A comparison of chickpeas and pasture legumes for sustaining yields and nitrogen status of subsequent wheat

1997 ◽  
Vol 48 (3) ◽  
pp. 305 ◽  
Author(s):  
I. C. R. Holford ◽  
G. J. Crocker
Keyword(s):  
Protein Content ◽  
Crop Residues ◽  
N Uptake ◽  
Yield Potential ◽  
Wheat Crop ◽  
N Fixation ◽  
Soil N ◽  
Red Clay ◽  
Mineral N ◽  
Positive Effects

Six treatments were compared for their effects on wheat yields, nitrogen (N) uptake, protein content, and fertiliser N requirements in a long-term rotation study on a black earth and a red clay in northern New South Wales. Three of the treatments were lucerne, subterranean clover, and snail medic, all grown simultaneously from 1988 to 1990 and all followed by 3 years of wheat. The other 3 treatments were biennial rotations of chickpea–wheat and long-fallow–wheat as well as a continuous wheat monoculture, all lasting 6 years. With the exception of the first wheat crop, which experienced very low growing-season rainfall, lucerne was more beneficial than other legumes to following wheat crops in terms of yield, protein content, and fertiliser N requirement. Clover closely followed lucerne in the magnitude of its positive effects, whereas medic and chickpea produced much smaller effects. Because of the amount of N removed in the chickpea grain, it appeared that the small positive effects of chickpea were due to soil N sparing or rapid mineralisation from crop residues rather than any net contribution of N fixation to soil N accretion. Average yields of the 3 wheat crops following lucerne and clover were much higher than average yields 20 years previously following lucerne, even though average yields of continuously grown wheat have declined over the past 20 years. However, lucerne eliminated the need for N fertiliser for no more than 2 following wheat crops, and clover for only the first wheat crop. It appears that the longer duration of lucerne benefits reported in earlier studies was due to the higher background soil N levels as well as the lower yield potential in the earlier years. Nevertheless, lucerne lowered the fertiliser requirement of the third wheat crop by more than 50%. In contrast to lucerne, annual legumes are probably most beneficial if grown in alternate years with wheat. The large benefits of long fallowing particularly on the black earth were apparently caused by its enhancement of soil moisture and mineral N accumulation. However, these N effects were surprisingly large considering the degree of depletion of organic matter in long-fallowed soils.

Productivity and nitrogen use of three different wheat-based rotations in North West Syria

1998 ◽  
Vol 49 (3) ◽  
pp. 451 ◽  
Author(s):  
M. Wood ◽  
C. J. Pilbeam ◽  
H. C. Harris ◽  
J. Tuladhar
Keyword(s):  
Crop Residues ◽  
Wheat Crop ◽  
N Mineralisation ◽  
Soil N ◽  
N Budget ◽  
Mineral N ◽  
North West ◽  
System A ◽  
To Come ◽  
C 50

Productivity of 3 different 2-year crop rotations, namely continuous wheat, wheat-chickpea, and wheat-fallow, was measured over 4 consecutive seasons beginning in 1991-92 at the ICARDA station, Tel Hadya, Syria. Nitrogen (N) fertiliser (30 kg N/ha at sowing) was broadcast every other year in the continuous wheat only. 15N-labelled fertiliser was used to quantify the amount of nitrogen supplied to the crops through current and past applications of fertiliser and by N2 fixation. The remaining N in the crop was assumed to come from the soil. In any single season, wheat yields were unaffected by rotation or N level. However, 2-year biomass production was significantly greater (32%, on average) in the continuously cropped plots than in the wheat-fallow rotation. On average, <10% of the N in the wheat crop came from fertiliser in the season of application, and <1·2 kg N/ha of the residual fertiliser was recovered by a subsequent wheat crop. Chickpea fixed 16-48 kg N/ha, depending on the season, but a negative soil N budget was still likely because the amount of N removed in the grain was usually greater than the amount of atmospheric N2 fixed. Uptake of soil N was similar in the cereal phase of all 3 rotations (38 kg N/ha, on average), but over the whole rotation at least 33% more soil N was removed from continuously cropped plots than from the wheat-fallow rotation, suggesting that the latter is a more sustainable system. A laboratory study showed that although wheat and chickpea residues enhanced the gross rate of N mineralisation by c. 50%, net rates of N mineralisation were usually negative. Given the high C/N ratio of the residue, immobilisation, rather than loss processes, is the likely cause of the decline in the mineral N content of the soil. Consequently, decomposition of crop residues in the field may in the short term reduce rather than increase the availability of N for crop growth.

scholarly journals Residual effect of clover-rich leys on soil nitrogen and successive grain crops

2008 ◽  
Vol 17 (1) ◽  
pp. 73 ◽  
Author(s):  
A. NYKÄNEN ◽  
A. GRANSTEDT ◽  
L. JAUHIAINEN
Keyword(s):  
Field Experiments ◽  
Clayey Soil ◽  
N Uptake ◽  
Residual Effect ◽  
Red Clover ◽  
N Leaching ◽  
N Fixation ◽  
Mineral N ◽  
Total N ◽  
Biological N Fixation

Legume-based leys form the basis for crop rotations in organic farming as they fix nitrogen (N) from the atmosphere for the succeeding crops. The age, yield, C:N, biological N fixation (BNF) and total N of red clover-grass leys were studied for their influence on yields, N uptake and N use efficiency (NUE) of the two sequential cereal crops planted after the leys. Mineral N in deeper soil (30-90 cm) was measured to determine N leaching risk. Altogether, four field experiments were carried out in 1994-1998 at two sites. The age of the ley had no significant effect on the yields and N uptake of the two subsequent cereals. Surprisingly, the residual effect of the leys was negligible, at 0–20 kg N ha-1yr-1. On the other hand, the yield and C:N of previous red clover-grass leys, as well as BNF-N and total-N incorporated into the soil influenced subsequent cereals. NUEs of cereals after ley incorporation were rather high, varying from 30% to 80%. This might indicate that other factors, such as competition from weeds, prevented maximal growth of cereals. The mineral N content deeper in the soil was mostly below 10 kg ha-1 in the sandy soil of Juva, but was 5-25 kg ha-1 in clayey soil of Mietoinen.;

Quantifying N response and N use efficiency in rice–wheat (RW) cropping systems under different water management

2009 ◽  
Vol 147 (3) ◽  
pp. 303-312 ◽  
Author(s):  
Q. JING ◽  
H. VAN KEULEN ◽  
H. HENGSDIJK ◽  
W. CAO ◽  
P. S. BINDRABAN ◽  
...  
Keyword(s):  
Water Management ◽  
Management Practices ◽  
Cropping Systems ◽  
N Uptake ◽  
Production Costs ◽  
Wheat Crop ◽  
N Recovery ◽  
Soil Nitrate ◽  
Soil N ◽  
N Use

SUMMARYAbout 0·10 of the food supply in China is produced in rice–wheat (RW) cropping systems. In recent decades, nitrogen (N) input associated with intensification has increased much more rapidly than N use in these systems. The resulting nitrogen surplus increases the risk of environmental pollution as well as production costs. Limited information on N dynamics in RW systems in relation to water management hampers development of management practices leading to more efficient use of nitrogen and water. The present work studied the effects of N and water management on yields of rice and wheat, and nitrogen use efficiencies (NUEs) in RW systems. A RW field experiment with nitrogen rates from 0 to 300 kg N/ha with continuously flooded and intermittently irrigated rice crops was carried out at the Jiangpu experimental station of Nanjing Agricultural University of China from 2002 to 2004 to identify improved nitrogen management practices in terms of land productivity and NUE.Nitrogen uptake by rice and wheat increased with increasing N rates, while agronomic NUE (kg grain/kg N applied) declined at rates exceeding 150 kg N/ha. The highest combined grain yields of rice and wheat were obtained at 150 and 300 kg N/ha per season in rice and wheat, respectively. Carry-over of residual N from rice to the subsequent wheat crop was limited, consistent with low soil nitrate after rice harvest. Total soil N hardly changed during the experiment, while soil nitrate was much lower after wheat than after rice harvest. Water management did not affect yield and N uptake by rice, but apparent N recovery was higher under intermittent irrigation (II). In one season, II management in rice resulted in higher yield and N uptake in the subsequent wheat season. Uptake of indigenous soil N was much higher in rice than in wheat, while in rice it was much higher than values reported in the literature, which may have consequences for nitrogen fertilizer recommendations based on indigenous N supply.

Nitrogen benefits of lupins, field pea, and chickpea to wheat production in south-eastern Australia

1997 ◽  
Vol 48 (1) ◽  
pp. 39 ◽  
Author(s):  
E. L. Armstrong ◽  
D. P. Heenan ◽  
J. S. Pate ◽  
M. J. Unkovich
Keyword(s):  
N2 Fixation ◽  
Aboveground Biomass ◽  
Crop Residues ◽  
Field Pea ◽  
Superior Performance ◽  
Wheat Crop ◽  
Wagga Wagga ◽  
Soil N ◽  
Narrow Leaf ◽  
Eastern Australia

Nitrogen balances of narrow leaf lupin (Lupinus angustifolius L.), albus lupin (L. albus L.), field pea (Pisum sativum L.), chickpea (Cicer arietinum L.), and barley (Hordeum vulgare L.) sown over a range of dates were examined in 1992 in a rotation study at Wagga Wagga, NSW. Each N budget included assessment of dependence on fixed as opposed to soil N, peak aboveground biomass N, and N removed as grain or returned as unharvested aboveground crop residues. N balances of wheat sown across the plots in 1993 were assessed similarly in terms of biomass and grain yield. Yields, N2 fixation, and crop residue N balances of the legumes were markedly influenced by sowing time, and superior performance of lupins over other species was related to higher biomass production and proportional dependence on N2 fixation, together with a poorer harvest index. Residual N balances in aboveground biomass after harvest of the 1992 crops were significantly correlated with soil mineral N at 1993 sowing and with biomass and grain N yields of the resulting wheat crop. Best mean fixation and grain N yield came from albus lupin. Wheat grain N yields following the 2 lupins were some 20% greater than after fiield pea and chickpea and 3 times greater than after barley. Net soil N balance based solely on aboveground returns of N of legumes in 1992 through to harvest of wheat in 1993 was least for narrow leaf lupin-wheat ( –20 kg N/ha), followed by albus lupin-wheat ( –44), chickpea-wheat ( –74), and field pea-wheat ( –96). Corresponding combined grain N yields (legume+wheat) from the 4 rotations were 269, 361, 178, and 229 kg N/ha, respectively. The barley-wheat rotation yielded a similarly computed soil N deficit of 67 kg/ha. Data are discussed in relation to other studies on legume-based rotations.

Nitrogen balance in Australia and nitrogen use efficiency on Australian farms

Soil Research ◽  
2017 ◽  
Vol 55 (6) ◽  
pp. 435 ◽  
Author(s):  
J. F. Angus ◽  
P. R. Grace
Keyword(s):  
Agricultural Land ◽  
International Standards ◽  
N Balance ◽  
Yield Potential ◽  
N Fixation ◽  
Soil N ◽  
N Losses ◽  
Dryland Farming ◽  
Australian Continent ◽  
Fertiliser Application

The amount of reactive N in soils on the Australian continent appears to be increasing, mainly because of biological N-fixation by permanent pastures in the dryland farming zone. This gain is partly offset by N-mining by crops, which we estimate have removed between one-fifth and one-quarter of the original soil N. The vast areas of non-agricultural land and arid rangelands appear to be in neutral N balance and the relatively small area of intensive agriculture is in negative balance. There are regional N losses from the sugar and dairy industries to groundwater, estuaries and lagoons, including the Great Barrier Reef. Fertiliser N application is increasing, and is likely to increase further, to compensate for the soil-N mining and to meet increasing crop yield potential, but fertiliser-N represents a relatively small fraction of the Australian N balance. The dryland farming zone utilises the largest amounts of native and fertiliser N. The average fertiliser application to dryland cereals and oilseeds, 45 kg N ha–1, is low by international standards because of the small N-demand by dryland crops and because there are no subsidies on crops or fertiliser that promote overuse. The efficiency of N-use is relatively low, for example about 40% of fertiliser N is recovered in the aboveground parts of dryland wheat and the rest is retained in the soil, denitrified or otherwise lost. We suggest further research on fertiliser-application methods to increase crop recovery of fertiliser, as well as research to reduce the surplus N from permanent pasture.

Nitrogen and water flows under pasture - wheat and lupin - wheat rotations in deep sands in Western Australia. 2. Drainage and nitrate leaching

1998 ◽  
Vol 49 (3) ◽  
pp. 345 ◽  
Author(s):  
G. C. Anderson ◽  
I. R. P. Fillery ◽  
F. X. Dunin ◽  
P. J. Dolling ◽  
S. Asseng
Keyword(s):  
Water Content ◽  
Soil Water ◽  
Soil Water Content ◽  
Western Australia ◽  
Root Zone ◽  
N Uptake ◽  
Subterranean Clover ◽  
Lower Amount ◽  
Wheat Crop ◽  
Mineral N

Quantification of nitrate (NO-3) leaching is fundamental to understanding the efficiency with which plants use soil-derived nitrogen (N). A deep sand located in the northern wheatbelt of Western Australia was maintained under a lupin (Lupinus angustifolius)-wheat (Triticum aestivum) and a subterranean clover (Trifolium subterraneum) based annual pasture-wheat rotation from 1994to 1996. Fluxes of water and NO-3 through, and beyond, the root-zone were examined. Drainage was calculated on a daily basis from measurements of rainfall, evapotranspiration, and the change in soil water content to a depth of 1·5 m. Evapotranspiration was estimated from Bowen ratio measurements,and soil water content was determined by time domain reflectrometry. Soil was sampled in layers to1·5 m at the onset of winter rains and analysed for NO-3 . Ceramic suction cups were installed at 0·25, 0·4, 0·6, 0·8, 1·0, 1·2, and 1·4 m to sample soil solution from June to mid August. The NO-3 leached from each layer was computed by multiplying the daily drainage through each layer by the estimated concentration of NO-3 within the layer. The estimated concentration of NO-3 in a layer was calculated by taking into account NO-3 either entering that layer through mineralisation and leachingor leaving the layer through plant uptake. Mineral N was added to the surface 0·2 m in accordance with measured rates of net N mineralisation, and daily N uptake was calculated from the measured above-ground plant N derived from soil N. Root sampling was undertaken to determine root lengthdensity under pastures, lupin, and wheat. Cumulative drainage below 1·5 m was similar under wheat and lupin, and accounted for 214 mmfrom 11 May to 15 August 1995 and 114 mm from 2 July to 15 September 1996. The cumulative evapotranspiration (Ea) over these periods was 169 mm from a wheat crop in 1995, and 178 mm from a lupin crop in 1996. The amount of NO-3 in soil at the start of the growing season was afiected by previous crop, with a lower range following wheat (31-68 kg N/ha) than following legumes (40-106 kgN/ha). These large quantities of NO-3 in the soil at the break of the season contributed substantially to NO-3 leaching. Leaching of NO-3 below 1·5 m in wheat crops accounted for 40-59 kg N/ha where these followed either lupin or pasture. In contrast, less NO-3 was found to leach below 1·5 m in pastures (17-28 kg N/ha). Greater N uptake by capeweed (Arctotheca calendula L.) than by either wheat or lupin was the main reason for the lower amount of NO-3 leached in pastures.

Fluxes of nitrogen derived from plant residues and fertiliser on a cracking clay in a semi-arid environment.

1998 ◽  
Vol 49 (3) ◽  
pp. 437 ◽  
Author(s):  
R. D. Armstrong ◽  
K. McCosker ◽  
G. Millar ◽  
M. E. Probert
Keyword(s):  
Ammonium Sulfate ◽  
N Uptake ◽  
Arid Environment ◽  
Grain Sorghum ◽  
Wheat Crop ◽  
Microbial Biomass N ◽  
Plant Residues ◽  
Lablab Purpureus ◽  
Mineral N ◽  
N Fertility

The feasibility of using legume leys to redress declining levels of soil nitrogen (N) fertility on the heavy clay Vertisols of the northern Australian grain belt depends partly on the ability of plant residues to supply N directly to subsequent cereal crops. An alternative is the use of fertiliser N in continuous cereal cropping. Two experiments were conducted (one in the field, the other under polyhouse conditions) to compare the uptake of N from either plant residues or ammonium sulfate fertiliser that had been labelled with 15N. In a field trial, 15N-labelled shoots of grain sorghum and Desmanthus virgatus and ammonium sulfate were applied to micro-plots and the flux of the added N between different soil pools and a wheat crop was followed over 219 days. Only small amounts of residue-derived N (<5%) were recovered in the mineral N of the soil at a depth of 0-10 cm, whereas over 88% of the fertiliser N was present as mineral N soon after adding the fertiliser. Soil microbial biomass-N was increased following addition of residues. Recovery of added 15N in the wheat crop was much higher from the fertiliser (35%) than from the 2 residue sources (<5%). The pot trial compared a wider range of 15N-labelled residues (shoot and root residues of Desmanthus virgatus, Lablab purpureus, and sorghum) with several rates of ammonium sulfate, applied in the presence and absence of non-labelled grain sorghum residues, over 4 cropping cycles. Dry matter production and N uptake were increased by application of fertiliser N, although the response was reduced in the presence of non-labelled sorghum residues; responses to residue N were much smaller than those to fertiliser N. In the first crop following residue application <7% of residue N was recovered, increasing to 12-23% over the 4 crops. Recovery of fertiliser N by the crops increased with the rate of application, and also depended on whether it was applied together with residues. A feature of the results, in both the field and pot experiments, was the large proportion of applied 15N that could not be accounted for in either the soil or the crops, and these losses have been attributed to denitrification.

Comparison of legume-based cropping systems at Warra, Queensland. 2. Mineral nitrogen accumulation and availability to the subsequent wheat crop

Soil Research ◽  
1996 ◽  
Vol 34 (2) ◽  
pp. 289 ◽  
Author(s):  
SA Hossain ◽  
WM Strong ◽  
SA Waring ◽  
RC Dalal ◽  
EJ Weston
Keyword(s):  
Grain Yield ◽  
Fertility Restoration ◽  
Cropping Systems ◽  
N Uptake ◽  
Mineral Nitrogen ◽  
Yield Response ◽  
Wheat Crop ◽  
Nitrogen Accumulation ◽  
Mineral N ◽  
Yield Increase

Mineral nitrogen release following legume-based cropping systems for restoring the fertility of a Vertisol and the yield response and N uptake of subsequent wheat crops was studied. Legume phases of pastures, including a 4 year grass+legume ley, and lucerne and medic leys (~1 year) were terminated in October 1988 or 1989 and rotated with wheat. Chickpea-wheat rotations matched those of lucerne and medic leys. Mineral N accumulations during a subsequent fallow period were determined by core sampling to 1.5 m in October, February and May. Grain yield and N uptake of wheat enabled comparisons of the fertility restorative effects of the various systems relative to continuous wheat cropping. Averaged for two fallow periods, increases in mineral N down to 1.2 m depth were 93, 91, 68, and 37 kg/ha following grass+legume, lucerne and medic leys, and chickpea, respectively, compared with the continuous wheat treatment. Wheat yields were generally lower in 1989 (1.85–2.88 t/ha) than in 1990 (2.08–3.59 t/ha) following all leys and crops due to seasonal conditions. There was a grain yield increase of 0.11 and 0.52 t/ha in 1989 and 1.23 and 1.26 t/ha in 1990 following lucerne and medic leys, respectively and 0.85 t/ha in 1990 following a 4 year grass+legume ley. Following chickpea there was a yield increase of 0.81 and 1.36 t/ha in 1989 and 1990 respectively. Nitrogen uptake by wheat was increased by 40 and 49 kg/ha in 1989 and 48 and 58 kg/ha in 1990 following lucerne and medic leys respectively and 63 kg/ha in 1990 following a 4 year grass+legume ley. Following chickpea N uptake by wheat was increased by 27 and 32 kg/ha in 1989 and 1990 respectively. Grain protein concentration of wheat was substantially higher following all pasture leys (11.7–15.8%) than following wheat (8.0–9.4%) or chickpea (9.4–10.1%). Therefore, there was substantial evidence of the effectiveness of pasture leys in soil fertility restoration, as reflected in mineral N, yield response and N uptake by subsequent wheat crops.

scholarly journals Frequency Versus Quantity: Phenotypic Response of Two Wheat Varieties to Water and Nitrogen Variability

2021 ◽  
Author(s):  
Olivia H. Cousins ◽  
Trevor P. Garnett ◽  
Amanda Rasmussen ◽  
Sacha J. Mooney ◽  
Ronald J. Smernik ◽  
...  
Keyword(s):  
Soil Moisture ◽  
Plant Growth ◽  
Carbon Allocation ◽  
N Uptake ◽  
N Availability ◽  
Soil N ◽  
High Moisture ◽  
Mineral N ◽  
Wheat Varieties ◽  
The Impact

AbstractDue to climate change, water availability will become increasingly variable, affecting nitrogen (N) availability. Therefore, we hypothesised watering frequency would have a greater impact on plant growth than quantity, affecting N availability, uptake and carbon allocation. We used a gravimetric platform, which measures the unit of volume per unit of time, to control soil moisture and precisely compare the impact of quantity and frequency of water under variable N levels. Two wheat genotypes (Kukri and Gladius) were used in a factorial glasshouse pot experiment, each with three N application rates (25, 75 and 150 mg N kg−1 soil) and five soil moisture regimes (changing water frequency or quantity). Previously documented drought tolerance, but high N use efficiency, of Gladius as compared to Kukri provides for potentially different responses to N and soil moisture content. Water use, biomass and soil N were measured. Both cultivars showed potential to adapt to variable watering, producing higher specific root lengths under low N coupled with reduced water and reduced watering frequency (48 h watering intervals), or wet/dry cycling. This affected mineral N uptake, with less soil N remaining under constant watering × high moisture, or 48 h watering intervals × high moisture. Soil N availability affected carbon allocation, demonstrated by both cultivars producing longer, deeper roots under low N. Reduced watering frequency decreased biomass more than reduced quantity for both cultivars. Less frequent watering had a more negative effect on plant growth compared to decreasing the quantity of water. Water variability resulted in differences in C allocation, with changes to root thickness even when root biomass remained the same across N treatments. The preferences identified in wheat for water consistency highlights an undeveloped opportunity for identifying root and shoot traits that may improve plant adaptability to moderate to extreme resource limitation, whilst potentially encouraging less water and nitrogen use.

Dynamics of nitrogen capture without fertilizer: the baseline for fertilizing winter wheat in the UK

2001 ◽  
Vol 136 (1) ◽  
pp. 15-33 ◽  
Author(s):  
R. SYLVESTER-BRADLEY ◽  
D. T. STOKES ◽  
R. K. SCOTT
Keyword(s):  
Winter Wheat ◽  
N Uptake ◽  
Soil Horizon ◽  
Soil N ◽  
Soil Mineral N ◽  
Fertilizer N ◽  
Soil Mineral ◽  
Mineral N ◽  
Fertilizer Use ◽  
The Uk

Experiments at three sites in 1993, six sites in 1994 and eight sites in 1995, mostly after oilseed rape, tested effects of previous fertilizer N (differing by 200 kg/ha for 1993 and 1994 and 300 kg/ha for 1995) and date of sowing (differing by about 2 months) on soil mineral N and N uptake by winter wheat cv. Mercia which received no fertilizer N. Soil mineral N to 90 cm plus crop N (‘soil N supply’; SNS) in February was 103 and 76 kg/ha after large and small amounts of previous fertilizer N respectively but was not affected by date of sowing. Previous fertilizer N seldom affected crop N in spring because sowing was too late for N capture during autumn, but it did affect soil mineral N, particularly in the 60–90 cm soil horizon, presumably due to over-winter leaching. Tillering generally occurred in spring, and was delayed but not diminished by later sowing. Previous fertilizer N increased shoot survival more than it increased shoot production. Final shoot number was affected by previous fertilizer N, but not by date of sowing. Overall, there were 29 surviving tillers/g SNS.N uptakes at fortnightly intervals from spring to harvest at two core sites were described well by linear rates. The difference between sowings in the fitted date with 10 kg/ha crop N was 1 month; these dates were not significantly affected by previous fertilizer. N uptake rates were increased by both previous fertilizer N and late sowing. Rates of N uptake related closely to soil mineral N in February such that ‘equivalent recovery’ was achieved in late May or early June. At one site there was evidence that most of the residue from previous fertilizer N had moved below 90 cm by February, but N uptake was nevertheless increased. Two further ‘satellite’ sites behaved similarly. Thus at 14 out of 17 sites, N uptake until harvest related directly and with approximate parity to soil mineral N in February (R2 = 0·79), a significant intercept being in keeping with an atmospheric contribution of 20–40 kg/ha N at all sites.It is concluded that, on retentive soils in the UK, SNS in early spring was a good indicator of N availability throughout growth of unfertilized wheat, because the N residues arising from previous fertilizer mineralized before analysis, yet remained largely within root range. The steady rates of soil mineral N recovery were taken as being dependent on progressively deeper root development. Thus, even if soil mineral N equated with a crop's N requirement, fresh fertilizer applications might be needed before ‘equivalent recovery’ of soil N, to encourage the earlier processes of tiller production and canopy expansion. The later process of grain filling was sustained by continued N uptake (mean 41 kg/ha) coming apparently from N leached to the subsoil (relating to previous fertilizer use) as well as from sources not related to previous fertilizer use; significant net mineralization was apparent in some subsoils.

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