Massey University Organic-Conventional Dairy Systems Trial: Report after the seventh season of full certification

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1 Massey University Organic-Conventional Dairy Systems Trial: Report after the seventh season of full certification N Shadbolt, A Thatcher, D Horne, P Kemp, K Harrington, A Palmer, P Hutton, M Minor, N Martin June 2010 Contents Massey University Organic-Conventional Dairy Systems Trial:... 1 Report after the seventh season of full certification... 1 Summary... 1 Introduction... 2 Background , the conversion period and the first six seasons of certified production , the seventh season of certified production... 6 Production... 6 Animal Health... 8 Soil Monitoring Pasture Composition Monitoring Weed Monitoring References Summary The Organic-Conventional Comparative Dairy Systems trial at Massey University began in August 2001, and the organic farm achieved certification in August In general, the results of the first two years of the trial showed little difference in productivity, animal health, and soil and herbage quality between the two farms. The conventional and in conversion organic farms produced similar amounts of milksolids per cow and per hectare, and somatic cell counts were low for both herds. During the third season, which was a very good dairy season in the Manawatu, the organic farmlet consistently grew slightly less pasture than did the conventional farmlet and consequently produced less milk (15% less per cow and 19% less per hectare). These production differences continued in the fourth season ( ), which was characterised by a cool wet spring and early summer followed by a warm and dry late summer-autumn period, resulting in reduced pasture growth and milk production levels from the previous season. The season began well with excellent early spring conditions, but began to deteriorate in October with more variable conditions, and a prolonged summer dry spell meant an early dry-off in March for the organic herd, resulting marked differences in production between the two herds. The season began badly with a cold wet winter and spring, but settled in to a good late summer/autumn so lactation lengths were an improvement on the previous season. Relative to the previous season, milk production was up for the organic herd and similar for the conventional herd. The season began well through early spring, but drought conditions through the summer meant that growth

2 rates dropped to well below average and didn t recover until late autumn. As a result, both herds were dried off before the end of the season and milk yield was down 10% and 16% on the previous year for the conventional and organic units respectively as a result. The season was hampered by an extremely wet late winter and spring, translating to low pasture growth rates. Things improved through the summer and autumn, resulting in improved milksolids production for both farmlets. Animal health in both herds remained good. Introduction In 2001, Massey University set up its Dairy Cattle Research Unit (DCRU) as a system comparison between organic and conventional farming. It is unique because it is the only comparative grassland-based open grazing dairy study in the world. The DCRU began its organic conversion period on 1 August 2001, at which time the unit was split into two similar farms, one conventionally managed and the other organically managed. On 1 August 2003, the organic farm achieved its full AgriQuality organic certification. The long-term aim of this research is to better understand organic dairy farming systems by investigating component interactions in these systems, and by determining how impacts and interactions change over time as organic systems mature. Extensive monitoring continues to be carried out on both farms, which forms the basis for a long-term project with the following objectives: 1. develop farm and herd management systems that optimise performance over time; 2. compare the impacts of organically and conventionally managed dairy systems on: a) soil health (quality, flora and fauna) & water quality, b) pasture and forage crop productivity (quantity and quality), and c) animal production and health; 3. identify practices that improve the biological activity of soils; 4. develop pasture management practices for organic dairy pastures that optimize clover content and best maintain biological N fixation; 5. determine the stability and sustainability of high biodiversity organic dairy pastures including the control of weeds; and 6. develop best management practices for mastitis control and other health issues in organic milk production systems. This report primarily covers the eighth year of the study, the sixth full season of certified organic production on the organic farmlet. Although the organic farmlet is six years out from full certification, the actual transition from conventional to organic production still continues, with many of the biological systems taking a long time to make the adjustment from conventional management (Dabbert and Madden 1986). Thus, the whole organic farming system is still considered to be in transition. Soil and land are the most valuable resources on a dairy farm aside from human capital. It is well known that the combination of soil, landscape and climate is a major determinant of production on New Zealand dairy farms. Thus it is much easier to reach high production levels on Allophanic Soils in the Waikato than on adjacent poorly drained Gley Soils. Farming organically places extra restrictions on the dairy farmer, requiring him/her to be even more aware of the soil resource. Previous research comparing conventional and organic dairy farms indicates that the management changes made by organic farmers can lead to both positive and negative changes to parameters that are used to indicate soil quality, depending to a large degree on inherent soil quality (Reganold et al, 1993; Macgregor 2002). 2

3 Background At the inception of the trial, the DCRU was split into the two farms in such a way that both farms were as similar as possible, including the herds. The herd was split by BW and PW, somatic cell count history, age and size to provide two herds as similar as possible. After some debate it was decided to run the same number of cows in each herd (44) in the first year with the expectation that the number of cows in the organic herd would decrease over time. At the time the area of each farm was believed to be 20ha and it was recognised that the stocking rate of 2.2cows/ha was lower than the local norm. In the second year the stocking rate was increased on both farms with 49 cows on the conventional and 48 cows on the organic farms respectively. A more precise mapping exercise during the second year identified the organic farm as being 20.4ha and the conventional farm (now including the quarantine area) was 21.3ha. This meant that the stocking rate on the organic farm (2.34cows/ha) was higher than that on the conventional farm (2.27cows/ha) so at the beginning of the third year numbers were further adjusted to 46 cows on the organic farm (2.27cows/ha) and 51 cows on the conventional farm (2.39cows/ha). Each of the two DCRU farmlets is managed individually according to best practice for its particular type of management system and environmental conditions. Thus, no attempt is made to try to do the same thing on one farm as is done on the other farm. As far as possible, the organic farm is managed according to best practice for an organic dairy farm in similar soil and climate conditions, and the conventional farm is managed according to best practice for a conventional dairy farm in similar soil and climate conditions. For the organic farm, best practice is guided by the certifying agency (Agriquality) and by an organic farmer advisory group. Comparisons between the two systems are made through regular intensive monitoring, and full economic costing methods are used to determine the differences in cost of production under the two systems, and to influence management decision making. It was recognized early on that, despite attempts to create two similar farms, there are natural differences between them in terms of soil conditions, topography, pasture composition and quality, and the unavoidable inherent differences in the animals. This must be remembered when comparing data from the two systems. On the organic unit a more biological approach was gradually adopted after conversion. This required that soil health be seen as paramount and all practices used were assessed in relation to their impact on the soil and its ability to support good levels of production, not just measured in terms of dry matter, but also of nutrient rich, high quality herbage, to maximize returns and animal health. The primary objective of the biological products applied was the feeding and subsequent development of a populous and diverse biological community. The aim was that these populations would then support good nutrient cycling and soil structural development. In turn it was suggested that this would result in enhanced nutrient uptake by the herbage, which would be seen not only in the elements applied but in others being more readily assimilated from soil reserves. The structural limitations of the Tokomaru silt loam require very careful management during wet periods plus remedial work where damage has occurred. This soil is a very difficult soil to manage biologically and if organic management on it is to be successful, it would require ongoing capital investment in drainage, aeration, development of suitable stand-off areas, and arrangement of off-farm winter grazing. During the first winter (2002), all the organic herd remained on the farm due to a lack of alternative certified grazing. As this was an extremely wet winter/spring, this compounded the structural limitations of this soil and may partly explain the relatively lower pasture production seen in the subsequent years. 3

4 , the conversion period and the first six seasons of certified production In general, the results of the first two years of the trial showed little difference in productivity, animal health, and soil and herbage quality between the two farms. Differences in pasture growth and hence production between the two farms began to emerge in the third year (Table 1), though animal health and soil and herbage quality generally remained similar on both farms. The first year for the two herds ( ) had favourable grass growing conditions which, with the lower stocking rates, meant similar quantities of supplement were fed and good production levels were achieved, which compared favourably with the district average that year (Dairy Monitoring Report, MAFPolicy). The dairy season was characterised by lower than average temperatures from August to February, wetter than average June and July, and much drier than average for 7 months from October to April: 549 mm 10 year average; 304 mm in 2002/03. This combination of a wet winter, long cool period in spring and early summer and exceptionally long, dry summer (with autumn rain delayed until late May), resulted in a very difficult dairy season, with many Manawatu herds dried off in March. The impact of these dry conditions was that feed costs were increased significantly on both farms. The decision to provide similar ME intakes to both herds throughout the milking season to maintain target condition scores and predicted production levels meant 20t more feed had to be supplied to the organic cows in that year, and the organic feed was more expensive. Thus, though milk production was similar on both farmlets, the cost per kg of milksolids produced was higher on the organic farmlet. The third season (2003/04), the first in fully certified production, was characterised by average rainfall, but lower than average temperature and sunshine during spring and summer. February was extremely wet (300 ml compared with 60ml average) with little sunshine. March and April were slightly cooler and drier than average but May was average. Overall, it was a very good dairy season. During this first season of full certification (01/07/03 30/06/04), the organic farmlet consistently grew less pasture than did the conventional farmlet, so that less pasture was consumed and more supplements were fed on the organic farmlet. In particular, the conventional farmlet produced more pasture in early spring due to the application of urea fertiliser. The number of cows on the organic farmlet that season was lower than on the conventional farmlet. Because of these differences, milksolids production by the organic herd was lower both per cow (410 kgms/cow vs. 457 kgms/cow) and per hectare (947 kgms/ha vs kgms/ha) than the conventional herd. The season, the fourth of the trial and second of full certification, was characterised by a long cold wet spring and early summer, which did not dry out or warm up until February The six-month period from June to September 2004 was colder and wetter than the ten-year average, with many local farmers believing it was the worst spring they could remember. To make the season worse, late summer/early autumn was hotter and drier than the ten-year average (particularly February), and the consequent green drought resulted in pasture growth rates slightly below 20 kgdm/ha daily in February and March, compared with kgdm/ha/day during the same period in Growth in April and May was similar to All of this resulted in lower levels of feeding in spring, and earlier dry-off than in Consequently, milk solids production per cow and per hectare was lower than in for both herds. Milk production on the organic farmlet was lower per cow (-14%) and per hectare (-17%) than on the conventional farmlet. These differences between herds were similar to those recorded in

5 Table 1: DCRU Comparative Farmlet Data / / / / / / / /09 Conv Org Conv Org Conv Org Conv Org Conv Org Conv Org Conv Org Conv Org Cows Milked Area (effective ha) Stocking Rate Production (kgms/cow) (kgms/ha) Pasture Grown (tdm/ha 1 July-30 June) Operating Profit ($/ha) Cost of Milk ($/kgms) Difference (%) 9% 17% 13% 24% 35% 20% 26% 29%

6 The season was noted for good growing conditions in early spring and again in late autumn, but with variable conditions from October to January, followed by a brief but relatively intense dry spell in February and March. The excellent early spring conditions resulted in early surpluses being shut for silage, but the return to slower growth in October made it necessary to graze some of these in October. Those events led to decreases in pasture quality on some paddocks. The dry spell in February and March and the unavailability of suitable supplements, at the right cost, led to the early dry-off in March of the organic herd, in order to prevent excessive loss of body condition and pasture cover. Palm Kernel Extract meal was purchased to feed to the conventional herd in March and early April, enabling them to be milked through into May, with their last 8 weeks on once-daily milking and their last four weeks on pasture only. The season began badly, but settled in to a good late summer/autumn so lactation lengths were an improvement on the previous season. Winter and spring were cold and wet with muddy conditions predominating, and this continued through to January. Soil and air temperatures were generally below average for this period while rainfall was above average. December 2006 was recorded as the coolest ever while May 2007 was the warmest. The organic farmlet grew less grass and produced less milk than the conventional farmlet, but this gap was smaller than in the previous season, arresting a trend that saw the production gap increasing over time. Despite the poor weather conditions through the spring, the number of cases of clinical mastitis was very low in both herds. The season began well with reasonable pasture growth through early spring, but drought conditions through the summer meant that growth rates dropped to well below average and didn t recover until late autumn. Both herds were dried off before the end of the season and milk yield was down 10% and 16% on the previous year for the conventional and organic units respectively as a result. Although the drought was more severe than the one in 2005/06, the organic production per hectare in the organic farmlet was higher in 07/08 than in 05/06. This was due to policy changes after the 05/06 drought that included carrying more supplement on hand and a doubling of the area of the run-off. Following the autumn drought in 2008, the season kicked off with good pasture growth rates from June with the onset of the first decent rain in many months. This translated to a great June and July, but August through to November was extremely wet, making managing pasture on the poorly drained soils very difficult. Spring was hard on the organic farmlet, having missed the autumn 08 fertiliser (Osflo) application and being unable to get any fertiliser on until the end of November because of the wet soils. Growth rates were unusually low through September, October and much of November. Things improved with the onset of summer, with great growth throughout summer and most of the autumn on both farmlets, converting to above average production on a largely unsupplemented diet. Pasture growth started to decline after a dry April, compounded by a quick transition to a very wet May. The last cows were dried off on May 20, with milksolids production per hectare 15% up on last season for both farmlets , the seventh season of certified production Production Monthly pasture production from both farmlets is shown in Figure 1. The totals for pasture production were 8.7 tdm/ha and 9.6 tdm/ha respectively for the organic and conventional farmlets (Table 2). The organic unit produced 6% less milk per cow and 13.5% less milk per hectare than the conventional unit. Average cow condition scores and liveweights were quite similar for both herds throughout the season (Figure 2), finalizing with an average condition of 4.2.

7 Pasture Growth (kgdm/ha/day) Milk Production (kgms/month) June July August September October November December January February March April May 0 Conventional kgdm Organic kgdm Conv kgms Organic kgms Figure 1 DCRU monthly pasture growth and milk production for Table 2. D.C.R.U Farm Data 01/06/09 31/05/10 Conventional Organic Cows on farm (most of the season) Area (Ha) Milksolids to Fonterra (kgms/cow) (kgms/ha) Avg. Days in Milk Pasture Grown (tdm/ha) Nitrogen applied (kg/ha) (as Urea and (as organic fert.) ammonium sulphate) Pasture conserved (tdm/ha) Turnips (tdm/ha) Supplement fed (tdm/ha) Grazing off (kgdm/ha) (assumes 10kgDM/cow/day) 7

8 Weight (kg) C.S. 560 CS & LWT's DCRU June July August September October November December January February March April May 0 Conv OrganicMonth Conv CS Org CS Figure 2 Average cow live weights and condition scores for Animal Health Climatically, the 2009/10 season was similar to the previous one. The spring rains arrived a little later making for an easy calving and minimal pasture damage. The animal health status of both herds remained good. There was a brief period in late spring where bloat prevention measures were necessary but no clinical cases occurred. The organic herd was drenched daily with fish oil and the conventional cows treated with a commercial alcohol ethoxylate. The relatively moist summer resulted in good levels of fresh feed availability. However autumn was unusually dry may which may have affected the mineral status of both herds (see below). Facial Eczema spore counts were moderately elevated but measures taken at the DCRU (zinc sulphate added to troughs) were sufficient to prevent any effects. However, counts on the organic unit were significantly higher than on the conventional, probably due to some paddocks being topped in late summer. Mineral Testing Monitoring has continued as per the sample protocol. A feature of the last five springs has been a significant difference in serum magnesium levels between the two herds (organic > conventional). The difference was again marked this season. Although the conventional cows tested within the reference range, the organic cows tested well above. Magnesium supplementation to the organic herd was decreased. Each herd had been supplemented with magnesium to the same degree and it could be argued that higher milk production from the conventional herd may have resulted in a higher 8

9 demand for magnesium. However, despite no magnesium fertiliser having been applied to the organic block since September 2003, herbage magnesium levels remain above those of the conventional unit. This may in part be due to a wider range of pasture species on the organic unit, some of which show magnesium levels significantly above those typical of ryegrass/clover. It should be noted that although neither unit receives specific potassic fertilisers, the application of Osflo (1.7% potassium) to the organic unit in recent years appears to be raising pasture potassium levels. Additionally, effluent from the organic herd is separated and returned to paddocks as per certification requirements. Despite these two inputs, there appears to be little effect on magnesium levels in the organic cows. There was one case of clinical milk fever (an older Jersey cow) on the organic unit and two on the conventional. All cows recovered. There was no significant difference in serum selenium levels between the herds at the spring test. Selenium supplementation was similar - prills added to fertiliser on the conventional farmlet, certified selenium Chip applied to the organic. However, liver sampling in the autumn indicated levels in the organic herd were declining and it was resolved to review supplementation if necessary following the spring blood test. Spring serum copper levels were slightly lower in the conventional herd and supplementation in the form of copper sulphate added to the water supply was carried out for a short time. However, liver biopsies taken in the autumn showed both herds with a wide variation in values. Copper sulphate supplementation for the conventional herd was resumed while certified fish-based copper proteinate was applied to organic pasture. A contributing factor to the test results may have been dry cool weather at a time when cows would be expected to replace depleted liver copper reserves. The conventional herd had been fed moderate amounts of palm kernel which contains elevated levels of copper. The only external source of copper available to the organic herd was via Osflo fertiliser applied twice during the season at a rate of 1500 kg/ha. According to the company s analysis, Osflo contains 42 ppm of copper which would equate to approximately 125g applied per Ha. On an annual basis, this is approximately one third of the lower end of the recommendation by Grace for deficient areas ( kg Cu/Ha every 3 to 4 years). The presence of chicory and plantain, both moderate accumulators of copper, on the organic unit may also have contributed to intake. Autumn pasture analysis showed a significant difference in copper levels between the two units (organic > conventional) but also a difference in molybdenum (organic > conventional). Molybdenum has the potential to reduce copper absorption by cattle but in this case, levels are probably not sufficiently high to have more than a minor effect. Parasitism A combination of ready availability of fresh feed throughout the summer, a change in management of the calves and a cool dry autumn resulted in minimal parasitism in the organic young stock. Growth rates were very good. In contrast to the previous two seasons, drenching with a conventional anthelmintic was not required. This season appears to have demonstrated the importance of: the availability of high quality feed at all times moving calves onto clean pasture at strategic times to minimise exposure to larvae. In the case of DCRU it appears critical to move the calves from the low-lying Dry Stock Unit to the higher, more exposed Haurongo run-off just as the autumn rains arrive. Any growth check while larvae are present on pasture may lead to increased susceptibility to worm infestation which in turn leads to appetite suppression. The experience of the 06/07 and 07/08 seasons suggests that the resulting downward spiral is then difficult to correct 9

10 without resorting to a conventional drench. Management in the late summer/early autumn period appears particularly important in this respect. Mastitis A bacteriological study commencing at the middle of the 2003/04 season, was carried on through the 2008/09 season. Milk samples taken at four different times from all quarters of both herds were cultured for bacteria. For the first three seasons the percentage of quarters with positive bacterial growth was higher in the organic herd, but the differences were generally only significant for Staphylococcus aureus. Both herds tend to exhibit a relatively high prevalence of milk samples positive to Streptococcus uberis at calving which declines somewhat by 14 days post-calving with no significant differences between the herds. The vast majority of those that culture positive do not go on to develop mastitis, indicating the organism is probably not penetrating beyond the teat canal. Individual somatic cell counts are measured monthly. There is a trend for the conventional herd to have lower SCC levels and at times that difference is significant. However, the 09/10 season was characterised by very low bulk SCC in both herds with seasonal averages of 67,000 and 75,000 in the organic and conventional herds respectively. The organic herd had the 44 th lowest average bulk SCC of all Fonterra suppliers nationwide and the conventional herd the 77 th. Control of mastitis in both herds is based on the SAMM Plan, although no antibiotics have been used in the organic herd since Bulk SCC measurements for the organic herd in the past suggested a higher incidence of subclinical S.aureus infections than detected by culture. This is not an unusual situation due to the difficulty in culturing S. aureus from cows with low grade infections. However, individual SCC records show the majority of cells originate from a relatively small proportion of cows. Control of mastitis in both herds is quite intensive. Detection of sub-clinical and early clinical mastitis is efficient. Known high SCC cows are closely monitored with RMT-positive quarters hand-stripped after milking. The organic herd is treated with tonics and homeopathic remedies as appropriate, either on an individual or whole herd basis. Taken overall it seems the integrated approach adopted particularly in the last three seasons has been successful. This approach can be summarised as: vigilance, minimal environmental contamination of teats, high quality teat spraying, stripping of high SCC quarters, supportive therapy, drying off chronically infected quarters and appropriate culling. It should be noted that although these are relatively simple management procedures, their efficacy probably relies on all being carried out together. There are two variations within this approach as demonstrated by two different managers over the last four seasons. The first is to maximise saleable milk while preventing spread of infection but tolerating a higher bulk SCC and the second is to reduce the prevalence of infection to low levels by concentrating on lowering bulk SCC. These two approaches were detailed in a paper presented to the conference of the NZ Society of Animal Production in June (1). Soil Monitoring Soil type The first concern of soil scientists in the trial was that the two farms had comparable soils. Both farms are covered by a single soil, the Tokomaru silt loam (Perch-Gley Pallic Soil) with small areas of Halcombe hill soil on gully sides. This soil is far from ideal for any form of dairying, even though it is a common land use in the district. The soil is composed of silt textured loess, which in its upper part has weathered to silty clay loam. A compacted silt pan 10

11 called a fragipan has developed in the lower subsoil. The whole profile has low permeability, and water perches above the fragipan in winter and spring. The earliest soil measurements suggest that at the beginning of this study, soil quality of the two farms was very similar. As might be expected, during the first two years of this study the early phase of the transition process - there was no significant or consistent differences in soil chemical, biological or physical properties between the organic and conventional farms. This augurs well for the future in that should soil indicators begin to diverge under the different management systems, we can have confidence that these differences in soil properties are due to treatment or management effects. Drainage In the prevailing climate, the soil becomes saturated in most winter and spring periods, dries through spring, then enters moisture deficit in late summer. Artificial drainage via moles and plastic pipes or tiles is necessary. Drainage can increase the number of safe grazing days for dairy cows, decreasing pugging damage to pastures, and allowing greater pasture utilization. Both farms have a network of tile drains and are regularly moled. The tile drains are being checked to ensure their effectiveness. Even if drainage is installed, pugging, leading to pasture damage and poor pasture growth, is a problem for dairy farmers in winter and spring. Conventional farmers mitigate some of the effects of damage by applying nitrogen as urea to boost pasture growth. It is vital that organic farms graze as many cows off farm during winter as possible. Later calving is also desirable. In most late summer-autumn seasons, the Tokomaru silt loam dries and grass growth declines markedly. Drought is common, necessitating supplementary feed. Organic dairy farms need to have supplements on hand for this period, but often it is difficult to shut up pastures for silage because of lower pasture covers during spring. Earthworm populations There were no statistically significant differences between earthworm populations in the organic and conventional paddocks. Table 3. Mean Earthworm numbers and mass measured in the winter of 2009 on two conventional and two organic paddocks. Conventional paddocks Organic paddocks Earthworm numbers (litre -3 ) Nitrate leaching Annual rainfall in 2005 was 885 mm, which was well below the annual average rainfall for the Manawatu of 1000 mm. As a result, winter drainage volume was 115 mm, which was less than half of annual average winter drainage. In 2005, most drainage occurred during two distinct periods; 23 June to 16 August, and 22 September to 23 October. Annual rainfall in 2006 was 1146 mm, which was well above the annual average rainfall for the Manawatu. Total winter cumulative drainage was 377 mm. In 2007, at only 120 mm, drainage was relatively small. Both the winter/spring periods of 2008 and 2009 were very wet with 403 mm and 370 mm of drainage, respectively. 11

12 Nitrate leaching, via the mole-pipe drainage system, to surface waters has been monitored throughout the winter-spring periods since Drainage samples were collected throughout each season from 3 pipe outlets draining organic paddocks and 2 pipe outlets draining conventional paddocks. Table 4. Mean nitrate-n concentrations in mole-pipe drainage (mean values of 3 and 2 pipe outlets for the organically and conventionally managed paddocks, respectively) Conventional Organic farmlet farmlet Average concentration of nitrate-n (g m -3 ) Nitrate-N lost in drainage (kg ha -1 ) Average concentration of nitrate-n (g m -3 ) Nitrate-N lost in drainage (kg ha -1 ) 11 3 Average concentration of nitrate-n (g m -3 ) Nitrate-N lost in drainage (kg ha -1 ) 21 7 Average concentration of nitrate-n (g m -3 ) Nitrate-N lost in drainage (kg ha -1 ) Average concentration of nitrate-n (g m -3 ) Nitrate-N lost in drainage (kg ha -1 ) Average concentration of nitrate-n (g m -3 ) Nitrate-N lost in drainage (kg ha -1 ) As in 2004 and 2005, there was substantially less leaching of nitrate-n from the organic farmlet than from the conventional farmlet in Nitrate-N concentrations in drainage water exiting pipe drains on the conventionally managed area ranged from 14.4 to 1.3 mg l -3, with a mean value of 5.6 mg l -3 (Table 4). In comparison, nitrate-n concentrations in pipe drainage from the organic farmlet ranged from 5.3 to 0.2 mg l -3, with a mean value of 1.8 mg l -3. Nitrate-N losses from the conventional and organic farmlets in 2005 were 21.3 kg nitrate- N ha -1 and 6.8 kg nitrate-n ha -1, respectively. These larger values reflect the quantity of drainage experienced in In contrast, 2007 had very little drainage and so nitrate-n losses were relatively small but again less nitrate-n was lost from the organic farmlet. Both 2008 and 2009 were relatively wet years with large drainage totals. The quantity of nitrate-n leaching from the organic farmlet was smaller than that lost from the conventional farmlet in both years. 12

13 Nitrogen ingested and excreted by the cow Urinary urea is the major source of leachable nitrate on dairy farms due to the fact the quantity of nitrogen typically deposited in a urine patches is much greater than pasture demand. To further investigate N leaching, intensive monitoring of milk urea-n concentrations (an indirect measure of urinary-n output), cow liveweight and body condition, and pasture crude protein (CP) on both farmlets was carried out from September to January 2005/6. An annual feed-budget was constructed for the season of based on the data measured for the monitoring period above (September to January). Urinary-N outputs for the year were estimated using the Cornell Net Carbohydrate and Protein System model (Fox et al., 2004) The conventional cows ingested and urinated substantially more N than the organic cows (Table 4). The N in urine patches from conventional cows was much more concentrated than it was in urine patches on the organic farmlet. Table 4. N intake, urine N output and milk urea-n for the monitoring period of September to January of Conventional farmlet Organic farmlet Stocking rate (cows/ha) Milksolids yield (kg/cow) DM intake (kg/cow) Dietary CP (% of DM) N intake (kg /cow) Mean Milk Urea N (mmol/litre) Urine N output (kg /cow) A feed budgeting exercise suggested that the annual pasture yields in were 11.4 and 10.3 tonnes DM/ha for the conventional and organic farmlets, respectively. In the feed budgets, the farmlets were stocked at 2.4 (conventional) and 2.2 (organic) cows/ha, and the cows produced 409 (conventional) and 345 (organic) kg MS/cow and 980 (conventional) and 770 (organic) kg MS/ha. This information was then inputed into the Cornell Net Carbohydrate and Protein System model to simulate the quantities of N that the cows ingested and excreted in urine during the year. As expected, the annual values for N intake and urine-n output by cows on the farmlets in (Table 5) reflected those differences observed during the monitoring period (Table 4). An important assumption made in this exercise was that the differences in pasture CP between the farmlets observed during the monitoring period would be sustained for the entire year. This warrants further investigation. 13

14 Table 5. N intake, urine N output for the year Conventional farmlet Organic farmlet Stocking rate (cows/ha) DM intake (kg/cow) Dietary CP (% of DM) N intake (kg /cow) Urine N output (kg /cow) Urine N output (kg /ha) N in urine patches 1 (kg /ha) Assumes urine from a cow covers approx ha Modelling Leaching losses of N were simulated using both the Nitrogen Leaching Estimation (NLE) model of Di & Cameron (2000) and Overseer Nutrient Budgeting software (Wheeler et al., 2003). Interestingly, there was reasonable agreement between the modeled and observed values particularly for the organic farmlet. It is noteworthy that both models predicted the approximately 50% reduction in N loss from the organic farmlet relative to the conventional farmlet. Table 6. A comparison of measured and modelled values for N losses in drainage from the farmlets. N leached Conventional farmlet Organic farmlet Measured (kg /ha) 19 8 NLE model (kg N/ha) 15 7 Overseer model (kg N/ha) 16 8 It has been suggested that the environmental efficiency index (kg N/ tone milksolids) is the most equitable indicator of the relative impact of a production system on the aquatic environment. This ratio was much more favorable for the organic production system than it was for the conventional farm (Fig. 1). 14

15 25 20 kg N/t MS Conventional Organic 5 0 Measured data Overseer Figure 1. The environmental efficiency index for the farmlets. Investigation of effectiveness of organic fertilisers There is much interest in the effectiveness and the role of alternative fertilisers in both organic and conventional dairy systems. A field trial has been established to look at two of these products a chicken manure-based compost (Osflo) and compost tea. From some quarters comes the claim that elevated Calcium levels (at higher ph values) are also beneficial to plant production and soil quality. So, lime is also one of the treatments in this trial. The trial layout is pictured in Figure 3. There are 4 replicates of the five treatments (see Table 5). Results to date are interesting and are presented in Table 5. Table 5. Pasture growth under some alternative fertiliser regimes. Treatment Harvest 1 07 Dec 06 (kg DM/ha) Harvest 2 18 Jan 07 (kg DM/ha) Harvest 3 19 Feb 07 (kg DM/ha) Total Harvest 1-3 (kg DM/ha) Osflo 310 a 198 a 359 a 867 a Compost tea & Osflo 306 a 199 a 327 a 832 ab Lime 227 b 157 a 284 ab 669 bc Control 174 c 184 a 280 ab 637 c Compost tea & lime 214 bc 153 a 180 b 546 c Significance *** NS * ** CV% LSD 5% Trial Mean (kg DM/ha) NS = Not Significant; (+) = P<0.10; * = P<0.05; ** = P<0.01; *** = P< LSD 5% = Least significant difference for the comparison of treatment means at the 5% probability level. Yields followed by the same letter are not significantly different. Soil mites The objective of the pilot sampling was to explore the usability of soil mite fauna as one of indicators in comparing the impacts of organic and conventional dairy systems on soil health. Mites are well suited as indicator organisms in agricultural environments because of their 15

16 Mite Density (ind. / m2) Average no. species/ sample high density, species richness, sensitivity to soil conditions and well-developed sampling methodologies. This pilot study focused on two taxonomic groups of soil mites (Oribatida and Mesostigmata) that occupy different trophic levels in below-ground systems. In spring 2005 soil samples (125 cm 3, at 5 cm depth) were collected at random within 10 dairy paddocks (5 organic, 5 conventional) using a stainless steel corer. One sample per paddock was collected. Soil mites were extracted from soil samples into 75% ethanol using a modified Tullgren apparatus. The oribatid mites (Oribatida), and mesostigmatid mites (Mesostigmata) from each sample were counted and identified to a species (morphospecies). All other mites were counted and identified to an order. In total, 175 mites from 20 species were recorded in the samples from organic paddocks, while 54 mites (18 spp) were recorded in the samples from conventional paddocks. Although the organic pasture had higher average density and species richness of soil mites (Fig. 4 and Fig. 5), the differences in density and species richness of soil mites between organic and conventional pasture were not statistically significant (Table 6). However, there was significant difference in density of oribatid mites between organic and conventional pasture (Table 6). The species richness of oribatid mites was low both in organic and conventional samples. Table 6. ANOVA results for the hypothesis of no effect of farm type on soil mites (organic vs. conventional). Means with the same letter are not significantly different (LSD t-test). Farm type Organic Conventional ANOVA results All mites (density/sample) 35.0 a 10.8 a F 1,8 =2.95 p= All mites (species richness/sample) 7.4 a 5.4 a F 1,8 =1.65 p= Oribatid mites only (density/sample) 6.2 a 0.8 b F 1,8 =6.81 p=0.0311* Average density of soil mites in organic and conventional dairy pasture Average species richness of soil mites in organic and conventional dairy pasture Organic Conventional 0.0 Organic Conventional Figure 4. Figure 5. 16

17 Any future work on soil mites should be limited to oribatid mites (Acari: Oribatida), which have long been used in soil biodiversity studies, and have an established reputation as indicators of soil quality and of stability of soil biological environment (Pankhurst, 1997; van Straalen, 1997). These mites seem to be a sensitive indicator group in these trial conditions. Since the number of species collected here is very limited, identification to a species (morphospecies) level should be used in the future similar research. Although the density of Oribatid mites in samples from organic and conventional paddocks differs significantly, it is invalid to attribute the levels of their biodiversity to the organic vs. conventional management practices and not to the effect of soil type, paddock location, local microhabitat, etc. To allow conclusive comparison of organic vs. conventional systems using statistical analysis, two or more more replicates of organic/conventional dairy systems, preferably in the same region, should be sampled. While no monitoring of soil mites was done in , a PhD student will further this work beginning in Pasture Composition Monitoring The pasture composition of the organic and conventional farm systems has been surveyed in October/November, except 2002, and in May since 2001 (Table 7). The species composition within the two systems has been relatively stable with the main differences between the systems being the percentage of ryegrass, other grasses and white clover. Since 2004 the conventional system has had at least 7 % more ryegrass than the organic system and the difference is currently approximately 13 %. It would be expected that the higher percentage of ryegrass in the conventional system improves its pasture growth in winter and early spring relative to the organic system. TThe white clover percentage in the pastures has recovered since the initial clover root weevil infestation in summer 2007, but most noticeably in the organic pastures. Although Tokomaru silt loam is a difficult soil for white clover production, as shown by the low clover percentage in both systems, the trend is for the organic system to have a greater white clover percentage. Although the white clover percentage was only 5.5 % in the organic pasture in November 2010 the range across the monitored paddocks was 1.2 to 12.9 % compared with a range of only 0.0 to 5.9 % in the conventional paddocks. The herbs, chicory and plantain, have been running out in the organic pastures sown with these species, but a successful establishment of new pastures incorporating herb species in Autumn 2009 has reversed this trend. The new organic pastures were sown with a mix of AR1 perennial ryegrass (16 kg/ha), white clover (4 kg/ha), red clover (4 kg/ha), chicory (2 kg/ha) and plantain (2 kg/ha). Table 7. Botanical composition (% dry matter) of pastures on the organic and conventional farm systems from 2001 to Ryegrass Other sown grass Other grass White clover Weeds Herbs Dead May 2010 Conventional

18 Organic Nov 2009 Conventional Organic May 2009 Conventional Organic Nov 2008 Conventional Organic May 2008 Conventional Organic Nov 2007 Conventional Organic May 2007 Conventional Organic Nov 2006 Conventional Organic May 2006 Conventional Organic Nov 2005 Conventional Organic

19 May 2005 Conventional Organic Nov 2004 Conventional Organic May 2004 Conventional Organic Nov 2003 Conventional Organic May 2003 Conventional Organic May 2002 Conventional Organic Oct 2001 Conventional Organic Weed Monitoring The 6-monthly monitoring of weed composition in ten organic paddocks and ten conventional paddocks has continued over the past year. This monitoring is conducted by assessing the percentage cover by every weed species within ten fixed 1-square-metre quadrats within each of the 20 monitored paddocks, both in late May and late November each year. A number of the paddocks have undergone regrassing over the period of the trial. However, it has been possible to still monitor the weed composition in each of the fixed quadrats due to the way they are located each assessment time. Each quadrat is located at a set position along a line transect, and this transect is located each time by spanning a 100-metre measuring tape between two permanent marked posts in each paddock. As these measurements have now been made every 6 months since November 2003, considerable amounts of data have been generated. Data for 2007 and 2008 are shown in 19

20 Table 8. On the bottom line of the table, the actual percentage cover by weeds is shown, and this indicates that there is no difference between the organic and conventional pastures in the amount of weed cover. It fluctuates from year to year depending on factors such as grazing pressure, pasture renewal and climatic effects. Table 8: The relative importance of various weed species on the organic and conventional dairy farmlets in May and November of 2007 and 2008, as estimated by determining the percentage of the total weed cover that each species comprised. The actual percentage of pasture estimated to be covered by weeds is shown in the bottom line. Species May 2007 November 2007 May 2008 Nov 2008 Organ. Convn. Organ. Convn. Organ. Convn. Organ. Convn. buttercup docks dandelion pennyroyal Californian thistle broad-leaved plantain daisy selfheal Scotch thistle narrow-leaved plantain ** 1.7 ** 0.6 ** 0.2 ** 0.3 other species % weed cover **Chicory and plantain not included as planted species The main part of the table shows which species are making up this weed cover. Hairy buttercup can be bad in some years and much less prevalent in other years. This annual weed establishes each year in autumn, but the extent of establishment each year depends on variables such as how much pasture competition there is over autumn and also the moisture content of the soil when pasture is not dense. Docks are the other major weed species, and these tend to be fairly constant over time, though they can be worse when new pastures have just been established, and also when pastures have not been grazed very hard. Note that the other species category was high for May 2008 as new pastures had been established on both farmlets, allowing many annual weeds to establish. These disappeared over time, either due to spraying on the conventional unit or grazing and natural death in the organic pastures. A paper discussing the weed composition of the pastures in this trial was presented to the New Zealand Plant Protection Conference in August 2008, and the full version of this paper is available to the public on the internet at: References Thatcher, A., Petrovski, KR *. and Fraser, K. (2010): Influence of Management Techniques on the Levels of Mastitis in an Organic Dairy Herd. Proceedings of the New Zealand Society of Animal Production (in publication) 20