Cattle slurry on grassland - application methods and nitrogen use efficiency

Cattle slurry represents a significant resource on grassland-based farming systems. The objective of this thesis was to investigate and devise cattle slurry application methods and strategies that can be implemented on grassland farms to improve the efficiency with which nitrogen (N) in cattle slurry is recycled. The research focused on slurry application method and timing techniques that have been shown to reduce ammonia emissions following slurry application. Further, it was investigated whether the reduction in ammonia emissions translates into an increase in the N fertiliser replacement value (NFRV) of applied slurry. The study also included an economic analysis of the costs and benefits of low-emission slurry application methods, including a sensitivity analysis of the impact of costs that are likely to vary between farms. A modelling study showed that low-emission application methods, which reduce herbage contamination and therefore permit slurry application into taller grass swards, increase the opportunity for application in spring when the slurry NFRV is relatively high due to the prevailing weather conditions that reduce ammonia volatilisation. The extent to which the opportunity for application in spring can be extended is affected by soil type, with more opportunity being afforded on more freely drained soil types. The extent to which herbage contamination is reduced by the low-emission application method was also affected by the grass height at application. Application methods that permit damage free traffic into taller swards permit greater potential to extend the opportunity for spring application. In multi-year and multi-site field experiments, the NFRV of cattle slurry applied to grassland was increased by application using trailing shoe in short grass swards compared with conventional broadcast application using splash-plate. The NFRV was also higher when slurry was applied in April compared with June. However, there was no advantage over splash-plate in using the trailing shoe application method in taller grass swards, as the damage to the sward by the machinery traffic negated the benefits of reduced ammonia volatilisation. An economic assessment showed that there was a net cost associated with adopting low-emission application methods on farms. The benefit of mineral N fertiliser savings due to ammonia emission abatement was not sufficient to offset the additional costs of adoption. The sensitivity analysis showed that the factors that had greatest impact on the costs were the assumed ammonia emission abatement potentials, the volume of slurry being applied annually with each machine, and the hourly work rate of the equipment. The capital costs of increased tractor power contributed significantly to the total capital costs of adoption of low-emission equipment. The results of this work were combined with literature data to devise updated NFRVs for slurry application to grassland in Ireland. The new advice includes differentiation of NFRVs based on application method, timing and residual N release. This represents a major step forward in advice to farmers for slurry application, and farmers have responded through improved management of application timing. The study shows that the combination of more application in spring and adopting low-emission application methods have a role to play in improving N efficiency from slurry in the future.</p

Growing grass for a green biorefinery - an option for Ireland?

Growing grass for a green biorefinery – an option for Ireland? Mind the gap: deciphering the gap between good intentions and healthy eating behaviour Halting biodiversity loss by 2020 – implications for agriculture A milk processing sector model for Irelan

Residual N effects from livestock manure inputs to soils

Organic inputs including livestock manures provide nitrogen (N) to crops beyond the year of their application. This so-called residual N effect should be taken into account when making decisions on N rates for individual fields, but also when interpreting N response trials in preparation of recommendations. This paper addresses general principles of residual N effects, gives literature-based estimates of them, and reviews to which extent residual N effects are included in recommendations and regulations in selected countries

Effect of application timing and grass height on the nitrogen fertilizer replacement value of cattle slurry applied with a trailing-shoe application system

This study investigated the effect of using a trailing-shoe system to apply cattle slurry, under different conditions of grass height (low [LG]: freshly cut sward [4–5 cm height] vs. high [HG]: application delayed by 7–19 d and applied to taller grass sward [4–11 cm] height) and month of application (June vs. April), on the nitrogen fertilizer replacement value (NFRV) and apparent N recovery (ANRS) of cattle slurry applied to grassland. NFRV was calculated using two methods: (i) NFRVN based on the apparent recovery of slurry-N relative to that of mineral-N fertilizer; and (ii) NFRVDM based on DM yield. The effect of applying slurry into HG swards, relative to LG swards, decreased the DM yield by 0·47 t ha-1 (P = 0·001), N uptake by 5 kg ha-1 (P = 0·05), ANRS by 0·05 kg kg-1 (P = 0·036), NFRVN by 0·05 kg kg-1 (P = 0·090) and NFRVDM by 0·11 kg kg-1 (P <0·001). It was concluded that the main factor causing these decreases with HG, compared with LG applications, was wheel damage affecting subsequent N uptake and growth of the taller grass sward

Green biorefinery (GBR) scenarios for a two-cut silage system: Investigating the impacts of sward botanical composition, N fertilisation rate and biomass availability on GBR profitability and price offered to farmers

In Ireland, grass is a readily available bioresource. It has previously been established that Green biorefinery (GBR) could become a potential use of Irish grasslands, and a blueprint for a sustainable GBR industry in Ireland has been developed. The objective of this paper is to use scenario analysis to investigate the sensitivity of the profitability of the GBR blueprint to variations in grass quantity and quality as a function of botanical composition, fertiliser application, and biomass availability. As an outcome of these scenario analyses, the price the GBR can offer to farmers above their production costs (€ t-1 dry matter) was calculated. Results of the scenario analyses determined that GBR systems located in a catchment area of permanent pasture (Lolium perenne > 60%) with annual grass yields in the range of 9–12 t dry matter (DM) ha-1, and supplied with grass biomass with a fibre content of 500–555 g kg-1 DM and a protein content of 110–130 g kg-1 DM, were viable. The most profitable scenarios were generated when nitrogen fertiliser application was greater than 90 kg ha-1 a-1. Biomass availability of less than 30% resulted in reduced profitability and for some scenarios resulted in a loss for both the GBR and farmer due to increased transport costs. Within the scenario assumptions of this study, grass feedstock was valued at €4–€56 t-1 dry matter above production costs. However, this value depended on the yields and biomass availability of the GBR catchment area

Nitrogen fertilizer replacement value of cattle slurry in grassland as affected by method and timing of application

Slurry application with methods such as trailing shoe (TS) results in reduced emissions of ammonia (NH3) compared with broadcast application using splashplate (SP). Timing the application during cool and wet weather conditions also contributes to low NH3 emissions. From this perspective, we investigated whether reduced NH3 emissions due to improved slurry application method and timing results in an increase in the nitrogen (N) fertilizer replacement value (NFRV). The effects of application timing (June vs. April) and application method (TS vs. SP) on the apparent N recovery (ANR) and NFRV from cattle slurry applied to grassland were examined on three sites over 3 yr in randomized block experiments. The NFRV was calculated using two methods: (i) NFRVN based on the ANR of slurry N relative to mineral N fertilizer; and (ii) NFRVDM based on DM yield. The TS method increased the ANR, NFRVN, and NFRVDM compared with SP in the 40- to 50-d period following slurry application by 0.09, 0.10, and 0.10 kg kg(-1), respectively. These values were reduced to 0.07, 0.06, and 0.05 kg kg(-1), respectively, when residual harvests during the rest of the year were included. The highest NFRVDM for the first harvest period was with application in April using TS (0.30 kg kg(-1)), while application in June with SP had the lowest (0.12 kg kg(-1)). The highest NFRVDM for the cumulative harvest period was with application in April using TS (0.38 kg kg(-1)), while application in June with SP had the lowest (0.17 kg kg(-1)). Improved management of application method, by using TS instead of SP, and timing, by applying slurry in April rather than June, off er potential to increase the NFRVDM of cattle slurry applied to grassland