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1.
Ten charges of 15N-labelled straw with different C/N ratios were incubated with lightly loamed sand at 25 °C and 50 % of the maximum water capacity. At the start of the 18-week incubation, mineral nitrogen was added and the 15Nmin (NH4 and NO3-N) content was determined six times during the course of the experiment. A slow release of 15N was observed. After 111 days, between 2.5 and 13.0% of the total applied 15N was mineralized. The addition of ammonium sulphate caused an increasing degradation of organic N compounds of the straw material even during the first weeks. Finally, between 6.4 and 33.3 %15N was released. The 15N release only partially shows the straw degradation.  相似文献   

2.
Effect of monoethanolamine on yield of crops
I. Studies on the effect of monoethanolamine on the grain yield and the nitrogen household in cereal plants (pot experiments)
The effect of monoethanolamine (EA, applied as foliar spray, 10 mg per pot) on grain yield and yield components was investigated in pot experiments with spring barley, winter wheat, and winter rye. Under conditions of a moderate drought stress the applied EA increased the grain yield of spring barley from 5 % to 7 % (significance only at α= 0.05). A stimulating effect of EA on the grain yield of winter wheat and winter rye was also obtained.
The positive influence of EA on the grain yield of spring barley was reproducible under the conditions of a limited water supply in small-scale plot experiments (increase of yield about 9 %).
In case of spring barley and winter rye the increase of the grain yield by EA, applied at growth stage 31 (= DC 31) was connected with a greater number of ear-bearing tillers. The increase of the winter wheat yield resulted from more grains per ear of the tillers.
The enhanced formation of tiller grain mass and total tiller biomass by EA was in correlation with a higher nitrogen import into tillers (r = 0.8+). Since an export of N from the main shoots into the tillers was not observed a higher N uptake (≥ 6 %) was calculated from N balances. After a fertilization with 15N-labelled fertilizers the additional 15N uptake was 13 % to 20 %.
Possible stress reducing activities caused by EA are discussed.  相似文献   

3.
The residual effect of 2-year-old swards of clover-ryegrass mixture and ryegrass in monoculture on yield and N uptake in a subsequent winter wheat crop was investigated by use of the 15N dilution method and by mathematical modelling. The amount of N in the wheat crop, derived from clover-ryegrass residues was 25–43% greater than that derived from residues of ryegrass which had been growing in monoculture. Expressed in absolute values, the N uptake in the subsequent winter wheat crop was 23–28 kg N ha −1 greater after clover-ryegrass mixture than after ryegrass in monoculture. Up to about 54 kg N ha−1 of the N mineralised from the clover-ryegrass crop was calculated to be leached, whereas only 11 kg N ha−1 was leached following ryegrass in monoculture.  相似文献   

4.
A field experiment comparing different arable crop rotations was conducted in Denmark during 1997–2008 on three sites varying in climatic conditions and soil types, i.e. coarse sand (Jyndevand), loamy sand (Foulum), and sandy loam (Flakkebjerg). The crop rotations followed organic farm management, and from 2005 also conventional management was included for comparison. Three experimental factors were included in the experiment in a factorial design: 1) crop rotation (organic crop rotations varying in use of whole-year green manure (O1 and O2 with a whole-year green manure, and O4 without), and a conventional system without green manure (C4)), 2) catch crop (with and without), and 3) manure (with and without). The experiment consisted of three consecutive cycles using four-course rotations with all crops present every year, i.e. 1997–2000 (1st cycle), 2001–2004 (2nd cycle), and 2005–2008 (3rd cycle). In the 3rd cycle at all locations C4 was compared with two organic rotations, i.e. O2 and O4. The O2 rotation in the third cycle included spring barley, grass-clover, potato, and winter wheat, whereas C4 and O4 included spring barley, faba bean, potato, and winter wheat. For the O2 rotation with green manure there was a tendency for increased DM yield over time at all sites, whereas little response was seen in N yield. In the O4 rotation DM and N yields tended to increase at Foulum over time, but there was little change at Flakkebjerg. The DM yield gap between organic and conventional systems in the 3rd cycle varied between sites with 34–66% at Jyndevad, 21–44% at Foulum, and 32–52% at Flakkebjerg. The inclusion of grass-clover resulted in lower cumulated yield over the rotation than the treatment without grass-clover. The use of manure reduced the DM yield gap between conventional and organic systems on an average by 15 and 21%-points in systems with and without grass-clover, respectively, and the use of catch crops reduced the yield gap by 3 and 5%-points in the respective systems. Across all crops the agronomic efficiency of N in manure (yield benefit for each kg of mineral N applied) was greater in O4 compared with O2 for all crops.  相似文献   

5.
A lysimeter study was conducted to investigate how nitrogen uptake of spring wheat and oats and N leaching losses are differing when either oilseed rape or faba bean are grown as green manure. The experiment was conducted during 1982–1988, and fertilizer applied to the cereals was either farmyard manure, FYM, (6 and 12 g N/m2/year) or mineral fertilizer, MiF, at a rate of 6 g N/m2. On average of the 7 year period faba bean increased N uptake of the cereals fertilized with FYM at harvest by 3–4 g/m2. Differences between the two application rates were negligible. N-leaching losses increased twofold when faba bean was grown instead of oilseed rape. Growing faba bean after cereals supplied with MiF, too, increased N uptake of the cereals and significantly increased leaching losses.  相似文献   

6.
Field experiment with 8 different organic fertilizers (cattle dung with and without litter, pig slurry, peat compost formed from hen and pig slurry, sawdust-duck manure, noncomposted peat and straw litter with pig slurry) was carried out on loamy brown podzoluvisol since 1985.
The organic fertilizers were applied in the spring of 1985 on two backgrounds: with and without mineral fertilizers. The material is based on the data of four years (1985–1988). The arrangement of crops was the following: potato, spring wheat, barley and early barley.
On both backgrounds cattle dung with litter turned out to be the best organic fertilizer, while noncomposted peat manure had a low direct and residual effect. However, before the application it must be composted with pig or hen slurry. The effect of peat composts was dependent on the background of mineral fertilizers. Pig slurry had a low residual effect and acted only as a liquid nitrogen fertilizer. The joint application of straw and pig slurry can be a suitable opportunity for diminishing their undesirable effects.  相似文献   

7.
Long term incubation studies to determine the nitrogen (N) mineralization rates and kinetics in soils freshly amended with some commonly used green manures such as Sesbania rostrata. Gliricidia maculata. Leucaena leucocephala and Azolla pinnata are scarce. A long term aerobic study was, therefore, conducted by incubating soils freshly amended with the above-mentioned green manures in PVC columns at 35 ± 1 C and with 0.01 Mpa moisture content. The soils were then leached at periodic intervals for up to 36 weeks.
The N-mineralization rates were greatest during the first week and decreased with time in all soils. The green manure amended soils leached 247 mg kg−1 more NO3+ NO2– N than the unamended control. In general, the total N mineralized (mean 61%) was almost twice that of net N mineralized (mean 30%) in the amended soils. The percent N mineralized (total and net), however, varied with the nature of green manure incorporated into the soil. It was greatest in the soil amended with sesbania and lowest in the soil amended with azolla. The kinetic parameters derived using the double exponential model indicated that green manure amended soils possessed significantly higher N-mineralization potentials and rate constants compared to the unamended control. The kinetic parameters also varied with the nature of green manure incorporated into the soil. Among the various parameters lignin content, lignin to N ratio and lignin + polyphenol to N ratio of the green manures were the key factors governing the rate of decomposition and subsequent N mineralization from the amended soils.  相似文献   

8.
Phosphorus (P) is an essential nutrient and a limited resource, yet excess P is applied to agricultural land and can cause environmental problems in areas with intensive animal farming. In this study, the fertilizing effects of P in several animal manure-based products (including thermal treatment) were tested after application to two agricultural soil types (Jyndevad soil: clay 5.1%, silt 4.1%, sand 88.9%, organic matter 2.1%, total C 1.2% soil dry matter (DM), total P 266 mg kg−1 soil DM, pH 6.3; Rønhave soil: clay 15.4%, silt 32.6%, sand 49.6%, organic matter 2.3%, Total C 1.3% soil DM, total P 488 mg kg−1 soil DM, pH 6.6). The first-year effect of P application was tested in a spring barley crop (Hordeum vulgare L.) and residual P effects were tested in a perennial ryegrass (Lolium perenne L.) crop the following year. Untreated ash from thermally gasified animal manure biogas residue (GA) and a corresponding neutralized acid extract of the ash (ExL) in liquid form were the products in focus. Other products in use were: pelletized pig manure biogas residue (PEL), incinerated PEL (IA), anaerobically digested pig slurry (DS), dried ExL, dried fraction of separated pig slurry (SS), thermally gasified SS (GAs), thermally gasified poultry manure (GAp), crushed triple super phosphate (TSP) and disodium phosphate (DSP) was used as reference P fertilizer. For application of 20 kg P ha−1 mineral P fertilizer replacement value (RV) in the second year in the sandy soil was 76% and 99% for GA, 79% and 123% for IA, 95% and 155% for PEL, 94% and 73% for ExL, 55% and 15% for ExD, 64% and 82% for SS, 104% and 109% for DS, 60% and 95% for GAp, 73% and 111% for GAs, where the first value is based on barley DM yield and the second on barley total P uptake. Tripling the GA application rate to 60 kg P ha−1 in both soils had no significant effect on barley DM yield and P uptake. The overall efficiency for liquid fertilizers was much higher than for solid ones and relative effectiveness (RE) of ExL was comparable to RE of DSP. Despite the low P level in soils, the ryegrass crop grew very well on both soils in the second year, and there was no detectable residual effect of the treatments on grass yield and P uptake. In conclusion, untreated ash and solid manures used in this study were not suitable as starter P fertilizer, but could be used to maintain the level of available P in soil, as there were indications that ash/manure P contributed significantly to plant P uptake during the growing season of barley.  相似文献   

9.
A field experiment was carried out on maize (Zea mays, L.) to study the effects of different fertilizer management on nitrogen status in soil and plant response. Three different fertilizers, mineral (MN), mineral plus buffalo manure (MN + BM) and organo-mineral with peat (OMP), were added at the usual (140, 61 and 116 kg ha−1) and the reduced (70, 31 and 58 kg ha−1) rates of N, P and K. respectively. Soil samples were analyzed for N by both the Kjeldahl method and the electro-ultrafiltration technique (EUF). The soil Kjeldahl-N concentrations were scarcely affected by the different fertilizer treatments, while the EUF-N concentrations were closely correlated with the amounts of N added. The EUF also discriminated between the NO3-N and the sum of the ammonium and the easily extractable organic N forms (EUF-Norg + NH4). The largest proportions of EUF-Norg + NH4 were found in the untreated plots and in the plots treated with buffalo manure. The different fertilizer treatments significantly affected grain yield, which ranged from a minimum of 6.3 t ha−1 from the untreated plots, to a maximum of 11.9 t ha−1 from those supplied with 140 kg N, 61 kg P and 116 kg K ha−1 by OMP fertilizer. The highest agronomic efficiency index for N was exhibited in the OMP treatment at the reduced rate. The grain yield was closely correlated with the total extractable EUF-N, but different relationships were found between the rate of N added, the level of EUF-NO,-N in soil and grain yield for the different fertilizer treatments.  相似文献   

10.
Most farmers in the rainfed parts of Jordan who use fertilizers use less than optimum rates of N and P because of the uncertainties associated with rainfall. Research results obtained by the national program indicated that the use of improved barley cultivars and fertilizers would result in substantial yield increases. The objective of the present investigation was to determine the optimum combination level of N and P for newly promising cultivars. The effect of 0–0, 5–10, 10–20 and 15–30 kg.ha−1 of nitrogen (N) and phosphorus (P) levels on barley cultivas Rum, Giza, Fun, Harmel and Arta under rainfed conditions in the Mediterranean climate was studied during two cropping seasons, 1994-95 and 1995–96. Increased grain and straw yields, total N and P uptake and RUE were recorded with increasing N and P levels for almost all cultivars. Rum was significantly (P = 0.05) the highest grain and straw producer and highest RUE at the 10 N- and 20 P kg.ha−1 level. The cultivar × fertility level (N–P) interactions were not significant for both grain and straw yields and for total N and P uptake.  相似文献   

11.
为探究氨基酸态氮对烤烟生长及氮素营养贡献的影响，以南江三号为试验材料，以L-谷氨酸(Glu)为有机氮源，15NH415NO3为无机氮源，设置不同氮源配比的5个处理：不施氮(CK)、100%无机氮(T1)、25%谷氨酸态氮+75%无机氮(T2)、50%谷氨酸态氮+50%无机氮(T3)、75%谷氨酸态氮+25%无机氮(T4)和100%谷氨酸态氮(T5)，测定烟株生物量、氮含量及相关酶的活性。结果表明，施用谷氨酸对生育前期烟株的生物量及氮素含量均有一定的抑制作用，团棵期抑制效果最明显；生育后期，25%～50%的氨基酸能促进烟株的生长；随谷氨酸比重的增加，上、中部烟叶全氮占比有不同程度的增加，而下部烟叶全氮占比从16.77%到8.03%逐渐降低，施用谷氨酸有利于烟株中、上部烟叶氮素含量的积累；烟株根、茎、叶的谷丙转氨酶和谷氨酸脱氢酶活性均随谷氨酸占比的增加呈增长趋势。可见，烤烟可以直接吸收且利用谷氨酸分子，低浓度谷氨酸与无机氮配施能促进烟株的生长，调节烟株体内氮素的分布，但高浓度谷氨酸则对烟株的生长起抑制作...  相似文献   

12.
New high yielding early maturing cultivars of lupins have been introduced in north-west Europe as grain protein crops in crop rotations. This paper reports on a comparative study of lupins with peas and oats, and of their effect on yield of subsequent winter barley crops. These crops were given five levels of N under irrigated and non-irrigated conditions on sand and loam. Under rain fed conditions the grain yield of pea, oat and lupin varied between 24–36, 34–53 and 18–37 hkg DM ha−1, respectively. Supplemental irrigation raised grain yield of oat to 50–60 hkg DM ha−1, while grain yield in pea was not affected and grain yield in lupin in most cases decreased due to gray mould attack and excessive vegetative growth in the indeterminate lupin variety. Under rain fed conditions, the grain nitrogen content of pea, oat and lupin varied between 137–172, 61–80 and 189–226 kg N ha−1, respectively, and was significantly higher in lupin as compared with pea. On sandy soil, similar low-root densities were found for pea, oat and lupin below 30 cm depth. On sand, at final harvest the residual soil-N of lupin and pea, as measured in a subsequent winter barley crop not supplied with N fertilizer, was 15 and 8–10 kg N ha−1 higher than in winter barley following oat, respectively. The nature of the probably more N-root residues of lupin is discussed. On loam, the residual N of lupin and pea was similar, 18–27 kg N ha−1. On sand, under rain fed conditions preceding lupin and pea as compared with oat, increased the barley grain yield at zero N-application 77 and 49%, respectively; the effect of lupin was significantly higher than that of pea until the highest N-level 120 kg N-application ha−1. On loam under rain fed conditions preceding lupin and pea increased the barley grain yield at zero N-application by 36 and 62%, respectively, as compared with oat; at N-application>60 kg N ha−1 the grain yield was similar after all three crops. For both soil types the same level of effect was found under irrigated conditions. Conclusions: Supplemental irrigation might result in lower grain yield in lupin due to gray mould attack and excessive growth if indeterminate lupin varieties are used. Grain nitrogen yield of lupin is significantly higher than that of pea. On sand, the effect of lupin on the subsequent winter barley grain yield is significantly higher than that of pea, probably due to greater N-root nitrogen residues. On loam, lupin and pea have similar effects on the subsequent winter barley crop.  相似文献   

13.
In intensive farming systems, farmers split up and apply the N fertilization to winter cereals and oilseed rape (OSR) at several dates to meet the need of the crop more precisely. Our objective was to determine how prior fertilizer N application as slurry and/or mineral N affects contributions of fertilizer‐ and soil‐derived N to N uptake of barley (1997), oilseed rape (OSR; 1998) and wheat (1999). In addition, residual fertilizer N effects were observed in the subsequent crop. Since autumn 1991, slurry (none, slurry in autumn, in spring, in autumn plus in spring) and mineral N fertilizer (0, 12 and 24 g N m−2) were applied annually. Each year, the treatments were located on the same plots. In 1997–1999, the splitting rates of the mineral N fertilization were labelled with 15N. Non‐fertilizer N uptake was estimated from the total N uptake and the fertilizer 15N uptake. All three crops utilized the splitting rates differently depending on the time of application. Uptake of N derived from the first N rate applied at the beginning of spring growth was poorer than that from the second splitting rate applied at stem elongation (cereals) or third splitting rate applied at ear emergence or bud formation (all three crops). In contrast, N applied later in the growing season was taken up more quickly, resulting in higher fertilizer N‐use efficiency. Mineral N fertilization of 24 g N m−2 increased significantly non‐fertilizer N uptake of barley and OSR at most of the sampling dates during the growing season. In cereals, slurry changed the contribution of non‐fertilizer N to the grain N content only if applied in spring, while OSR utilized more autumn slurry N. In OSR and wheat, only small residual effects occurred. The results indicate that 7 years of varying N fertilization did not change the contribution of soil N to crop N uptake.  相似文献   

14.
To investigate the genetic variation of phosphate (P) uptake and P utilization efficiency, 24 high-yielding spring barley cultivars were grown in two pot experiments on a loess loam-sand mixture. In the first experiment, the plants grew until maturity under P stress (50% of the maximum yield), and in the second experiment, the plants grew until the stage of tillering (DC 25) at a low or at a high P supply.

At maturity, the range between cultivars with the highest and the lowest values were 30% for total dm yield (grain and straw), 28% for grain yield, 24% for P uptake efficiency (P in grain and straw), 26% for P concentration in grains and 24% for P utilization efficiency quotient PEQ (g dm grain per mg P in shoots) (mean of all cultivars = 100%). Grain yield was correlated with P uptake per plant, r = 0.71***, and with PEQ, r = 0.60**. Between P uptake and PEQ, there was only a weak relationship (r = −0.14). Therefore, a combination of high uptake efficiency and high PEQ in a cultivar may be possible.

At growth stage DC 25, the cultivars showed a significant variability in shoot biomass, P concentration, P removal, P influx, acitvity of acid phophatases (Pase) and root length. The ranking of the cultivars, however, was very different at the two P levels, but the root-length and the Pase activity were more influenced by genotype than by the P supply.

As the relationships between grain yield, P removal, PEQ and the characters of the young plants cultivated under P stress were very weak (r < 0.43), selection for P efficiency at the stage of tillering cannot be recommended.  相似文献   


15.
Effect of several organic manures on the efficiency of Azospirillum lipoferum
Under greenhouse conditions, it was examined how grass mulch, farmyard manure and compost influence the efficiency of Azospirillum lipoferum with Sorghum bicolor. The organic manures were added at 5 concentrations: 0, 50, 100, 200 and 300 dt/ha.
With the exception of the highest amount the grass mulch always induced a good effect of Azospirillum on plant yield and nutrient uptake. The application of farmyard manure or compost did not improve the growth of the inoculated plants. With farmyard manure the inoculation even lowered shoot dry weights. But in both treatments the inoculated plants showed considerably increased N and P contents. In addition to the N2 fixation the inoculation with Azospirillum lipoferum apparently can increase the capacity of the sorghum plant roots to absorb P. Primarily, the organic manures create better growing conditions for the bacteria and simultaneously serve as P sources.  相似文献   

16.
The absorption and utilization of nitrogen (N) by plants are affected by salinity and the form of N in the root medium. A hydroponic study was conducted under controlled conditions to investigate growth and N uptake by barley ( Hordeum vulgare L.) supplied with five different NH4+-N/NO3−-N ratios at electrical conductivity of 0 and 8 dS m−1. The five NH4+-N/NO3-N ratios were 0/100, 25/75, 50/50, 75/25 and 100/0, each giving a total N supply of 100 mg N l−1 in the root medium. A mixed N supply of NH4+ and NO3− resulted in greater accumulation of N in plants than either NO3− or NH4+ as the sole N source. Plants produced a significantly higher dry matter yield when grown with mixed N nutrition than with NH4+ or NO3− alone. Total dry matter production and root and shoot N contents decreased with increasing salinity in the root medium. The interaction between salinity and N nutrition was found to be significant for all the variables. A significant positive correlation (r=0.97) was found between nitrogen level in the plant shoot and its dry matter yield.  相似文献   

17.
The objective of this study was to determine the effect of biochar addition on the soil N balance and cotton yield in a drip-irrigated cotton field. The experiment included four soil amendments: control, cotton straw biochar, corn cob biochar, and poultry manure biochar. The biochar was applied at a rate of 4.5 t·hm－2 except control. The results showed that all three types of biochar significantly reduced both the apparent soil N loss and the N surplus. The effect of cotton straw biochar treatment was most significant, relative to the control. Plant nitrogen uptake differed significantly between the different treatments, decreasing in the order cotton straw biochar > poultry manure biochar > corn cob biochar. Cotton yield also differed significantly between the different treatments, decreasing in the order poultry manure biochar > corn cob biochar, and cotton straw biochar.  相似文献   

18.
In long-term field experiments on loamy sand and sandy loam, legumes (pea and lupine) stimulated microbial activity in the rhizosphere more than cereals (winter rye, winter wheat and spring barley), maize and oil flax. In the rhizosphere of winter wheat and maize, microbial activity and the bacteria species Pseudomonas , Agrobacterium and Xanthomonas were more stimulated by organic manuring than by mineral fertilization. A positive correlation between the stimulated bacteria species and the growth of young plants was found. Various mineral nitrogen applications had no influence on the rhizosphere microflora. The leghemoglobin content of pea nodules – an indicator of nitrogen fixation activity – was reduced by high nitrogen application in crop rotation.  相似文献   

19.
A lysimeter trial is described in which the fate of 15N was monitored in a sand, loam and clay soil by using it over a period of 6 years. The following results were obtained.
1. The uptake of fertilizer nitrogen by plants, determined by using 15N, is lower than by using the conventional method ("difference method"). Nitrate 15N is better utilized by the plants than is ammonium 15N. The total nitrogen uptake only gives hints of these differences.
2. The extent to which plants utilize fertilizer 15N is between 38 and 58%; in the case of the method of differences this figure is between 48 and 68%.
3. Plants remove more nitrogen from the soil when fertilizer N is applied than when without fertilization. The influence of these two nutrient forms is of subordinate significance.
4. After a trial period of six years between 26 and 54 % of the fertilizer 15N remains in the soil. The resulting sequences are clay > loam > sand > and ammonium > nitrate.
5. The immobilization of the fertilizer 15N is most pronounced in the first four years but then decreased considerably; in the case of the sandy soil it is then even slightly regressive.
6. The biggest part of the 15N is deposited in the uppermost layer of the soil. The amount of 15N in the deeper layers is diminished appreciably. The type of soil has a greater influence than the form of nitrogen.
7. If the amount of fertilizer N left in the soil is compared with the N losses from the soil's reservoir (plants' uptake, leaching) there is a negative balance for the soil nitrogen which mainly is determined by the type of soil.  相似文献   

20.
Organic farming systems are characterized by the strong regulation of the import of nutrients into the farming system. Recently, nutrient budgets in organic farming especially with regard to potassium (K) and phosphorus (P) have gained interest. In the present study inner farm mineral nutrient flows of P, K and magnesium (Mg) among the farmland sub-compartments arable land and permanent grassland via the dairy stable were analysed. The objectives of the current study were (1) to quantify the inner farm nutrient flows among different farmland sub-compartments, and (2) to assess the effect of purchased biomass on inner farm nutrient cycles. Results indicated that the ratio of the nutrients N, P and K in the stable inputs (feed, bedding) greatly differed depending on the kind of biomass introduced into the stable (roughage in comparison to concentrates or straw for bedding), i.e. via grassland biomass much more K (7.9 kg) per kg P were introduced than with feeds harvested on arable land like silage maize (4.9 kg K per kg P), concentrates like cereals (1.3–1.6 kg K per kg P) or grain pulses like peas (2.4 kg K per kg P). The different inputs are mixed in the manures leading to intermediate concentration in the stable manures, with the consequence that nutrient composition of the manures does not match the composition of the single stable inputs. Therefore, balances of nutrient flows in such mixed systems indicate a relative transfer of K from grassland to arable land via the stable manure (approximately 10–30% of the manure derived from grassland K, depending among others on the amounts of straw high in K needed for animal bedding), if P was used as reference nutrient for stable manure allocation to permanent grassland and arable land. Yields of non-legumes in arable cropping in organic farming systems is very often limited by nitrogen (N) supply, whereas it is well known that manure additions are rather ineffective on permanent grassland high in legumes. The higher N demand of arable crops as well as P and K offtakes from arable land via sold animal and plant products give some scope for a preferable use of stable manures for manuring arable land to replace mineral nutrient outputs and to improve the soil N and the soil humus status, increasing the demand for supplement of mineral nutrients on the permanent grassland area to avoid long-term impoverishment of soil fertility.  相似文献   

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