Contributions of nitrogen by field pea (Pisum sativum L.) in a continuous cropping sequence compared with a lucerne (Medicago sativa L.)-based pasture ley in the Victorian Wimmera

2000 ◽  
Vol 51 (1) ◽  
pp. 13 ◽  
Author(s):  
M. H. McCallum ◽  
M. B. Peoples ◽  
D. J. Connor
Keyword(s):  
N2 Fixation ◽  
Farming Systems ◽  
Field Pea ◽  
Continuous Cropping ◽  
Soil Mineral N ◽  
Soil Mineral ◽  
Mineral N ◽  
Total N ◽  
Biological N2 Fixation ◽  
Cropping Sequence

The nitrogen (N) dynamics (N2 fixation inputs, changes in soil mineral N and total N, N removed in agricultural produce) of a lucerne-based phase farming system (grazed lucerne–annual medic–ryegrass pastures grown in rotation with crops) was compared with that of continuous cropping (cereal, oilseed, and legume pulse crops) in the Victorian Wimmera. The contribution of biological N2 fixation to the N economy of these different systems was strongly linked to biomass production by the legume components of pastures, or field pea in the cropping sequence. The amount of fixed N present in field pea shoots or the total amount of N2 estimated to be fixed by the whole plant (shoots and roots) (121–175 kg N/ha.crop and 181–262 kg N/ha.crop, respectively) was generally greater than the combined measured annual inputs of fixed N by lucerne and annual medic during a pasture ley (40–95 kg N/ha.year in herbage, 80–190 kg N/ha.year in total plant), although large amounts of N were removed in the field pea grain at harvest (115–151 kg N/ha.crop). Over 2 years (1995–96), the seasonal rainfall patterns had a much larger impact on the growth, dry matter production, and N2 fixation of annual medic compared with lucerne. Winter-cleaning of ryegrass from the pasture before cropping resulted in a greater legume content in the pasture and generally increased amounts of fixed N in herbage (by up to 55 kg N/ha.year). Total soil N at depth (0.5–1.0 m) was significantly greater after 2–4 years of pasture than under continuous cropping. In one year (1996), the amount of soil mineral N following a winter-cleaned pasture was greater (by 32–45 kg N/ha, 0–1 m) than after either canola or wheat, producing a yield benefit in a subsequent canola crop that was equivalent to pre-drilling 46 kg N/ha as fertiliser. However, despite some improvements in N fertility, large crop responses to N fertiliser were still observed following pasture. Grain yield was increased by 0.33–0.55 t/ha in canola and by 1.0 t/ha in wheat, grain protein raised by 0.7–2.3% in canola and by 1.3% in wheat, and oil yield in canola enhanced by 124–205 kg/ha with pre-drilled applications of fertiliser N (46 kg/ha). It is speculated that more legume-dominant pastures (>80%) could provide greater flow-on N benefits to farming systems in the Wimmera than the mixed legume–grass swards used in the present study. However, it is likely that a need will remain for supplementary fertiliser N to optimise the nutrition of subsequent non-legume crops in the region.

New ley legumes increase nitrogen fixation and availability and grain crop yields in subtropical cropping systems

2017 ◽  
Vol 68 (1) ◽  
pp. 11 ◽  
Author(s):  
Lindsay W. Bell ◽  
John Lawrence ◽  
Brian Johnson ◽  
Mark B. Peoples
Keyword(s):  
N2 Fixation ◽  
Farming Systems ◽  
Grain Sorghum ◽  
Soil N ◽  
Soil Mineral N ◽  
Soil Mineral ◽  
Forage Legumes ◽  
Mineral N ◽  
Forage Sorghum ◽  
Grain Crops

Several new and existing short-term forage legumes could be used to provide nitrogen (N) inputs for grain crops in subtropical farming systems. The fixed-N inputs from summer-growing forage legumes lablab (Lablab purpureus), burgundy bean (Macroptilium bracteatum) and lucerne (Medicago sativa) and winter-growing legume species snail medic (Medicago scutellata), sulla (Hedysarum coronarium) and purple vetch (Vicia benghalensis) were compared over several growing seasons at four locations in southern Queensland, Australia. Available soil mineral N and grain yield of a following cereal crop were compared among summer-growing legumes and forage sorghum (Sorghum spp. hybrid) and among winter-growing legumes and forage oats (Avena sativa). In the first year at all sites, legumes utilised the high initial soil mineral N, with <30% of the legume N estimated to have been derived from atmospheric N2 (%Ndfa) and legume-fixed N <30 kg/ha. In subsequent years, once soil mineral N had been depleted, %Ndfa increased to 50–70% in the summer-growing legumes and to 60–80% in winter-growing legumes. However, because forage shoot N was removed, rarely did fixed N provide a positive N balance. Both lablab and burgundy bean fixed up to 150 kg N/ha, which was more than lucerne in all seasons. Prior to sowing cereal grain crops, soil nitrate was 30–50 kg/ha higher after summer legumes than after forage sorghum. At one site, lablab and lucerne increased the growth and yield of a subsequent grain sorghum crop by 1.4 t/ha compared with growth after forage sorghum or burgundy bean. Of the winter-growing legumes, sulla had the highest total N2 fixation (up to 150 kg N/ha.year) and inputs of fixed N (up to 75 kg N/ha), and resulted in the highest concentrations of soil N (80–100 kg N/ha more than oats) before sowing of the following crop. Wheat protein was increased after winter legumes, but there was no observed yield benefit for wheat or grain sorghum crops. New forage legume options, lablab, burgundy bean and sulla, showed potential to increase N supply in crop rotations in subtropical farming systems, contributing significant fixed N (75–150 kg/ha) and increasing available soil N for subsequent crops compared to non-legume forage crops. However, high soil mineral N (>50 kg N/ha) greatly reduced N2 fixation by forage legumes, and significant N2 fixation only occurred once legume shoot N uptake exceeded soil mineral N at the start of the growing season. Further work is required to explore the impact of different management strategies, such as livestock grazing rather than harvesting for hay, on the long-term implications for nutrient supply for subsequent crops.

N2 fixation and its value to soil N increase in lupin, field pea and other legumes in south-eastern Australia

1989 ◽  
Vol 40 (4) ◽  
pp. 791 ◽  
Author(s):  
J Evans ◽  
GE O'Connor ◽  
GL Turner ◽  
DR Coventry ◽  
N Fettell ◽  
...  
Keyword(s):  
N2 Fixation ◽  
Sowing Date ◽  
Annual Rainfall ◽  
Potential Contribution ◽  
Soil N ◽  
Soil Mineral N ◽  
Soil Mineral ◽  
Mineral N ◽  
Total N ◽  
Eastern Australia

N2 fixation and its potential contribution to increasing soil total N were estimated in field-grown crops of lupin and pea in 21 trials at 10 locations in New South Wales and Victoria, during 1984 to 1987. Chickpea, faba bean and annual medic were included at some sites. Across experiments there were differences in annual rainfall (267 to 646 mm), soil N (0.02 to 0.20%), soil pH (CaCl2,4.3 to 8.0) and sowing date (24 April to 16 June). Most experiments were conducted on acidic (pH < 4.8) red-earth, the others on grey-cracking clay or sandy soil, both of higher pH The differing sites, seasons, and sowing time contributed to variation in legume biomass (2.02 to 14.33 t/ha) and total N (45 to 297 kg N/ha), and the amount of N harvested with grain (8 to 153 kg N/ha), which were related.Lupin fixed an average of 65% of total crop N, and pea 61%, but there was considerable variation about these averages (20 to 97%). Significant differences in % N2 fixation between legumes within sites were few. The amount of N2 fixed averaged 98.5 kg N/ha by lupin and 80.5 kg N/ha by pea, varying 26 to 288 kg N/ha and 16 to 177 kg N/ha, respectively. Variation in proportional and total N2 fixation was associated with biomass, soil mineral N, and sowing date. N2 fixation increased with more biomass and declined with higher soil mineral N, and later sowing (lupin). Each additional tonne of dry matter increased fixed N by c. 20 kg N/ha. Differences in amounts of fixed N between legumes within sites were due primarily to biomass differences.N2fixed by lupin contributed an average of 38.2 kg N/ha to soil N, and by pea, 17.9 kg N/ha. The contribution was variable, -41 to 135 kg N/ha (lupin) and -32 to 96 kg N/ha (pea), and correlated with proportional and total N2 fixation. Positive increase to soil total N occurred when lupin fixed at least 50% of its crop N, and pea 65%. This occurred in most crops. Legumes frequently used less of the available soil N than cereals.

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;

scholarly journals Split nitrogen application in potato: effects on accumulation of nitrogen and dry matter in the crop and on the soil nitrogen budget

1999 ◽  
Vol 133 (3) ◽  
pp. 263-274 ◽  
Author(s):  
J. VOS
Keyword(s):  
Dry Matter ◽  
N Recovery ◽  
Separate Analysis ◽  
Soil Mineral N ◽  
Soil Mineral ◽  
Mineral N ◽  
N Application ◽  
N Content ◽  
Total N ◽  
N Utilization

In four field experiments, the effects of single nitrogen (N) applications at planting on yield and nitrogen uptake of potato (Solanum tuberosum L.) was compared with two or three split applications. The total amount of N applied was an experimental factor in three of the experiments. In two experiments, sequential observations were made during the growing season. Generally, splitting applications (up to 58 days after emergence) did not affect dry matter (DM) yield at maturity and tended to result in slightly lower DM concentration of tubers, whereas it slightly improved the utilization of nitrogen. Maximum haulm dry weight and N content were lower when less nitrogen was applied during the first 50 days after emergence (DAE). The crops absorbed little extra nitrogen after 60 DAE (except when three applications were given). Soil mineral N (0–60 cm) during the first month reflected the pattern of N application with values up to 27 g/m2 N. After 60 DAE, soil mineral N was always around 2–5 g/m2. The efficiency of N utilization, i.e. the ratio of the N content of the crop to total N available (initial soil mineral N+deposition+net mineralization) was 0·45 for unfertilized controls. The utilization of fertilizer N (i.e. the apparent N recovery) was generally somewhat improved by split applications, but declined with the total amount of N applied (range 0·48–0·72). N utilization and its complement, possible N loss, were similar for both experiments with sequential observations. Separate analysis of the movement of Br− indicated that some nitrate can be washed below 60 cm soil depth due to dispersion during rainfall. The current study showed that the time when N application can be adjusted to meet estimated requirements extends to (at least) 60 days after emergence. That period of time can be exploited to match the N application to the actual crop requirement as it changes during that period.

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

scholarly journals Impact of Legumes as a Pre-Crop on Nitrogen Nutrition and Yield in Organic Greenhouse Tomato

Plants ◽  
2021 ◽  
Vol 10 (3) ◽  
pp. 468
Author(s):  
Anastasios Gatsios ◽  
Georgia Ntatsi ◽  
Luisella Celi ◽  
Daniel Said-Pullicino ◽  
Anastasia Tampakaki ◽  
...  
Keyword(s):  
Tomato Fruit ◽  
Soil Mineral N ◽  
Soil Mineral ◽  
Mineral N ◽  
Tomato Crop ◽  
Total N ◽  
Green Manuring ◽  
Preceding Crop ◽  
Greenhouse Tomato ◽  
Tomato Yield

An organic greenhouse crop of tomato was established in February following cultivation of cowpea (CP) or common bean (CB) for green pod production, or faba bean (FB) for green manuring. The vegetative residues of CP and CB were incorporated to the soil together with farmyard manure (FYM), prior to establishing the tomato crop. The FB plants were incorporated to the soil at anthesis together with either FYM or composted olive-mill waste (CO). Green manuring with FB resulted in higher soil mineral N levels during the subsequent tomato crop and higher tomato fruit yield when combined with FYM, compared to compost. The level of soil mineral N was the main restrictive factor for yield in organic greenhouse tomato. FB for green manuring as preceding crop to tomato increased significantly the level of soil mineral N and tomato yield compared to CB or CP aiming to produce green pods. The lowest tomato yield was obtained when the preceding crop was CB cultivated for green pod production. The soil mineral N was significantly higher when FYM was applied as base dressing compared with CO, despite the higher total N concentration in CO, pointing to slower mineralization rates of CO during tomato cultivation.

scholarly journals The Effect of Meat and Bone Meal (MBM) on Crop Yields, Nitrogen Content and Uptake, and Soil Mineral Nitrogen Balance

Agronomy ◽  
2021 ◽  
Vol 11 (11) ◽  
pp. 2307
Author(s):  
Anna Nogalska ◽  
Aleksandra Załuszniewska
Keyword(s):  
Crop Yields ◽  
N Uptake ◽  
Mineral Nitrogen ◽  
Soil Mineral N ◽  
Soil Mineral ◽  
Meat And Bone Meal ◽  
Bone Meal ◽  
Mineral N ◽  
N Content ◽  
Total N

A long-term (six year) field experiment was conducted in Poland to evaluate the effect of meat and bone meal (MBM), applied without or with mineral nitrogen (N) fertilizer, on crop yields, N content and uptake by plants, and soil mineral N balance. Five treatments were compared: MBM applied at 1.0, 1.5, and 2.0 Mg ha−1, inorganic NPK, and zero-fert check. Mineral N accounted for 100% of the total N rate (158 kg ha−1) in the NPK treatment and 50%, 25%, and 0% in MBM treatments. The yield of silage maize supplied with MBM was comparable with that of plants fertilized with NPK at 74 Mg ha−1 herbage (30% DM) over two years on average. The yields of winter wheat and winter oilseed rape were highest in the NPK treatment (8.9 Mg ha−1 grain and 3.14 Mg ha−1 seeds on average). The addition of 25% and 50% of mineral N to MBM had no influence on the yields of the tested crops. The N content of plants fertilized with MBM was satisfactory (higher than in the zero-fert treatment), and considerable differences were found between years of the study within crop species. Soil mineral N content was determined by N uptake by plants rather than the proportion of mineral N in the total N rate. Nitrogen utilization by plants was highest in the NPK treatment (58%) and in the treatment where mineral N accounted for 50% of the total N rate (48%).

Nitrogen Uptake of Field-grown Cotton. I. Distribution in Plant Components in Relation to Fertilization and Yield

1983 ◽  
Vol 19 (1) ◽  
pp. 91-101 ◽  
Author(s):  
D. M. Oosterhuis ◽  
J. Chipamaunga ◽  
G. C. Bate
Keyword(s):  
Nitrogen Uptake ◽  
Dry Matter ◽  
Field Trials ◽  
Early Growth ◽  
Soil Mineral N ◽  
Soil Mineral ◽  
Inorganic N ◽  
Mineral N ◽  
Total N ◽  
Plant Components

SUMMARYThree levels of nitrogen (N) were applied to cotton grown in irrigated field trials at two locations in Zimbabwe in 1978. Dry matter (DM) production, total uptake and distribution of N among vegetative and reproductive components, and soil mineral-N contents were recorded about every 14 days. About 60% of total DM was produced, and 40% of total N taken up, between 10 and 16 weeks after sowing. Most N was present in vegetative parts, particularly leaves and branches, during early growth but, later, it accumulated in buds, flowers and bolls. At maturity, seeds and lint contained 42% of total above-ground plant N. N concentrations were similar in sympodial and mainstem leaves, petioles and branches. Inorganic N applied at sowing had little effect on plant N, but when given after 10 weeks it increased the N content of leaves, stems, branches, petioles and bolls.

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.

Can legumes provide greater benefits than millet as a spring cover crop in southern Queensland farming systems?

2017 ◽  
Vol 68 (8) ◽  
pp. 746
Author(s):  
E. M. Wunsch ◽  
L. W. Bell ◽  
M. J. Bell
Keyword(s):  
Soil Water ◽  
Cover Crops ◽  
Cover Crop ◽  
Farming Systems ◽  
N Fixation ◽  
Soil Mineral N ◽  
Soil Mineral ◽  
Mineral N ◽  
Legume Cover Crops ◽  
Chemical Fallow

Cover crops grown during fallows can increase organic matter inputs, improve soil surface cover to reduce erosion risk, and enhance rainfall infiltration. An experiment compared a chemical fallow control with six different cover crops terminated at either 60 or 90 days after sowing. The commercial choice of millet (Echinochloa esculenta) was compared with two summer legumes (lablab (Lablab purpureus) and soybean (Glycine max)), and three winter legumes (field pea (Pisum sativum), faba bean (Vicia faba) and common vetch (Vicia sativa)). Cover crop biomass growth, atmospheric nitrogen (N) fixation, surface residue cover, and soil water and mineral N dynamics during the growth period and subsequent fallow were measured. Soil water and N availability and yield of wheat crops following the experimental treatments were simulated over a 100-year climate record using APSIM. Both experiments and simulations found the legumes inferior to millet as spring-sown cover crops, because they were slower to accumulate biomass, required later termination and provided groundcover that was less persistent, resulting in lower soil water at the end of the fallow. After 90 days of growth, the summer legumes, lablab and soybean, produced the most biomass and fixed more N (up to 25 kg N/ha) but also extracted the most soil water and mineral N. Legume N fixation was low because of high soil mineral N status (>100 kg N/ha) and occurred only when this had been depleted. At the end of the subsequent fallow in April, soil water was 30–60 mm less and soil mineral N 80–100 kg/ha less after both millet and 90-day terminated summer legume cover crops than the chemical fallow control. Simulations predicted soil-water deficits following legume cover crops to be >50 mm in the majority of years, but soil mineral N was predicted to be lower (median 80 kg N/ha) after millet cover crops. In conclusion, monoculture legume cover crops did not provide advantages over the current commercial standard of millet, owing to less effective provision of groundcover, low N fixation and possibly delayed release of N from residues. Further work could explore how legumes might be more effectively used as cover crops to provide N inputs and soil protection in subtropical farming systems.

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