Flood irrigation of wheat on a transitional red-brown earth. II. Effect of duration of ponding on availability of soil and fertilizer nitrogen

1991 ◽  
Vol 42 (7) ◽  
pp. 1037 ◽  
Author(s):  
E Humphreys ◽  
FM Melhuish ◽  
ZB Xi ◽  
RJG White ◽  
WA Muirhead
Keyword(s):  
Wheat Yield ◽  
Soil Layer ◽  
Experimental Period ◽  
Field Studies ◽  
Soil N ◽  
N Loss ◽  
Mineral N ◽  
Total N ◽  
Denitrification Potential ◽  
Soil Recovery

Grain yield of wheat growing on a transitional red-brown earth was reduced by long periods of ponding during irrigation. To determine whether fertilizer N loss was a major cause of this yield decline, 15N-labelled urea was applied to microplots at the same time and rate as the crop was topdressed with urea (end of tillerfng, 100 kg N ha-1). In addition, 15N-labelled nitrate was used to assess denitrification potential during and after each irrigation. Prior to the first irrigation (19days after urea application), 76% of the urea N was immobilized in the plants (33%) and soil (43%), 15% was present as soil mineral N, and 9% was not accounted for. The majority (85%) of the urea-derived mineral N was present as ammonium in the 0-0.1 m soil layer. After the first irrigation, amounts of mineral N in the soil remained very low at 3-6 kg N ha-l in the 0-0.2 m layer, with only 5-15% of this in the nitrate form. There was no significant effect of duration of ponding on plant or soii recovery of urea N after any irrigation. Mean plant recovery increased to 52%, over the first 55 days following urea application, while soil recovery declined to 22%. Beyond this stage changes in plant and soil recoveries were negligible. Plant total N content increased throughout the season due to ongoing mineralization of native soil N; however, there was negligible net mineralization of recently immobilized 15N beyond day 55. At physiological maturity, 46% of the N acquired by the plants was derived from the fertilizer. Losses of urea N increased to 25% over the first 55 days, and appeared to be due to nitrification-denitrification. Field studies with labelled nitrate indicated that denitrification potential in the soil was high throughout the experimental period. After the final two irrigations there were some significant (P < 0.05) effects of duration of ponding on N loss from urea, with lowest losses in the sprinkler, 1 h and 12 h treatments. The data indicate that, on the transitional red-brown earth, the adverse effect of long periods of ponding on wheat yield was not due to decreased availability or uptake of fertilizer or soil N in the longer term.

scholarly journals Effects of two wood-based biochars on the fate of added fertilizer nitrogen—a 15N tracing study

2021 ◽  
Author(s):  
Subin Kalu ◽  
Gboyega Nathaniel Oyekoya ◽  
Per Ambus ◽  
Priit Tammeorg ◽  
Asko Simojoki ◽  
...  
Keyword(s):  
Plant Uptake ◽  
Plant Biomass ◽  
Application Rate ◽  
Control Treatment ◽  
Organic N ◽  
N Leaching ◽  
Soil N ◽  
Mineral N ◽  
Total N ◽  
Application Rates

AbstractA 15N tracing pot experiment was conducted using two types of wood-based biochars: a regular biochar and a Kon-Tiki-produced nutrient-enriched biochar, at two application rates (1% and 5% (w/w)), in addition to a fertilizer only and a control treatment. Ryegrass was sown in pots, all of which except controls received 15N-labelled fertilizer as either 15NH4NO3 or NH415NO3. We quantified the effect of biochar application on soil N2O emissions, as well as the fate of fertilizer-derived ammonium (NH4+) and nitrate (NO3−) in terms of their leaching from the soil, uptake into plant biomass, and recovery in the soil. We found that application of biochars reduced soil mineral N leaching and N2O emissions. Similarly, the higher biochar application rate of 5% significantly increased aboveground ryegrass biomass yield. However, no differences in N2O emissions and ryegrass biomass yields were observed between regular and nutrient-enriched biochar treatments, although mineral N leaching tended to be lower in the nutrient-enriched biochar treatment than in the regular biochar treatment. The 15N analysis revealed that biochar application increased the plant uptake of added nitrate, but reduced the plant uptake of added ammonium compared to the fertilizer only treatment. Thus, the uptake of total N derived from added NH4NO3 fertilizer was not affected by the biochar addition, and cannot explain the increase in plant biomass in biochar treatments. Instead, the increased plant biomass at the higher biochar application rate was attributed to the enhanced uptake of N derived from soil. This suggests that the interactions between biochar and native soil organic N may be important determinants of the availability of soil N to plant growth.

Gross rates of soil N2O emission and uptake and denitrification gene abundance in temperate cropland agroforestry and monoculture systems

2021 ◽  
Author(s):  
Jie Luo ◽  
Lukas Beule ◽  
Guodong Shao ◽  
Edzo Veldkamp ◽  
Marife D. Corre
Keyword(s):  
Greenhouse Gas ◽  
Management Systems ◽  
Soil N ◽  
Soil Mineral N ◽  
Soil Mineral ◽  
Mineral N ◽  
Total N ◽  
Soil P ◽  
Gene Abundance ◽  
Denitrification Gene

&lt;p&gt;Monoculture croplands are considered as major sources of the greenhouse gas, nitrous oxide (N&lt;sub&gt;2&lt;/sub&gt;O). The conversion of monoculture croplands to agroforestry systems, e.g., integrating trees within croplands, is an essential climate-smart management system through extra C sequestration and can potentially mitigate N&lt;sub&gt;2&lt;/sub&gt;O emissions. So far, no study has systematically compared gross rates of N&lt;sub&gt;2&lt;/sub&gt;O emission and uptake between cropland agroforestry and monoculture. In this study, we used an in-situ &lt;sup&gt;15&lt;/sup&gt;N&lt;sub&gt;2&lt;/sub&gt;O pool dilution technique to simultaneously measure gross N&lt;sub&gt;2&lt;/sub&gt;O emission and uptake over two consecutive growing seasons (2018 - 2019) at three sites in Germany: two sites were on Phaeozem and Cambisol soils with each site having a pair of cropland agroforestry and monoculture systems, and an additional site with only monoculture on an Arenosol soil prone to high nitrate leaching. Our results showed that cropland agroforestry had lower gross N&lt;sub&gt;2&lt;/sub&gt;O emissions and higher gross N&lt;sub&gt;2&lt;/sub&gt;O uptake than in monoculture at the site with Phaeozem soil (P &amp;#8804; 0.018 &amp;#8211; 0.025) and did not differ in gross N&lt;sub&gt;2&lt;/sub&gt;O emissions and uptake with cropland monoculture at the site with Cambisol soil (P &amp;#8805; 0.36). Gross N&lt;sub&gt;2&lt;/sub&gt;O emissions were positively correlated with soil mineral N and heterotrophic respiration which, in turn, were correlated with soil temperature, and with water-filled pore space (WFPS) (r = 0.24 &amp;#8210; 0.54, P &lt; 0.01). Gross N&lt;sub&gt;2&lt;/sub&gt;O emissions were also negatively correlated with nosZ clade I gene abundance (involved in N&lt;sub&gt;2&lt;/sub&gt;O-to-N&lt;sub&gt;2&lt;/sub&gt; reduction, r = -0.20, P &lt; 0.05). These findings showed that across sites and management systems changes in gross N&lt;sub&gt;2&lt;/sub&gt;O emissions were driven by changes in substrate availability and aeration condition (i.e., soil mineral N, C availability, and WFPS), which also influenced denitrification gene abundance. The strong regression values between gross N&lt;sub&gt;2&lt;/sub&gt;O emissions and net N&lt;sub&gt;2&lt;/sub&gt;O emissions (R&lt;sup&gt;2 &lt;/sup&gt;&amp;#8805; 0.96, P &lt; 0.001) indicated that gross N&lt;sub&gt;2&lt;/sub&gt;O emissions largely drove net soil N&lt;sub&gt;2&lt;/sub&gt;O emissions. Across sites and management systems, annual soil gross N&lt;sub&gt;2&lt;/sub&gt;O emissions and uptake were controlled by clay contents which, in turn, correlated with indices of soil fertility (i.e., effective cation exchange capacity, total N, and C/N ratio) (Spearman rank&amp;#8217;s rho = -0.76 &amp;#8211; 0.86, P &amp;#8804; 0.05). The lower gross N&lt;sub&gt;2&lt;/sub&gt;O emissions from the agroforestry tree rows at two sites indicated the potential of agroforestry in reducing soil N&lt;sub&gt;2&lt;/sub&gt;O emissions, supporting the need for temperate cropland agroforestry to be considered in greenhouse gas mitigation policies.&lt;/p&gt;

Potential for biological denitrification of fertilizer nitrogen in sugarcane soils

1996 ◽  
Vol 47 (1) ◽  
pp. 67 ◽  
Author(s):  
KL Weier ◽  
CW McEwan ◽  
I Vallis ◽  
VR Catchpoole ◽  
RJ Myers
Keyword(s):  
Nitrous Oxide ◽  
Sampling Period ◽  
Field Studies ◽  
N Loss ◽  
Total N ◽  
Biological Denitrification ◽  
Sugarcane Crop ◽  
Ratoon Sugarcane ◽  
Red Earth ◽  
Crop Management Systems

Nitrogen (N) fertilizer is being lost from sugarcane soils following application to the crop. This study was conducted to estimate the quantity of N being lost from the soil through biological denitrification and to determine the proportion of gaseous N being emitted either as N2O or as N2. Field studies were conducted on four different soils (humic gley, alluvial massive earth, red earth and gleyed podzolic), and on different crop management systems, by installing plastic (PVC) cylinders (23.5 cm diam., 25 cm long) in the soil to a depth of 20 cm beside the plant row in a ratoon sugarcane crop. 15N-labelled KNO3 was applied as a band across each cylinder to a depth of 2.5 cm at a rate of 160 kg N/ha. After rainfall or irrigation, the cylinders were capped for 3 h intervals and gas in the headspace sampled in the morning and afternoon, for up to 4 days. Denitrification losses from the humic gley ranged from 247 g N/ha.day for cultivated plots to 1673 g N/ha.day for no-till plots. Over the sampling period, this was equivalent to 3.2% and 19.7% of the N applied, respectively. Nitrous oxide accounted for 46% to 78% of the total N lost. For the alluvial, massive earth and the red earth and gleyed podzolic, losses over the sampling period ranged from 25 to 117 g N/h.day and represented <1% of the N applied. Recovery of 15N in the soil ranged from 67% at the first sampling on the red earth soil to 4.9% at the third sampling on the alluvial, massive earth soil. In a glasshouse study, intact soil cores (23.5 cm diam., 20 cm long), taken from the humic gley and the alluvial, massive earth, were waterlogged after band application of 15N-labelled KNO3 at a rate of 160 kg N/ha. Gas samples from the headspace were taken after 3 h, and then morning and afternoon for the next 14 days. Denitrification losses ranged from 13.2 to 38.6% of N applied with the majority of gaseous N loss occurring as N2. Total recoveries after 14 days, including the evolved gases, ranged from 68.7 to 88.2%. We conclude that denitrification is a major cause of fertilizer N loss from fine-textured soils, with nitrous oxide the major gaseous N product when soil nitrate concentrations are high.

Wheat response after temperate crop legumes in south-eastern Australia

1991 ◽  
Vol 42 (1) ◽  
pp. 31 ◽  
Author(s):  
J Evans ◽  
NA Fettell ◽  
DR Coventry ◽  
GE O'Connor ◽  
DN Walsgott ◽  
...  
Keyword(s):  
New South ◽  
Wheat Yield ◽  
Wheat Crop ◽  
First Year ◽  
Mineral N ◽  
Total N ◽  
Available N ◽  
Relative Contribution ◽  
South Wales ◽  
Eastern Australia

At 15 sites in the cereal belt of New South Wales and Victoria, wheat after lupin or pea produced more biomass and had a greater nitrogen (N) content than wheat after wheat or barley; on average these crops assimilated 36 kg N/ha more. The improved wheat yield after lupin averaged 0 . 9 t/ha and after pea 0.7 t/ha, increases of 44 and 32% respectively. The responses were variable with site, year and legume. Soil available N was increased by both lupin and pea and the levels of surface inorganic N measured at the maturity of first year crops was often related to N in wheat grown in the following year. Of two possible sources of additional N for wheat after legumes, namely mineral N conserved in soil by lupin or pea (up to 60 kg N/ha) and the total N added in the residues of these legumes (up to 152 kg N/ha), both were considered significant to the growth of a following wheat crop. Their relative contribution to explaining variance in wheat N is analysed, and it is suggested wheat may acquire up to 40 kg N/ha from legume stubbles. Non-legume break crops also increased subsequent wheat yield but this effect was not as great as the combined effect of added N and disease break attained with crop legumes.

N2O fluxes in soils of contrasting textures fertilized with liquid and solid dairy cattle manures

2008 ◽  
Vol 88 (2) ◽  
pp. 175-187 ◽  
Author(s):  
Philippe Rochette ◽  
Denis A Angers ◽  
Martin H Chantigny ◽  
Bernard Gagnon ◽  
Normand Bertrand
Keyword(s):  
Dairy Cattle ◽  
Clay Soil ◽  
Soil Surface ◽  
Soil N ◽  
Soil Mineral N ◽  
Soil Mineral ◽  
Mineral N ◽  
Total N ◽  
Silage Maize ◽  
The Impact

Manure is known to increase soil N2O emissions by stimulating nitrification and denitrification processes. Our objective was to compare soil-surface N2O emissions following the application of liquid and solid dairy cattle manures to a loamy and a clay soil cropped to silage maize. Manures were applied in 2 consecutive years at rates equivalent to 150 kg total N ha-1 and compared with a control treatment receiving an equivalent rate of synthetic N. Soil-surface N2O fluxes, soil temperature, and soil water, nitrate and ammonium contents were monitored weekly in manured and control plots. From 60 to 90% of seasonal N2O emissions occurred during the first 40 d following manure and synthetic fertilizer applications, indicating that outside that period one or several factors limited N2O emissions. The period of higher emissions following manure and fertilizer application corresponded with the period when soil mineral N contents were highest (up to 17 g NO3−-N m-2) and water-filled pore space (WFPS) was greater than 0.5 m3 m-3. The absence of significant N2O fluxes later in the growing season despite high WFPS levels indicated that the stimulating effect of organic and synthetic N additions on soil N2O production was relatively short-lived. Fertilization of silage maize with dairy cattle manure resulted in greater or equal N2O emissions than with synthetic N. This was observed despite lower overall soil mineral N contents in the manured plots, indicating that other factors affected by manure, possibly additional C substrates and enhanced soil respiration, resulted in greater denitrification and N2O production. Silage maize yields in the manured soils were lower than those receiving synthetic N, indicating that the N2O emissions per kilogram of harvested biomass were greater for manures than for synthetic N. Our results also suggest that the main source of N2O was nitrification in the loam and denitrification in the clay soil. There was no clear difference in N2O emissions between liquid and solid manures. The variable effects of liquid and solid manure addition reported in the literature on soil N2O emissions likely result from the variable composition of the manures themselves as well as from interactions with other factors such as soil environment and farming practices. A better characterization of the availability of manure C and N is required to assess the impact of manure application on soil N2O emissions under field conditions. Key words: Greenhouse gases, N2O, maize, manure

Comparison of legume-based cropping systems at Warra, Queensland. 1. Soil nitrogen and organic carbon accretion and potentially mineralisable nitrogen

Soil Research ◽  
1996 ◽  
Vol 34 (2) ◽  
pp. 273 ◽  
Author(s):  
SA Hossain ◽  
RC Dalal ◽  
SA Waring ◽  
WM Strong ◽  
EJ Weston
Keyword(s):  
Soil Nitrogen ◽  
Soil Layer ◽  
Organic Matter Content ◽  
Plant Residues ◽  
N Availability ◽  
Pasture Management ◽  
Mineral N ◽  
Total N ◽  
Rhodes Grass ◽  
Organic C

Effects on soil nitrogen accretion and potentially mineralisable nitrogen were studied as part of a long-term field experiment established in 1986 to test alternative legume-based systems for restoring fertility in a Vertisol. Organic C accretion was also measured to ascertain the changes in organic matter content. The systems, which were studied only during 1989 and 1990, were a grass+legume ley (purple pigeon grass, Rhodes grass, lucerne, annual medics) of 4 years duration followed by wheat; a 2-year rotation of wheat (lucerne undersown) and lucerne; a 2-year rotation of wheat (medic undersown) and medic; a 2-year rotation of chickpea and wheat; and continuous wheat as control. Soil total N and organic C significantly increased in the 0–10 cm soil layer only under the grass+legume ley. There was no significant change in the soil C/N ratio. Plant residues contained from 52 to 104 kg N/ha in 1990 at the end of the legume phase, with high values for root N in the grass+legume ley. A comparison of N accretion versus fixation at the end of the legume-based systems in 1990 showed that net accumulation of N exceeded fixation in soil under lucerne and grass+legume leys; in the latter, net accumulation of 779 kg N/ha over 3.75 years was measured compared with 384 kg N/ha for N2 fixation. Part of the accumulation of N may have been due to uptake of NH4-N from the deep subsoil. Although values for soil mineral N (0–120 cm) were low at the end of all the legume-based systems, a deep subsoil (120–300 cm) accumulation of NH4-N was found in all treatments. The nitrogen mineralisation potentials (No) for 0–10 cm depth samples taken at the end of the legume phase in 1989 were higher in all the legume-based systems (105–182 mg N/kg) than the wheat control (57 mg N/kg). The rapid biological tests of N availability, both waterlogged and aerobic incubation, were more sensitive to treatment differences than No, in the surface and subsoil (range 12–78 mg N/kg for 0–10 cm soil for the waterlogged procedure). The rapid chemical tests, hot KCl extraction and the autoclave index, showed small treatment effects and did not appear to be useful availability indices. The pasture management (graced v. mown and removed) had no significant effect on total N, organic C and N availability indices in this alkaline Vertisol during the study period.

The impact of mineral soil cover fill on N2O emissions in peatland drained for agriculture

2020 ◽  
Author(s):  
Yuqiao Wang ◽  
Sonja Paul ◽  
Markus Jocher ◽  
Christine Alewell ◽  
Jens Leifeld
Keyword(s):  
Soil Moisture ◽  
Soil Cover ◽  
Mineral Soil ◽  
Experimental Period ◽  
Organic Soil ◽  
Soil N ◽  
Total N ◽  
Significant Difference ◽  
N Input ◽  
The Impact

&lt;p&gt;Drainage for agriculture has converted peatlands from a carbon sink to one of the world&amp;#8217;s major greenhouse gas (GHG) sources. In order to improve the sustainability of peatland management in agriculture, and to counteract soil subsidence, mineral soil coverage is becoming an increasingly used practice in Switzerland. Cover fills may change the GHG balance from the corresponding organic soil. To explore the effect of cover fill on soil N&lt;sub&gt;2&lt;/sub&gt;O emissions, we carry out a field experiment in the Swiss Rhine Valley and measure the soil &amp;#8211; borne N&lt;sub&gt;2&lt;/sub&gt;O exchange from two adjacent sites: drained organic soil without mineral soil cover (DN), and drained organic soil with mineral soil cover (DC). Mineral soil material was applied 12 years ago and varies in thickness between 20 &amp;#8211; 80 cm. Both sites have the identical farming practice (intensive permanent meadow). In our experiment, an automatic chamber system is used for collecting the N&lt;sub&gt;2&lt;/sub&gt;O at an interval of 3 h. Soil moisture, expressd as volumetric water content (VWC), is recorded every 10 min. After ten month (303 days) of continous measurement, the data reveal that: (1) The average N&lt;sub&gt;2&lt;/sub&gt;O emission from DN is higher than DC by a factor of 11 (11.24 &amp;#177; 3.46 &lt;em&gt;vs&lt;/em&gt; 0.97 &amp;#177; 0.22 mg N&lt;sub&gt;2&lt;/sub&gt;O-N m&lt;sup&gt;-2&lt;/sup&gt; day&lt;sup&gt;-1&lt;/sup&gt;). Hence, mineral soil cover of organic soil seems to induce a strong reduction in N&lt;sub&gt;2&lt;/sub&gt;O emissions. (2) Exogenous N inputs (mineral N fertilizer and cow slurry) are the main drivers of N&lt;sub&gt;2&lt;/sub&gt;O emissions. N&lt;sub&gt;2&lt;/sub&gt;O peaks occured shortly after the N application and lasted for 2 to 3 weeks before returning to background N&lt;sub&gt;2&lt;/sub&gt;O emission. At the DC site post N- input N&lt;sub&gt;2&lt;/sub&gt;O emissions accounted for 68 % of the total N&lt;sub&gt;2&lt;/sub&gt;O emission over the whole measurement period. An equivalent of around 1 % of the exogenous N- input was emitted as N&lt;sub&gt;2&lt;/sub&gt;O. At the DN site, emission peaks after fertilization accounted for 79 % of the total N&lt;sub&gt;2&lt;/sub&gt;O emission, equivalent to around 13 % of the exogenous N- input. Background emissions between peak events shows no significant difference between DC (0.51&amp;#177; 0.15 mg N&lt;sub&gt;2&lt;/sub&gt;O-N m&lt;sup&gt;-2&lt;/sup&gt; day&lt;sup&gt;-1&lt;/sup&gt;) and DN (2.73&amp;#177; 2.44 mg N&lt;sub&gt;2&lt;/sub&gt;O-N m&lt;sup&gt;-2&lt;/sup&gt; day&lt;sup&gt;-1&lt;/sup&gt;). The comparison of peak and background fluxes tentatively indicates that higher average emission rates from the DN site are related directly to fertilization. Finally, surface soil characteristics (soil pH, bulk density, and soil N) changed after mineral soil cover, and soil moisture content differed between sites. During the experimental period, the mean daily soil moisture from DN site (24.1 % VWC &amp;#8211; 60.18 % VWC) is higher than DC site (20.17 % VWC &amp;#8211; 51.26 % VWC). In summary, our data from this first experimental period suggest that mineral soil cover fill could strongly reduce the N&lt;sub&gt;2&lt;/sub&gt;O emission from drained organic soil, and may therefore be an interesting GHG mitigation option in agriculture.&amp;#160;&amp;#160;&lt;/p&gt;

Dissolved organic nitrogen contributes significantly to leaching from furrow-irrigated cotton–wheat–maize rotations

Soil Research ◽  
2017 ◽  
Vol 55 (1) ◽  
pp. 70 ◽  
Author(s):  
B. C. T. Macdonald ◽  
A. J. Ringrose-Voase ◽  
A. J. Nadelko ◽  
M. Farrell ◽  
S. Tuomi ◽  
...  
Keyword(s):  
Soil Surface ◽  
Significant Loss ◽  
Organic N ◽  
Irrigated Agriculture ◽  
Cotton Production ◽  
N Loss ◽  
Deep Drainage ◽  
Mineral N ◽  
Undisturbed Soil ◽  
Total N

Leaching of nitrogen (N) in intensive irrigated agriculture can be a significant loss pathway. Though many studies have focussed on losses of mineral N, and in particular nitrate, dissolved organic N (DON) has received less coverage. In the present study, over a 5-year period (2008–2013), 740kgNha–1 fertiliser was applied to an irrigated cotton–wheat–maize rotation on a cracking clay (grey Vertosol). Deep drainage from the undisturbed soil profile at the site was measured at 2.1m below the soil surface using a variable tension lysimeter. In total, 108mm of drainage occurred during the 5 years and the majority of the drainage and the irrigations occurred during the cotton seasons. The majority of the N loss occurred during the first 3–4 irrigations and neither the N loss nor its composition were affected by the product or timing of the fertiliser application. The N in the drainage was composed of 12.8kgNOx-Nha–1, 8.7 DON-N and 0.1 NH4+-Nkgha–1, which shows that DON is an important component (40%) of the deep drainage N from irrigated Vertosol cotton production systems. Overall the total N flux lost via deep drainage represents 3% of the applied N fertiliser.

Impact of legume 'break' crops on the residual amount and distribution of soil mineral nitrogen

2003 ◽  
Vol 54 (8) ◽  
pp. 763 ◽  
Author(s):  
J. Evans ◽  
G. Scott ◽  
D. Lemerle ◽  
A. Kaiser ◽  
B. Orchard ◽  
...  
Keyword(s):  
Green Manure ◽  
Grain Legumes ◽  
Potential Contribution ◽  
Soil N ◽  
Soil Mineral N ◽  
Soil Mineral ◽  
Mineral N ◽  
Total N ◽  
Legume Crops ◽  
Green Manure Crops

Important factors in the successful uptake of grain legumes by cereal growers have been their capacity to increase soil N and control cereal disease, as these have underpinned high yields in following wheat crops. However, alternative 1-year legume crops are required to introduce additional biodiversity and management flexibility for cereal growers. The effects on soil mineral N and potential contribution to soil total N of other legume enterprises were studied. These included vetch (Vicia bengalhensis) or clovers (mix of Trifolium alexandrinum, T.�versiculosum, T. resupinatum) managed for green manure; pea (Pisum sativum), vetch, or clovers managed for silage; and clovers managed for hay. These were compared with pea and lupin (Lupinus angustifolius) managed for grain production. Wheat was also included as a control. The legumes were grown in acidic Red Kandasol soil at Wagga Wagga in southern New South Wales, in 1996, 1997, and 1998. Mineral N was measured in the autumn or winter of seasons 1997 and 1998 respectively. Amounts of stubble residue N were measured in all seasons. The green manure crops, particularly vetch, produced more mineral N than both grain legumes. The forage conservation crops (silage or hay) produced similar amounts of mineral N to grain pea and more than grain lupin. For the grain and green manure legume crops, variation in amounts of mineral N was explained by the total N content of legume stubble residue, but for the forage conservation crops, more mineral N was measured than was predictable from stubble N. The amounts of mineral N at different soil depths differed between legume treatments and experiments (sites and years). Based only on above-ground plant N, the green manure crops contributed more to increasing total soil N than grain legumes; in turn, the grain legumes contributed more than the forage conservation crops. It was concluded that alternative annual legume enterprises to grain legumes may provide at least similar enrichment of soil mineral N early in the following season, and that all annual legume enterprises may accumulate nitrate deep in the soil profile in some seasons.

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