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1.
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   

2.
Abstract. Three successive crops of winter wheat were grown on a sandy loam to test the residual effect of long‐term annual incorporation of spring barley straw at rates of 0, 4, 8 and 12 t ha?1, and ryegrass catch crops with or without additions of pig slurry. Soil receiving 4, 8 and 12 t ha?1 of straw annually for 18 years contained 12, 21 and 30% more carbon (C), respectively, than soil with straw removal, and soil C and nitrogen (N) contents increased linearly with straw rate. The soil retained 14% of the straw C and 37% of the straw N. Ryegrass catch‐cropping for 10 years also increased soil C and N concentrations, whereas the effect of pig slurry was insignificant. Grain yield in the first wheat crop showed an average dry matter (DM) increase of 0.7 t ha?1 after treatment with 8 and 12 t straw ha?1. In the two subsequent wheat crops, grain yield increased by 0.2–0.3 t DM ha?1 after 8 and 12 t straw ha?1. No grain yield increases were found after 4 t straw ha?1 in any of the three years. Previous ryegrass catch crops increased yields of wheat grain, but effects in the third wheat crop were significant only where ryegrass had been combined with pig slurry. Straw incorporation increased the N offtake in the first wheat crop. In the second crop, only 8 and 12 t straw ha?1 improved wheat N offtake, while the N offtake in the third wheat crop was unaffected. Ryegrass catch crops increased N offtake in the first and second wheat crop. Again, a positive effect in the third crop was seen only when ryegrass was combined with slurry. Long‐term, annual incorporation of straw and ryegrass catch crops provided a clear and relatively persistent increase in soil organic matter levels, whereas the positive effects on the yield of subsequent wheat crops were modest and transient.  相似文献   

3.
Catch crop strategy and nitrate leaching following grazed grass-clover   总被引：1，自引：0，他引：1  
Cultivation of grassland presents a high risk of nitrate leaching. This study aimed to determine if leaching could be reduced by growing spring barley (Hordeum vulgare L.) as a green crop for silage with undersown Italian ryegrass (Lolium multiflorum Lam.) compared with barley grown to maturity with or without an undersown conventional catch crop of perennial ryegrass (Lolium perenne L.). All treatments received 0, 60 or 120 kg of ammonium‐N ha?1 in cattle slurry. In spring 2003, two grass‐clover fields (3 and 5 years old, respectively, with different management histories) were ploughed. The effects of the treatments on yield and nitrate leaching were determined in the first year, while the residual effects of the treatments were determined in the second year in a crop of spring barley/perennial ryegrass. Nitrate leaching was estimated in selected treatments using soil water samples from ceramic cups. The experiment showed that compared with treatments without catch crop, green barley/Italian ryegrass reduced leaching by 163–320 kg N ha?1, corresponding to 95–99%, and the perennial ryegrass reduced leaching to between 34 and 86 kg N ha?1, corresponding to a reduction of 80 and 66%. Also, in the second growing season, leaching following catch crops was reduced compared with the bare soil treatment. It was concluded that the green barley/Italian ryegrass offers advantages not only for the environment but also for farmers, for whom it provides a fodder high in roughage and avoids the difficulties with clover fatigue increasingly experienced by Danish farmers.  相似文献   

4.
The aim of the present investigation was to study the effect of white clover (var. Milka and Donna), red clover (var. Fanny) and ryegrass (var. Tove) undersown in winter wheat on a succeeding oat crop. Under the climatic conditions prevailing in Sweden, growing a catch crop after winter cereals is of particular interest because the latter are usually followed by a spring sown crop, leaving the ground bare during autumn and winter. Field trials were carried out during three growing seasons in an integrated farming system and for one year in an organic farming system. Competition from the dense wheat crop in the integrated farming system had a negative effect on the undersown species, and at harvest of the wheat they showed quite poor growth in all three years, with nitrogen contents under 5 kg ha?1. No significant yield increase was measured without added nitrogen when the averages for all three years were calculated. On average, the grain yields were improved by 750 kg ha?1 (14% moisture content) for the treatments with undersown clover for all three years when 90 kg N ha?1 were added. The experiment within the organic system showed a different pattern with a better development of the undersown clover species, with nitrogen contents approximately 25 kg ha?1 and an improvement in oat grain yield, from around 2?000 kg ha?1 for the control to almost 3?500 kg ha?1 with clover undersown the previous year.  相似文献   

5.
The objective of this work was to determine the fate of fertilizer nitrogen (labelled with nitrogen-15) applied to an undisturbed shallow soil overlying Chalk contained in 10 lysimeters (80 cm diameter, 135 cm deep). Measurements are reported of the nitrogen uptake by four spring barley crops and the rate and extent of leaching of nitrate beyond the roots. The crops were fertilized with 0, 80 or 120 kg N ha?1 in each of four years, but only the first application in 1977 was labelled with nitrogen ?15. Rainfall and irrigation approximated to the long-term average, but in two treatments dry or wet spring conditions were imposed for the 10 weeks after sowing the first crop in 1977. The dry matter and grain yields of the spring barley crops varied from year to year in the ranges 8.7–14.0 t ha?1 and 3.5–6.1 t ha?1 respectively. The total nitrogen harvested in the crop approximated to the amount of nitrogen applied in each year with an apparent recovery of fertilizer in the range 38–76%. The recovery of nitrogen derived from fertilizer (labelled with nitrogen-15) was 46–54% in the first crop and after 2 years rapidly declined to below 1%. The total amount of nitrogen-15 labelled fertilizer recovered in four barley crops was 49–57% of that applied. Mean annual nitrate concentrations in water draining from the base of the lysimeters were in the range 11.8–26.7 mg N 1?1 and did not differ significantly between nitrogen fertilizer treatments (0, 80 and 120 kg N ha?1 a?1). In all treatments nitrate concentrations varied considerably within each growing season, with a cycle of peaks and troughs. Annual losses of nitrate were in the range 39–128 kg N ha?1, and the mean annual losses over the 4 years varied between lysimeters from 65 to 83 kg N ha?1. Nitrogen-15 labelled nitrate was detected in the first drainage water collected in autumn following its spring application, 5 months earlier. Recovery of fertilizer-derived nitrogen in drainage water was greatest during the winter following the second barley crop, and was 3.4–3.7% of the nitrogen-15 applied. Over the 4 years of the experiment 6.3–6.6% of labelled fertilizer was accounted for in drainage water, representing 2–3% of the total nitrogen lost by leaching.  相似文献   

6.
In order to combine the ability of legumes to fix atmospheric nitrogen and the cruciferous capacities to mobilize soil nutrients and herbicide action, the aim of this work was to evaluate an alternative winter intercrop (faba bean-rapeseed) as a replacement of Italian ryegrass culture in a rotational system with maize as summer crop. For this purpose, two adjacent plots were used during three agronomic years (2011–2012, 2012–2013 and 2013–2014) to evaluate the agronomic performance through the forage production, nutritional composition of forage and silage, and the effects on soil fertility. The Italian ryegrass was cultivated under conventional management: using chemical fertilization and recommended dosages of herbicides. The faba bean-rapeseed intercrop was cultivated under an alternative management: organic fertilization and less herbicide supply. The intercrop provides higher forage yield per hectare than Italian ryegrass, with greater protein (kg ha?1) and similar energy (GJ ha?1) yields. The intercrop allows reducing the inputs of chemical fertilization and herbicides, and it has a positive effect on the balance of soil nutrients, especially increasing the potassium, calcium and magnesium contents. The results show that faba bean-rapeseed intercrop could be an alternative to the Italian ryegrass as winter crop.  相似文献   

7.
Fate of fertilizer nitrogen.   总被引：3，自引：0，他引：3  
Results are presented from a three year lysimeter investigation, employing single (15NH4NO3) and double (15NH415NO3) labelled ammonium nitrate to study the uptake of soil and fertilizer nitrogen by cut ryegrass at 250, 500 and 900 kg N ha?1 a?1. Average annual recoveries of nitrogen were equivalent to 99,76 and 50% of the nitrogen added at 250, 500 and 900 kg N ha?1, respectively. At 250 kg N ha?1 the difference between the overall nitrogen recovery and the fertilizer recovery was almost entirely attributable to pool substitution resulting from mineralization/immobilization turnover (MIT). At 900 kg N ha?1 both the low overall recovery of nitrogen and the low fertilizer recovery reflected the large excess of available nitrogen over crop requirements. No evidence of ‘priming’ was obtained. Analysis of the results from single and double labelled lysimeters using simultaneous equations indicated that at 250 kg N ha?1,～70% of the nitrogen in the crop was derived from the ammonium pool. At 500 kg N ha?1 this dropped to 64%, while at 900 kg N ha?1 the figure was 59%. There was a suggestion that at the lower application rates, preferential uptake of ammonium was occurring but that as N supply exceeded crop requirements, nitrate was the major N source. Despite the preferential exploitation of the ammonium pool, at 250 and 500 kg N ha?1 pool substitution resulting from MIT resulted in lower recoveries of fertilizer ammonium compared with fertilizer nitrate.  相似文献   

8.
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   

9.
Abstract

Up to 50% of nitrogen (N) fertilizer can remain in soil after crop harvest in dryland farming. Understanding the fate of this residual fertilizer N in soil is important for evaluating its overall use efficiency and environmental effect. Nitrogen-15 (15N)-labeled urea (165 kg N ha?1) was applied to winter wheat (Triticum aestivum L.) growing in three different fertilized soils (no fertilizer, No-F; inorganic nitrogen, phosphorus and potassium fertilization, NPK; and manure plus inorganic NPK fertilization, MNPK) from a long-term trial (19 years) on the south of the Loess Plateau, China. The fate of residual fertilizer N in soils over summer fallow and the second winter wheat growing season was examined. The amount of the residual fertilizer N was highest in the No-F soil (116 kg ha?1), and next was NPK soil (60 kg ha?1), then the MNPK soil (43 kg ha?1) after the first winter wheat harvest. The residual fertilizer N in the No-F soil was mainly in mineral form (43% of the residual 15N), and for the NPK and MNPK soils, it was mainly in organic form. The loss rate of residual 15N in No-F soil over summer fallow was as high as 48%, and significantly (P < 0.05) higher than that in the NPK soil (22%) and MNPK soil (19%). The residual 15N use efficiency (RNUE) by the second winter wheat was 13% in the No-F soil, 6% in the NPK soil and 8% in the MNPK soil. These were equivalent to 9.0, 2.0 and 2.2% of applied 15N. The total 15N recovery (15N uptake by crops and residual in 0–100 cm soil layer) in the MNPK and NPK soils (84.5% and 86.6%, respectively) were both significantly higher than that in the No-F soil (59%) after two growing seasons. The 15N uptake by wheat in two growing seasons was higher in the MNPK soil than in NPK soil. Therefore, we conclude that a high proportion of the residual 15N was lost during the summer fallow under different land management in dryland farming, and that long-term combined application of manure with inorganic fertilizer could increase the fertilizer N uptake and decrease N loss.  相似文献   

10.
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   

11.
Data from a 49-year-long organic–mineral fertilization field experiment with a potato–maize–maize–wheat–wheat crop rotation were used to analyse the impact of different fertilizer variations on yield ability, soil organic carbon content (SOC), N and C balances, as well as on some characteristic energy balance parameters. Among the treatments, the fertilization variant with 87 kg ha?1 year?1 N proved to be economically optimal (94% of the maximum). Approximately 40 years after initiation of the experiment, supposed steady-state SOC content has been reached, with a value of 0.81% in the upper soil layer of the unfertilized control plot. Farmyard manure (FYM) treatments resulted in 10% higher SOC content compared with equivalent NPK fertilizer doses. The best C balances were obtained with exclusive mineral fertilization variants (?3.8 and ?3.7 t ha?1 year?1, respectively). N uptake in the unfertilized control plot suggested an airborne N input of 48 kg ha?1 year?1. The optimum fertilizer variant (70 t ha?1 FYM-equivalent NPK) proved favourable with a view to energy. The energy gain by exclusive FYM treatments was lower than with sole NPK fertilization. Best energy intensity values were obtained with lower mineral fertilization and FYM variants. The order of energy conversion according to the different crops was maize, wheat and potato.  相似文献   

12.
A 2-year field experiment was conducted to assess system productivity, nutrient use efficiency and apparent balances of phosphorus (P) and potassium (K) in diversified rice-based cropping systems at Gazipur, Bangladesh. Four cropping systems: wheat–fallow–rice, maize–fallow–rice, potato–fallow–rice and mustard–fallow–rice in main plots and four nutrient combinations: NPK, NK, NP and PK in sub-plots were arranged in a split-plot design with three replications. Receiving the NPK treatment, all the component crops gave the highest yield, and omission of N from fertilizer package gave the lowest yield. The maize–rice system removed the highest amount of N (217 kg ha?1), P (41 kg ha?1) and K (227 kg ha?1) followed by wheat–rice, potato–rice and the least in mustard–rice system. The wheat–rice and maize–rice system showed negative K balance of –35.5 and –60.4 kg ha?1 in NPK treatment, while potato–rice system showed a positive K balance of 31.0 kg ha–1 with NPK treatment. The N, P and K uptake and apparent recovery by the test crops may be used for site-specific nutrient management. The K rates for fertilizer recommendation in wheat and maize in Indo-Gangetic plain need to be revised to take account for the negative K balance in soil.  相似文献   

13.
Abstract

Results of 240 annual N fertilizer trials in 1991–2007 in spring and winter cereals are presented. On average, spring barley and oat yields increased little beyond 120 kg N ha?1 in fertilizer. Somewhat higher figures were found for spring and winter wheat. Regression equations for yield and N uptakes in grain and straw were derived, related to N fertilizer input and the yield level in individual trials (indicator of yield expectancy). These equations accounted for 90% of the variation in yield and 80% of that in N uptake. Quadratic N responses were significant in all cases, as were interactions between N responses and yield level. They were verified with data from 27 separate trials performed in 2008–2010. The yield equations were used to calculate economically optimum N fertilizer levels with varying ratios of product price to fertilizer cost at contrasting levels of yield. The optimum N fertilizer level for barley and oats was found to increase by 8.3 kg N ha?1 per Mg increase in expected yield. The equivalent figure in wheat was 16.3 kg N ha?1. Optimum N fertilizer levels decreased by 4.1 and 6.7 kg N ha?1, for barley/oats and wheat respectively, per unit increase in the cost/price ratio. The equations for N uptake were used to calculate simple N balances between fertilizer input and removal in crop products. Large N surpluses were indicated at low levels of yield expectancy, but the surplus declined markedly with increasing yield level, despite greater N fertilizer inputs at high yield. Calculations made for national average yield levels in recent years showed N surpluses of 50–60 kg N ha?1 when only grain is removed and 25–40 kg N ha?1 when straw is removed also. Limiting N input to obtain zero balance reduces yields considerably at average levels of yield expectancy.  相似文献   

14.
Fertilizer phosphorus (P) is generally added to agricultural soils to meet the needs of crop production. In this study, the crop yield and soil Olsen P were measured every year (5–18 years) at 16 winter wheat (Triticum aestivum L.) –maize (Zea mays L.) crop rotation sites in cinnamon soil (Luvisols in FAO system). The mean agronomic critical value of Olsen P for maize was 14.2 mg kg?1 and for winter wheat was 14.4 mg kg?1 when using the Liner-plateau and Mitscherlich models. The change in soil Olsen P was positively linearly correlated with the P budget (P < 0.01), and an increase of 4.70 mg kg?1 in soil Olsen P for each 100 kg ha?1 of P budget in the 0–20 cm soil layer. A model of P fertilizer recommendation rate that integrated values of the change in soil Olsen P in response to P budget and the agronomic critical value of Olsen P was used, in order to adjust current levels of soil Olsen P to the agronomic critical value at the experimental sites over the next 5 years, P fertilizer application rate should be in the range of 0–87.5 kg P ha?1.  相似文献   

15.
Soil microarthropod populations in maize plots mulched with the prunings of three woody agroforestry plant residues (Acioa barteri, Gliricidia sepium and Leucaena leucocephala) and two crop residues [maize (Zea mays) stover (leaves and stems) and rice (Oryza sativa) straw] were monitored throughout the 1991 growing season and compared with those in fallow, bare fallow and unmulched control plots with three rates of nitrogen application. The mean densities of detritivore and phytophage microarthropods in the experimental plots decreased in the following order: rice straw > Gliricidia prunings > Leucaena prunings > maize stover > Acioa prunings > control 2 (90 kg N ha-1 year-1) > fallow > control 3 (135 N) > control 1 (45N) > bare fallow. Mulching also affected the population dynamics of predatory microarthropods and omnivorous ants. The chemical composition of plant residues probably influenced the densities of detritivore and phytophage microarthropods, which in addition were also greatly influenced by microclimatic conditons imposed by vegetation cover. Extremely low densities of microarthropods were recorded in the bare fallow plots probably as a result of the combined effects of absence of plant residues and vegetation cover. The potential of mulching as a component of farming practice for increasing the density of microarthropods and for influencing their species composition and population dynamics in agroecosystems is discussed.  相似文献   

16.
Calcium nitrate fertilizer containing 92.3 atoms % excess nitrogen-15 was applied on 5 May 1981 at a rate equivalent to 100 kg N ha?1 to a clay soil in southern England cropped to winter wheat. Samples of the soil gases were collected frequently during the following 3 weeks. The soil oxygen concentration declined to 5% after 60 mm rain. A maximum of 1.5 ± 0.5 atom % N-15 enrichment in labelled N2 gas (29N2) was detected in the soil atmosphere on 28 May. Total denitrification losses, calculated from air-filled pore space and rates of gas loss from the soil estimated using a Fick's law approximation, were 9.5 kg N ha?1 with a daily rate of 0.30 ± 0.07 kg N ha?1. Estimated total losses were greater than 30 kg N ha?1, 93% in the form N2, but the estimation depends on several assumptions about the amount of double labelled gas (30N2), rates of gas diffusion and flux.  相似文献   

17.
Nitrous oxide emission (N2O) from applied fertilizer across the different agricultural landscapes especially those of rainfed area is extremely variable (both spatially and temporally), thus posing the greatest challenge to researchers, modelers, and policy makers to accurately predict N2O emissions. Nitrous oxide emissions from a rainfed, maize-planted, black soil (Udic Mollisols) were monitored in the Harbin State Key Agroecological Experimental Station (Harbin, Heilongjiang Province, China). The four treatments were: a bare soil amended with no N (C0) or with 225?kg?N ha?1 (CN), and maize (Zea mays L.)-planted soils fertilized with no N (P0) or with 225?kg?N ha?1 (PN). Nitrous oxide emissions significantly (P?<?0.05) increased from 141?±?5?g N2O-N?ha?1 (C0) to 570?±?33?g N2O-N?ha?1 (CN) in unplanted soil, and from 209?±?29?g N2O-N?ha?1 (P0) to 884?±?45?g N2O-N?ha?1 (PN) in planted soil. Approximately 75?% of N2O emissions were from fertilizer N applied and the emission factor (EF) of applied fertilizer N as N2O in unplanted and planted soils was 0.19 and 0.30?%, respectively. The presence of maize crop significantly (P?<?0.05) increased the N2O emission by 55?% in the N-fertilized soil but not in the N-unfertilized soil. There was a significant (P?<?0.05) interaction effect of fertilization?×?maize on N2O emissions. Nitrous oxide fluxes were significantly affected by soil moisture and soil temperature (P?<?0.05), with the temperature sensitivity of 1.73–2.24, which together explained 62–76?% of seasonal variation in N2O fluxes. Our results demonstrated that N2O emissions from rainfed arable black soils in Northeast China primarily depended on the application of fertilizer N; however, the EF of fertilizer N as N2O was low, probably due to low precipitation and soil moisture.  相似文献   

18.
It was hypothesized that the application of eucalyptus biochar enhances nutrient use efficiencies of simultaneously supplied fertilizer, as well as provides additional nutrients (i.e., Ca, P, and K), to support crop performance and residual effects on subsequent crops in a degraded sandy soil. To test this hypothesis, we conducted an on‐farm field experiment in the Khon Kaen province of Northeastern Thailand to assess the effects of different application rates of eucalyptus biochar in combination with mineral fertilizers to upland rice and a succeeding crop of sugarcane on a sandy soil. The field experiment consisted of three treatments: (1) no biochar; (2) 3.1 Mg ha?1 biochar (10.4 kg N ha?1, 3.1 kg P ha?1, 11.0 kg K ha?1, and 17.7 kg Ca ha?1); (3) 6.2 Mg ha?1 biochar (20.8 kg N ha?1, 6.2 kg P ha?1, 22.0 kg K ha?1, and 35.4 kg Ca ha?1). All treatments received the same recommended fertilizer rate (32 kg N ha?1, 14 kg P ha?1, and 16 kg K ha?1 for upland rice; 119 kg N ha?1, 21 kg P ha?1, and 39 kg K ha?1 for sugarcane). At crop harvests, yield and nutrient contents and nitrogen (N) use efficiency were determined, and soil chemical properties and pH0 monitored. The eucalyptus biochar material increased soil Ca availability (117 ± 28 and 116 ± 7 mg kg?1 with 3.1 and 6.2 Mg ha?1 biochar application, respectively) compared to 71 ± 13 mg kg?1 without biochar application, thus promoting Ca uptake and total plant biomass in upland rice. Moreover, the higher rate of eucalyptus biochar improved CEC, organic matter, available P, and exchangeable K at succeeding sugarcane harvest. Additionally, 6.2 Mg ha?1 biochar significantly increased sugarcane yield (41%) and N uptake (70%), thus enhancing N use efficiency (118%) by higher P (96%) and K (128%) uptake, although the sugar content was not increased. Hence, the application rate of 6.2 Mg ha?1 eucalyptus biochar could become a potential practice to enhance not only the nutrient status of crops and soils, but also crop productivity within an upland rice–sugarcane rotation system established on tropical low fertility sandy soils.  相似文献   

19.
Abstract. The residual value of mineral N fertilizer applied in the spring was investigated in a field experiment where four cereals (winter wheat, winter barley, spring barley and spring oats) had been grown at reduced (0.7N), normal (1N) or high (1.3N) N fertilizer rates for 20 to 28 years. The effect of previous N fertilizer dressing was tested in two succeeding years by replacing the original N rate with five test N rates ranging from 0 to 240 kg N ha?1 for winter cereals and 0 to 200 kg N ha?1 for spring cereals. In the first test year, winter wheat grown on plots previously supplied with the high rate of mineral fertilizer (202 kg N ha?1 yr?1) yielded more grain and straw and had a higher total N uptake than wheat on plots previously supplied with the normal (174 kg N ha?1 yr?1) or reduced (124 kg N ha?1 yr?1) rate. The grain yield response and N uptake was not significantly affected by the N supply in the test year. The winter wheat grown in the second test year was unaffected by the previous N supply. Grain and straw yield response and total N uptake for spring barley, winter barley and oats, were almost identical irrespective of the previous N rate. After 20 to 28 years there were no significant differences in soil C and N (0 to 20 cm) between soil receiving three rates of N fertilizer. Soil from differently fertilized oat plots showed no significant differences in N mineralizing capacity. Nitrate leaching losses from the soils at the three N rates were estimated and the N balances for the 20 to 28 years experimental period calculated. The data indicated a reduction in overall loss of 189 to 466 kg N ha?1 at the normal and high N rates compared with the reduced N rate. We conclude that the N supplying capacity and soil organic matter content of this fertile sandy loam soil under continuous cereal cropping with straw removal was not significantly affected by differences in N fertilizer residues.  相似文献   

20.
The effects of 25 years of annual applications of P fertilizer on the accumulation and migration of soil Olsen‐P, and the effects of soil residual P on crop yields by withholding P application for the following 5 years, were evaluated in a subtropical region. Annual application of P fertilizer for 25 years to crops in summer (groundnut), winter (wheat, mustard or rapeseed) or in both seasons raised the Olsen‐P status of the plough layer (0–15 cm) from initially very low (12 kg P ha?1) to medium (18 kg P ha?1) and very high levels (40–59 kg P ha?1), depending on the amount of P surplus (amount of fertilizer applied in excess of removal by crops) (r = 0.86, P ≥ 0.01). However, only 4–9% of the applied P fertilizer accumulated as Olsen‐P to a depth of 15 cm (an increase of 2 mg kg?1per 100 kg ha?1 surplus P) in the sandy loam soil. In the following 5 years, the raising of 10 crops without P fertilizer applications decreased the accumulated Olsen‐P by only 20–30% depending upon the amount of accumulated P and crop requirements. After 29 years, 45–256 kg of residual P fertilizer had accumulated as Olsen‐P ha?1 in the uppermost 150 cm with 43–58% below 60 cm depth; this indicates enormous movement of applied P to deeper layers in this coarse textured soil with low P retention capacity for nutrients. Groundnut was more efficient in utilizing residual P than rapeseed; however, for both crops the yield advantage of residual P could be compensated for by fresh P applications. These results demonstrated little agronomic advantage above approximately 20 mg kg?1 Olsen‐P build‐up and suggested that further elevation of soil P status would only increase the risk of environmental problems associated with the loss of P from agricultural soils in this region.  相似文献   

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