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pastoral development
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Tussock Grasslands MIS
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pastoral development
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P. J. JARVIS
10 Hawford Road, Opawa, Christchurch, New Zealand
C. C. BOSWELL
AgResearch, Invermay Agricultural Centre, Private Bag 50034, Mosgiel, New Zealand
A. K. METHERELL
AgResearch, c/o Soil Plant and Ecological Sciences Division, P.O. Box 84, Lincoln University, Canterbury, New Zealand
R. M. DAVISON
J. A. MURPHY
Meat and Wool Economic Service of New Zealand,PO Box 5179, Wellington, New Zealand
Data on the physical and financial performance of farms are collected annually by the Meat and Wool Economic Service of New Zealand. We used the available data from 1968/69 to 1995/96 to calculate a nutrient balance for the model high country farm. Our nutrient budget takes account of the loss of nutrients in the form of livestock products (meat and wool), and losses or movement due to leaching and rainfall run-off. Inputs of nutrients occur with the application of fertiliser, in rainfall, and by legumes fixing nitrogen. While there have been large fluctuations in both the quantity of nutrients applied as fertiliser and the quantity of nutrients removed, the whole-farm nutrient balance has remained in credit each year for the whole of the time series for all major nutrients. Separate budgets for developed and undeveloped grassland showed that the nutrient balances were in credit for four of the five nutrients in each case; in developed grassland mean potassium balances were slightly negative while in the undeveloped grassland phosphorus balances were slightly negative. The annual surplus of calcium is significantly higher than for other nutrients. The results indicate a need for re-interpretation of nutrient losses calculated for post-European settlement as they affect understanding of the effects of grazing on the sustainability of high-country grasslands. Over the 30 years studied there appears to have been a cessation and probably some redress of nutrient losses from the system. This indicates that losses were greater earlier in the 150-year period of European settlement than are indicated by the long-term averages. Keywords calcium; nitrogen; nutrient losses; phosphorus; potassium; sulphur; sustainability; tussock grassland
The natural vegetation of South Island, New Zealand, high-country farming systems is mainly short native tussocks. Tall tussock grassland (especially Chionochloa spp) is primarily found above about 1100 m asl. Tussock grasslands are a comparatively recent vegetation type on all but the driest valleys of the inter-montane basins (short tussocks) and the alpine areas (tall tussocks) where they were originally dominant plants (Douglas & Allan 1992). In the past 3000 years natural fires and fires lit by Polynesian and European settlers have resulted in the conversion of native forests into tussock grasslands. The sustainability of the tussock grasslands themselves has been threatened by the introduction of grazing sheep and rabbits during the past 150 years of European settlement (O’Connor and Harris 1991).
The sustainability of high-country farming systems involves the maintenance of an acceptable level of soil, plant, and animal quality (e.g., soil fertility, soil structure, vegetation cover, andbiodiversity ) such that an ecologically and economically sustainable pastoral system can be maintained We follow O’Connor & Harris (1991) in considering "sustainable use" the "use of renewable resources (in the ecosystem) at rates within their capacity for renewal." Economic sustainability requires a viable level of income which will ensure that inputs into the system can be maintained and the income needs of the farm family are met. High country plant and soil resources are only weakly buffered against degradation and loss. It is difficult to reverse a degradation of these resources. It is therefore important to be able to recognise when a system is not sustainable and make corrective changes in its management. Sustainability is a complex concept which is impossible to measure directly at least in the short term. Therefore we rely on indirect measurement using information obtained from regular monitoring of suitable indicators.
There is currently concern about the sustainability of pastoral farming systems in the high country (Martin et al. 1994) in particular in the dry sub-humid and semi-arid regions. Here there has been an increase in the weed Hieracium (Hunter 1991), and at least until recently, a continued concern with rabbit pests (Jarvis et al.1995).
A wealth of data is available for monitoring purposes on high country farms (Boswell 1997a; Boswell et al, 1998) but often the information from different data sets needs to be combined for improved interpretation of trends in sustainability of the ecosystems. Available data includes rabbit numbers and vegetation characteristics collected as part of the MAF Rabbit and Land Management Programme; livestock performance, paddock grazing, farm inputs (including fertiliser), and financial. One source of financial and production data is collected by the Meat and Wool Economic Service of New Zealand (M&WES). We have used some of the data collected by M&WES to measure long-term sustainability of an average high country farming system. Data involved was of nutrients removed from the property (e.g. mainly in animal products, but also crops) and fertiliser inputs. These were incorporated with other nutrient additions and losses to determine whether or not the outputs exceed the inputs of nutrients to the property - a long-term negative nutrient balance indicates a system cannot be sustained.
With the exception of the period 1988 to 1990, high country farm incomes have generally been depressed over the period since 1975 due to low wool prices in particular; reducing farm expenditure has been the primary means of achieving balanced financial budgets. One of the discretionary items farmers’ cut is expenditure on fertiliser, the major method of nutrient input into farm systems. This could lead to negative nutrient budgets. However, farmers generally make up for withholding fertiliser in lean years by applying capital fertiliser when farm incomes improve (see Figure 1). In this paper we have adopted the nutrient budget approach for an "average" high country property to provide an indication of the sustainability of high country grassland over the past three decades.
It is acknowledged that mean inputs and losses of nutrients for the whole property gloss over differences between the developed and undeveloped areas within the farms. The sustainability of the undeveloped portion of the average high country attracts particular interest. For this reason we include details of a first approximation of the nutrient balances on undeveloped land incorporating data from the whole farm analyses.
The technique may be easily adapted from the average to particular farms. Similarly, we present only a budget for a limited number of nutrients but it is conceivable that the method could be expanded to include other resources, such as energy, in a whole-farm environmental accounting framework.
The M&WES collects production and financial data for their Class 1 High Country farm model and report these data in their annual Sheep and Beef Farm Survey publication. These data have been collected since the 1950s although the nature of the data collected has been adjusted to meet the Service’s needs over time. A consistent data set, based on the detailed survey of 30 high-country farms, has been collected since 1968/69. The data present the average results for the farms in the survey and it is these data which are published in the Sheep and Beef Farm Survey. The average size of the M&WES Class 1 farm during this study period was about 10 400 ha .
We have used the data to prepare an historical, whole-farm nutrient budget for nitrogen (N), phosphorus (P), potassium (K), sulphur (S), and calcium (Ca). Nitrogen is the key nutrient in grassland ecosystems, and, in the tussock grassland ecosystems which prevail in the South Island high country, the extent of inputs and outputs of the nutrient is least understood. Sulphur and P are recognised as the two major nutrient deficiencies in New Zealand soils, and Ca and K are among the elements most commonly measured through chemical analyses of plant material and soil.
Our nutrient budget simply sums the gains and losses of these five elements each year . Gains come from applied fertiliser, N fixed by legumes, and input from rainfall. Losses occur when livestock gain weight, livestock or their products (e.g. wool, meat) are removed through sale or on-farm consumption, or water movement causes run-off or leaching. The nutrient balance is the difference between the gains and losses over the whole farm.
To calculate the total nutrients removed we calculated the total weight of product removed from the farm .From 1968/69 to 1990/91 the meat sold from each farm in the survey was averaged from individual farm killing sheets. We converted this to a liveweight basis using the liveweight/carcass weight ratio (Table 1) for each type of livestock. To this figure was added an estimate for the weight of livestock sold less an estimate of the weight of stock purchased. In addition, the difference in weight between closing and opening stock, by age class, was included to give a total liveweight removed from the farm (since this reflects sales of sheep and consumption on the property). This balance sheet approach provides the magnitude of liveweight and/or meat production for each farm class. For 1991/92 we have estimated total liveweight by using the livestock reconciliation and trading accounts and the annual average slaughter weight for lamb, sheep, cattle, deer and goats converted to a liveweight basis using weight ratios. We then multiplied these data by the amount of nutrients contained per kilogram of liveweight for each type of animal (Table 1). Sources of data on nutrient contents of different animals included Grace (1983a, 1983b), and Anon (1998); goat values were assumed to be the same as for sheep.
Wool production included the difference between wool on hand at open and close of the annual balance date, sheep shorn, total shorn wool sold, and lambs wool sold. Total calculated wool production included wool removed from pelts of slaughtered animals plus estimated wool on sheep’s back when sheep were sold off the property, less estimated wool on purchased sheep’s back. Up to 1989/90 this was calculated at the farm level by the M&WES field staff. We have estimated these data at the farm class level from 1990/91 to show the trend in wool production and removal. Nutrient content of greasy wool multipliers (Anon 1998a, A. Bray pers. comm.) were then used to calculate nutrients removed in the wool.
Deer velvet and goat fibre sales were insignificant and were only recorded for this class of farm from 1992.
Aggregating the data for nutrients removed in the form of livestock and wool provided most of the total nutrients removed from the farm. No allowance was made for loss of nutrients in rabbits killed and removed from the property.
All urine and dung was recycled within the property and so there was no net loss from transfer of nutrients by grazing animals in the nutrient budget.
Leaching is the loss of nutrients in drainage water, whether in the form of rain or from irrigation, beyond the rooting zone of plants. Run-off is the loss of rainwater together with the nutrients it contains, which is lost by overland flow and not absorbed by the soil.
We have calculated the cumulative loss of nutrients in runoff and by leaching as 75% of the N and S, 50% of Ca, 20% of K, and 10% of P inputs into the system, based on S fertiliser uptakes (Boswell 1997b), and leaching studies (Sakkadevan et al. 1993). Thus, 25% of the inputs of N and S, 50% of Ca, 80% of K, and 90% of P were retained for use within the soil/plant ecosystem to be utilised directly by plants and indirectly by animals.
Erosion is conspicuous on the high-country landscape but much is now recognised as having natural causes especially on the greywacke high country of the South Island, New Zealand (O’Connor & Harris 1991). O’Connor & Harris (1991) reported that there had been little measurement of anthropic erosion in the South Island high country at the time of their review. Hewitt (1996) showed that erosion losses could be significant on semi-arid Central Otago, New Zealand, soils with a history of overgrazing especially by rabbits. North-west winds accounted for most of the soil losses but also for subsequent deposition of soil at his site. We lack information as to the extent of such soil loss and its nutrients, but, at localised areas where erosion of mature soil has been observed, it is clear that there are nutrient losses because soil renewal is too slow to match losses. Despite the recent work, evidence of a general inbalance between soil nutrient losses due to erosion and nutrient renewal remains "conjectural or insufficient" (O’Connor and Harris 1991) and the budgets presented do not include erosion losses.
Inputs of nutrients for the farm were from applied fertiliser (and lime), rainfall, and natural fixation of N (e.g., by legumes). Only the total amount of fertiliser applied was available for the Class 1 farm from 1968/69 to 1982/83. To calculate the inputs of nutrients over this period we have assumed that the area in crop received an annual fertiliser application of Cropmaster 20 (20% N, 10% P, 0% K, 13% S, 0% Ca) at a rate of 250 kg ha-1. The balance of fertiliser was assumed to be sulphur super (8% P, 20% S, 18% Ca). From 1983/84 to 1995/96 the actual amount of each nutrient was recorded by M&WES. Calcium application rates were calculated from the tonnes of sulphur super fertiliser and the lime applied; we assumed lime to be 95% pure, with 40% of pure component in the form of calcium (thus 1000 x 0.95 x 0.4 = 380 kg Ca per tonne of lime) (During 1984).
The nutrient content of rainfall (Table 2) was based on the means from a limited data set (collected by NZ Department of Agriculture from 1959 to 1963) at Tara Hills High Country Research Station (Omarama) and Broken River (Cass). The mean amounts of nutrients received in rainfall (Table 2) were derived by multiplying the farm area by the rainfall nutrient values. The rainfall collected at Tara Hills in the days before road sealing may have included dust raised by passing traffic. However, analyses of rainfall collected since road sealing at Tara Hills included in a data set from four North Otago sites during the 1980s (P. B. Greenwood pers. comm.), indicated inputs of about 4 kg Ca ha--1 yr--1 (i.e., similar to the value in Table 2). It is possible that the rainfall Ca used reflects the inputs of Ca probably as rain-borne dust. Scott (2000) referred to his Mt John (Mackenzie Basin) research site as receiving regular wind-borne deposits of particulate material (incorporating nutrients).
Most high-country farms have an area in improved pasture in the form of oversown and topdressed (OSTD) hill country or cultivated land sown with introduced pasture species including clovers such as white clover, red clover, and alsike clover. In addition, two annual clovers, haresfoot clover (trefoil) and suckling clover, contributed to the pasture in both improved and unimproved grassland especially when soil moisture conditions were favourable. This may occur on average about one year in three but the pattern is irregular. In the whole farm budget we estimated the mean rate of nitrogen fixed by clovers to be 30 kg N ha-1 yr-1 over the developed portion of the property and 1.7 kg N ha-1 on the undeveloped grassland. These conservative values are based on the lowest regional rate of N fixation recorded in a New Zealand-wide survey (39 kg N/ha from browntop-dominant hill pasture; Hogland et al. 1979), and an estimate based primarily on the biomass, N content, and plant distribution of haresfoot clover from dry, unimproved tussock grassland (C. C. Boswell unpubl. data), respectively.
Determination of the area of typical Class 1 high-country farm land that has been developed by cultivation, overdrilling, or OSTD was by reference to two data sources. Annual M&WES data include the area of pasture land on which fertiliser had been applied; this may be indicative of trends in land development but cannot be used on its own because not all of the developed land is fertilised every year. For example, OSTD tussock grassland (the largest area developed) may be fertilised at approximately three-year intervals (Boswell & Floate 1992), and in times of cash shortfall (e.g., in years of low product prices) application of fertiliser may be deferred.
In order to model the area of land developed, we took blocks of three years of data from the M&WES surveys and assumed that the trend in the mean area of land developed followed a moving three-year average of (year(t-1), year(t), year(t+1)) multiplied by 3; to be equivalent to three times the area of land to which fertiliser is applied. We applied an additional caveat that the land area developed by a particular year cannot be less than that developed in previous years. The three-year moving average (Table 3) gives a fairly good fit to known data points obtained from Kerr & Lefever (1984), which describe the extent of land development during three survey periods between 1971 and 1982. The weighted average area of land development on high country farms for 1971/73, 1976/78, 1981/82, with a five year projection to 1987 (Kerr & Abrahamson 1988), is shown in Table 4 . The model areas were subsequently adjusted to coincide with the three known data points from the survey. The area of developed land each year in the model is shown in Fig. 2.
The relative amount of grazing obtained from areas that are developed and undeveloped is open to conjecture. We modelled nutrient balances with the developed land carrying a mean of 3 stock units ha-1 su ha-1 and the stocking rates on the undeveloped tussock grassland were calculated as the remaining stock carried each year divided by the residual undeveloped area. A stock unit (or ewe equivalent) represents the annual feed requirement for a ewe of 55 kg live weight raising a single lamb (Coop 1965). Subsequently, we compared balances with the developed land carrying 3, 3.5, and 4 su ha-1 yr-1, respectively.
The whole-farm balance was in credit over the whole of the 28-year series for Ca, N, P, S, and K (Fig. 3). This suggests that over the whole farm the combined influences of natural and farmer management of nutrient inputs adequately replaced the nutrients removed in the form of animal products. The net surplus for Ca was significantly greater than for other nutrients. The surplus reflects its high concentrations in fertiliser and lime and comparatively high concentrations in high-country rainfall, plus our assumption that it is not readily leached from soils. The annual whole-farm N balance increased over the time series, with lifts in 1983 and 1989 reflecting the increases in the area of grassland development modelled in Fig. 2. A similar modelled increase in developed grassland in 1973 had a less clearcut effect on the N balance. Phosphorus and S had a consistent moderate positive balance over the time series (P = 0.56 kg ha-1 yr-1; S = 0.62 kg ha-1 yr-1). Potassium had a consistent small positive balance (mean 0.11 kg ha-1 yr-1, range 0.02-0.18 kg ha-1 yr-1).
The positive balances are in general agreement with those of Metherell (1997) who investigated current nutrient inputs and losses in high country pastoral systems and who also had to make a number of assumptions especially regarding N inputs and leaching and animal transfer losses. Similarly, Scott (2000) produced a net positive balance of nutrients in his long-term (c. 15 years) pasture development and annual fertiliser application experiment at Mt John near Lake Tekapo. O’Connor & Harris (1991) showed the importance of the application of fertiliser post-1950 altered the balances of S and P in particular, although they did not completely balance the modelled losses on two selected types of high country farms.
In contrast, McIntosh (1997) reported maximum losses of N of 27 kg ha-1 yr-1, P 5.5 kg ha-1 yr-1, K 19 kg ha-1 yr-1, and Ca 30 kg ha-1 yr-1, when estimated from a worst-case scenario soil and biomass losses since grazing began 150 years ago. Losses were lower when based on a nutrient cycle under a grazing and burning regime, losses of N were 2-10 kg ha-1 yr-1, P 0.1-0.6 kg ha-1 yr-1, K 0.5-2.2 kg ha-1 yr-1, and Ca 0.3-1.2 kg ha-1 yr-1.
Nutrients removed from the farm were calculated from the liveweight of animals and wool removed from the farm (Fig. 4). The increase in the amount of nutrients removed was a result of the increase in stock numbers which occurred on the Class 1 farm up to 1985 (Fig. 5). Stock numbers peaked in the period 1985-1988.
Farmers applied most fertiliser (and thus Ca, S, and P nutrients especially) during or directly after good income years. These in turn were primarily determined by the price of wool. The trend in fertiliser application matched the trend in wool price fairly well but the fluctuation in the trend for fertiliser application was more exaggerated than for wool price (Fig. 1). When wool price decreased the application of fertiliser decreased even more. The period 1990/91 to 1994/95 was the exception to this; strong lamb prices helped compensate for low wool prices, and, in Canterbury, fertiliser application qualified for an environmental maintenance grant under the Rabbit and Land Management Programme. The reduced fertiliser application in 1974/75 occurred as a result of low wool prices combined with low lamb prices; application then increased markedly over the period of the Land Development Encouragement Loan (LDEL) scheme (1977 to 1982). In 1986/87, fertiliser application rates declined as a result of the removal of Supplementary Minimum Prices (SMPs) on lamb and mutton in addition to depressed prices for wool.
While such a trend may apply on average over the whole of the farm, within the farm there are areas where nutrients (especially P and N) are consistently removed by grazing animals and transferred via faeces and urine to stock camps. Concentration of faeces and urine at stock camps results in a positive transfer of nutrients to these relatively small areas by the grazing animals at the expense of other parts of the farm.. While there is no published record of the extent of this transfer in high-country grassland, Gillingham & During (1973) demonstrated nutrient transfer on long-established hill pasture in the North Island, New Zealand,. O’Connor & Harris (1991) and Metherell (1997) stressed the importance of uneven distribution of animal excreta in tussock grassland nutrient budgets. Thus, while a farm-scale nutrient budget records no losses through animal transfer; in sustainability studies with a narrower focus, such losses are important and must be taken into account. .
When the average stocking rate on developed farmland is set at 3.0 su ha-1, the nutrient balances for Ca, N, P, and S on developed farmland are positive in all years (Fig. 6). The only exception is K (Fig. 6) with a marginally negative balance. The average K level is -8 grams K ha-1 yr-1 (range from –38 grams K ha-1 yr-1 to 48 grams K ha-1 yr-1). Fertiliser K was only included in the budget from 1984. Details of the nutrient contents of fertilisers applied prior to this year are not available in the M&WES database. Potassium is likely to be released from many high-country soils by weathering of minerals in the underlying rock. A very slow rate of weathering would offset the marginal negative balances. The trend for applied nutrients (Ca, P, K, S, N; ) follows the trend in fertiliser application. The Ca balance is particularly high in 1985 when the average farm applied 68 t of liFig. 6me (a far higher rate than in any other period); this was a good income year and came at the end of a good decade for farmers, just prior to the removal of SMPs in 1986. In 1987, the balance of Ca, P, and S all declined reflecting the lowest fertiliser and lime inputs over the whole time series.
On undeveloped grassland, Ca, N, S, and K were all maintained in positive balance in the undeveloped tussock grassland ecosystem under grazing at the stocking rates typically applied over the past 30 years (Fig. 7). In contrast, the balance for P was precarious. The average nutrient balance for P over the series is -94 kg P per farm (-11grams P/ha/yr), with a range from -254 kg per farm (-35 g P ha-1/ yr-1) in 1985 to +51 kg per farm (6 g P ha-1 yr-1) in 1994. Generally, the values for P tend to be in negative balance in the early years in the series when the area of land developed was relatively low, and more positive in later years when more land had been developed (thus relieving grazing pressure on undeveloped land). On undeveloped grassland, inputs were from rainfall (Table 2), and nitrogen from fixation by N-fixing plants. Leaching losses were again calculated as a proportion of the nutrients input. Transfers of nutrients by animals in faeces and urine occur mainly within the blocks so that there were no net losses from this source. There may be some net transfer of nutrients from developed farmland to undeveloped grassland when stock are moved between the two types of grassland, but no account was taken of them in this study. Net inputs of Ca were approximately 2.75 kg ha-1 yr-1. Net inputs of S were approximately 0.25 kg ha-1 yr-1. Net inputs of K were 0.16 kg ha-1 yr-1. Unpublished research (C. C. Boswell unpubl. data) has suggested that small inputs of N from plant N-fixation can be expected in most undeveloped tussock grassland. Allowance for small N inputs by fixation resulted in a net balance of about 1.3 kg N ha-1 yr-1. In contrast, there has been no allowance for any input of P to the system through the weathering of rock or other parent material in this study. This reflects the lack of weathering information. Just as with K, some P is likely to be added to the system by weathering and very low rates of weathering would offset the calculated P shortfalls.
The effects of altering stocking rate on the developed country of the high-country farms on average net nutrient balances on both the developed and undeveloped grassland are shown in Table 5. On developed grassland the effect of increasing stocking rates is to reduce the net balance of all nutrients. The only important change is the worsening of the marginal K balance in these pastures. Assuming the total numbers of stock on the property remains unchanged, the increased stocking of developed grassland reduces the number of stock that have to be supported by the undeveloped tussock grassland and so nett balances of the nutrients are improved. In this scenario P moves from marginally negative to marginally positive balance.
The stocking rates compared were relevant to farming practice. A rule of thumb calculation used by some runholders (farmers) is that about 20% of a run area is likely to have been developed and the developed area is likely to carry 80% of the grazing. If the average property is about 10 000 ha and carries about 7500 su; then 6000 su are likely to be grazed on 2000 ha developed and 1500 su are likely to be supported by the remaining 8000 ha. In this example, the stocking rates on the two classes of grassland are 3 su ha-1 and 0.19 su ha-1, respectively. At 10 000 su carried the stocking rates would be 4 su ha-1 and 0.25 su ha-1 for developed and undeveloped parts of the property, respectively. Over the period of the survey, mean total stock per farm ranged from 6900 su to 9700 su.
The study covers the majority of the last 3 decades of the 20th century. It assumes that there has been no loss of nutrients by burning of high-country vegetation in this time. The pattern of consistent positive nutrient balance for all nutrients except K differs from the budgets reported by Martin et al. (1994), O’Connor & Harris (1991), and McIntosh (1997) regarding changes in the high country nutrient status during 150 years of European settlement. Losses of nutrients from repeated burning of vegetation, overgrazing by sheep and rabbit plagues, and soil erosion processes were estimated and averaged by Martin et al. (1994) and McIntosh (1997) as annual losses of nutrients over the 150 years, with the implication that the process of loss is continuing. The data presented here show that over the past 30 years the nutrient losses process for several elements has ceased and is likely to have been reversed.
This is an indicative study; the assumptions we have used with respect to N fixation, atmospheric (rainfall) inputs, leaching, and run-off need validating, and any change in these may significantly alter the nutrient balance. We have ignored any possible gains in nutrients by weathering of parent material in this study. This may be too simplistic, and the recorded small negative balance of K in the developed grassland budget and the small deficit in the P budget on undeveloped grassland may be replaced via the weathering process. We have also disregarded nutrient losses through erosion processes largely because of the lack of data applicable to large areas of the high country. At an individual farm level it should be possible to calculate fairly accurately the nutrients removed in produce and gained from the application of fertiliser. The condition and area of pastures, which include both oversown and volunteer clovers, can similarly be assessed on individual farms to provide better estimates of inputs via nitrogen fixation. The weakness of the whole-farm approach is that it does not tell us what is happening at specific sites on the farm (especially areas depleted by the net removal of nutrients as a result of animal transfer) or at the paddock level. This emphasises the need to monitor those sites that are most at risk of nutrient decline and any subsequent decline in soil and vegetation quality that may occur.
Use of spatially-based computer information systems, and the possibilities for automated recording of data such as climate records and soil moisture contents, are likely to be used for predicting plant productivity and monitoring tools. The implication of this is that it will become increasingly realistic for planners to collect data at more sites on farms and, as a result, it may eventually become possible to develop environmental accounting systems at the paddock as well as at the whole-farm level. A consequence could be an understanding of risks to the sustainability of the natural resources on a given property, and development of management options to reduce such risks.
By using data for the M&WES Class 1 farm, we have demonstrated that it is possible to calculate a nutrient budget at the whole farm level, using data which are also readily available to farmers. The concept is a case study of applying simple accounting to data collected for a system of farming that has been rigorously monitored over a long period.
The whole farm budget calculated a positive balance for all nutrients. When developed and undeveloped parts of the average farm were separated there were small negative balances in K in the undeveloped tussock grassland, and in P in all but the more recent years in developed more heavily stocked grassland.
The budgets have highlighted the need to better understand the role of weathering of high country soil parent material on the release of P and K in particular.
The results of this study indicate a need for rethinking on the use of long-term averages in determining the timing of nutrient losses since European settlement. The data presented show that over the past 30 years there appears to have been, on average, at least a cessation and even some redress of nutrient losses from the system. This does not refute earlier calculations of losses, but indicates that losses were greater earlier in the 150-year period than are indicated by the long-term averages.
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Thanks to the New Zealand Journal of Agricultural Research for enabling the reproduction of this paper on our site. Your feedback or comments about any of the material on this, or related, pages is welcomed. Please feel free to contact Colin Boswell colin.boswell@agresearch.co.nz;
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