT), and four levels of nitrogen fertilizer, i.e., 0 kg N ha–1 (F1), 45 kg N ha–1 (F2), 60 kg N ha–1 (F3) and 75 kg N ha–1 (F4). Both tillage and fertilizer rate significantly affected cumulative N2O emissions (p < 0.05). Fertilizer at 45 and 60 kg N ha–1 in RT resulted in higher N2O emissions over than did the CT. Compared with the recommended level of 60 kg N ha?1, a 25% reduction in the fertilizer to 45 kg N ha?1 in both CT and RT increased nitrogen use efficiency (NUE) and maintained grain yield, resulting in the lowest yield-scaled N2O-N emission. The application of 45 kg N ha?1 reduced the cumulative emission by 6.08% and 6% in CT and RT practices, respectively, without compromising productivity.  相似文献   

4.
Crop rotations and tillage practices influence the quantity and quality of soil organic N (SON). We evaluated the impact of crop rotations and tillage practices on SON and mineralizable N at a depth of 0–15 cm in six field experiments, varying in duration over 8–25 years, that were being conducted in three Chernozemic soil zones in Saskatchewan, Canada. In a Brown Chernozem, continuous wheat increased SON at 0–15 cm by 7–17 kg N ha–1year–1 more than fallow/wheat. In a Dark Brown Chernozem, continuous cropping increased SON by 30 kg N ha–1year–1, compared with cropping systems containing fallow once every 3 years; and, in a Rego Black Chernozem, the increase in SON was 29 kg N ha–1 year–1, compared with cropping systems containing fallow once every 4 years. The increase in SON due to increased cropping frequency was accompanied by an increase in the proportion of mineralizable SON in the Brown Chernozem, but not in the Dark Brown and Black Chernozems. In the Brown Chernozemic soil zone, no-tillage management increased SON, compared with conventional tillage, varying from 16 kg N ha–1year–1 to 28 kg N ha–1year–1. In the Dark Brown Chernozemic soil zone, it increased SON by 35 kg N ha–1year–1 and, in the Black Chernozemic soil zone, by about 40 kg N ha–1year–1. Increases in SON at a depth of 0–7.5 cm due to no-tillage management was accompanied by a greater increase in the mineralizable N for Hatton fine sandy loam, Melfort silty clay and Indian Head clay than for other soils, indicating that the material responsible for the increased SON due to no-tillage was more labile than the soil humus N. However, the increased SON under no-till in Swinton loam, Sceptre clay and Elstow clay loam was not associated with an increase in the mineralizable N, indicating that this increased SON was no more susceptible to decomposition than the soil humus N. Therefore, increases in SON under improved management practices, such as conservation tillage and extended crop rotations, do not necessarily increase the potential soil N availability.  相似文献   

5.
Information on N cycling in dryland crops and soils as influenced by long-term tillage and cropping sequence is needed to quantify soil N sequestration, mineralization, and N balance to reduce N fertilization rate and N losses through soil processes. The 21-yr effects of the combinations of tillage and cropping sequences was evaluated on dryland crop grain and biomass (stems + leaves) N, soil surface residue N, soil N fractions, and N balance at the 0–20 cm depth in Dooley sandy loam (fine-loamy, mixed, frigid, Typic Argiboroll) in eastern Montana, USA. Treatments were no-tilled continuous spring wheat (Triticum aestivum L.) (NTCW), spring-tilled continuous spring wheat (STCW), fall- and spring-tilled continuous spring wheat (FSTCW), fall- and spring-tilled spring wheat–barley (Hordeum vulgare L.) (1984–1999) followed by spring wheat–pea (Pisum sativum L.) (2000–2004) (FSTW-B/P), and spring-tilled spring wheat–fallow (STW-F). Nitrogen fractions were soil total N (STN), particulate organic N (PON), microbial biomass N (MBN), potential N mineralization (PNM), NH4-N, and NO3-N. Annualized crop grain and biomass N varied with treatments and years and mean grain and biomass N from 1984 to 2004 were 14.3–21.2 kg N ha−1 greater in NTCW, STCW, FSTCW, and FSTW-B/P than in STW-F. Soil surface residue N was 9.1–15.2 kg N ha−1 greater in other treatments than in STW-F in 2004. The STN at 0–20 cm was 0.39–0.96 Mg N ha−1, PON 0.10–0.30 Mg N ha−1, and PNM 4.6–9.4 kg N ha−1 greater in other treatments than in STW-F. At 0–5 cm, STN, PON, and MBN were greater in STCW than in FSTW-B/P and STW-F. At 5–20 cm, STN and PON were greater in NTCW and STCW than in STW-F, PNM and MBN were greater in STCW than in NTCW and STW-F, and NO3-N was greater in FSTW-B/P than in NTCW and FSTCW. Estimated N loss through leaching, volatilization, or denitrification at 0–20 cm depth increased with increasing tillage frequency or greater with fallow than with continuous cropping and ranged from 9 kg N ha−1 yr−1 in NTCW to 46 kg N ha−1 yr−1 in STW-F. Long-term no-till or spring till with continuous cropping increased dryland crop grain and biomass N, soil surface residue N, N storage, and potential N mineralization, and reduced N loss compared with the conventional system, such as STW-F, at the surface 20 cm layer. Greater tillage frequency, followed by pea inclusion in the last 5 out of 21 yr in FSTW-B/P, however, increased N availability at the subsurface layer in 2004.  相似文献   

6.
Field experiments (established in autumn 1979, with monoculture barley from 1980 to 1990 and barley/wheat–canola–triticale–pea rotation from 1991 to 2008) were conducted on two contrasting soil types (Gray Luvisol [Typic Haplocryalf] loam soil at Breton; Black Chernozem [Albic Agricryoll] silty clay loam soil at Ellerslie) in north-central Alberta, Canada, to determine the influence of tillage (zero tillage and conventional tillage), straw management (straw removed [SRem] and straw retained [SRet]), and N fertilizer rate (0, 50 and 100 kg N ha?1in SRet, and only 0 kg N ha?1in SRem plots) on seed yield, straw yield, total N uptake in seed + straw (1991–2008), and N balance sheet (1980–2008). The N fertilizer urea was midrow-banded under both tillage systems in the 1991 to 2008 period. There was a considerable increase in seed yield, straw yield, and total N uptake in seed + straw with increasing N rate up to 100 kg N ha?1 under both tillage systems. On the average, conventional tillage produced greater seed yield (by 279 kg ha?1), straw yield (by 252 kg ha?1), and total N uptake in seed + straw (by 6.0 kg N ha?1) than zero tillage, but the differences were greater at Breton than Ellerslie. Compared to straw removal treatment, seed yield, straw yield, and total N uptake in seed + straw tended to be greater with straw retained at the zero-N rate used in the study. The amounts of applied N unaccounted for over the 1980 to 2008 period ranged from 1114 to 1846 kg N ha?1 at Breton and 845 to 1665 kg N ha?1 at Ellerslie, suggesting a great potential for N loss from the soil-plant system through denitrification, and N immobilization from the soil mineral N pool. In conclusion, crop yield and N uptake were lower under zero tillage than conventional, and long-term retention of straw suggests some gradual improvement in soil productivity.  相似文献   

7.
The period after ploughing of grass–clover leys within a ley‐arable rotation is when nitrogen accumulated during the ley phase is most vulnerable to loss. We investigated how ploughing date and timing of cessation of grazing before ploughing affected nitrous oxide (N2O) losses of the first cereal crop. Ploughing dates were July and October for a winter wheat pilot study and January and March for spring barley in the main experiment. Timings of cessation of grazing (main experiment only) were October, January and March. Spring barley yield, nitrogen uptake and soil mineral nitrogen were also assessed. A separate large‐scale laboratory incubation was made to assess the effect of temperature and rainfall on nitrous oxide emissions and nitrate leaching under controlled conditions. Nitrous oxide emissions in the 1‐ to 2‐month period after autumn or spring ploughing, or sowing were typically between 20 and 150 g N ha?1 day?1 and increased with temperature and rainfall. Tillage for crop establishment stimulated N2O emissions with up to 2.1 kg N ha?1 released in the month after spring tillage. Cumulative nitrous oxide emissions were greatest (～8 kg ha?1 over 17 months) after cessation of grazing in March before March ploughing, and lowest (～5.5 kg ha?1) after cessation of grazing in January before January ploughing. These losses were 1.2–3.9% of the N inputs. In the laboratory study, winter ploughing stimulated nitrate leaching more than nitrous oxide emissions. The optimum time of ploughing appears to be early spring when the cold restricts nitrogen mineralization initially, but sufficient nitrogen becomes available for early crop growth and satisfactory N offtake as temperature increases. Early cessation of grazing is advantageous in leaving an adequate supply of residues of good quality (narrow C:N ratio) for ploughing‐in. Restricting tillage operations to cool, dry conditions, being aware of possible compaction and increasing the use of undersown grass–clover should improve the sustainability of organic farming.  相似文献   

8.
Abstract. Nitrogen (N) loss by leaching poses great challenges for N availability to crops as well as nitrate pollution of groundwater. Few studies address this issue with respect to the role of the subsoil in the deep and highly weathered savanna soils of the tropics, which exhibit different adsorption and drainage patterns to soils in temperate environments. In an Anionic Acrustox of the Brazilian savanna, the Cerrado, dynamics and budgets of applied N were studied in organic and inorganic soil pools of two maize (Zea mays L.) – soybean (Glycine max (L.) Merr.) rotations using 15N tracing. Labelled ammonium sulphate was applied at 10 kg N ha?1 (with 10 atom%15N excess) to both maize and soybean at the beginning of the cropping season. Amounts and isotopic composition of N were determined in above‐ground biomass, soil, adsorbed mineral N, and in soil solution at 0.15, 0.3, 0.8, 1.2 and 2 m depths using suction lysimeters throughout one cropping season. The applied ammonium was rapidly nitrified or immobilized in soil organic matter, and recovery of applied ammonium in soil 2 weeks after application was negligible. Large amounts of nitrate were adsorbed in the subsoil (150–300 kg NO3?‐N ha?1 per 2 m) matching total N uptake by the crops (130–400 kg N ha?1). Throughout one cropping season, more applied N (49–77%; determined by 15N tracers) was immobilized in soil organic matter than was present as adsorbed nitrate (2–3%). Most of the applied N (71–96% of 15N recovery) was found in the subsoil at 0.15–2 m depth. This coincided with an increase with depth of dissolved organic N as a proportion of total dissolved N (39–63%). Hydrophilic organic N was the dominant fraction of dissolved organic N and was, together with nitrate, the most important carrier for applied N. Most of this N (>80%) was leached from the topsoil (0–0.15 m) during the first 30 days after application. Subsoil N retention as both adsorbed inorganic N, and especially soil organic N, was found to be of great importance in determining N losses, soil N depletion and the potential of nitrate contamination of groundwater.  相似文献   

9.
In this study, three types of cropping systems with different nutrient management strategies were studied on a clay soil with the aim of comparing leaching of N, P and K and obtaining knowledge on nutrient budgets. A conventional cropping system with cereals and application of mineral fertilizers (CON) was compared with two organic cropping systems, one without animal manure in which green manure crops were used for N supply (OGM) and one where animal manure (cattle slurry) was applied (OAM). Leaching and crop uptake of N, P and K, and soil mineral N were measured in pipe‐drained plots over a 6‐year period. The mean annual leaching loads of N were moderate and did not differ significantly (P > 0.05) between treatments; 13 kg N ha?1 in CON, 11 kg N ha?1 in OGM and 7.4 kg N ha?1 in OAM. Average annual P leaching showed greater variation than N leaching and was significantly greater in OGM (0.81 kg ha?1 year?1) than in CON (0.36 kg ha?1) and OAM (0.41 kg ha?1). For all cropping systems, removal in harvested crops was the most important export of nutrients from the field and constituted between 80 and 94% of total N outputs (harvested and leached N). Yields of cereals in the organic systems were considerably less (15–50%) than in the CON system, leading to a less efficient use of N than in the conventional system.  相似文献   

10.
Growing cotton (Gossypium hirsutum L.) after wheat (Triticum aestivum L.) is an important cropping system in Pakistan. However, numerous tillage practices commonly applied for cotton production are not productive. Conservation tillage may optimize cotton yield and quality if nitrogen (N) is not a limiting factor. Field experiments were conducted on silty clay soil (Hyperthermic, and Typic Torrifluvents) of Dera Ismail Khan, Pakistan to study the impact of tillage techniques (zero (ZT), reduced (RT), and conventional tillage (CT)) and nitrogen, namely 0, 50, 100, 150, and 200 kg ha–1 on cotton yield and quality. Mean values for N revealed that bolls plant–1, boll weight, seed cotton yield, ginning out turn (GOT), fiber length, strength, and micronaire were highest at 150–200 kg N ha–1. Averaged over years, tillage × nitrogen revealed that RT had higher bolls plant–1, boll weight, GOT, fiber length, and strength at 150–200 kg N ha–1 compared to other tillage system. The micronaire revealed that RT had no adverse effect on fiber fineness compared to ZT/CT. RT had accumulated higher soil organic matter and total soil N compared to CT. RT with 150–200 kg N ha–1 may be a sustainable and environmentally safe strategy to enhance cotton yield and quality.  相似文献   

11.
Abstract

Because of erosion problems, an effort has been undertaken to evaluate the effect of tillage intensity on carbon (C) and nitrogen (N) cycling on a vertisol. Soil samples at 0–10, 10–20, and 20–30 cm depth were collected from a split plot experiment with five different levels of tillage intensity on Houston Black soil (fine, montmorillonitic, thermic Udic Pellusterts). The experiment was a split plot design with 5 replications. The main plots were chisel tillage, reduced tillage, row tillage, strip tillage, and no tillage. The subplots were soil fertility levels with either high or low fertilizer application rate. Total N, total phosphorus (P), organic C, inorganic N, and C:N ratio were measured on soil samples as well as the potential C mineralization, N mineralization, C turnover, and C:N mineralization ratio during a 30 d incubation. Total P and organic C in soil were increased, with 0.9 and 0.8 kg P ha‐1 and 20.6 and 20.0 kg C ha‐1, for high and low soil fertility, respectively. Fertilizer application had no effect on either total N at the 0–10 cm depth, or on soil nutrient status below 10 cm. Potential soil N mineralization was decreased at the 0–10 cm depth and increased at the 20–30 cm depth by the high fertilizer treatment. Chisel tillage decreased total N and P in the 0–10 cm depth, with 1.4 and 1.6 kg N ha‐1 and 0.8 and 0.9 kg P ha‐1. However, chisel tillage increased total N and P at the 10–20 cm depth, with 1.3 and 1.2 kg N ha‐1, and 0.72 and 0.66 kg P ha‐1 for chisel tillage and no tillage, respectively. Tillage intensity increased C mineralization and C turnover, but reduced N mineralization at the 0–10 cm depth. The results indicate that intensively tilled soil had a greater capacity for C mineralization and for reductions in soil organic C levels compared to less intensively tilled systems.  相似文献   

12.
Approximately 40% of New Zealand's land mass is fertilized grassland with entirely non‐native plants, but currently there is substantially increased interest in restoration of native plants into contemporary agricultural matrices. Native vegetation is adapted to more acid and less fertile soils and their establishment and growth may be constrained by nutrient spillover from agricultural land. We investigated plant–soil interactions of native N‐fixing and early successional non N‐fixing plants in soils with variable fertility. The effects of soil amendments of urea (100 and 300 kg N ha?1), lime (6000 kg CaCO3 ha?1), and superphosphate (470 kg ha?1) and combinations of these treatments were evaluated in a glasshouse pot trial. Plant growth, soil pH, soil mineral N, Olsen P and nodule nitrogenase activity in N‐fixing plants were measured. Urea amendments to soil were not inhibitory to the growth of native N‐fixing plants at lower N application rates; two species responded positively to combinations of N, P and lime. Phosphate enrichment enhanced nodulation in N‐fixers, but nitrogen inhibited nodulation, reduced soil pH and provided higher nitrate concentrations in soil. The contribution of mineral N to soil from the 1‐year old N‐fixing plants was small, in amounts extrapolated to be 10–14 kg ha?1 y?1. Urea, applied both alone and in conjunction with other amendments, enhanced the growth of the non N‐fixing species, which exploited mineral N more efficiently; without N, application of lime and P had little effect or was detrimental. The results showed native N‐fixing plants can be embedded in agroecology systems without significant risk of further increasing soil fertility or enhancing nitrate leaching.  相似文献   

13.
Most of the nitrous oxide (N2O) in the atmosphere, thought to be involved in global warming, is emitted from soil. Although the main factors controlling the production of N2O in soil are well known, we need more quantitative data on the interactions of soil and the environment in the soil that affect the emission. We therefore studied the effects of irrigation, cropping (fallow, barley with grass undersown) and N fertilization (unfertilized, 103 kg N ha?1) on the composition of soil air and direct N2O emission from soil (using the closed chamber method) in a factorial field experiment on a well‐structured loamy clay soil during 1 June?22 October 1993. The measurements were made weekly during the growing season and three times after harvesting. The composition of the soil air did not indicate severe anoxia in any treatment or combination of treatments, but the accumulation of N2O in the soil air indicated that hypoxia was common. At the start of the irrigation the emissions were small, even though there was much ammonium and nitrate in the soil and therefore a potential for emission of N2O produced by both nitrification and denitrification. Larger emissions occurred later. The largest emissions were found when 60–90% of the soil pore space was filled with water. Irrigation and fertilization with N both roughly doubled the cumulative N2O emission. Growing a crop decreased it by a factor of 3–7. Most N2O was lost from the irrigated fertilized soil under fallow (3.5 kg N ha?1), and least from the unirrigated unfertilized soil under barley (0.1 kg N ha?1).  相似文献   

14.
The intensive winter wheat (Triticum aestivum L.)–summer maize (Zea mays L.) cropping systems in the North China Plain (NCP) rely on the heavy use of mineral nitrogen (N) fertilizers. As the fertigated area of wheat and maize in the NCP has grown rapidly during recent years, developing N management strategies is required for sustainable wheat and maize production. Field experiments were conducted in Hebei Province during three consecutive growth seasons in 2012–2015 to assess the influence of different N fertigation rates on N uptake, yield, and nitrogen use efficiency [NUE: recovery efficiency (REN) and agronomic efficiency (AEN)]. Five levels of N application, 0 (FN0), 40 (FN40%), 70 (FN70%), 100 (FN100%), and 130% (FN130%) of the farmer practice rate (FP: 250 kg N ha?1 and 205.5 kg N ha?1 for wheat and maize, respectively), corresponding to 0, 182.2, 318.9, 455.5, and 592.2 kg N ha?1 y?1, respectively, were tested. Nitrogen in the form of urea was dissolved in irrigation water and split into six and four applications for wheat and maize, respectively. In addition, the treatment “drip irrigation + 100% N conventional broadcasting” (DN100%) was also conducted. All treatments were arranged in a randomized complete block design with three replications. The results revealed the significant influence of both N fertigation rate and N application method on grain yield and NUE. Compared to DN100%, FN100% significantly increased the 3‐year averaged N recovery efficiency (REN) by 0.09 kg kg?1 and 0.04 kg kg?1, and the 3‐year averaged N agronomic efficiency (AEN) by 2.43 kg kg?1 and 1.62 kg kg?1 for wheat and maize, respectively. Among N fertigation rates, there was no significant increase in grain yield in response to N applied at a greater rate than 70% of FP due to excess N accumulation in vegetative tissues. Compared to FN70%, FN100%, and FN130%, FN40% increased the REN by 0.17–0.57 kg kg?1 and 0.03–0.34 kg kg?1and the AEN by 4.60–27.56 kg kg?1 and 2.40–10.62 kg kg?1 for wheat and maize, respectively. Based on a linear‐response relationship between the N fertigation rate and grain yield over three rotational periods it can be concluded that recommended N rates under drip fertigation with optimum split applications can be reduced to 46% (114.6 kg N ha?1) and 58% (116.6 kg N ha?1) of FP for wheat and maize, respectively, without negatively affecting grain yield, thereby increasing NUE.  相似文献   

15.
When fertilizing with compost, the fate of the nitrogen applied via compost (mineralization, plant uptake, leaching, soil accumulation) is relevant both from a plant‐production and an environmental point of view. In a 10‐year crop‐rotation field experiment with biowaste‐compost application rates of 9, 16, and 23 t ha–1 y–1 (f. m.), the N recovery by crops was 7%, 4%, and 3% of the total N applied via compost. Due to the high inherent fertility of the site, N recovery from mineral fertilizer was also low. In the minerally fertilized treatments, which received 25, 40, and 56 kg N ha–1 y–1 on average, N recovery from mineral fertilizer was 15%, 13%, and 11%, respectively. Although total N loads in the compost treatments were much higher than the N loads applied with mineral fertilizer (89–225 kg Ntot ha–1 y–1 vs. 25–56 kg Ntot ha–1 y–1; both on a 10‐year mean) and the N recovery was lower than in the treatments receiving mineral N fertilizer, soil NO ‐N contents measured three times a year (spring, post‐harvest, autumn) showed no higher increase through compost fertilization than through mineral fertilization at the rates applied in the experiment. Soil contents of Norg and Corg in the plowed layer (0–30 cm depth) increased significantly with compost fertilization, while with mineral fertilization, Norg contents were not significantly higher. Taking into account the decrease in soil Norg contents in the unfertilized control during the 10 years of the experiment, 16 t compost (f. m.) ha–1 y–1 just sufficed to keep the Norg content of the soil at the initial level.  相似文献   

16.
Four successive spring barley crops were grown in monoliths of a shallow soil overlying Chalk, contained in lysimeters. After harvest of the fourth crop, 25% of the nitrogen-15 labelled fertilizer applied 4 years earlier was found remaining in the roots and soil. Of this, 73% was present in the upper 30cm of the profile. From the amounts of fertilizer derived nitrogen that remained at the beginning of each cropping season we estimate that 5–6% of the residual nitrogen-15 turned over each year, representing a net release of 20% of the labelled nitrogen contained in the microbial biomass. Mineralization of the total biomass at the same fractional rate would release 120 kg N ha?1 a?1. This estimate is supported by the difference between input and outputs of total nitrogen during the experiment of 76–94 kg N ha?1 a?1 in fertilized lysimeters and 129kg N ha?1 a?1 in unfertilized control lysimeters. The total recovery of the applied labelled nitrogen was 81–87%. The nitrogen not accounted for was taken to be lost by denitrification of nitrate to dinitrogen, as no nitrous oxide emissions were detected during the experiment. Laboratory studies in aerobic and anaerobic conditions in presence of acetylene confirmed that 10–20% of the applied nitrogen-15 could have been transformed to dinitrogen.  相似文献   

17.
The objective was to study the effects of tillage and cattle slurry application on organic C dynamics in grassland soils. Treatments included long‐term grassland and reinstalled grassland (after tillage and winter wheat cropping) with and without cattle slurry application (240 kg N ha–1 y–1). A period of 4 y slurry application sufficed to increase microbial activity 1.6‐fold in surface soil (0–10 cm). Tillage affected aggregate distribution and basal respiration in the surface soil.  相似文献   

18.
Abstract. After six years of bush‐fallow, residual effects on soil productivity of tillage practices prior to the fallow were investigated on an Alfisol in south western Nigeria. In 1996 fallow was followed by maize intercropped with cover crops of Pueraria phaseoloides, Mucuna pruriens or cowpea (Vigna unguiculata) and no intercrop. Parameters measured included soil properties, ground cover, crop growth and yield, rainfall erosivity, runoff and soil loss. In spite of six‐years of bush‐fallow and establishment of cover crops, soil erosion was significantly greater on plots that had been conventionally cultivated previously using disc ploughs, harrows and mechanical rotovators (1.78 t ha?1season?1) compared to previously no‐till plots (1.34 t ha?1season?1). Crop growth and yields were least and soil loss greatest (2.83 t ha?1season?1) on the previous bare plot. Maize grain yield was highest using Pueraria phaseoloides as an intercrop (2.15 t ha?1) followed by a cowpea intercrop (1.92 t ha?1), maize without intercrop (1.87 t ha?1) and Mucuna pruriens intercrop (1.71 t ha?1). The maize grain yields reflected levels of competition from the cover crops. Cowpea–maize intercrop may be most suitable for farmers because maize yields were satisfactory and cowpea grain serves as additional subsistence. Cowpea yields were 390 kg ha?1. Soil erosion was also moderate using cowpea as an intercrop (1.71 t ha?1season?1). However, Pueraria phaseoloides gave the best erosion control with a soil loss of 1.34 t ha?1season?1.  相似文献   

19.
Tillage and residue retention affect nitrogen (N) dynamics and nutrient losses and therefore nitrogen use efficiency (NUE) and crop fertilizer use, however, there is little information about residual fertilizer effects on the subsequent crop. Micro‐plots with 15N‐labelled urea were established in 2014/2015 on a long‐term experiment on a Vertisol in north‐west Mexico. N fertilizer recovery (NFR) and the effects of residual fertilizer N for summer maize (Zea mays L.) and the subsequent wheat (Triticum durum L.) crop were studied in three tillage–straw management practices (CTB: conventionally tilled beds; PB‐straw: permanent raised beds with residue retention; PB‐burn: permanent raised beds with residue burning). Fertilizer 15N recovery rates for maize grain across all treatments were low with an average of 11%, but after wheat harvest total recovered 15N (15N in maize and wheat straw and grain, residual soil 15N) was over 50% for the PB‐burn treatment. NFR was lowest in CTB after two cropping cycles (32%). Unaccounted N from applied fertilizer for the maize crop averaged 120 kg 15N ha?1 after wheat harvest. However, more than 20% of labelled 15N was found in the 0–90 cm soil profile in both PB treatments after wheat harvest, which highlights the need for long‐term studies and continuous monitoring of the soil nutrient status to avoid over‐application of mineral N fertilizer.  相似文献   

20.
Abstract. In dairy farming systems the risk of nitrate leaching is increased by mixed rotations (pasture/arable) and the use of organic manure. We investigated the effect of four organic farming systems with different livestock densities and different types of organic manure on crop yields, nitrate leaching and N balance in an organic dairy/crop rotation (barley–grass-clover–grass-clover–barley/pea–winter wheat–fodder beet) from 1994 to 1998. Nitrate concentrations in soil water extracted by ceramic suction cups ranged from below 1 mg NO3-N l?1 in 1st year grass-clover to 20–50 mg NO3-N l?1 in the winter following barley/pea and winter wheat. Peaks of high nitrate concentrations were observed in 2nd year grass-clover, probably due to urination by grazing cattle. Nitrate leaching was affected by climatic conditions (drainage volume), livestock density and time since ploughing in of grass-clover. No difference in nitrate leaching was observed between the use of slurry alone and farmyard manure from deep litter housing in combination with slurry. Increasing the total-N input to the rotation by 40 kg N ha?1 year?1 (from 0.9 to 1.4 livestock units ha?1) only increased leaching by 6 kg NO3-N ha?1. Nitrate leaching was highest in the second winter (after winter wheat) following ploughing in of the grass-clover (61 kg NO3-N ha?1). Leaching losses were lowest in 1st year grass-clover (20 kg NO3-N ha?1). Averaged over the four years, nitrate concentration in drainage water was 57 mg l?1. Minimizing leaching losses requires improved utilization of organic N accumulated in grazed grass-clover pastures. The N balance for the crop rotation as a whole indicated that accumulation of N in soil organic matter in the fields of these systems was small.  相似文献   

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