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Nitrogen Workshop 2012
Integration of measures in pastoral dairy systems to mitigate reactive nitrogen loss to the environment de Klein, C.A.M., Monaghan, R.M., van der Weerden, T.J., Chrystal J.
AgResearch Ltd, Invermay Agricultural Centre, Private Bag 50034, Mosgiel 9053, New Zealand
1. Background and objectives There are ongoing concerns about the impact of dairying on reactive nitrogen (N) losses to the environment. Although dairy systems have become more N efficient, the rate of productivity gains has typically been faster than the rate of efficiency gains (reduced N losses per unit of product), and thus total N losses to the environment have increased. The need for integrated N efficiency solutions for dairy systems to meet the challenge of increasing global production of animal-based protein while reducing N losses to the environment has never been greater. The objectives of this paper are to provide an overview of current N efficiency and mitigation measures for pastoral dairy farm systems and to assess the impact of integrating a range of these measures on reactive N loss to the environment and on farm profitability. We also provide an assessment of the impact of tactical decision making to exploit spatial and temporal variability on nitrous oxide (N2O) losses.
2. Current N efficiency & Mitigation measures The best way of achieving the dual and generally conflicting goals of increased productivity and reducing N losses to the environment is to ensure we achieve ‘more for less’, i.e. more milk per animal or per unit of dry matter (DM) intake; or more DM per unit of N input. In addition, reactive N losses to the environment can be further reduced through the adoption of measures that minimise the N loss risk. Table 1 provides an overview of some key options.
Table 1. Summary of the key ‘efficiency’ or ‘reduced N loss risk’ measures for pastoral dairy systems (e.
g. Beukes et al., 2011; Clark et al, 2011; de Klein and Monaghan, 2011; Velthof et al., 2009).
3. Integrating N efficiency and mitigation measures We assessed the impact of integrating key strategic N efficiency measures for a New Zealand dairy farm system (Table 2). This assessment used the farm systems model Farmax Dairy (Bryant et al., The “Better feeding” option was designed to get animals in better condition before spring calving by feeding them an extra 2 kg DM/day, calving 2 week later to provide reliable spring pasture growth and introducing annual ryegrass swards to boost production later in the season. These measures collectively helped to decrease N fertiliser requirements by more than half. The “restricted grazing” option uses a housing system to remove animals from pasture for 6 hours per day during autumn and wet spring periods. It is also used for over-wintering animals using pasture silage as the main feed source, thus avoiding the need for a winter brassica crop. Modelling indicates that milk production increased by 10% in both systems, and profit by an average 13%. The reduction in N leaching losses per ha was largest in the ‘restricted grazing’ option, but N2O emissions per hectare increased under this option. This was largely a result of increased DM intake resulting in higher urine N excretion rates, in combination with increased losses from the housing and effluent management. However, N losses per unit of milk were all reduced compared to the Base farm.
Beukes et al. (2011) also assessed the impact of integrating N efficiency and mitigation measures on greenhouse gas emissions from New Zealand dairy systems. Although this study did not document N2O emission or N leaching results, it did show differences in N excretion rates, which are a good indicator of differences in N2O emissions and N leaching. Their analysis showed that reducing N fertiliser inputs from 180 to 50 kg N ha-1 yr-1 while using a nitrification inhibitor to increase pasture
Nitrogen Workshop 2012
growth by 2%, reduced urinary N excretion by about 20%. Improving cow reproductive performance or genetic merit, or taking the cows off-pasture for 12 hours/day for 2 months in autumn, reduced urinary N deposition to pasture by about 5%. When all these measures were integrated within one farm system, N excretion rates reduced by c. 30% while milk production per ha increased by 15-20% (Beukes et al., 2011).
4. Exploiting spatial and temporal variability Nitrogen use efficiency (NUE) and N losses can be highly variable, both in space and time, due to variability in soil and climatic drivers of NUE and N loss risk. This variability could be exploited by tactical management options to further increase NUE (‘more for less’) or the effectiveness of mitigation options such as nitrification inhibitors (‘reduced N loss risk’). For example, Shepherd et al. (2011) showed that 40-50% of urine deposited in late summer/early autumn (i.e. well before the start of the drainage season) could be lost through leaching. Therefore, targeting N mitigations early could substantially reduce the risk of N leaching, particularly in summer dry areas where pasture growth rates, and thus N uptake, are limited.
We also conducted a preliminary assessment of the impact of a tactical management option to reduce N2O emissions. This was based on the premise that N2O emissions are low or negligible when soils are at or below field capacity (FC; van der Weerden et al., 2012) and the hypothesis that if urine N deposition can be delayed or diverted to dry areas, N2O emissions can be significantly reduced (Figure 1).
% reduction in direct and indirect
Figure 1. The effect of avoiding urine N deposition on ‘wet’ soil ( field capacity) on direct and indirect N2O emissions, for three different urine N emission factors (EF3) for ‘wet’ conditions: 1.
5, 2 and 4% of urine N applied (e.g. Ball et al., 2012; de Klein et al., 2003; van der Weerden et al., 2011), with 1.5% being a conservative value, 2% a medium value and 4% assuming that grazing on wet conditions also causes soil compaction and damage through trampling. The assumed EF3 value for deposition on ‘dry’ soil (field capacity) was 0.5%.
We used a monthly soil water balance model (van der Weerden et al., 2011) to estimate the average number of days that New Zealand’s dairy pastoral soils were above field capacity. We then combined this with monthly dairy urine N excretion rates as used in the New Zealand GHG inventory calculation to provide N excretion rates on either ‘wet’ ( FC) or ‘dry’ soil ( FC). Using the three different urine N emission factors (EF3) for ‘wet’ conditions, we estimated that N2O emissions could be reduced by c. 4 to 7 % for every 10% reduction in urine N deposition on wet Nitrogen Workshop 2012 soils (Figure 1). This very preliminary assessment suggested that there is sufficient potential for exploiting spatial and temporal variability to reduce N2O emissions to warrant further refinement of the methodology and soil moisture-dependent EF3 values.
5. Discussion Modelling assessments suggest that integrating a range of strategic and tactical management and mitigation measures can reduce N losses to the environment, while maintaining or increasing milk productivity. However, experimental evidence is required to confirm the results as well as the practical feasibility of integrating these measures on farm. In addition, potential un-intended consequences need to be considered. For example, taking animals off pasture at high risk times to reduce reactive N losses requires a housing or feedpad system to enable the farmer to adopt this practice in New Zealand. The unintended consequence of this could be that farmers might use the opportunity to increase stock numbers by bringing in more supplements to maximise the return on investment. As a result, reactive N cycling in the system could be intensified and total N losses increased, although losses per unit of product are likely to be lower. Similarly, an unintended consequence of changing to animals with higher genetic merit could be that farmers retain the existing stocking rate, and thus might need to bring in more feed to maintain milk production.
Again, this could potentially increase the intensity of the N cycling and total losses, but is likely to reduce losses per unit of product. A major farmlet systems research programme is currently underway in four regions in New Zealand to assess the impact of region-specific dairy systems redesign (based on options listed in Table 1) on productivity, profit, environmental losses, practical feasibility and un-intended consequences.
References Ball, B.C., Cameron, K.C., Di, H.J. and Moore, S., 2012. Effects of trampling of a wet dairy pasture soil on soil porosity and on mitigation of nitrous oxide emissions by a nitrification inhibitor, dicyandiamide. Soil Use Management (in press).
Beukes, P.C., Gregorini, P. and Romera, A.J., 2011. Estimating greenhouse gas emissions from New Zealand dairy systems using a mechanistic whole farm model and inventory methodology. Animal Feed Science and Technology 166-167, 708-720.
Bryant, J.R., Ogle, G., Marshall, P.R., Glassey, C.B., Lancaster, J.A.S, Garcı´, S.C. and Holmes, C.W. 2010.
Description and evaluation of the Farmax Dairy Pro decision support model. New Zealand Journal of Agricultural Research 53, 13-28.
Clark, D.A., Beukes, P.C., Romera, A.J. and Chapman, D. 2011. Future farming systems. South Island Dairy Event – Challenging the future. 27-29 June 2011. Lincoln University, New Zealand pp 239-252 http://www.side.org.nz/IM_Custom/ContentStore/Assets/11/29/1675e220a3688373ef088d5eadc3c730/SIDE-Futurefarming-systems.pdf de Klein, C.A.M., Barton, L., Sherlock, R.R., Li, Z. and Littlejohn, R.P. 2003. Estimating a nitrous oxide emission factor for animal urine from some New Zealand pastoral soils. Australian Journal of Soil Research 41, 381-399.
de Klein, C.A.M. and Monaghan, R.M., 2011. The effect of farm and catchment management on nitrogen transformations and N2O losses from pastoral systems-can we offset the effects of future intensification? Current Opinion in Environmental Sustainability 3, 396-406.
Shepherd, M., Phillips, P. and Snow, V., 2011. The challenge of late summer urine patches in the Waikato region. In:
Currie, L.D.,Christensen, C.L. (Eds.), Adding to the knowledge base for the nutrient manager. Occasional Report No.
24. Fertilizer and Lime Research Centre, Massey University, Palmerston North, New Zealand.
Shepherd, M. and Wheeler, D., 2012. OVERSEER® nutrient budgets – the next generation. In: Advanced Nutrient Management: Gains from the Past - Goals for the Future. (Eds L.D. Currie and C.L. Christensen) http://flrc.massey.ac.nz/publications.html Occasional Report No. 25. Fertilizer and Lime Research Centre, Massey University, Palmerston North, New Zealand. 9 pages.
van der Weerden, T., Manderson, A., Kelliher, F., de Klein, C. and Harvey, M. 2011. Nitrous oxide spatial integration. Report for MAF Policy, Wellington. Pp. 66.
Velthof, G.L., Oudendag, D., Witzke, H.P., Asman, W.A.H., Klimont, Z. and Oenema, O. 2009. Integrated assessment of nitrogen losses from agriculture in EU-27 using MITERRA-EUROPE. Journal of Environmental Quality 38, 402-417.
Nitrogen Workshop 2012 Economic Cost of Nitrogen Management Oenema, O.a, Cóndor, R.D.b, Gyldenkaerne, S.c, Oenema, J.d a Wageningen University, Alterra, P.O. Box 47, NL-6700 AA Wageningen, NL.
b Istituto Superiore per la Protezione e la Ricerca Ambientale, ISPRA, Rome, Italy.
c National Environmental Research Institute, University of Aarhus, Denmark d Wageningen University, Plant Research International, Wageningen, NL
1. Background & Objectives Nitrogen (N) management is commonly defined as ‘a coherent set of activities related to the allocation and handling of N in agriculture to achieve agronomic and environmental/ecological objectives’ (e.g. Oenema and Pietrzak, 2002). Common agronomic objectives relate to crop yield, crop quality and animal performance, while environmental/ecological objectives commonly relate to minimizing N losses and to increasing N use efficiency (NUE). The objectives of N management are often region-, watershed-, site-, farm-, and/or field- specific.
Nitrogen management is evaluated successful when objectives are achieved. Economic costs and associated risks of N management measures are often seen as an obstacle and/or delay for implementing such measures in practice (Sheriff, 2005; Oenema et al., 2011a). Indeed, management measures require additional activities and possible changes in practices, which cost money. Thereby the competitiveness of the farms may decrease. In an open, globalized market, it is necessary to establish a level playing field; otherwise producers will remain reluctant to fully implement measures that put them at a comparative disadvantage. However, there is surprisingly little empirical information about the cost and benefits of improved N management. The objective of this paper is to review available literature, which relates to developed countries.
2. Economic cost of establishing N input-output balances at farm level Nitrogen input-output balances are key tools for monitoring the success of N management. There are various procedures for making N input-output balances, which may slightly differ in outcome, accuracy and in efforts needed to establish the input-output balance. Hence, it is important to use standardized formats for making N input-output balances, to allow comparisons between farms. Information from countries that have implemented farm N balances in practice (e.g. Denmark, The Netherlands) indicates that farmers learn easily to interpret such N balances.
They may also easily learn to compile these N balances. However, in many cases N balances are compiled by accountancy offices, which charge farmers on average 250-500 euro per farm per year for farm N & P balances (e.g. Jacobsen et al., 2005). In the Czech Republic, the estimated costs of farm N & P gate balances are in the higher end of this range, because of poor data availability.
3. Assessing economic cost of decreasing N surpluses and increasing NUE Estimating the economic costs of N management activities can be done at various scales.