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.

The potential of semi-dwarf oilseed rape genotypes to reduce the risk of N leaching

2007 ◽  
Vol 146 (1) ◽  
pp. 77-84 ◽  
Author(s):  
K. SIELING ◽  
H. KAGE
Keyword(s):  
Oilseed Rape ◽  
N Uptake ◽  
Maximum Yield ◽  
N Fertilization ◽  
Wheat Crop ◽  
Soil Conditions ◽  
Plant Residues ◽  
N Leaching ◽  
Mineral N ◽  
Reduced Height

SUMMARYIn northwest (NW) Europe, oilseed rape (OSR) is often used as a preceding crop for winter wheat. Due to its low N harvest index (HI) and to favourable soil conditions after harvest, large amounts of mineral N remain in the soil, which cannot completely be taken up by the subsequent wheat crop. This increases the risk of N leaching into the groundwater during the following winter. Recently, semi-dwarf genotypes of OSR were developed and made commercially available that show similar yields but reduced height growth compared to conventional genotypes. The present authors hypothesized that the introduction of dwarfing genes leads to an increase in HI for dry matter (DM) and for N of OSR. As a consequence, semi-dwarf genotypes would accumulate less aerial biomass, return fewer plant residues to the soil and need less N to achieve yield maximum compared to conventional hybrids or open pollinating varieties. This may lead to a reduced risk of N leaching after growing OSR. In order to test this hypothesis, field trials conducted in 2003/04–2005/06 near Kiel in NW Germany combined four commercial varieties of OSR (Express, Talent, Trabant and Belcanto as semi-dwarf genotype), two seeding dates (mid-August and beginning of September) and eight mineral N fertilization rates (0–240 kg N/ha). On average in 2003/04–2004/05, the semi-dwarf genotype Belcanto achieved significantly less seed yield (4·44 t/ha) than the other varieties (4·65–4·88 t/ha). However, all varieties tested required similar N fertilization to achieve maximum yield. In addition, N offtake by the seeds did not differ. No interaction between genotype and N treatment was observed. Detailed analysis of DM accumulation and N uptake during the growth period revealed only small differences between the varieties in the averages of all N treatments and both years. At harvest, Belcanto produced more pods/m2 and a slightly higher 1000 seed weight. Nevertheless, HI and N HI were similar for all genotypes. It is concluded that, despite its lower plant height, the semi-dwarf genotype did not provide the opportunity to reduce the risk of N leaching after growing OSR.

Influence of Nitrogen Rates and Wheat (Triticum aestivum) Cultivars on Weed Control

Weed Science ◽  
1992 ◽  
Vol 40 (1) ◽  
pp. 115-121 ◽  
Author(s):  
Stephen A. Valenti ◽  
Gail A. Wicks
Keyword(s):  
Winter Wheat ◽  
Weed Control ◽  
Grain Sorghum ◽  
Wheat Crop ◽  
Green Foxtail ◽  
Before And After ◽  
Winter Wheat Cultivars ◽  
N Fertility ◽  
N Rates ◽  
Nitrogen Rates

Experiments were conducted to determine the influence of nitrogen (N) fertility and winter wheat cultivars on weed infestations in a winter wheat-ecofallow sorghum-fallow rotation near North Platte, NE. Centurk 78 and Lancota winter wheat suppressed density and growth of barnyardgrass and green foxtail significantly more than Eagle winter wheat before and after wheat harvest. Increasing N rates applied to winter wheat decreased annual grass weed population and weed yields. However, 67 and 101 kg N ha−1reduced winter wheat grain yields compared to 34 kg N ha−1. Plots treated at 2.8 plus 0.3 kg ai ha−1of atrazine plus paraquat 31 d after wheat harvest had more barnyardgrass before grain sorghum planting in 1983 than plots treated 17 d after wheat harvest but the reverse was true for green foxtail after grain sorghum emergence in 1984. Increasing N rates from 34 kg ha−1to 67 and 101 kg ha−1in the previous wheat crop decreased weed density before and after grain sorghum planting. There was no advantage in weed control in the grain sorghum from applying N to winter wheat in the fall vs. spring.

Biological and chemical assays to estimate nitrogen supplying power of soils with contrasting management histories

Soil Research ◽  
2004 ◽  
Vol 42 (7) ◽  
pp. 737 ◽  
Author(s):  
D. Curtin ◽  
F. M. McCallum
Keyword(s):  
Best Management Practices ◽  
Management Practices ◽  
N Uptake ◽  
N Mineralisation ◽  
Aerobic Incubation ◽  
Arable Soils ◽  
Mineral N ◽  
Mineralisation Potential ◽  
N Fertility

Nitrogen (N) mineralised from soil organic matter can be an important source of N for crop uptake, particularly following cultivation of pastures. Difficulty in predicting the contribution of mineralisation continues to be a serious obstacle to implementating best management practices for fertiliser N. We evaluated biological tests (i.e. net N mineralised in a 28-day aerobic incubation and anaerobically mineralisable N, AMN) and chemical tests (ammonium-N hydrolysis in hot 2 m KCl) as predictors of N supply to a glasshouse-grown oat (Avena sativa L.) crop. The oat plants were grown to maturity without added N on 30 soils representing a range of management histories, including soils collected from long-term pastures and intensive arable cropping sites. The majority (average 83%) of the N accumulated in grain and straw was mineralised N. Plant N derived from mineralisation (PNDM), estimated by subtracting soil mineral N at sowing from N uptake, was generally higher for long-term pasture soils (mean 82 mg/kg, n = 9) than for long-term arable soils (mean 48 mg/kg, n = 9). The 2 measures of N mineralisation were not closely related [R2 = 0.11 (0.37*** when one outlying observation was omitted)], indicating that aerobic and anaerobic assays can give quite different N fertility rankings. Aerobically mineralisable N was the best predictor of PNDM (R2 = 0.79***). The ratio of CO2-C evolved to net N mineralised in the aerobic incubation was highly variable (e.g. mean of 13.6 for pasture soils v. 7.5 for long-term arable soils), likely due to differences in N immobilisation. The correlations of AMN (R2 = 0.32**) and hot KCl N (R2 = 0.24**) with PNDM were not much better than that between total soil N and PNDM (R2 = 0.16*), suggesting that these tests would not provide reliable estimates of N mineralisation potential in soils with diverse management histories.

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.

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.

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.

The effect of stubble management on the availability of 15N-labelled residual fertilizer nitrogen and crop stubble nitrogen in an irrigated black earth

1986 ◽  
Vol 26 (1) ◽  
pp. 99 ◽  
Author(s):  
PJ White ◽  
I Vallis ◽  
PG Saffigna
Keyword(s):  
Ammonium Sulfate ◽  
Field Experiments ◽  
Crop Yields ◽  
N Uptake ◽  
Fertilizer Application ◽  
Wheat Crop ◽  
Total N ◽  
Stubble Retention ◽  
Residual Fertilizer N ◽  
Subtropical Environment

Field experiments on an irrigated alkaline black earth soil of the Darling Downs, south-east Queensland, examined transformations of nitrogen (N) and its subsequent availability for the growth of wheat after stubble had been removed, mulched or incorporated. Two crop sequences were used: sorghum-3- month fallow-wheat (S-W); and wheat-7-month fallow-wheat (W-W). The crops were grown in microplots enclosed by steel cylinders (75 cm diam. and 35 cm deep) to a depth of 30 cm. For the initial crop, some plots were fertilized with l5N-labelled ammonium sulfate and others with unlabelled ammonium sulfate (50 kg N/ha). After harvest of the initial crop, labelled stubble was added to unlabelled soil, either as a mulch or incorporated, and unlabelled stubble was similarly added to soil labelled with residual 15N from the fertilizer application. Uptake of 15N by a test wheat crop and distribution of 15N in the soil-plant system were then determined. In the test crop fertilized with unlabelled urea (50 kg N/ha), incorporation of stubble depressed plant growth and N uptake by 35% in the S-W sequence but had no effect in the W-W sequence. Residual fertilizer 15N in the soil was more available to the test crop than was 15N in retained stubble (6 v. 2% and 12 v. 6% for the S-W and W-W sequences respectively). However, the test crop obtained only 0.9-1.2% of its total N uptake from residual fertilizer N and 0.4-2.9% from the stubble of the initial crop. The effects of stubble management on the availability of N from these two sources were small. If suitable rates of N fertilizer are applied, it is unlikely that crop yields will be adversely affected by stubble retention in this subtropical environment.

Chickpea in wheat-based cropping systems of northern New South Wales I. N2 fixation and influence on soil nitrate and water

1998 ◽  
Vol 49 (3) ◽  
pp. 391 ◽  
Author(s):  
H. Marcellos ◽  
W. L. Felton ◽  
D. F. Herridge
Keyword(s):  
N2 Fixation ◽  
New South ◽  
New South Wales ◽  
Wheat Crop ◽  
Soil N ◽  
Cereal Crop ◽  
Mineral N ◽  
South Wales ◽  
N Fertility ◽  
Summer Fallow

Chickpea has potential as a rotation or break crop in the northern grains region of New South Wales and Queensland. Definition of that potential requires information on chickpea N2 fixation and on effects of chickpea on maintenance of soil N fertility and delivery of mineral N for use by a following cereal crop. Results from 6 experiments in northern NSW in which chickpea and wheat in one season were followed by wheat in subsequent seasons indicated variable N2 fixation by chickpea (mean 73 kg/ha; range 4-116 kg/ha), associated with variable Pfix (percentage of chickpea N derived from N2 fixation) (mean 57%; range 4-79%). There were no consistent differences between chickpea and wheat in effects on soil water, either pre-harvest or after the summer fallow. Chickpea ‘spared’ nitrate, relative to wheat (mean 15 kg/ha; range 1-35 kg/ha), and mineralised additional nitrate during the summer fallow (mean 18 kg/ha; range 5-40 kg/ha). Nitrate-N in the top 1·2 m of the soil profile at sowing of the following wheat crop was on average 89 kg/ha after chickpea (range 63-113 kg/ha) and 56 kg/ha after wheat (range 33-94 kg/ha). Nitrogen mineralisation rates during the summer fallow at 2 sites of 0·17 and 0· 21 kg N/ha · day (after chickpea), although greater than the rates after wheat (0· 07 and 0·12 kg N/ha · day), were not sufficient to meet the N requirements of a moderate to high yielding cereal crop. We concluded that chickpea did not fix sufficient N2 or mineralise sufficient N from residues either to maintain soil N fertility or to sustain a productive chickpea{wheat rotation without inputs of additional fertiliser N.

Preface

1998 ◽  
Vol 49 (3) ◽  
pp. I
Keyword(s):  
Water Content ◽  
Soil Water ◽  
Soil Water Content ◽  
Root Zone ◽  
N Uptake ◽  
Subterranean Clover ◽  
Trifolium Subterraneum ◽  
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.

Soil degradation under cropping and its influence on wheat yield on a weakly structured New Zealand silt loam

Soil Research ◽  
2001 ◽  
Vol 39 (2) ◽  
pp. 291 ◽  
Author(s):  
G. S. Francis ◽  
F. J. Tabley ◽  
K. M. White
Keyword(s):  
New Zealand ◽  
N Uptake ◽  
Wheat Yield ◽  
Wheat Crop ◽  
Soil Conditions ◽  
Silt Loam ◽  
Total N ◽  
Organic C ◽  
N Fertility

Results from the first phase of a long-term experiment showed that, after 6 years under pasture, several soil quality attributes had improved compared with soil cropped annually. The objectives of this study were to quantify the effects of pasture-induced increases in structural stability and organic matter (N fertility) on wheat grown in 3 successive seasons following pasture cultivation. Growing winter wheat after the ploughing of land that had previously grown perennial grass resulted in gradual reductions in soil organic C and total N. Reductions in soil microbial biomass C and earthworm populations were much more rapid. Soil aggregate stability declined rapidly in the first year after ploughing, but more slowly after that. Soil macroporosity increased after ploughing, mainly due to the relief of compaction caused by sheep treading during grazing. The contrasting soil conditions that existed at the end of the first experimental phase significantly affected the harvest yield of the first and second wheat crops, with yields 2—3 t/ha greater after perennial grasses than after annual crops. Variations in harvest yield and N uptake were explained by differences in soil N fertility and soil structural conditions. Treatment effects on yield were not detected in the third wheat crop. For the structural condition and N fertility of this soil, the extent of improvement during 3 years under perennial pasture was similar to the extent of decline under 3 years of cropping. This suggests that similar lengths of pastoral and arable cropping are needed in crop rotations for the long-term maintenance of these properties in weakly structured silt loam soils in New Zealand.

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