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Nutrient losses in runoff water following application of different fertilisers to grassland cut for silage
Agriculture Ecosystems & Envtronment
,w ELSEVIER
Agriculture, Ecosystemsand Environment55 (1995) 181-191
Nutrient losses in runoff water following application of different fertilisers to grassland cut for silage D. Scholefield *, A.C. Stone Institute of Grassland and Environmental Research, North WykeResearch Station, Okehampton, EX20 2SB, UK
Accepted 16 June 1995
Abstract Studies were made to assess the losses of nutrients in runoff from pastures, and to ascertain whether application of N as NIL rather than NO3 both reduced N losses and enhanced yields of herbage. Two experiments were conducted during consecutive springs in which surface lysimeter plots were established on sloping grassland with soils of low permeability, and different forms of fertiliser applied for first-cut silage. Despite weather conditions conducive to large nutrient losses, less than 10% of the N applied was found in runoff. However, the peak concentrations of nutrients were large relative to standards for good water quality. The concentrations of NO3-N were greater in water from plots that received NIL NO3 than from those that received either (NH4) 3 PO4 or urea. Large concentrations of NIL-N were measured in runoff in response to all treatments, with the largest in water from plots that received urea. The mechanisms that may account for the observed resistance to loss in runoff are discussed. In the first experiment there was no advantage (or disadvantage) in applying an (NIL)3 PO4 formulation 2 weeks earlier than applying either NI-I4NO3 or urea. In the second experiment, where all treatments were applied on the same dates, herbage mass accumulated more slowly on plots that received NIL NO3 compared to those that received more NH4-rich forms. However, in neither experiment did the fertiliser treatments influence the yields of herbage cut for silage. Keywords: Nutrient leaching; Runoff water; Grassland agronomy;Water quality
1. Introduction Fertilisers are applied to crops when the land is trafficable and the temperature is sufficient for nutrient uptake and growth. In maritime regions of western Europe however, the winters are often mild and the use of reduced ground-pressure vehicles has made possible the application of fertilisers before the end of the wet winter period. In the UK, for example, fertiliser is normally applied to pasture in February to promote early growth for first-cut silage. It is generally believed that the nutrients applied to the surface of impermeable soils * Corresponding author: Tel. 0837 82558, Fax 0837 82139. 0167-8809/95/$09.50 © 1995 Elsevier Science B.V. All fights reserved SSDIO167-8809(95)00623-0
at this time would be at extreme risk of loss in runoff water. There have been few reports of direct leaching of fertiliser from grassland. Intense summer rainfall immediately after a top-dressing of fertiliser N to dry soil can result in large but transient peak concentrations of nitrate in percolating leachate, presumably because of macropore flow (Barraclough et al., 1983; Haigh and White, 1986). Chichester (1977) measured NO 3 loss in percolate and runoff water from monolith lysimeters during a 4 year period and noted that the greatest loss in runoff occurred in summer when heavy rain followed a fertiliser application. The quantities lost in runoff decreased as the extent of soil cover increased,
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such that 10 kg N ha-~ year-~ was lost from 'clean cultivated corn', whereas less than 1 kg ha-~ yearwas lost from the lysimeters with grass cover. Costin (1980), however, who established runoff lysimeter plots in leguminous pastures in Australia, showed that where fertiliser was not applied, the greatest losses of soil and nutrients occurred during the wetter winter months. In studies conducted in the colder regions of Europe it was the melting of snow and ice in spring that caused the greatest losses of nutrients in runoff (Uhlen, 1989; Stratmann and Kfihbauch, 1987). Studies conducted in the USA (Moe et al., 1967a; Moe et al., 1967b) have indicated that N applied to wet, impermeable soils as NH4NO3 or urea may be particularly resistant to loss, even during intense storms. In contrast, recent measurements of NO 3 lost from grazed grassland lysimeters in the UK have demonstrated the loss in runoff of approximately 30% of the fertiliser N applied in March (Scholefield et al., 1993). In addition to soil conditions and weather, the form of the applied fertiliser may be an important factor in determining the extent of nutrient loss in runoff. Stevens (1988) found that the percentage utilisation by herbage of N applied as (NH4)2 SO4 to a wet, upland site in spring was greater than that of N applied either as Ca(NO3) 2 or as urea. Such a finding may be a result of the relative immobility of the NH4 ion, or its potential for better absorption by roots at temperatures below 9°C (Clarkson et al., 1986). The present experiments were conducted with the primary objectives of: (1) measuring the amounts of N lost in runoff from sloping grassland on an impermeable soil, after applications of fertiliser for first-cut silage; (2) assessing the potential of applying N in the NH4 and urea forms both to reduce such loss and to achieve quicker plant uptake under cool conditions; (3) assessing the effects of the different fertiliser forms and any differential leaching losses on the cut yield of herbage. A secondary objective was to measure the losses of P and K in runoff. Two experiments were conducted using surface water lysimeter plots; the first in 1989, and the second at a different site in 1990. 2. Materials and methods
2.1. Sites and soils Experiment 1 was conducted at the Institute of Grassland and Environmental Research, North Wyke, in
southwest England on a 2 ha field sown to perennial ryegrass in 1982, that had received 300--450 kg N ha- 1 year- 1as NH4NO3 and been intensively grazed by beef cattle. The soil is a non-calcareous pelosol of the Halstow series (Gleyic Cambisol) which consists typically of a silty clay loam Ap horizon (31% clay, 47% silt) to 21 cm, overlying a silty clay Bw horizon (38% clay, 46% silt) at 21-41 cm depth (Harrod, 1981). It was anticipated that a substantial proportion of winter discharge on this site would be by runoff and sub-surface lateral flow down the 5-9 ° slope to the south. The mean soil temperature (100 mm depth) for February 1989 was 5.3°C. Experiment 2 was conducted at North Wyke on a 3 ha field sown to perennial ryegrass in 1985, that had received 350 kg N ha- ~ year- ~and been grazed intensively by sheep. The soil was a clayey pelo-stagnogley of the Hallsworth series (Stagno-Dystric Gleysol), which consists typically of a clayey Apg horizon (38% clay, 50% silt) to 27 cm, overlying a clay Bg horizon (43% clay, 43% silt) at a depth of 27-66 cm. (Harrod, 1981). It was anticipated that, because of the finer texture of the upper horizon, a greater proportion of winter discharge would be by runoff, down the 7 ° slope to the north, than at the site of Experiment 1. Rainfall data were obtained from a Meteorological Office station (North Wyke, Station 8836) which is situated less than 1 km from both sites. The mean soil temperature ( 100 mm depth) for February 1990 was 6.3°C.
2.2. Surface water lysimeter plots: design and installation Each lysimeter plot consisted of a diamond-shaped area of 100 m 2 ( 10 m × 10 m), hydrologically isolated to collect runoff and lateral surface flow to 100 mm depth. Thus, four narrow trenches were dug (75 mm wide by 100 mm deep) to contain 60 mm diameter flexible perforated drainage tube, resting on the compacted clay base and surrounded by 'pea' gravel to the surface. With the axis of the diamond aligned with the direction of slope, the two up-slope trenches diverted water away from the plot, and the two down-slope trenches collected water draining from the plot itself (Fig. 1). This water was channelled via a 'Y'-connector to a tipping bucket device that both monitored the flow and sampled on a flow-proportional basis.
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by the rate of tipping. Tips were counted using a simple reed switch connected either to an electro-mechanical counter or to a data-logger (Squirrel type 1203). Assuming that the rainfall could all be accounted for in surface discharge, 25 mm of rainfall at 2 mm h - 1 would result in 5000 tips, with a tip every 9 s. 2.3. Experimental treatments
I
T
Fig. 1. Schematic diagram of lysimeter plot, showing means of collecting runoff from the bounded area. A, sample area; B, diversion drains; B1, diverted water; C, collection drains; CI, sample water; D, solid down-pipe; E, protective cover; F, 'Y' connector; G, flexible perforated pipe covered with gravel.
A D
G
A
\
Fig. 2. Diagram of tipping bucket apparatus showing sample tube to enable flow-proportional sampling. A, funnel; B, sample tube; C, reed switch; D, pivot; E, adjustable screws; F, frame; G, sample container. The tipping bucket comprised two conical poly-propylene funnels (200 m m diameter, 500 ml capacity) sealed at the necks and bolted to a steel angle plate with 75 ° between the axes (Fig, 2). One of the funnels was used for sampling by inserting a curved metal tube (4 m m bore) through the wall via a bulkhead coupling. A small sample could thus be diverted to a 101 container while the remainder was tipped to 'waste' The volume of water sampled in this tube on alternate tips was adjustable according to the bore and depth of immersion of the tube. Normally, the sample volume was 0.3 ml per tip, and, within the range of drainage intensities encountered at these sites, this volume was unaffected
Nine lysimeters (three replicates of three fertiliser treatments) were installed at the site of Experiment 1 in September 1988, and 16 lysimeters (four replicates of four treatments) were installed at the site of Experiment 2 in October 1989 (Fig. 3). The treatments applied in Experiment 1 were typical of formulations and timings currently recommended to farmers in the region. These treatments were not necessarily 'matched' with regard to nutrient content and timing. Treatment l was the 'First-cut' formulation ( N P K compound with 70% of the N as NH4 and all the P as (NH4) 3 PO4 ) applied on 22 February, followed by N H 4 NO3 ( ' N i t r a m ' ) applied 1 month later; Treatment 2 was an N P K formulation with the N as NH4 NO 3, ( 'ICI No 8') applied on 8 March, again followed by NH4 NO3 ( ' N i t r a m ' ) applied 1 month later; Treatment 3 was two applications of urea timed as for Treatment 2, and with amounts of P and K equated with Treatment 2 by mixing the urea with triple super-phosphate and KC1 respectively (Table 1). In Experiment 2 the treatments were matched with regard to nutrient content and timing to enable comparisons to be made among nutrient forms, rather than between fertilizer advice packages, as in Experiment 1.
L
_
/
°1
***<7 0
50
1
Metres
Fig. 3. Layout of lysimeter plots for (a) Experiment 1 and (b) Experiment 2. Arrows show directions of slope. Treatments 1 and 4, stripe; Treatments 2 and 5, hatch; Treatments 3 and 6, black; Treatment 7, clear.
184
D. Scholefield, A. C. Stone/Agriculture, Ecosystems and Environment 55 (1995) 181-191 40 F
Table 1 Formulation and date of application of fertilisers in Experiment 1
a
v
Treatment
1. First cut Nitram 2. ICI No. 8 Nitram
Date applied Rate (kg h a - ~)
22.2.89 21.3.89 8.3.89 5.4.89
3. Urea Triple super-phosphate 8.3.89 KCI Urea 5.4.89
N
P2Os
K20
45 85 86 64 86 0 0 64
24 0 15 0 0 15 0 0
62 0 50 0 0 0 50 0
"o
2o
~
17/2 18
19 2O 22 25 26
27 28 1/3
3
9
13
16
17 21
28 17/4
Date
14
e
12
Table 2 Formulation and date of application of fertilisers in Experiment 2 Treatment
4. First cut Nitram 5. Nitram Triple superphosphate KC1 Nitram 6. First-cut ASN ~ 7. Urea Triple superphosphate KCI Urea
Date applied Rate ( k g / h a - ~) N
P
K
23.2.90 23.3.90 23.2.90 23.2.90
45 86 45 0
24 0 0 24
62 0 0 0
23.2.90 23.3.90 23.2.90 23.3.90 23.2.90 23.2.90
0 86 45 86 45 0
0 0 24 0 0 24
62 0 62 0 0 0
23.2.90 23.3.90
0 86
0 0
62 0
17J2 18 19 20 22 25 26 27 28 1/6
3
9
13 18 17 21 26 1714
3
9
13 16 17 21 26 1714
3
9
13 16 17 21 26 1714
Date
C
17/2 18 19 20 22 25 26 27 28
Thus, in each treatment, 45 kg N h a - ~, 24 kg P h a - ] and 62 kg K ha-1 were applied on 23 February, followed by 86 kg N h a - ~on 23 March (Table 2). Only in Treatment 7 (urea) was the same form of N applied on both dates. The fertilisers were applied manually after the herbage on each plot had been trimmed to 50 mm using a Mayfield reciprocating blade mower which minimises soil structural damage under wet conditions.
2.4. Measurements and analyses The same measurements and analyses were performed in both experiments. Samples of discharge from
1/3
Date
~ASN-ammonium sulphate/ammonium nitrate (26% N of which 7% is as NO3). 15 E
5£
C
8
0 17/2 18 19 20 22 25
28
27
28
1/3
Date Fig. 4. Nutrient leaching in Experiment 1: (a) rainfall (black) and runoff (stripe); (b) concentration of nitrate plus ammonium-N; (c) concentration of phosphate-P; (d) concentration of K +. In ( b ) - ( d ) Treatments 1, 2 and 3 are in order across page on a given date.
D. Scholefield, A.C. Stone/Agriculture, Ecosystems and Environment 55 (1995) 181-191 each lysimeter were collected periodically (daily during periods of intense rainfall), filtered through prewashed Whatman No. 1 filter paper to remove turbidity and divided into three sub-samples to be analyzed for NO3-N and NH4- N, P (ortho-phosphate) and K ÷. Nitrate, NH4 and PO4 were analyzed using standard colorimetric auto-analyzer procedures (Boltz and Mellon, 1948; Navone, 1964; Verdouw et al., 1977) and K + was analyzed with a flame photometer (EEL). The amounts of dissolved nutrients were calculated by multiplying their respective concentrations in each composite sample by the volume recorded. Ten soil samples (25 mm diameter, 150 mm deep) were taken weekly from random positions within each plot. These were bulked and weighed. Representative sub-samples were taken for the determination of water content (drying to constant weight in a forced drought oven), and to permit calculation of the bulk density of the soil. Three further sub-samples were taken of the bulked soil from each plot and these were extracted with aqueous solutions of 1.0 M KCI, 0.5 M NaHCO3 (pH 8.5) or 1.0 M ammonium acetate (pH 7.0) to obtain 'plant available' N,P and K respectively. Analyses of these solutions were carried out as per the analysis of the drainage water. Values for soil water content and bulk density were used to enable the expression of nutrient concentrations on a kilogram per hectare basis.
185
Assessments of above-ground herbage mass were made weekly using a rising plate sward stick (Holmes, 1974). The total herbage to 70 mm on each plot was cut and weighed using a Haldrup small plot harvester when the nominal dry matter digestibility value of herbage harvested from the area was 70% (Agricultural Development and Advisory Service forecast based on weekly near infra-red analysis). The dates of cutting were 10 May and 18 May for Experiment 1 and 2, respectively. Representative samples of herbage were collected and oven-dried at 80°C for the determination of dry matter yields. Data for the total amounts of nutrients lost and dry matter yields were analyzed for treatment effects using analysis of variance. (GENSTAT 5 Committee, 1987)
3. R e s u l t s
3.1. Experiment l Rainfall and drainflow First runoff was measured on 29 September 1988, and by early February 1989, 270 nun of rainfall had leached the soil surface. This resulted in small background concentrations of N and P in water draining from each lysimeter, but each rainfall event produced a relatively larger peak concentration of K. During the
Table 3 Extractablesoil nutrients, Experiment 1 (kg ha- ~) Date
21.2.89 6.3.89 20.3.89 4.4.89 4.5.89
Treatment
1 2 3 1 2 3 1 2 3 1 2 3 1
2 3
Soil nutrient concentration (0-10 cm ) NH4-N
N03-N
4.6 5.8 5.3 23.5 1.3 0.6 5.3 9.6 14.7 17.8 12.6 10.7 9.4 7.9 9.4
2.2 2.2 3.9 4.5 1.9 2.4 21.9 44.5 43.0 45.1 17.2 16.6 8.2 6.8 8.5
P 2.6 0.4 1.4 6.0 4.5 3.3 0.8 2.8 1.8 9.0 9.3 8.8
K 52.0 45.8 34.2 54.8 49.6 37.9 40.6 58.4 41.8 41.1
42.1 37.2
D. Scholefield, A.C Stone/Agriculture, Ecosystems and Environment 55 (1995) 181-191
186
Table 4 Nutrient losses in runoff (kg ha- ~) in Experiment 1 Treatment
Experiment 1
~
N
P
K
3.1 3.0 3.0 0.58 NS
0.42 0.05 0.13 0.09 NS
7.0 3.9 6.4 1.24 NS
ao
i
a
2O
1
2 3 sea sig.
~ ~ 1o ~0
1412
17/2
21/2
2612
28/2
4/3
26/2
28/2
4/3
28/2
2812
4/3
Date
Table 5 Dry matter yield of herbage (t ha- ~) in Experiment 1 Experiment 1
•
Treatment
Yield
1
4.8 4.8 4.5 0.26 NS
2 3 seA sig.
14
z f g
8
N
e
g~ 2 0
~
14/2
17/2
21/2
Date
week before the first application of Treatment 1 ( 1521 February) 56.1 mm of rainfall was recorded, and the first runoff during the experimental period was observed on 17 February. During the following week 84.1 mm of rainfall was recorded, and, during the week after the first application of Treatments 2 and 3 52.8 mm of rainfall was recorded (Fig. 4a). Thus, the first applications of all treatments were made when the soil in the lysimeter plots was wet, and the nutrients applied were at risk of being lost in runoff water. During this initial period ( 17 February-27 March) 62% of the rainfall received was recovered by the tipping bucket system. Discharge ceased after this period and so the second applications of Treatments 2 and 3 were not subjected to loss in the runoff.
3
Q.
8
14/2
17/2
21/2
Date
d
E
14
~
8
N
6
g
Soil available nutrients and losses in runoff Before the first application of fertilizers in Treatment 1 the amount of inorganic-N in the soil was less than 10 kg ha- 1 in all plots (Table 3). On 6 March, after 2 weeks and some 50 mm of runoff, 28 kg N haremained in the soil of which 23.5 kg ha- ~ was NH4N. Three kg N ha- ~ was leached from this first application (Table 4), at a maximum concentration corresponding to maximum drainflow (Fig. 4b) of 8.8
0
8 2 ~ ~ 0"
14/2
17/2
21/2
26/2
28/2
4/3
Date
Fig. 5. Nutrient leaching in Experiment 2: (a) rainfall (black) and runoff (stripe); (b) concentration of nitrate plus ammonium-N; (c) concentration of phosphate-P; (d) concentration of K +. In ( b ) - ( d ) Treatments 4, 5, 6 and 7 are in order across page on a given date.
D. Scholefield, A.C. Stone/Agriculture, Ecosystems and Environment 55 (1995) 181-191
187
Table 6 Extractable soil nutrients, Experiment 2 (kg ha- ~) Date
16.2.90
1.3.90
8.3.90
15.3.90
29.3.90
5.4.90
19.4.90
4.5.90
Treatment
4 5 6 7 4 5 6 7 4 5 6 7 4 5 6 7 4 5 6 7 4 5 6 7 4 5 6 7 4 5 6 7
Soil nutrient concentration (0-10 cm) NH4-N
N03-N
P
K
12.1 18.5 12.0 11.4 21.5 18.6 31.8 44.0 13.0 14.7 11.6 13.2 8.7 7.8 8.9 9.6 48.0 62.3 68.3 40.0 10.4 10.8 15.8 12.3 10.5 10.0 9.0 10.2 14.2 13.6 15.1 13.8
1.7 0.5 1.6 1.6 1.9 3.2 5.2 3.6 4.4 4.5 6.7 9.2 0.7 1.0 1.6 1.6 13.8 38.5 15.7 22.3 31.6 31.8 8.6 12.2 1.7 2.6 1.4 1.9 2.5 4.6 4.8 1.9
8.2 8.2 8.6 9.4 7.2 11.3 11.4 8.4 6.7 7.3 10.1 5.9 12.9 14.8 10.5 11.5 9.6 10.4 12.5 10.2 11.6 13.1 14.6 11.5 9.0 9.5 8.4 8.9 -
183 159 212 203 240 214 237 257 254 279 246 230 282 232 236 285 229 227 242 227 184 183 204 190
m g d m - 3 ( 2.7 m g d m - 3 N H 4 - N ) . O n l y 0.1 kg N h a - 1 Table 7 Nutrient losses in runoff (kg ha- ~) in Experiment 2 Treatment
4 5 6 7 sed sig.
Experiment 2 N
P
K
3.2 4.1 2.9 3.0 0.82 NS
0.37 0.54 0.28 0.54 0.15 NS
4.1 3.4 3.6 5.1 1.49 NS
w a s l e a c h e d f r o m the l y s i m e t e r s that r e c e i v e d Treatm e n t 1 after this initial period. O n 2 0 M a r c h , after the first a p p l i c a t i o n o f T r e a t m e n t s 2 a n d 3 ( I C I No. 8 a n d u r e a ) , m o s t o f the NI-L-N o f T r e a t m e n t 2 a n d the u r e a - N o f T r e a t m e n t 3 h a d a p p a r e n t l y b e e n nitrified, ( T a b l e 3) d e s p i t e a n a v e r a g e soil t e m p e r a t u r e ( 1 0 0 n u n d e p t h ) o f 6.1°C d u r i n g the period. T h e a m o u n t o f N l e a c h e d in r e s p o n s e to e a c h o f t h e s e t r e a t m e n t s w a s 3.0 k g h a -~ ( T a b l e 4 ) . T h e m a x i m u m c o n c e n t r a t i o n s o f N in l e a c h a t e w e r e 10.9 a n d 9.0 m g d m - 3 (1.7 a n d 4.5 m g d m - ~ N H a - N ) in r e s p o n s e to T r e a t m e n t s 2 a n d 3, r e s p e c t i v e l y ( F i g . 4 b ) .
188
D. Scholefield, A. C. Stone ~Agriculture, Ecosystems and Environment 55 (1995) 181-191
4
J=
~3
,,X'~lll
10
~2 z
"3
E l
"<
o
1412
17/2
2112
28/2
2812
413
Date 0
1/1
b
i
i
r
i
2/3
9/3
16/3
22/3
i
i
3013 614 Date
i
i
i
i
i
12/4
20/4
2714
4/5
515
.¢
Fig. 7. Accumulation of herbage mass as measured by the rising plate sward-stick in Experiment 2. Treatment 4 ( - + - ) ; Treatment 5 ( A-); Treatment 6 (-o-); Treatment 7 ( - D - ) . z c ,< 1412
17/2
2112
2812
2812
413
2812
2812
413
Date
1412
1712
21/2
Date
Leaching of P occurred during the periods of drainflow responsible for the leaching of N (Fig. 4). The amounts of P leached were much less than those of N however, and the amounts of extractable P in the soil did not reflect the fertiliser P added, nor indicate the amounts leached. Although the total losses of P were small, losses from plots that received Treatment 1 were greater than from those that received Treatments 2 and 3 (Table 4). Potassium was as susceptible as N to loss in runoff at this site (Fig. 4d and Table 4). The exact responses to applications of fertiliser were more difficult to ascertain because of the relatively large background concentrations in all runoff water. The amounts lost corresponded to less than 10% of those applied, with more lost from plots that received Treatments 1 and 3 (NH4-N) than from those that received Treatment 2. Table 8 Dry matter yield of herbage (t ha- ~) in Experiment 2 Experiment 2
14/2
17/2
21/2
2812
2812
4/3
Date
Fig. 6. Amounts of nitrate and ammonium N leached in runoff in Experiment 2: (a) with Treatment 4; (b) Treatment 5; (c) Treatment 6; (d) Treatment 7. The ammonium component is shaded black.
Treatment
Yield
4 5 6 7 sed sig.
4.6 4.2 5.1 4.4 0.35 NS
D. Scholefield, A. C. Stone/Agriculture, Ecosystems and Environment 55 (1995) 181-191
189
Herbage yield
Herbage yield
Table 5 shows that herbage dry matter yield ranged from 4.5-4.8 t ha- 1 but there was no significant effect of fertiliser treatment.
Table 8 shows that herbage dry matter yield ranged from 4.2-5.1 t ha- ~, but there was no significant effect of fertiliser treatment. The assessment by sward stick (Fig. 7), however, indicated consistently (ten measurement dates) that the NHa-rich treatments were promoting more rapid growth of herbage than Treatment 5 (Nitram).
3.2. Experiment 2 Rainfall and drainflow February 1990 was extremely wet with a rainfall of 251 mm recorded of which 48 mm fell over the 5 days following the first application of fertilisers. During February 85% of the rainfall received was recorded as runoff (Fig. 5a). Discharge ceased on 22 March and so again the second applications were not subject to loss in the runoff. There was no correlation between the slope of individual lysimeters and the fraction of the rainfall collected. Also, less of the rainfall was accounted for as runoff after a few days of dry weather.
Soil available nutrients and losses in runoff Both the additions and form (NO3 or NH4) of fertiliser N were detectable in the soil 1 week after application (Table 6). The amounts of N lost in response to Treatments 4-7 (Table 7) respectively were 7.0, 9.1, 6.5 and 6.7% of the 45 kg N ha- ~ applied in the first application. Treatment 5 suffered the greatest loss of N with the greatest proportion as NO 3, whereas Treatment 7 resulted in the smallest loss, but with the greatest proportion as NH4 (Fig. 6). The storm event on 26 February resulted in the greatest concentrations of N in runoff, ranging from 15.2 mg dm-3 for Treatment 5 to 7.6 mg dm -3 for Treatment 7 (Fig. 5b). The amount of bicarbonate extractable P varied between 6 and 15 kg ha-1 during the experimental period (Table 6). This was not sensitive to either the inputs of fertiliser P or the various N treatments. The amounts of P lost in runoff were < 0.5 kg ha- 1, with concentrations above 'background' observed only on 26 February (Fig. 5c). Treatments 5, with P as triple super-phosphate, resulted in greater loss of P than Treatments 4 and 6, with P a s ( N H 4 ) 3 P O 4 (Table 7). The soil was rich in ammonium acetate extractable K, with amounts ranging between 200 and 300 kg haduring the experimental period (Table 6). The amount of K leached in runoff was of the same order as that of N with approximately 5 kg ha- 1 being lost during the drainage period (Table 7, Fig. 5d). This amount was not influenced by any of the fertiliser treatments.
4. Discussion
The weather conditions that prevailed before and immediately following the first applications of the fertiliser treatments during both experimental periods were highly conducive to major losses of nutrients in runoff: only the application to snow-covered or frozen ground could be considered more risky. Despite these conditions, the losses of N, P and K were small relative to the amounts applied. The amounts and patterns of N loss are at first sight very similar to those obtained by Kilmer et al. (1974) who monitored nutrient losses from grassland fertilised with NH4 NO3 in North Carolina, USA. The difference is that, in the American study, the peak concentrations of N in runoff did not appear to correspond to the additions of fertiliser. This discrepancy may have been the result of infrequent sampling and lack of rainfall immediately after applications, because in a 5 year study of 890 runoff events, Owens et al. (1984) observed that all peak nitrate concentrations occurred shortly after applications of fertiliser N. In another North American study (Moe et al., 1967a), intense storms (63.5 mm h -~ for 1 h) were applied with a rainfall simulator to sloping, wet grassland 24 h after application of NH4 NO3 at 224 kg N ha- 1. Less than 15% of the N applied was accounted for in runoff. These results and those of the present study indicate that a large fraction of fertiliser N may be rapidly 'locked up' after application to wet, fine-textured soil. It is unlikely that the processes of plant uptake, assimilation by the microbial biomass and denitrification combined could be responsible for this amount of retention at such low temperatures; the involvement of soil physical processes must be assumed. Rapid transport of NO 3 ions to zones of relatively immobile water both by mass flow and diffusion is a feasible mechanism. Such zones would exist in the micropores of a well-
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D. Scholefield, A.C. Stone/Agriculture, Ecosystems and Environment 55 (1995) 181-191
structured soil, and/or also at depths where rates of lateral flow are small. However, under the experimental conditions, that is with runoff occurring continuously from the day before fertiliser application to the time that the peak concentrations of N was detected in runoff, retention of N as a result of transport to depth via a wetting front might be considered relatively unimportant. In addition to the mechanism suggested to account for the small NO3 losses above, the NH 4 ions are subject to adsorption by soil colloids in ion exchange reactions. Set against this reduced mobility of NH4-N is the process of nitrification, which will be initiated on contact with the soil, but will only proceed rapidly to produce NO3 in aerobic, warm conditions (Macduff and White, 1985). Fig. 6 shows the outcome of these different controls on ion mobility in Experiment 2. Treatment 5 supplied N with a NO~:NH~-ratio of 1.0, whereas the ratio in runoff from this treatment on 26 February was 2.7. In contrast, Treatments 4 and 6 supplied N with a ratio of 0.4, but the ratio in the runoff from each treatment on 26 February was 1.4. This ratio tended to increase for all treatments with time after application, presumably as nitrification progressed. Because urea hydrolysis would have been rapid (Moe et al., 1967b), but nitrification rather slow, it is not surprising that the addition of the urea treatment resulted in the greatest loss of ammonium and the smallest NO3:NH + ratio (0.3) in runoff water. Moe et al. (1967b) compared the ionic composition of runoff from grassland plots applied with equal amounts of fertiliser N either as NH4 NO3 or as urea. Equal amounts of NH4 were lost, which was assumed to arise from a greater initial rate of transport to depth by the un-ionised urea molecules. In the present experiments about twice the amount of NH4 was lost from the urea-treated plots compared to those that received NH4 NO3 (5.6 compared with 2.7 kg N h a - l ) , and therefore such a mechanism need not be invoked. The amounts and concentrations of ortho-phosphate P in runoff were similar to those obtained in other studies (Kilmer et al., 1974; Costin, 1980; Uhlen, 1989). It appeared that in Experiment 1 more P was lost from plots that received Treatment 1 ((NH4)3 PO4) than from those that received triple-superphosphate, but in Experiment 2 there was no influence of treatment. In common with the losses of N, the losses of P were small relative to the amounts applied but peak
concentrations in runoff could be considered large relative to standards for good water quality (Department of the Environment, 1985). It is well known that inorganic P, added to soils, is quickly fixed by sorption on to colloids, biological transformations and strong chemical binding to iron and aluminium compounds (Sanyal and De Datta, 1991 ). Thus, little of the fertiliser P added in the present experiments could be detected in the bicarbonate-extractable fraction a few days after addition, (Table 3 and Table 6) and the amounts extracted did not correlate with the amounts leached (Fig. 4c and 5c). The concentrations and amounts of K in runoff were similar to those obtained in other studies (Uhlen, 1989; Kilmer et al., 1974). More K was lost in Experiment 1 than in Experiment 2 (Table 4 and Table 7), but the soil in Experiment 2 had about five times the amount of exchangeable K as the soil in Experiment 1 (Table 3 and Table 6). These two results suggest that the soil used in Experiment 1 either had fewer exchange sites or that they were occupied by cations with greater affinity for the sites than K ÷. However, in Experiment 1, there was more K lost in treatments which received NH4 sources suggesting that NH4 may have displaced K from the exchange complexes. The DM yields of herbage obtained in both experiments were consistent with those expected at first cut on lowland farms within the UK (Baker et al., 1991 ). There was no disadvantage to yield in applying the (NH4) 3PO4based 'First-Cut' fertiliser 2 weeks earlier and at a smaller N rate than the other treatments in Experiment 1. In Experiment 2 however, with all treatments applied on the same dates, application of the NHa-rich fertilisers was advantageous to herbage growth, (Fig. 7) although the resulting cut yields were not significantly greater than that resulting from application of NHaNO3. Thus, the differential effects on herbage yield of NO3 and NH4 fertiliser formulations applied in spring were much smaller than might have been expected from previous studies using solution culture (Clarkson et al., 1986) and in the field (Stevens, 1988).
5. Conclusions The fertiliser N applied to surface-drained grassland under wet conditions in spring was resistant to loss in
D. Scholefield, A.C. Stone/Agriculture, Ecosystems and Environment 55 (1995) 181-191
runoff: less than 10% of the N applied was lost despite prolonged rainfall immediately after application. Although more soluble than NH4, NO3was effectively locked up, possibly through rapid transport to and diffusion within NO3- deficient soil pores containing relatively immobile water. This demonstrates the potential of such soils to act as nutrient buffers in the protection of the quality of surface waters. Although the amounts of N, P and K lost were small, the transient peak concentrations of N and P in runoff were large relative to indices of good water quality. These results indicated no advantage to very early fertiliser application, in terms of either nutrient leaching or herbage yield, yet when all fertilisers were applied very early a small advantage to applying NHarich formulations was indicated.
Acknowledgements The authors thank Jane Hawkins for performing the nutrient analyses, and ICI Fertilisers Ltd for financial support. Improvements to earlier drafts were made by anonymous referees and one of the Editors-in-Chief. The work was part of a commission from the Ministry of Agriculture, Fisheries and Food.
References Baker, D., Doyle, C. and Lidgate, H., 1991. Grass Production. In: C. Thomas, A. Reeve and G.E.J. Fisher (Editors), Milk From Grass. Appendix 1. Institute of Grassland and Environmental Research, Hurley. Billingham Press, Cleveland, pp. 105-109. Barraclough, D., Hyden, M.J. and Davies, G.P., 1983. Fate of fertiliser nitrogen applied to grassland. 1. Field leaching results. J. Soil Science, 34: 483-497. Boltz, D.F. and Mellon, M.G., 1948. Spectrophntometric determination of phosphorus as molydiphosphoric acid. In: Analytical Chemistry Volume 20, No. 8, Purdue University, Lafayette, pp. 749-751. Chichester, F.W., 1977. Effects of increased fertiliser rates on nitrogen content of run-off and percolate from monolith-lysimeters. J. Environ. Qual., 6:211-217. Clarkson, D.T., Hopper, M.J. and Jones, L.H.P., 1986. The effect of root temperature on the uptake of nitrogen and the relative size
191
of the root system in Lolium perenne. 1. Solutions containing both NH4÷ and NO~. Plant, Cell Environ., 9: 535-545. Costin, A.B., 1980. Run-offand soil nutrient losses from an improved pasture at Ginninderra, Southern Tablelands, New South Wales. Aust. J. Agric. Res., 31: 533-546. Department of the Environment. 1985. River water quality in England and Wales. HMSO, London. GENSTAT 5 Committee. 1987. GENSTAT 5 Reference Manual, Clarenden Press, Oxford. Haigh, R.A. and White, R.E., 1986. Nitrate leaching from a small underdrained, grassland, clay catchment. Soil Use Manage., 2: 65-70. Harrod, T.R., 1981. Soils in Devon. Soil Survey Record No. 70, Harpenden, 180 pp. Holmes, C.W., 1974. The Massey grassmeter. Dairy Farming Annual 1974, pp. 26-30. Kilmer, V.J., Gilliam, J.W., Lutz, J.F., Joyce, R.T. and Eklund, C.D., 1974. Nutrient losses from fertilised grassed watersheds in western North Carolina. J. Environ. Qual., 3: 214-218. Macduff, J.H. and White, R.E., 1985. Net mineralisation and nitrification rates in a clay soil measured and predicted in permanent grassland from soil temperature and moisture content. Plant and Soil, 86: 151-172. Moe, P.G., Mannering, J.V. and Johnson, C.B., 1967a. Loss of fertiliser nitrogen in surface runoff water. Soil Sci., 104: 389-394. Moe, P.G., Mannering, J.V. and Johnson, C.B., 1967b. A comparison of nitrogen losses from urea and ammonium nitrate in surface runoff water. Soil Sci., 105: 428-433. Navone, R. 1964. Proposed method for nitrate in potable waters. J. Am. Water Works Ass., 56:781-783. Owens, L.B., Edwards, W.M. and Van Keuren, R.W., 1984. Peak nitrate-nitrogen values in surface run-offfrom fertilised pastures. J. Environ. Qual., 13: 310-312. Sanyal, S.K. and De Datta, S.K., 1991. Chemistry of phosphorus transformations in soil. In: B.A. Stewart (Editor), Advances in Soil Science, Vol. 16. Springer, New York, pp. 1-120. Scholefield, D., Tyson, K.C., Garwood, E.A., armstrong, A.C., Hawkins, J. and Stone, A.C., 1993. Nitrate leaching from grazed grassland lysimeters: effectsof fertiliser input, field drainage, age of sward and patterns of weather. J. Soil Sci., 44: (in press). Stevens, R.J., 1988. Some factors influencing the efficiency of fertiliser nitrogen for grass production in spring. In: D.S. Jenkinson and K.A. Smith (Editors), Nitrogen Efficiency in Agricultural Soils. Elsevier Applied Science, London, pp. 177-191. Stratmann, B. and Kfihbauch, W., 1987. Einflu6 der Gulledung auf die Stickstoffverlagerung in hangigem Grunland. Zeitshrift Das wirtschaftseigene Futter, 33: 162-172. Uhlen, G., 1989. Nutrient leaching and surface runoff in field lysimeters on a cultivated soil. Nutrient balances 1974-81. Norwegian J. Agric. Sci., 3: 33-45. Verdouw, H., van Echteld, C.J.A. and Dekkers, E.M.J., 1977. Ammonia determination based on indolphenol formation with sodium salicylate. Water Res., 12: 399-402.
,w ELSEVIER
Agriculture, Ecosystemsand Environment55 (1995) 181-191
Nutrient losses in runoff water following application of different fertilisers to grassland cut for silage D. Scholefield *, A.C. Stone Institute of Grassland and Environmental Research, North WykeResearch Station, Okehampton, EX20 2SB, UK
Accepted 16 June 1995
Abstract Studies were made to assess the losses of nutrients in runoff from pastures, and to ascertain whether application of N as NIL rather than NO3 both reduced N losses and enhanced yields of herbage. Two experiments were conducted during consecutive springs in which surface lysimeter plots were established on sloping grassland with soils of low permeability, and different forms of fertiliser applied for first-cut silage. Despite weather conditions conducive to large nutrient losses, less than 10% of the N applied was found in runoff. However, the peak concentrations of nutrients were large relative to standards for good water quality. The concentrations of NO3-N were greater in water from plots that received NIL NO3 than from those that received either (NH4) 3 PO4 or urea. Large concentrations of NIL-N were measured in runoff in response to all treatments, with the largest in water from plots that received urea. The mechanisms that may account for the observed resistance to loss in runoff are discussed. In the first experiment there was no advantage (or disadvantage) in applying an (NIL)3 PO4 formulation 2 weeks earlier than applying either NI-I4NO3 or urea. In the second experiment, where all treatments were applied on the same dates, herbage mass accumulated more slowly on plots that received NIL NO3 compared to those that received more NH4-rich forms. However, in neither experiment did the fertiliser treatments influence the yields of herbage cut for silage. Keywords: Nutrient leaching; Runoff water; Grassland agronomy;Water quality
1. Introduction Fertilisers are applied to crops when the land is trafficable and the temperature is sufficient for nutrient uptake and growth. In maritime regions of western Europe however, the winters are often mild and the use of reduced ground-pressure vehicles has made possible the application of fertilisers before the end of the wet winter period. In the UK, for example, fertiliser is normally applied to pasture in February to promote early growth for first-cut silage. It is generally believed that the nutrients applied to the surface of impermeable soils * Corresponding author: Tel. 0837 82558, Fax 0837 82139. 0167-8809/95/$09.50 © 1995 Elsevier Science B.V. All fights reserved SSDIO167-8809(95)00623-0
at this time would be at extreme risk of loss in runoff water. There have been few reports of direct leaching of fertiliser from grassland. Intense summer rainfall immediately after a top-dressing of fertiliser N to dry soil can result in large but transient peak concentrations of nitrate in percolating leachate, presumably because of macropore flow (Barraclough et al., 1983; Haigh and White, 1986). Chichester (1977) measured NO 3 loss in percolate and runoff water from monolith lysimeters during a 4 year period and noted that the greatest loss in runoff occurred in summer when heavy rain followed a fertiliser application. The quantities lost in runoff decreased as the extent of soil cover increased,
182
D. Scholefield, A.C. Stone/Agriculture, Ecosystems and Environment 55 (1995) 181-191
such that 10 kg N ha-~ year-~ was lost from 'clean cultivated corn', whereas less than 1 kg ha-~ yearwas lost from the lysimeters with grass cover. Costin (1980), however, who established runoff lysimeter plots in leguminous pastures in Australia, showed that where fertiliser was not applied, the greatest losses of soil and nutrients occurred during the wetter winter months. In studies conducted in the colder regions of Europe it was the melting of snow and ice in spring that caused the greatest losses of nutrients in runoff (Uhlen, 1989; Stratmann and Kfihbauch, 1987). Studies conducted in the USA (Moe et al., 1967a; Moe et al., 1967b) have indicated that N applied to wet, impermeable soils as NH4NO3 or urea may be particularly resistant to loss, even during intense storms. In contrast, recent measurements of NO 3 lost from grazed grassland lysimeters in the UK have demonstrated the loss in runoff of approximately 30% of the fertiliser N applied in March (Scholefield et al., 1993). In addition to soil conditions and weather, the form of the applied fertiliser may be an important factor in determining the extent of nutrient loss in runoff. Stevens (1988) found that the percentage utilisation by herbage of N applied as (NH4)2 SO4 to a wet, upland site in spring was greater than that of N applied either as Ca(NO3) 2 or as urea. Such a finding may be a result of the relative immobility of the NH4 ion, or its potential for better absorption by roots at temperatures below 9°C (Clarkson et al., 1986). The present experiments were conducted with the primary objectives of: (1) measuring the amounts of N lost in runoff from sloping grassland on an impermeable soil, after applications of fertiliser for first-cut silage; (2) assessing the potential of applying N in the NH4 and urea forms both to reduce such loss and to achieve quicker plant uptake under cool conditions; (3) assessing the effects of the different fertiliser forms and any differential leaching losses on the cut yield of herbage. A secondary objective was to measure the losses of P and K in runoff. Two experiments were conducted using surface water lysimeter plots; the first in 1989, and the second at a different site in 1990. 2. Materials and methods
2.1. Sites and soils Experiment 1 was conducted at the Institute of Grassland and Environmental Research, North Wyke, in
southwest England on a 2 ha field sown to perennial ryegrass in 1982, that had received 300--450 kg N ha- 1 year- 1as NH4NO3 and been intensively grazed by beef cattle. The soil is a non-calcareous pelosol of the Halstow series (Gleyic Cambisol) which consists typically of a silty clay loam Ap horizon (31% clay, 47% silt) to 21 cm, overlying a silty clay Bw horizon (38% clay, 46% silt) at 21-41 cm depth (Harrod, 1981). It was anticipated that a substantial proportion of winter discharge on this site would be by runoff and sub-surface lateral flow down the 5-9 ° slope to the south. The mean soil temperature (100 mm depth) for February 1989 was 5.3°C. Experiment 2 was conducted at North Wyke on a 3 ha field sown to perennial ryegrass in 1985, that had received 350 kg N ha- ~ year- ~and been grazed intensively by sheep. The soil was a clayey pelo-stagnogley of the Hallsworth series (Stagno-Dystric Gleysol), which consists typically of a clayey Apg horizon (38% clay, 50% silt) to 27 cm, overlying a clay Bg horizon (43% clay, 43% silt) at a depth of 27-66 cm. (Harrod, 1981). It was anticipated that, because of the finer texture of the upper horizon, a greater proportion of winter discharge would be by runoff, down the 7 ° slope to the north, than at the site of Experiment 1. Rainfall data were obtained from a Meteorological Office station (North Wyke, Station 8836) which is situated less than 1 km from both sites. The mean soil temperature ( 100 mm depth) for February 1990 was 6.3°C.
2.2. Surface water lysimeter plots: design and installation Each lysimeter plot consisted of a diamond-shaped area of 100 m 2 ( 10 m × 10 m), hydrologically isolated to collect runoff and lateral surface flow to 100 mm depth. Thus, four narrow trenches were dug (75 mm wide by 100 mm deep) to contain 60 mm diameter flexible perforated drainage tube, resting on the compacted clay base and surrounded by 'pea' gravel to the surface. With the axis of the diamond aligned with the direction of slope, the two up-slope trenches diverted water away from the plot, and the two down-slope trenches collected water draining from the plot itself (Fig. 1). This water was channelled via a 'Y'-connector to a tipping bucket device that both monitored the flow and sampled on a flow-proportional basis.
183
D. Scholefield, A.C. Stone/Agriculture, Ecosystems and Environment 55 (1995) 181-191
by the rate of tipping. Tips were counted using a simple reed switch connected either to an electro-mechanical counter or to a data-logger (Squirrel type 1203). Assuming that the rainfall could all be accounted for in surface discharge, 25 mm of rainfall at 2 mm h - 1 would result in 5000 tips, with a tip every 9 s. 2.3. Experimental treatments
I
T
Fig. 1. Schematic diagram of lysimeter plot, showing means of collecting runoff from the bounded area. A, sample area; B, diversion drains; B1, diverted water; C, collection drains; CI, sample water; D, solid down-pipe; E, protective cover; F, 'Y' connector; G, flexible perforated pipe covered with gravel.
A D
G
A
\
Fig. 2. Diagram of tipping bucket apparatus showing sample tube to enable flow-proportional sampling. A, funnel; B, sample tube; C, reed switch; D, pivot; E, adjustable screws; F, frame; G, sample container. The tipping bucket comprised two conical poly-propylene funnels (200 m m diameter, 500 ml capacity) sealed at the necks and bolted to a steel angle plate with 75 ° between the axes (Fig, 2). One of the funnels was used for sampling by inserting a curved metal tube (4 m m bore) through the wall via a bulkhead coupling. A small sample could thus be diverted to a 101 container while the remainder was tipped to 'waste' The volume of water sampled in this tube on alternate tips was adjustable according to the bore and depth of immersion of the tube. Normally, the sample volume was 0.3 ml per tip, and, within the range of drainage intensities encountered at these sites, this volume was unaffected
Nine lysimeters (three replicates of three fertiliser treatments) were installed at the site of Experiment 1 in September 1988, and 16 lysimeters (four replicates of four treatments) were installed at the site of Experiment 2 in October 1989 (Fig. 3). The treatments applied in Experiment 1 were typical of formulations and timings currently recommended to farmers in the region. These treatments were not necessarily 'matched' with regard to nutrient content and timing. Treatment l was the 'First-cut' formulation ( N P K compound with 70% of the N as NH4 and all the P as (NH4) 3 PO4 ) applied on 22 February, followed by N H 4 NO3 ( ' N i t r a m ' ) applied 1 month later; Treatment 2 was an N P K formulation with the N as NH4 NO 3, ( 'ICI No 8') applied on 8 March, again followed by NH4 NO3 ( ' N i t r a m ' ) applied 1 month later; Treatment 3 was two applications of urea timed as for Treatment 2, and with amounts of P and K equated with Treatment 2 by mixing the urea with triple super-phosphate and KC1 respectively (Table 1). In Experiment 2 the treatments were matched with regard to nutrient content and timing to enable comparisons to be made among nutrient forms, rather than between fertilizer advice packages, as in Experiment 1.
L
_
/
°1
***<7 0
50
1
Metres
Fig. 3. Layout of lysimeter plots for (a) Experiment 1 and (b) Experiment 2. Arrows show directions of slope. Treatments 1 and 4, stripe; Treatments 2 and 5, hatch; Treatments 3 and 6, black; Treatment 7, clear.
184
D. Scholefield, A. C. Stone/Agriculture, Ecosystems and Environment 55 (1995) 181-191 40 F
Table 1 Formulation and date of application of fertilisers in Experiment 1
a
v
Treatment
1. First cut Nitram 2. ICI No. 8 Nitram
Date applied Rate (kg h a - ~)
22.2.89 21.3.89 8.3.89 5.4.89
3. Urea Triple super-phosphate 8.3.89 KCI Urea 5.4.89
N
P2Os
K20
45 85 86 64 86 0 0 64
24 0 15 0 0 15 0 0
62 0 50 0 0 0 50 0
"o
2o
~
17/2 18
19 2O 22 25 26
27 28 1/3
3
9
13
16
17 21
28 17/4
Date
14
e
12
Table 2 Formulation and date of application of fertilisers in Experiment 2 Treatment
4. First cut Nitram 5. Nitram Triple superphosphate KC1 Nitram 6. First-cut ASN ~ 7. Urea Triple superphosphate KCI Urea
Date applied Rate ( k g / h a - ~) N
P
K
23.2.90 23.3.90 23.2.90 23.2.90
45 86 45 0
24 0 0 24
62 0 0 0
23.2.90 23.3.90 23.2.90 23.3.90 23.2.90 23.2.90
0 86 45 86 45 0
0 0 24 0 0 24
62 0 62 0 0 0
23.2.90 23.3.90
0 86
0 0
62 0
17J2 18 19 20 22 25 26 27 28 1/6
3
9
13 18 17 21 26 1714
3
9
13 16 17 21 26 1714
3
9
13 16 17 21 26 1714
Date
C
17/2 18 19 20 22 25 26 27 28
Thus, in each treatment, 45 kg N h a - ~, 24 kg P h a - ] and 62 kg K ha-1 were applied on 23 February, followed by 86 kg N h a - ~on 23 March (Table 2). Only in Treatment 7 (urea) was the same form of N applied on both dates. The fertilisers were applied manually after the herbage on each plot had been trimmed to 50 mm using a Mayfield reciprocating blade mower which minimises soil structural damage under wet conditions.
2.4. Measurements and analyses The same measurements and analyses were performed in both experiments. Samples of discharge from
1/3
Date
~ASN-ammonium sulphate/ammonium nitrate (26% N of which 7% is as NO3). 15 E
5£
C
8
0 17/2 18 19 20 22 25
28
27
28
1/3
Date Fig. 4. Nutrient leaching in Experiment 1: (a) rainfall (black) and runoff (stripe); (b) concentration of nitrate plus ammonium-N; (c) concentration of phosphate-P; (d) concentration of K +. In ( b ) - ( d ) Treatments 1, 2 and 3 are in order across page on a given date.
D. Scholefield, A.C. Stone/Agriculture, Ecosystems and Environment 55 (1995) 181-191 each lysimeter were collected periodically (daily during periods of intense rainfall), filtered through prewashed Whatman No. 1 filter paper to remove turbidity and divided into three sub-samples to be analyzed for NO3-N and NH4- N, P (ortho-phosphate) and K ÷. Nitrate, NH4 and PO4 were analyzed using standard colorimetric auto-analyzer procedures (Boltz and Mellon, 1948; Navone, 1964; Verdouw et al., 1977) and K + was analyzed with a flame photometer (EEL). The amounts of dissolved nutrients were calculated by multiplying their respective concentrations in each composite sample by the volume recorded. Ten soil samples (25 mm diameter, 150 mm deep) were taken weekly from random positions within each plot. These were bulked and weighed. Representative sub-samples were taken for the determination of water content (drying to constant weight in a forced drought oven), and to permit calculation of the bulk density of the soil. Three further sub-samples were taken of the bulked soil from each plot and these were extracted with aqueous solutions of 1.0 M KCI, 0.5 M NaHCO3 (pH 8.5) or 1.0 M ammonium acetate (pH 7.0) to obtain 'plant available' N,P and K respectively. Analyses of these solutions were carried out as per the analysis of the drainage water. Values for soil water content and bulk density were used to enable the expression of nutrient concentrations on a kilogram per hectare basis.
185
Assessments of above-ground herbage mass were made weekly using a rising plate sward stick (Holmes, 1974). The total herbage to 70 mm on each plot was cut and weighed using a Haldrup small plot harvester when the nominal dry matter digestibility value of herbage harvested from the area was 70% (Agricultural Development and Advisory Service forecast based on weekly near infra-red analysis). The dates of cutting were 10 May and 18 May for Experiment 1 and 2, respectively. Representative samples of herbage were collected and oven-dried at 80°C for the determination of dry matter yields. Data for the total amounts of nutrients lost and dry matter yields were analyzed for treatment effects using analysis of variance. (GENSTAT 5 Committee, 1987)
3. R e s u l t s
3.1. Experiment l Rainfall and drainflow First runoff was measured on 29 September 1988, and by early February 1989, 270 nun of rainfall had leached the soil surface. This resulted in small background concentrations of N and P in water draining from each lysimeter, but each rainfall event produced a relatively larger peak concentration of K. During the
Table 3 Extractablesoil nutrients, Experiment 1 (kg ha- ~) Date
21.2.89 6.3.89 20.3.89 4.4.89 4.5.89
Treatment
1 2 3 1 2 3 1 2 3 1 2 3 1
2 3
Soil nutrient concentration (0-10 cm ) NH4-N
N03-N
4.6 5.8 5.3 23.5 1.3 0.6 5.3 9.6 14.7 17.8 12.6 10.7 9.4 7.9 9.4
2.2 2.2 3.9 4.5 1.9 2.4 21.9 44.5 43.0 45.1 17.2 16.6 8.2 6.8 8.5
P 2.6 0.4 1.4 6.0 4.5 3.3 0.8 2.8 1.8 9.0 9.3 8.8
K 52.0 45.8 34.2 54.8 49.6 37.9 40.6 58.4 41.8 41.1
42.1 37.2
D. Scholefield, A.C Stone/Agriculture, Ecosystems and Environment 55 (1995) 181-191
186
Table 4 Nutrient losses in runoff (kg ha- ~) in Experiment 1 Treatment
Experiment 1
~
N
P
K
3.1 3.0 3.0 0.58 NS
0.42 0.05 0.13 0.09 NS
7.0 3.9 6.4 1.24 NS
ao
i
a
2O
1
2 3 sea sig.
~ ~ 1o ~0
1412
17/2
21/2
2612
28/2
4/3
26/2
28/2
4/3
28/2
2812
4/3
Date
Table 5 Dry matter yield of herbage (t ha- ~) in Experiment 1 Experiment 1
•
Treatment
Yield
1
4.8 4.8 4.5 0.26 NS
2 3 seA sig.
14
z f g
8
N
e
g~ 2 0
~
14/2
17/2
21/2
Date
week before the first application of Treatment 1 ( 1521 February) 56.1 mm of rainfall was recorded, and the first runoff during the experimental period was observed on 17 February. During the following week 84.1 mm of rainfall was recorded, and, during the week after the first application of Treatments 2 and 3 52.8 mm of rainfall was recorded (Fig. 4a). Thus, the first applications of all treatments were made when the soil in the lysimeter plots was wet, and the nutrients applied were at risk of being lost in runoff water. During this initial period ( 17 February-27 March) 62% of the rainfall received was recovered by the tipping bucket system. Discharge ceased after this period and so the second applications of Treatments 2 and 3 were not subjected to loss in the runoff.
3
Q.
8
14/2
17/2
21/2
Date
d
E
14
~
8
N
6
g
Soil available nutrients and losses in runoff Before the first application of fertilizers in Treatment 1 the amount of inorganic-N in the soil was less than 10 kg ha- 1 in all plots (Table 3). On 6 March, after 2 weeks and some 50 mm of runoff, 28 kg N haremained in the soil of which 23.5 kg ha- ~ was NH4N. Three kg N ha- ~ was leached from this first application (Table 4), at a maximum concentration corresponding to maximum drainflow (Fig. 4b) of 8.8
0
8 2 ~ ~ 0"
14/2
17/2
21/2
26/2
28/2
4/3
Date
Fig. 5. Nutrient leaching in Experiment 2: (a) rainfall (black) and runoff (stripe); (b) concentration of nitrate plus ammonium-N; (c) concentration of phosphate-P; (d) concentration of K +. In ( b ) - ( d ) Treatments 4, 5, 6 and 7 are in order across page on a given date.
D. Scholefield, A.C. Stone/Agriculture, Ecosystems and Environment 55 (1995) 181-191
187
Table 6 Extractable soil nutrients, Experiment 2 (kg ha- ~) Date
16.2.90
1.3.90
8.3.90
15.3.90
29.3.90
5.4.90
19.4.90
4.5.90
Treatment
4 5 6 7 4 5 6 7 4 5 6 7 4 5 6 7 4 5 6 7 4 5 6 7 4 5 6 7 4 5 6 7
Soil nutrient concentration (0-10 cm) NH4-N
N03-N
P
K
12.1 18.5 12.0 11.4 21.5 18.6 31.8 44.0 13.0 14.7 11.6 13.2 8.7 7.8 8.9 9.6 48.0 62.3 68.3 40.0 10.4 10.8 15.8 12.3 10.5 10.0 9.0 10.2 14.2 13.6 15.1 13.8
1.7 0.5 1.6 1.6 1.9 3.2 5.2 3.6 4.4 4.5 6.7 9.2 0.7 1.0 1.6 1.6 13.8 38.5 15.7 22.3 31.6 31.8 8.6 12.2 1.7 2.6 1.4 1.9 2.5 4.6 4.8 1.9
8.2 8.2 8.6 9.4 7.2 11.3 11.4 8.4 6.7 7.3 10.1 5.9 12.9 14.8 10.5 11.5 9.6 10.4 12.5 10.2 11.6 13.1 14.6 11.5 9.0 9.5 8.4 8.9 -
183 159 212 203 240 214 237 257 254 279 246 230 282 232 236 285 229 227 242 227 184 183 204 190
m g d m - 3 ( 2.7 m g d m - 3 N H 4 - N ) . O n l y 0.1 kg N h a - 1 Table 7 Nutrient losses in runoff (kg ha- ~) in Experiment 2 Treatment
4 5 6 7 sed sig.
Experiment 2 N
P
K
3.2 4.1 2.9 3.0 0.82 NS
0.37 0.54 0.28 0.54 0.15 NS
4.1 3.4 3.6 5.1 1.49 NS
w a s l e a c h e d f r o m the l y s i m e t e r s that r e c e i v e d Treatm e n t 1 after this initial period. O n 2 0 M a r c h , after the first a p p l i c a t i o n o f T r e a t m e n t s 2 a n d 3 ( I C I No. 8 a n d u r e a ) , m o s t o f the NI-L-N o f T r e a t m e n t 2 a n d the u r e a - N o f T r e a t m e n t 3 h a d a p p a r e n t l y b e e n nitrified, ( T a b l e 3) d e s p i t e a n a v e r a g e soil t e m p e r a t u r e ( 1 0 0 n u n d e p t h ) o f 6.1°C d u r i n g the period. T h e a m o u n t o f N l e a c h e d in r e s p o n s e to e a c h o f t h e s e t r e a t m e n t s w a s 3.0 k g h a -~ ( T a b l e 4 ) . T h e m a x i m u m c o n c e n t r a t i o n s o f N in l e a c h a t e w e r e 10.9 a n d 9.0 m g d m - 3 (1.7 a n d 4.5 m g d m - ~ N H a - N ) in r e s p o n s e to T r e a t m e n t s 2 a n d 3, r e s p e c t i v e l y ( F i g . 4 b ) .
188
D. Scholefield, A. C. Stone ~Agriculture, Ecosystems and Environment 55 (1995) 181-191
4
J=
~3
,,X'~lll
10
~2 z
"3
E l
"<
o
1412
17/2
2112
28/2
2812
413
Date 0
1/1
b
i
i
r
i
2/3
9/3
16/3
22/3
i
i
3013 614 Date
i
i
i
i
i
12/4
20/4
2714
4/5
515
.¢
Fig. 7. Accumulation of herbage mass as measured by the rising plate sward-stick in Experiment 2. Treatment 4 ( - + - ) ; Treatment 5 ( A-); Treatment 6 (-o-); Treatment 7 ( - D - ) . z c ,< 1412
17/2
2112
2812
2812
413
2812
2812
413
Date
1412
1712
21/2
Date
Leaching of P occurred during the periods of drainflow responsible for the leaching of N (Fig. 4). The amounts of P leached were much less than those of N however, and the amounts of extractable P in the soil did not reflect the fertiliser P added, nor indicate the amounts leached. Although the total losses of P were small, losses from plots that received Treatment 1 were greater than from those that received Treatments 2 and 3 (Table 4). Potassium was as susceptible as N to loss in runoff at this site (Fig. 4d and Table 4). The exact responses to applications of fertiliser were more difficult to ascertain because of the relatively large background concentrations in all runoff water. The amounts lost corresponded to less than 10% of those applied, with more lost from plots that received Treatments 1 and 3 (NH4-N) than from those that received Treatment 2. Table 8 Dry matter yield of herbage (t ha- ~) in Experiment 2 Experiment 2
14/2
17/2
21/2
2812
2812
4/3
Date
Fig. 6. Amounts of nitrate and ammonium N leached in runoff in Experiment 2: (a) with Treatment 4; (b) Treatment 5; (c) Treatment 6; (d) Treatment 7. The ammonium component is shaded black.
Treatment
Yield
4 5 6 7 sed sig.
4.6 4.2 5.1 4.4 0.35 NS
D. Scholefield, A. C. Stone/Agriculture, Ecosystems and Environment 55 (1995) 181-191
189
Herbage yield
Herbage yield
Table 5 shows that herbage dry matter yield ranged from 4.5-4.8 t ha- 1 but there was no significant effect of fertiliser treatment.
Table 8 shows that herbage dry matter yield ranged from 4.2-5.1 t ha- ~, but there was no significant effect of fertiliser treatment. The assessment by sward stick (Fig. 7), however, indicated consistently (ten measurement dates) that the NHa-rich treatments were promoting more rapid growth of herbage than Treatment 5 (Nitram).
3.2. Experiment 2 Rainfall and drainflow February 1990 was extremely wet with a rainfall of 251 mm recorded of which 48 mm fell over the 5 days following the first application of fertilisers. During February 85% of the rainfall received was recorded as runoff (Fig. 5a). Discharge ceased on 22 March and so again the second applications were not subject to loss in the runoff. There was no correlation between the slope of individual lysimeters and the fraction of the rainfall collected. Also, less of the rainfall was accounted for as runoff after a few days of dry weather.
Soil available nutrients and losses in runoff Both the additions and form (NO3 or NH4) of fertiliser N were detectable in the soil 1 week after application (Table 6). The amounts of N lost in response to Treatments 4-7 (Table 7) respectively were 7.0, 9.1, 6.5 and 6.7% of the 45 kg N ha- ~ applied in the first application. Treatment 5 suffered the greatest loss of N with the greatest proportion as NO 3, whereas Treatment 7 resulted in the smallest loss, but with the greatest proportion as NH4 (Fig. 6). The storm event on 26 February resulted in the greatest concentrations of N in runoff, ranging from 15.2 mg dm-3 for Treatment 5 to 7.6 mg dm -3 for Treatment 7 (Fig. 5b). The amount of bicarbonate extractable P varied between 6 and 15 kg ha-1 during the experimental period (Table 6). This was not sensitive to either the inputs of fertiliser P or the various N treatments. The amounts of P lost in runoff were < 0.5 kg ha- 1, with concentrations above 'background' observed only on 26 February (Fig. 5c). Treatments 5, with P as triple super-phosphate, resulted in greater loss of P than Treatments 4 and 6, with P a s ( N H 4 ) 3 P O 4 (Table 7). The soil was rich in ammonium acetate extractable K, with amounts ranging between 200 and 300 kg haduring the experimental period (Table 6). The amount of K leached in runoff was of the same order as that of N with approximately 5 kg ha- 1 being lost during the drainage period (Table 7, Fig. 5d). This amount was not influenced by any of the fertiliser treatments.
4. Discussion
The weather conditions that prevailed before and immediately following the first applications of the fertiliser treatments during both experimental periods were highly conducive to major losses of nutrients in runoff: only the application to snow-covered or frozen ground could be considered more risky. Despite these conditions, the losses of N, P and K were small relative to the amounts applied. The amounts and patterns of N loss are at first sight very similar to those obtained by Kilmer et al. (1974) who monitored nutrient losses from grassland fertilised with NH4 NO3 in North Carolina, USA. The difference is that, in the American study, the peak concentrations of N in runoff did not appear to correspond to the additions of fertiliser. This discrepancy may have been the result of infrequent sampling and lack of rainfall immediately after applications, because in a 5 year study of 890 runoff events, Owens et al. (1984) observed that all peak nitrate concentrations occurred shortly after applications of fertiliser N. In another North American study (Moe et al., 1967a), intense storms (63.5 mm h -~ for 1 h) were applied with a rainfall simulator to sloping, wet grassland 24 h after application of NH4 NO3 at 224 kg N ha- 1. Less than 15% of the N applied was accounted for in runoff. These results and those of the present study indicate that a large fraction of fertiliser N may be rapidly 'locked up' after application to wet, fine-textured soil. It is unlikely that the processes of plant uptake, assimilation by the microbial biomass and denitrification combined could be responsible for this amount of retention at such low temperatures; the involvement of soil physical processes must be assumed. Rapid transport of NO 3 ions to zones of relatively immobile water both by mass flow and diffusion is a feasible mechanism. Such zones would exist in the micropores of a well-
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D. Scholefield, A.C. Stone/Agriculture, Ecosystems and Environment 55 (1995) 181-191
structured soil, and/or also at depths where rates of lateral flow are small. However, under the experimental conditions, that is with runoff occurring continuously from the day before fertiliser application to the time that the peak concentrations of N was detected in runoff, retention of N as a result of transport to depth via a wetting front might be considered relatively unimportant. In addition to the mechanism suggested to account for the small NO3 losses above, the NH 4 ions are subject to adsorption by soil colloids in ion exchange reactions. Set against this reduced mobility of NH4-N is the process of nitrification, which will be initiated on contact with the soil, but will only proceed rapidly to produce NO3 in aerobic, warm conditions (Macduff and White, 1985). Fig. 6 shows the outcome of these different controls on ion mobility in Experiment 2. Treatment 5 supplied N with a NO~:NH~-ratio of 1.0, whereas the ratio in runoff from this treatment on 26 February was 2.7. In contrast, Treatments 4 and 6 supplied N with a ratio of 0.4, but the ratio in the runoff from each treatment on 26 February was 1.4. This ratio tended to increase for all treatments with time after application, presumably as nitrification progressed. Because urea hydrolysis would have been rapid (Moe et al., 1967b), but nitrification rather slow, it is not surprising that the addition of the urea treatment resulted in the greatest loss of ammonium and the smallest NO3:NH + ratio (0.3) in runoff water. Moe et al. (1967b) compared the ionic composition of runoff from grassland plots applied with equal amounts of fertiliser N either as NH4 NO3 or as urea. Equal amounts of NH4 were lost, which was assumed to arise from a greater initial rate of transport to depth by the un-ionised urea molecules. In the present experiments about twice the amount of NH4 was lost from the urea-treated plots compared to those that received NH4 NO3 (5.6 compared with 2.7 kg N h a - l ) , and therefore such a mechanism need not be invoked. The amounts and concentrations of ortho-phosphate P in runoff were similar to those obtained in other studies (Kilmer et al., 1974; Costin, 1980; Uhlen, 1989). It appeared that in Experiment 1 more P was lost from plots that received Treatment 1 ((NH4)3 PO4) than from those that received triple-superphosphate, but in Experiment 2 there was no influence of treatment. In common with the losses of N, the losses of P were small relative to the amounts applied but peak
concentrations in runoff could be considered large relative to standards for good water quality (Department of the Environment, 1985). It is well known that inorganic P, added to soils, is quickly fixed by sorption on to colloids, biological transformations and strong chemical binding to iron and aluminium compounds (Sanyal and De Datta, 1991 ). Thus, little of the fertiliser P added in the present experiments could be detected in the bicarbonate-extractable fraction a few days after addition, (Table 3 and Table 6) and the amounts extracted did not correlate with the amounts leached (Fig. 4c and 5c). The concentrations and amounts of K in runoff were similar to those obtained in other studies (Uhlen, 1989; Kilmer et al., 1974). More K was lost in Experiment 1 than in Experiment 2 (Table 4 and Table 7), but the soil in Experiment 2 had about five times the amount of exchangeable K as the soil in Experiment 1 (Table 3 and Table 6). These two results suggest that the soil used in Experiment 1 either had fewer exchange sites or that they were occupied by cations with greater affinity for the sites than K ÷. However, in Experiment 1, there was more K lost in treatments which received NH4 sources suggesting that NH4 may have displaced K from the exchange complexes. The DM yields of herbage obtained in both experiments were consistent with those expected at first cut on lowland farms within the UK (Baker et al., 1991 ). There was no disadvantage to yield in applying the (NH4) 3PO4based 'First-Cut' fertiliser 2 weeks earlier and at a smaller N rate than the other treatments in Experiment 1. In Experiment 2 however, with all treatments applied on the same dates, application of the NHa-rich fertilisers was advantageous to herbage growth, (Fig. 7) although the resulting cut yields were not significantly greater than that resulting from application of NHaNO3. Thus, the differential effects on herbage yield of NO3 and NH4 fertiliser formulations applied in spring were much smaller than might have been expected from previous studies using solution culture (Clarkson et al., 1986) and in the field (Stevens, 1988).
5. Conclusions The fertiliser N applied to surface-drained grassland under wet conditions in spring was resistant to loss in
D. Scholefield, A.C. Stone/Agriculture, Ecosystems and Environment 55 (1995) 181-191
runoff: less than 10% of the N applied was lost despite prolonged rainfall immediately after application. Although more soluble than NH4, NO3was effectively locked up, possibly through rapid transport to and diffusion within NO3- deficient soil pores containing relatively immobile water. This demonstrates the potential of such soils to act as nutrient buffers in the protection of the quality of surface waters. Although the amounts of N, P and K lost were small, the transient peak concentrations of N and P in runoff were large relative to indices of good water quality. These results indicated no advantage to very early fertiliser application, in terms of either nutrient leaching or herbage yield, yet when all fertilisers were applied very early a small advantage to applying NHarich formulations was indicated.
Acknowledgements The authors thank Jane Hawkins for performing the nutrient analyses, and ICI Fertilisers Ltd for financial support. Improvements to earlier drafts were made by anonymous referees and one of the Editors-in-Chief. The work was part of a commission from the Ministry of Agriculture, Fisheries and Food.
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of the root system in Lolium perenne. 1. Solutions containing both NH4÷ and NO~. Plant, Cell Environ., 9: 535-545. Costin, A.B., 1980. Run-offand soil nutrient losses from an improved pasture at Ginninderra, Southern Tablelands, New South Wales. Aust. J. Agric. Res., 31: 533-546. Department of the Environment. 1985. River water quality in England and Wales. HMSO, London. GENSTAT 5 Committee. 1987. GENSTAT 5 Reference Manual, Clarenden Press, Oxford. Haigh, R.A. and White, R.E., 1986. Nitrate leaching from a small underdrained, grassland, clay catchment. Soil Use Manage., 2: 65-70. Harrod, T.R., 1981. Soils in Devon. Soil Survey Record No. 70, Harpenden, 180 pp. Holmes, C.W., 1974. The Massey grassmeter. Dairy Farming Annual 1974, pp. 26-30. Kilmer, V.J., Gilliam, J.W., Lutz, J.F., Joyce, R.T. and Eklund, C.D., 1974. Nutrient losses from fertilised grassed watersheds in western North Carolina. J. Environ. Qual., 3: 214-218. Macduff, J.H. and White, R.E., 1985. Net mineralisation and nitrification rates in a clay soil measured and predicted in permanent grassland from soil temperature and moisture content. Plant and Soil, 86: 151-172. Moe, P.G., Mannering, J.V. and Johnson, C.B., 1967a. Loss of fertiliser nitrogen in surface runoff water. Soil Sci., 104: 389-394. Moe, P.G., Mannering, J.V. and Johnson, C.B., 1967b. A comparison of nitrogen losses from urea and ammonium nitrate in surface runoff water. Soil Sci., 105: 428-433. Navone, R. 1964. Proposed method for nitrate in potable waters. J. Am. Water Works Ass., 56:781-783. Owens, L.B., Edwards, W.M. and Van Keuren, R.W., 1984. Peak nitrate-nitrogen values in surface run-offfrom fertilised pastures. J. Environ. Qual., 13: 310-312. Sanyal, S.K. and De Datta, S.K., 1991. Chemistry of phosphorus transformations in soil. In: B.A. Stewart (Editor), Advances in Soil Science, Vol. 16. Springer, New York, pp. 1-120. Scholefield, D., Tyson, K.C., Garwood, E.A., armstrong, A.C., Hawkins, J. and Stone, A.C., 1993. Nitrate leaching from grazed grassland lysimeters: effectsof fertiliser input, field drainage, age of sward and patterns of weather. J. Soil Sci., 44: (in press). Stevens, R.J., 1988. Some factors influencing the efficiency of fertiliser nitrogen for grass production in spring. In: D.S. Jenkinson and K.A. Smith (Editors), Nitrogen Efficiency in Agricultural Soils. Elsevier Applied Science, London, pp. 177-191. Stratmann, B. and Kfihbauch, W., 1987. Einflu6 der Gulledung auf die Stickstoffverlagerung in hangigem Grunland. Zeitshrift Das wirtschaftseigene Futter, 33: 162-172. Uhlen, G., 1989. Nutrient leaching and surface runoff in field lysimeters on a cultivated soil. Nutrient balances 1974-81. Norwegian J. Agric. Sci., 3: 33-45. Verdouw, H., van Echteld, C.J.A. and Dekkers, E.M.J., 1977. Ammonia determination based on indolphenol formation with sodium salicylate. Water Res., 12: 399-402.