Pasture responses to phosphorus and nitrogen ...

New Zealand Journal of Agricultural Research

ISSN: 0028-8233 (Print) 1175-8775 (Online) Journal homepage: http://www.tandfonline.com/loi/tnza20

Pasture responses to phosphorus and nitrogen fertilisers on east coast hill country: 2. Clover and grass production from easy slopes A. G. Gillingham , J. D. Morton & M. H. Gray To cite this article: A. G. Gillingham , J. D. Morton & M. H. Gray (2008) Pasture responses to phosphorus and nitrogen fertilisers on east coast hill country: 2. Clover and grass production from easy slopes, New Zealand Journal of Agricultural Research, 51:2, 85-97, DOI: 10.1080/00288230809510438 To link to this article: http://dx.doi.org/10.1080/00288230809510438

Published online: 22 Feb 2010.

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Date: 02 January 2017, At: 12:05

New Zealand Journal of Agricultural Research, 2008, Vol. 51: 85-97 0028-8233/08/5102-0085 © The Royal Society of New Zealand 2008

85

Pasture responses to phosphorus and nitrogen fertilisers on east coast hill country: 2. Clover and grass production from easy slopes

A. G. GILLINGHAM* AgResearch Ltd Palmerston North, New Zealand

continued into late spring-autumn at most sites/ years. The consistency from year to year of the relative grass response in spring to N fertiliser allowed significant regression relationships to be developed † J. D. MORTON for the 3-year dataset for the North Island sites. The AgResearch same result did not occur in Marlborough, presumMosgiel, New Zealand ably because low rainfall limited pasture growth, or at Moeraki (not measured). The effects ofN fertiliser M. H. GRAY‡ on clover production throughout the total season AgResearch tended to be the opposite of those for grass producHavelock North, New Zealand tion. There was generally no response to N fertiliser *Present address: Research Consultant, 92 Waicola in early spring but a marked and consistent decline Drive, RD 1, Palmerston North 4471, New Zealand. in clover production in late spring-autumn with [email protected] creasing rate of N fertiliser application. Compared † Present address: Ballance-Agri-Nutrients, PO Box with clover production from plots that received 65, Rolleston 7643, New Zealand. 90 kg N ha-1, the average clover production in late ‡ Present address: Maurice Gray and Associates Ltd, spring-autumn from plots that received zero N ap1 Aotea Crescent, Havelock North 4130, New Zea- plication, was up to the order of three times greater at the Wairoa, Puketapu and Wallingford sites, and land. about 50% greater at the Waipawa and Wairarapa sites. There was a consistent response by clover Abstract From 2000 to 2002 a trial series was in both early spring and in the late spring-autumn established on seven farms from Wairoa (north- seasons, to an increase in soil Olsen P test. On the ern Hawke's Bay) to Moeraki (North Otago), with four northern-most sites an increase in Olsen P test contrasting amounts of spring-summer rainfall, to from less than 10 to about 20 raised clover producevaluate the pattern of pasture responses to a range tion by about 100% in early spring and by a greater of rates of nitrogen (N) fertiliser and a range of soil proportion in late spring-autumn. This was in direct phosphorus (P) levels. Small plots excluded from contrast to the absence of a response by the grass grazing were established on flat to gently sloping component during the same period. The management land containing pastures that had been established implications of the contrasting effects of N and P for many years. This paper describes the clover fertilisers on pasture clover and grass composition and grass component production responses to N are discussed. fertiliser and to a range in soil P status at each site. In early spring, in all years, the grass components Keywords clover; dryland pastures; hill country; of pasture at all sites except Marlborough, showed a nitrogen; phosphorus significant response in dry matter (DM) production to N fertiliser applied in mid winter. These responses INTRODUCTION

A07058; Online publication date 6 June 2008 Received 27 July 2007; accepted 13 March 2008

The application of nitrogen (N) fertiliser to pastures primarily stimulates grass production (Ball & Field 1982) in situations where there is inadequate N supply from associated legumes for potential pasture

86

New Zealand Journal of Agricultural Research, 2008, Vol. 51

growth when other factors are non-limiting. Within hill country pastures all grass species have been shown to respond strongly to N fertiliser application (luscombe 1980) as a consequence of the generally low soil N status of hill soils (Ball et al. 1982). in comparison, responses by clover to N fertiliser application rarely occur unless Rhizobia activity is inhibited or new pastures are in the early stages of establishment (Cullen 1969), when low rates of N fertiliser (20-30 kg N/ha) have been shown to be beneficial. Application of higher rates of N, such as used in dairying (Ball & Field 1982; harris & Clark 1996), or repeated applications of N (e.g., eight applications of 50 kg N ha–1), can cause a decline in clover content and production. The most commonly reported effect of nitrogen fertiliser application on pasture legumes is a depression in clover density and yield (ledgard & Saunders 1982; Caradus et al. 1993), whereas other reports (o'Connor & Gregg 1971; Crush et al. 1982) indicate no deleterious effects on clover production. The differences appear to be related to the opportunities provided for shading of legumes by accelerated grass growth. in management situations where relatively rank pasture is allowed to accumulate, or where grass tiller density is high, clover becomes less competitive (harris & Thomas 1973; harris & Clark 1996), especially in early spring. Conversely, where grazing is continuous, and to a high level of utilisation, the suppression of clover as a result of N fertiliser application is usually less, although it can still be significant (luscombe & Fletcher 1981). Williams et al. (1990) concluded that most pastures in summer-dry hill pastures contained low proportions of white (Trifolium repens l.) and subterraneum (T. subterraneum l.) clovers. This was associated with considerable variability in distribution related to such factors as drought, soil fertility, grazing intensity and frequency and temperature at contrasting sites (Suckling et al. 1983; macFarlane & Sheath 1984). Gillingham et al. (2003a) suggested that as a result of this variability in clover content, which was also related to slope and aspect, a differential N and P fertiliser application strategy on a range of hill pastures could result in higher overall pasture productivity, than from the use of P fertiliser alone. This conclusion was based largely on the results from the trials at the Waipawa research area in central hawke's Bay. A trial series, described by Gillingham et al. (2007), was established to assess if this also applied to seasonally dry hill country along the east coast of New Zealand. This paper describes the legume and grass responses on gently sloping

land to a range of phosphorus (P) soil tests, generated by a range in application rate of P fertiliser, and or, to a range in application rate of nitrogen (N) fertilisers. A subsequent paper describes results from steep slopes.

Methods sites in 2000 seven trial sites were selected on established pasture within sheep and beef hill farms near Wairoa, Napier (Puketapu), Waipawa, Waipukurau (Wallingford), masterton (Wairarapa), Seddon (marlborough) and moeraki in North otago to represent a range in annual rainfall and associated pasture growth conditions. mean annual rainfall ranged from 474 mm (marlborough) to 1348 mm (Wairoa). Farms were subject to an average spring rainfall that comprised 18-33% of the annual total, and summer rainfall which comprised 20-32% of the annual total (Gillingham et al. 2007). treatments in mid-late winter 2000, P and N were applied to plots at 0, 30, 60 or 90 kg ha–1 in a completely randomised design with incomplete replication of the intermediate rates as a means of limiting trial size. in winter 2001 and 2002 the rates of N fertiliser (urea) treatments were repeated. The application of P fertiliser (triple super) varied between treatments, based on the olsen soil test (Gillingham et al. 2007). The sites, methods and statistical analysis procedures were described by Gillingham et al. (2007). Measurements in addition to the measurement of total pasture production using a rising plate meter, as described by Gillingham et al. (2007), the clover cover (%) on each plot was visually assessed prior to each harvest. This was done because of the large differences in clover content that were generated by the fertiliser treatments, and the need to represent this in a simple and convenient way. All North island sites were measured by the same person, whereas the marlborough and moeraki sites were each measured by different people. it is acknowledged that different operators may have differing levels of error in this assessment. however, each should be expected to be relatively consistent on any one site over time. Care should therefore be taken in relating the clover content of trials in the North island with any in the

Gillingham et al.—Fertiliser responses on hill country South island. The assessed clover content in each plot was applied to the measured total pasture mass present (kg Dm ha–1) to provide an estimate of the clover Dm mass (kg Dm ha–1) at each harvest. it is acknowledged that, because of the differing structure of clover leaves compared with grass leaves, visual assessment may tend to overestimate the clover contribution to total dry matter (Dm) production. Pilot calibration measurements at the Waipawa site on pasture mass of about 2000 kg Dm ha–1 showed good agreement between assessed and measured clover dry matter production. At higher levels of pasture mass the visually assessed clover content tended to overestimate the contribution to dry matter production. Generally therefore, the estimate of clover production should be regarded as only an index of clover production. in most situations differences between treatments in the estimated clover production were due to both differences in botanical composition and total dry matter production. in order to simplify presentation, clover cover estimates are not shown in this paper. The percentage clover cover can be calculated by relating the clover production figure to the sum of clover and grass production for each treatment. The difference between total and clover Dm mass was estimated to be grass Dm (kg Dm ha–1). The clover component at each site was predominantly white clover (Trifolium repens) with small amounts of subterraneum clover (T. subterraneum), especially on the plots of lower olsen P status in years 2001 and 2002. The grass component was predominantly browntop (Agrostis capillaris) and naturalised grasses. The clover and grass production results are presented in the same seasonal patterns as by Gillingham et al. (2007) for total Dm, that is, early spring (usually from July to late october-early November) and late spring-autumn periods (from late october-early November-April). The start date in early spring was from the date of application of fertiliser and the actual end date of each period varied from site to site depending when the pasture was ready for harvest. The may-June period at each site was one of negligible pasture growth and was not measured. Assessments of clover cover were not made at the moeraki site in 2000 and 2001 and drought conditions in marlborough limited pasture growth in 2002. The soil olsen P status on each site in each year for Control (no P fertiliser applied), low, medium and high treatments is shown in Gillingham et al. (2007).

87

statistical analysis in each year, at each site, all of the harvests in the early spring period were combined and subjected to an analysis of variance using GenStat (Payne et al. 2006). All of the harvests in the late spring-autumn season, were similarly combined and analysed. The main effects of N fertiliser and olsen P on each of clover and grass Dm production are presented. For the early-spring season in each year, the maineffect clover or grass Dm production results for each of the N treatments were related to Dm measured from the respective 90N treatment (100%). The results from each of the 3 years were combined as a dataset, and an asymptotic regression (mitscherlich type response) derived (Payne et al. 2006). The general form of this relationship was y = A + B (Kx) where y = pasture yield, and where x = the rate of N fertiliser applied. The standard error of observations (SE) was calculated. For the same season the main-effect clover and grass Dm production results for each of the P treatments were related to the yield measured from the high P treatment (100%) and subjected to regression analysis as above. For the late spring-autumn season the clover and grass production data were treated as for the early spring season.

RESULTS Pasture production in early spring Early spring clover production There was a variable effect of N fertiliser on clover Dm production in early spring (Table 1). At the Wairoa site clover production was depressed in all years by increased N fertiliser rate. The same effect occurred at Puketapu in 2000, at Wallingford in 2000, and at the Wairarapa site in 2002. At Waipawa the opposite effect occurred and clover production was enhanced in 2001 and in 2002 by N fertiliser application. At other sites and times there was no effect of N fertiliser application on clover production. Clover production responses to increases in soil P in early spring were measured on all sites. however, only at the Wairoa, Waipawa and marlborough sites was the response to increased soil olsen P level significant in the first year (2000) of the trial (Table 1). in years 2001 and 2002 clover production responses to olsen P occurred at all sites except at moeraki where no data were available, and at the marlborough site in 2002 when production was

New Zealand Journal of Agricultural Research, 2008, Vol. 51 limited by low spring rainfall (77 mm from August to october, compared with 135 mm in 2000 and 205 mm in 2001). A response interaction between N and olsen P was recorded at only the Puketapu site in 2002 when there was a clover production response to olsen P at a zero or low N fertiliser level, but a depression in clover production, and no response to olsen P, at higher N rates.

At the Puketapu site in 2002, a significant quadratic N × P interaction was measured (Table 2) but there was no associated significant linear P response. At Waipawa in 2000 there was a significant quadratic P response with the highest grass production being measured from both the Control and high P treatments. There was no obvious soil P related explanation for this pattern of result.

Early spring grass production Grass production responded to N fertiliser in early spring of all three years (Table 2) at all sites except marlborough (not measured at moeraki in 2000 and 2001). in contrast, grass production showed few responses to increase in soil olsen P status in early spring, and these responses were varied (Table 2). At Wairoa, Waipawa and Wallingford the effect was for estimated grass production to decline with increase in soil P status, whereas at Puketapu, and at moeraki, grass production increased with increase in olsen soil P.

Average clover and grass dry matter responses in early spring Nitrogen fertiliser rate The mean relative grass production responses to fertiliser N were similar at all sites (Fig. 1). The higher-rainfall Wairoa site, and the Puketapu, Waipawa, Wallingford and Wairarapa sites provided data that best fitted the model, with 2values of 0.986, 0.908, 0.620, 0.944 and 0.917 respectively. At these sites grass production without N fertiliser averaged only about 50% of those receiving 90 kg N ha–1. The relatively dry marlborough site showed no response in grass production to N fertiliser.

table 1 Statistical significance of nitrogen (N) fertiliser and soil phosphorus (P) effects on pasture clover dry matter production (kg Dm ha–1) in the early spring season (Jul-oct) from 2000 to 2002 at each site. olsen soil P treatment levels relate to Control (Control = no P fertiliser applied), and the low, medium, and high rates of P fertiliser applied at each site in each year. *, Statistically significant at the 5% level of probability; **, statistically significant at the 1% level of probability; ***, statistically significant at the 0.1% level of probability; NS, not statistically significant; N:P, nitrogen:phosphorus interaction; nd, no data. Site Wairoa Puketapu Waipawa Wallingford Wairarapa marlborough moeraki

year 2000 2001 2002 2000 2001 2002 2000 2001 2002 2000 2001 2002 2000 2001 2002 2000 2001 2002 2000 2001 2002

0 1311 1153 1382 1594 161 1108 1566 2251 2583 963 742 724 990 1928 1448 483 265 267 nd nd 320

N fertiliser rate (kg ha–1) 30 60 90 865 603 631 775 632 721 1244 912301 924 874 941 1054 342 400 335 1127 1091 861 1229 1092 1420 2625 2836 2885 2622 3007 3155 670 506 565 592 550 618 678 670 768 1156 1146 600 1499 1328 1414 13133 1332 1033 417 386 431 227 012 219 204 180 253 394

435

415

Sig. ** * ** *** NS NS NS ** * *** NS NS NS NS * NS NS NS NS

olsen soil P treatment Control low medium high Sig. * 640 867 966 937 434 945 1076 826 * 149 1230 1708 1583 *** 1369 1195 1155 1250 NS 146 251 362 480 ** 721 1108 1240 1117 N:P* 845 1509 1659 1294 * 645 2656 3654 3641 *** 912 2728 3750 3977 *** 604 714 680 707 NS 311 636 788 767 * 78 630 986 1146 *** 1163 936 859 933 NS 1466 1416 1517 1770 * 1056 1254 1406 1510 * ** 287 406 489 535 187 222 248 266 * 245 243 225 192 NS 137

380

512

535

***

Gillingham et al.—Fertiliser responses on hill country Although there was a general trend for pasture clover productivity in early spring to decline with increase in N fertiliser rate (Fig. 1), the best data fit was at the Wairoa site only (R2 = 0.970). Olsen P status At all sites average grass production was little affected in early spring by increase in soil Olsen P test (Fig. 2), and the regression coefficient at each site was low. The exception was at Waipawa where grass production declined with increase in soil P status. At only the Wairoa, Waipawa and Wallingford sites did clover production in early spring generally increase with increase in soil olsen P test (Fig. 2). At these sites peak relative clover production, as indicated by the asymptotic regression trendline, was reached when soil olsen P test was in the range of about 12 μg ml–1 (Waipawa) to 20 μg ml–1 (Wairoa and Wallingford). At the Wairarapa and marlborough sites no clover production responses to increased olsen P occurred. At the Puketapu site, the sharp angled trendline does not provide a credible explanation of the response pattern.

89

The regression relationship between relative clover yield and soil olsen P test was generally low, being highest at the Wairoa (R2 = 0.613), Waipawa (R2 = 0.504) and Wallingford (R2 = 0.451) sites. Pasture production in late spring-autumn Late spring-autumn clover production At most sites, in the late spring-autumn period of each year, there was a depression in clover production with increase in N fertiliser rate (Table 3). The exceptions were the Puketapu and marlborough sites in 2001, where the effect was not significant. A feature of the results was the wide range in clover Dm production both between sites, but also within sites over the 3-year trial period. As in early spring, the pattern of clover responses to increase in soil olsen P varied. only the Wairoa, Waipawa and Wallingford sites consistently showed an increase in clover Dm production in all 3 years. in contrast, the Wairarapa and marlborough (2001 and 2002) sites showed no responses.

table 2 Statistical significance of nitrogen (N) and phosphorus (P) fertiliser application effects on grass dry matter production (kg Dm ha–1) in the early spring season (Jul-oct) from 2000 to 2002 at each site. olsen soil P treatment levels relate to Control (Control = no P fertiliser applied), and the low, medium, and high rates of P fertiliser applied at each site in each year. *, Statistically significant at the 5% level of probability; **, statistically significant at the 1% level of probability; ***, statistically significant at the 0.1% level of probability; NS, not statistically significant; NQPQ, nitrogen:phosphorus quadratic response interaction; PQuad, quadratic phosphorus response; nd, no data. N fertiliser rate (kg ha–1)

Wairoa Puketapu Waipawa Wallingford Wairarapa marlborough moeraki

year

0

2000 2001 2002 2000 2001 2002 2000 2001 2002 2000 2001 2002 2000 2001 2002 2000 2001 2002 2000 2001 2002

890 1072 1188 880 1711 1450 337 568 904 838 967 514 2450 1477 2100 1949 1098 1088

30 2044 2198 2037 1983 2333 2313 988 988 1044 1838 1324 778 2366 1943 2665 1992 1109 1107

60

90

2838 2944 2634 2540 2916 2914 1524 1194 1184 2511 1324 970 2702 2402 3132 2035 1155 1126

1490

1733

olsen soil P treatment

3167 3309 3073 2391 3461 3329 2252 1184 1462 2870 1894 1159 3818 2853 3768 2111 1235 1163

Sig. *** *** * *** *** *** *** ** * *** *** *** ** *** *** NS NS NS

Control 2211 2474 2648 2628 2381 2497 1655 1473 1476 2121 1537 963 2593 2105 3077 1919 1184 1052

2096

***

1399

low medium high Sig. 2211 2282 2235 NS 2212 2250 2587 NS 2234 2026 2024 *** 3094 3274 3181 * 2616 2723 2700 * 2367 2438 2705 NQPQ* 1422 PQuad** 1051 973 867 680 913 ** 1096 958 1063 NS 1894 2059 1983 NS 1420 1396 1466 NS 964 855 636 *** 2766 2921 3057 NS 2251 2242 2077 NS 2954 2855 2779 NS 2032 2078 2056 NS 1180 1147 1087 NS 1132 1161 1138 NS

nd nd 1207

1618

1740

1767

***


90

Puketapu

Wairoa y= 91.9+81(0.9701x)

SS 250 S 200

R2 = 0.970 se 19.8

R2 = 0

° 150 | 100 y= 123-90.11(0.9846 ), R2= 0.986 se = 3.09 20

40

60

80

•

1 50

x

V.

se = 46.9

y = 122.9 -85.2 (0.9852x)

R2 =0.908 se= 7.83

0 t-

100

0

20

Nitrogen Rate kg/ha

40

60

Nitrogen Rate kg/ha

Waipawa

Wallingford

R2 = 0 se = 14.6

S? 150

R2 = 0.247 se=22.5

D 100

—

.

y= 167-125 (0.9931X)

I 50

R2 = 0.620 se=16.7

o

* o

20

50 n

40

100

60

50

. . . ,-g 20

Wairarapa

Marlborough

40

100

V-s-X R2 = 0.018 se = 12.9

2

60

80

R2 = 0.207 se = 11.6

-?——____

20

60

Nitrogen Rate kg/ha

y=40.2 +17.4(1.01379 ) R = 0.917 se=4.98 D

40

R2 = 0.944 s e = 5.53

Nitrogen Rate kg/ha

x

•

*^

" y = 140.9-99.5(0.9902 x )

R 2 = 0.172 se = 32.0

250 200 150 100 -

1

100

80

!80

100

Nitrogen Rate kg/ha

20

40

60

80

100

Nitrogen Rate kg/ha

Fig. 1 Clover and grass responses (relative dry matter (Dm)%) at each site to increasing rates of fertiliser nitrogen (N) in early spring (Jul-Oct), showing observed values together with a fitted regression curve for clover (solid line, diamonds and upper equation and R2 value) and grass (dotted line, crosses and lower equation and R2 value). The equation of the curve is given, together with the proportion of variation in the data explained by the curve (R2), and the standard error (se) of the observations. Where R2 is low, the equation is omitted.

Late spring-autumn grass production most sites continued to show responses in grass production to N fertiliser in at least one of the 3 years during this period (Table 4). The exception was the Wairarapa site in 2001 where grass production decreased with increase in N fertiliser application.

There were fewer responses of grass production to olsen P than to N in this season. Where these occurred the main effect was for grass production to decrease with increase in soil olsen P test, although this effect did not occur every year at any site over the 3-year trial period. At the Puketapu (2002) and

Gillingham et al.—Fertiliser responses on hill country

91 Puketapu

Wairoa

$5 150

x

50

/

'

SS 150 i u.

Q 100

y = 109.9-510(0.817x)

/

50

R2 = 0.613 se = 20.1

'

&

R2 = 0 se=11.9

x • x • *£-***e-r^*

a 100

I

•

0 30

20

----

(91.04X) y=0.030.0321-178425 21 R2 = 0.363 se = 20.1

0

10

••*.;>

40

10

15

25

20

30

Olsen P

Olsen P

Waipawa

Wallingford x

y = 0.506 +860(87.3 ) R2 = 0.501 se = 19.5

200 X

150

X

R2 = 0se = 21.0

SS 200

X

| 150 x

.

» 100 R2 = 0.504 se = 24.1 y= 0.659-389(106.6x)

o oc

R2= 0.451 se = 21.0

0 10

20

15

10

y=0.827-237(103x)

1 50

Olsen P

R2 = 0se = 8.3 (X

Relativ

0)

R2 = 0 se = 14.2

0 ()

5

10

25

15

20

25

R2 = 0 se = 6.2

150 -i Relative DM

100 50

20

Marlborough

Wairarapa 150 -i

15

Olsen P

30

Olsen P

•

•

100

X

50

R2 = 0.148 se = 18.9

0 ()

5

10

15

20

25

30

Olsen P

Fig. 2 Clover and grass responses (relative dry matter (Dm)%) at each site to increasing soil olsen P in early spring (Jul-Oct), showing observed values together with a fitted regression curve for clover (solid line, diamonds and lower equation and R2 value) and grass (dotted line, crosses and upper equation and R2 value). The equation of the curve is given, together with the proportion of variation in the data explained by the curve (R2), and the standard error (se) of the observations. Where R2 is low, the equation is omitted.

moeraki (2001 and 2002) sites the grass production increased with an increase in olsen P test.

Average clover and grass dry matter responses over 2000-02 Nitrogen fertiliser rate At the Wairoa, Waipawa, Wallingford and Moeraki sites there was a significant decline in relative clover production in late

spring-autumn to N fertiliser applied in the previous mid winter. The clover production in the Control treatment was in the order of 50-200% greater than in the 90N treatment at these sites. This effect was not significant at the other sites. in contrast there was little change in relative grass production with increase in N fertiliser rate at all sites.

92


table 3 Statistical significance of nitrogen (N) fertiliser and soil phosphorus (P) effects on pasture clover dry matter production (kg Dm ha–1) in the late spring-autumn season (Nov-Apr) from 2000 to 2002 at each site. olsen soil P treatment levels relate to Control (Control = no P fertiliser applied), and the low, medium, and high rates of P fertiliser applied at each site in each year. *, Statistically significant at the 5% level of probability; **, statistically significant at the 1 % level of probability; ***, statistically significant at the 0.1 % level of probability; NS, not statistically significant; NQuad, quadratic nitrogen response; NlPQ, linear nitrogen and quadratic phosphorus response; nd, no data.

Site Wairoa Puketapu Waipawa Wallingford Wairarapa marlborough moeraki

year 2000 2001 2002 2000 2001 2002 2000 2001 2002 2000 2001 2002 2000 2001 2002 2000 2001 2002 2000 2001 2002

N fertiliser rate (kg ha–1) 0 30 60 90 Sig. *** 8509 6310 4971 4879 4042 2098 1151 022 *** 1464 1083 822 663 *** 3058 1769 924 564 *** 768 1018 994 697 NS 364 293 235 159 * 3768 3082 2553 1968 *** 4091 4473 4309 3600 NQuad* * 2215 2156 2017 1502 1495 784 355 344 *** 2461 1256 664 682 ** 1019 734 577 644 * 2915 2783 2482 1505 ** 3314 3502 3742 4034 ** 1218 981 819 719 ** nd 714 604 523 473 NS *** 743 826 909 1076 152 132 111 *** 177 32 31 26 18 NlPQ* 1398 1304 1205 997 ***

Soil Olsen P status At all sites mean grass productivity during this period was little affected by soil olsen P (Fig. 4). Relative clover growth showed a production response to increase in soil P at all sites except Wairarapa, marlborough and moeraki. The highest regression coefficient for the relationship was at the Waipawa site (R2 = 0.805) followed by Wairoa (R2 = 0.675), Wallingford (R2 = 0.588) and Puketapu (R2 = 0.448).

dIscussIon Whereas grass species showed a general and marked response in Dm production to N fertiliser application in early spring (Table 2), this was followed by a much less consistent pattern of response in grass growth over the balance of the season (Table 4). The effects of an increase in N fertiliser rate on clover production throughout the total season tended to be the reverse, with little effect on clover production in

olsen soil P treatment Control low medium high 5221 6037 6575 6835 950 2251 2774 2519 269 845 1296 1622 1497 1486 1573 1759 279 653 1056 1490 150 297 336 267 1015 2937 3804 3615 755 3759 5620 6337 670 1583 2429 3207 422 747 907 902 348 1321 1752 1641 100 602 994 1277 2837 2482 2211 2024 3886 3626 3518 3562 780 937 1013 1008 572 859 74 28 362

538 914 124 28 1309

561 916 168 27 1699

642 865 206 24 1534

Sig. * ** *** NS ** NS *** *** *** * *** *** NS NS NS NS NS *** NS ***

spring (Table 1), except at the most northern (Wairoa) site, but a generally consistent decline in clover production in the late spring-autumn season (Table 3). This effect on clover was also noted by ledgard et al. (1995) in Waikato dairy pastures. The absence of a clover response to N fertiliser in early spring, especially on the more southern sites, and except for the Wairoa site where clover production from the control treatment was 70% greater than from the 90N treatment, is probably a reflection of the general inactivity in clover growth at this time (Brougham 1959). only in the late spring summer—autumn period when clover growth was potentially more active, was it affected by N fertiliser. The depression in clover production at this time was most likely not a direct one of N fertiliser on the legume plant, but more an indirect result of the marked increase in grass Dm production in spring which shaded associated clover stolons and developing leaves during the period when clovers were commencing growth activity (harris & Thomas 1973; harris & Clark 1996; hepp et al. 2003). This

93


table 4 Statistical significance of nitrogen (N) fertiliser and soil phosphorus (P) effects on pasture grass dry matter production (kg Dm ha–1) in the late spring-autumn season (Nov-Apr) from 2000 to 2002 at each site. olsen soil P treatment levels relate to Control (Control = no P fertiliser applied), and the low, medium, and high rates of P fertiliser applied at each site in each year. *, Statistically significant at the 5% level of probability; **, statistically significant at the 1% level of probability; ***, statistically significant at the 0.1% level of probability; NS, not statistically significant; PQuad, quadratic phosphorus response; nd, no data.

Site Wairoa Puketapu Waipawa Wallingford Wairarapa marlborough moeraki

year 2000 2001 2002 2000 2001 2002 2000 2001 2002 2000 2001 2002 2000 2001 2002 2000 2001 2002 2000 2001 2002

0 2438 2737 2050 4457 1962 2512 1288 2313 1769 1387 1579 1009 3899 7677 813 nd 2818 1554 4369 4012 2275

N fertiliser rate (kg ha–1) 30 60 90 3362 3963 4195 3492 3864 3855 1965 1925 1983 5113 5495 5442 19621 1957 2068 2677 2840 3162 2092 2385 2380 2248 2275 2394 2022 2159 2088 1662 1840 1697 1702 1785 1829 1404 1079 1168 4133 4371 5435 6431 5946 6223 940 1039 1155 2867 1335 4341 3983 2548

3138 1203 4298 3913 25482

Sig. *** ** NS *** NS * * NS NS *** * *** ** * ***

3629 ** 1202 NS 4298 NS 3913 NS 25482 ***

was similar, but a more marked effect to that which occurs as a result of the normal pattern of pasture improvement when legume dominance gives way to grass dominance (Sears 1960), and as measured by lambert etal. (1986). The magnitude of the seasonal interactions between clover and grass production as a result of N fertiliser application would be expected to be greatest in sites or seasons where clover naturally forms a significant part of total pasture DM, as on the Wairoa, Puketapu, Waipawa and Wallingford sites (compare data for clover and grass production in Tables 1 and 2), and less so at the more southerly sites. The extent to which grass production that has been stimulated by N fertiliser application shades associated clovers will also be affected by the defoliation regime associated with the grazing management policy (hepp et al. 2003). Where regular grazing occurs, and grass Dm cover is not allowed to dominate, then the effects of clover shading would be expected to be less than reported here. As in the

Control 3868 3988 2285 5146 2188 1984 2810 3461 1975 1677 1875 1334 3978 5964 1073 2912 1348 3878 3423 3342

olsen soil P treatment low medium high Sig. 3353 3232 3504 NS 3342 3164 3453 NS 1861 1769 2008 PQuad* 5238 5173 4951 NS 2034 1900 1785 * *** 2719 3166 3323 1696 1474 2161 PQuad* 2299 1726 1744 *** 1942 2066 2055 NS 1629 1615 1635 NS 1721 1747 1652 NS ** 1210 1103 1011 4429 4742 4917 NS 6545 6860 6909 NS * 1046 973 856 3169 1323 4341 3923 2628

3241 1311 4523 4178 2257

3130 1313 4523 4178 2257

NS NS *** *** ***

protocol associated with normal field trial management, the pasture was harvested when the fastest growing treatments were considered to have a sufficient DM cover (e.g., approximately 2000-2500 kg total Dm ha–1). in this series the N fertilised treatments were the highest producing treatments in late spring-autumn and this pasture cover would have induced some shading of associated clovers. Trial management may therefore impose a greater than desirable amount of shading on clovers present, but this would be similar to that encountered on many rotationally grazed hill farms. Gillingham et al. (1998) reported a reduction in clover content of hill pastures that had received N fertiliser and were rotationally grazed by ewes and cattle. The consistent response in early spring of each year by grass to N fertiliser application allowed a significant regression relationship to be developed from the 3-year dataset between relative grass production and N fertiliser rate at all sites except the dry marlborough site. however, in late springautumn, although grass responses to N fertiliser


94

Puketapu

Wairoa

Relative DM

R2 = 0.651 se = 41.7

R2 = 0.289 se = 11.9 20

40

60

80

R2 = 0.209 se 113

600

y= 84.5+159.7(0.918x)

100

400 200 0

L c - •

0

y= 163-78 (0.9977x)

. . . -x - /rT7T5~rm----x 20

500 i 400 i

R2 = 0.446 se = 20.1

20

80

100

y= 79.2+239.7 (0.9673x)

y= 159.7-9.3 (1.0208x)

y = 102.5-22.3

60

Wallingford

Waipawa

50 x

40

Nitrogen Rate kg/ha

Nitrogen Rate kg/ha

•s

R2 = 0.491 se = 5.31

2 0 0

R2 = 0.586 se = 73.6 y = 4+63 (1.005x) R2 = 0.414 se14.8

(0.9711x) R2 = 0.352 se = 9.86 40

100

60

20

40

60

80

100

Nitrogen Rate kg/ha

Nitrogen Rate kg/ha

Marlborough

Wairarapa R2= 0.019 se = 46.8

I 100 S

X .TTTT^TTTT^ R2 =0 se = 15.8 20

40

60

80

100

Nitrogen Rate kg/ha

50

100

Nitrogen Rate kg/ha

Moeraki y= 184.3-24.9 (1.0136x) R2 = 0.665 se 15.8

20

40

60

80

100

Nitrogen Rate kg/ha

Fig. 3 Clover and grass responses (relative dry matter (Dm)%) at each site to increasing rates of fertiliser nitrogen (N) in late spring-autumn (Nov-Apr), showing observed values together with a fitted regression curve for clover (solid line, diamonds and upper equation and R2 value) and grass (dotted line, crosses and lower equation and R2 value). The equation of the curve is given, together with the proportion of variation in the data explained by the curve (R2), and the standard error (se) of the observations. Where R2 is low, the equation is omitted.


95 Puketapu

Wairoa

R2 = 0.020 se = 15.5

x

y= 106.6-284 (0.7539 ) R2 = 0.638 se = 5.34

>x i X

Relative

Q 100

150 -i Relative DM %

150

y ) ( y )|)X •—iX

• y= 103.1-343 (0.8482x) R2 = 0.675 se = 16.3

50 0 ()

10

20

30

x> x x>: x

100 50

40

x y= 101.5-468 (0.6830x) R2 =0.448 se=22.4

/ ()

5

10

Olsen P

15

20

25

30

Olsen P

Waipawa

Wallingford

y= 98.76+9027676(0.052x) R2 = 0.498 se = 23.3

5S 250

S ° > •S *

200 150 100 50 0

R2 = 0.132 se = 9.59

jS 150

"x~x - - x

I 100 0y= 106.6-284 (0.7539x) R2 = 0.805 se = 14.9

R2 = 0.588 se21.9

0

20

15

10

I 50H *

10

Olsen P

x

8.

50

I 100

I

R2 = 0 se = 16.8

Q\

c)

5

10

15

20

25

Y= 0.4-18211 (0.21 M1) R2 = 0.557 se = 2.19

S? 150

cx

Q 100

1

25

Marlborough 0 se = 14.7

.x

20

15

Olsen P

Wairarapa 5S 150

^r-oo

Y= 106.7-255(0.588x)

30

50

£

0

X. - - - . V . - - - X .

x^

-_,v__

R2 = 0 se = 9.47

10

15

20

25

30

Olsen P

Olsen P

Moeraki R 2 =0 se = 17.6

200 -i Q

X

150

Relati

100 50

R

0 0

i

i

i

5

10

15

2

= 0 se = 31.2 1

20

' 25

Olsen P

Fig. 4 Clover and grass responses (relative dry matter (Dm)%) at each site to increasing soil olsen P in late springautumn (Nov-Apr), showing observed values together with a fitted regression curve for clover (solid line, diamonds and lower equation and R2 value) and grass (dotted line, crosses and upper equation and R2 value). The equation of the curve is given, together with the proportion of variation in the data explained by the curve (R2), and the standard error (se) of the observations. Where R2 is low, the equation is omitted.

New Zealand Journal of Agricultural Research, 2008, Vol. 51 were widespread, the relative response at each site was sufficiently diverse that the derived regression relationship was significant at only the two most northerly sites. The variability at the other sites could be attributed to more variable rainfall and soil moisture conditions in this season from year to year. The derived regression relationship between relative clover production and Olsen P test was significant in both early spring and late spring-autumn seasons at only the four northern sites. This suggested that the relative clover production response was consistent from year to year. At the other sites this was not so. However, at these sites there was either no significant total DM production response to Olsen P (Gillingham et al. 2007), or only a very small increase. The clover component provided a more defined response to Olsen P than did total DM production (Gillingham et al. 2007), because of the variability in actual and relative total DM productivity between years in these trials. Sinclair et al. (1997) also found, following analysis of 46 datasets from 17 long-term trials, that the derived regression relationship for each site could not accurately describe the pasture DM or relative response in any one year. The consistent production response by clover in both spring and autumn to increase in Olsen P, contrasts with the results of Morton & Roberts (2001) who measured a decline in pasture clover content in spring associated with an increase in soil P status from 20 to 60 Olsen P. In autumn the clover content increased slightly again. The reason for this was unclear. The results here emphasise the importance of recognising the legume as the most active component in any total DM response to increase in Olsen P. Similarly, it illustrated that where there was little or no legume in the pasture there was little to be gained by raising soil P levels to those recommended for more balanced grass: clover swards. The same conclusion was reached by Gillingham et al. (1998) as a result of earlier trials on summ er dry hill country near Waipawa in Hawke's Bay. Where N fertiliser application resulted in a decline in pasture clover production in late-springautumn (Fig. 3), this must be expected to inhibit the response of the legume component, and therefore the total DM production response, to applied P fertiliser in the following spring and autumn. The effect is likely to be greater where soil P is already moderate to high, and where the clover content of the pasture is initially high.

Low legume content in the pasture during late spring-autumn must be expected to lower the feed quality (New Zealand Sheep Council 2000) during this period. This may have implications for finishing of store lambs and the provision of quality pasture for ewes in autumn prior to mating. From a management perspective the differing effects of N and P fertilisers on the main pasture sward components need to be recognised and considered when planning an annual fertiliser application programme. The advantages of additional pasture growth in early spring from N fertiliser application must be balanced against the potential for a reduced pasture response to P fertiliser in late spring-autumn. The extent of these effects will vary with slope and aspect of hill pastures as well as the general distribution and regularity of rainfall throughout these seasons which also affect pasture legume content and productivity. The proportions of clover and grass production assessed at each site and in each season were derived from the visual assessment of clover cover within each trial plot. The limitations of this technique were outlined earlier. However, the results do demonstrate the dynamics of the N fertiliser and Olsen soil P status effects on pasture species composition, and these can be used to anticipate changes in pasture clover content in grazed pasture. As concluded by Morton & Roberts (2001), the results from mown plots can be used to predict pasture responses under grazing. Nevertheless, the adoption of new information into a farm management plan is often not a simple exercise and may require associated changes to be also included if the gains are to be profitable (Gillingham et al. 2003a).

ACKNOWLEDGMENTS This series of trials was funded by Ravensdown Fertiliser Cooperative Ltd. The technical assistance of Stuart Macmillan and statistical guidance from Fred Potter and John Koolaard is gratefully acknowledged.

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Gillingham et al.—Fertiliser responses on hill country Brougham RW 1959. The effects of season and weather on the growth rate of a ryegrass and clover pasture. New Zealand Journal of Agricultural Research 2: 283-296. Caradus JR, Pinxterhuis JB, Hay RJ, Lyons T, Hoglund JH 1993. Response of white clover cultivars to fertiliser nitrogen. New Zealand Journal of Agricultural Research 36: 285-295. Crush JR, Cosgrove GP, Brougham RW 1982. The effect of nitrogen fertiliser on clover nitrogen fixation in an intensively grazed Manawatu pasture. New Zealand Journal of Experimental Agriculture 10: 395-399. Cullen NA 1969. Oversowing grasses and clovers. Proceedings of the New Zealand Grassland Association 31: 110-116. Gillingham AG, Gray MH, Smith D 1998. Pasture responses to phosphorus and nitrogen fertilisers on dry hill country. Proceedings of the New Zealand Grassland Association 60: 135-140. Gillingham AG, Morton JD, Gray MH 2003a. The role of differential fertiliser application in sustainable management of hill pastures. Proceedings of the New Zealand Grassland Association Conference 65: 253-257. Gillingham AG, Sheath GW, Gray MH, Webby RW 2003b. Management and fertiliser options for increased pasture productivity in dryland hill systems. Proceedings of the New Zealand Grassland Association Symposium—legumes for dryland pastures. Grassland Research and Practice Series No. 11, Lincoln University. Pp. 43-49. Gillingham AG, Morton JD, Gray MH 2007. Pasture responses to phosphorus and nitrogen fertilisers on East Coast hill country 1: total production from easy slopes. New Zealand Journal of Agricultural Research 50: 307-320. Harris SL, Clark DA 1996. Effect of high rates of nitrogen fertiliser on white clover growth, morphology, and nitrogen fixation activity in grazed dairy pasture in northern New Zealand. New Zealand Journal of Agricultural Research 39: 149-158.

Lambert MG, Clark DA, Grant DA, Costall DA 1986. Influence of fertiliser and grazing management on North Island moist hill country 2. Pasture botanical composition. New Zealand Journal of Agricultural Research 29: 1-10. Ledgard SF, Saunders WMH 1982. Effects of nitrogen fertiliser and urine on pasture performance and the influence of soil phosphorus and potassium status. New Zealand Journal of Agricultural Research 25: 541-547. Ledgard SF, SprosenMS, Steele KW, West CP 1995. Productivity of white clover cultivars under intensive grazing, as affected by high nitrogen fertiliser application. New Zealand Journal of Agricultural Research 38: 473-482. Luscombe PC 1980. Nitrogen fertiliser responses on hill pastures. Proceedings of the New Zealand Grassland Association 41: 155-162. Luscombe PC, Fletcher RH 1981. Nitrogen fertiliser on grazed hill pastures. Proceedings of the New Zealand Grassland Association 43: 171-181. MacFarlane MJ, Sheath GW 1984. Clover—what type for hill country? Proceedings of the New Zealand Grassland Association 45: 140-150. Morton JD, Roberts AHC 2001. Pasture response to soil phosphorus levels measured under mowing and dairy grazing. New Zealand Journal of Agricultural Research 44: 259-268. New Zealand Sheep Council 2000. A guide to improved lamb growth. Kerr P ed. Wellington, Meat and Wool New Zealand. O'Connor MB, Gregg PEH 1971. Nitrogen fertiliser trials on pastures. Proceedings of the New Zealand Grassland Association 33: 26-34. Payne RW, Harding SA, Murray DA, Soutar DM, Baird DB, Welham SJ, Kane AF, Gilmour AR, Thompson R, Webster R, Tunnicliffe Wilson G 2006. The guide to GenStat release 9. Part 2: Statistics. Hemel Hempstead, VSN International. Sears PD 1960. Grass/clover relationships inNew Zealand. Proceedings of the Eighth International Grassland Congress. Pp. 130-133.

Harris W, Thomas VJ 1973. Competition among pasture plants. III Effects of frequency and height of cutting on competition between white clover and two ryegrass cultivars. New Zealand Journal of Agricultural Research 16: 49-58.

Sinclair AG, Johnstone PD, Smith LC, Roberts AHC, O'Connor MB, Morton JD 1997. Relationship between pasture dry matter yield and soil Olsen P from a series of long-term field trials. New Zealand Journal of Agricultural Research 40: 559-567.

Hepp C, Valentine I, Hodgson J, Gillingham AG, Kemp PD 2003. Effects of grass suppression on legume abundance during two contrasting seasons in a summer-dry hill country site. Proceedings of the New Zealand Grassland Association Symposium—legumes for dryland pastures. Grassland Research and Practice Series No. 11, Lincoln University. Pp. 123-130.

Suckling FET, Forde MB, Williams WM 1983. Naturalised subterraneum clover in New Zealand. New Zealand Journal of Agricultural Research 26: 35-43. Williams WM, Sheath GW, Chapman DF 1990. Evaluation of clovers in dry hill country 1. General objectives and description of sites and plant material. New Zealand Journal of Agricultural Research 33: 521-526.