Research and Development / 30/06/1999
Final Project Report
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Section 1 : Identification sheet
1. / (a) / MAFF Project Code / NT1528
(b) / Project Title / MINERALISATION OF ORGANIC NITROGEN FROM FARM MANURE APPLICATIONS
(c) / MAFF Project Officer / Dr. P.A. Costigan
(d) / Name and address
of contractor / ADAS Gleadthorpe Research Centre
Meden Vale
Mansfield
Notts.PostcodeNG20 9PF
(e) / Contractor’s Project Officer
(f) / Project start date / 01/04/1998 / Project end date / 30/06/1999
(g) / Final year costs: / approved expenditure
actual expenditure
Project end date
(h) / Total project costs / total staff input: / approved project expenditure
actual project expenditure
Project end date
*approved staff input
*actual staff input
(i) / Date report sent to MAFF
(j) / Is there any Intellectual Property arising from this project (enter YES or NO)? / NO
*staff years of direct science effort
Section 2 : Scientific objectives / Milestones
2. / Please list the scientific objectives as set out in CSG 7 (ROAME B). If necessary these can be expressed in an abbreviated form. Indicate where amendments have been agreed with the MAFF Project Officer, giving the date of amendment. You may enter a maximum of 12 lines in this box. Press the DOWN arrow twice to move to the next question.
CSG 13 (1/97)1
Overall objective- To fully quantify N mineralisation from the organic fraction of farm manures following land application
- To quantify N mineralisation from selected farm manures in field studies at three sites with contrasting soil properties and climatic conditions
- To relate field N mineralisation rates to the manure organic N fractions determined by laboratory chemical extraction and the pot incubation studies undertaken in MAFF project NT1501 - “Fate of Nitrogen from Organic Manures”
- To evaluate the ability of existing manure N models (e.g. NCYCLE, MANNER) to quantify manure organic N mineralisation
CSG 13 (1/97)1
3. / List the primary milestones for the final year.It is the responsibility of the contractor to check fully that ALL primary milestones have been met and to provide a detailed explanation if this has not proved possible
Milestones / Target
date / Milestones met?
(enter YES or NO)
Number / Title / in full / on time
If any milestones have not been met in the final year,
an explanation should be included in Section 5.
Section 3 : Declaration
4. / I declare that the information I have given in this report is correct to the best of my knowledge and belief. I understand that the information contained in this form may be held on a computer system.
Signature / Date
Name
Position in Organistation
You should now complete Sections 4 and 5 of this report
CSG 13 (1/97)1
Section 4 : Executive summaryYou may enter a maximum of 58 lines of text in this box. Press the DOWN arrow twice to move on.
CSG 13 (1/97)1
The overall objective of the project was to fully quantify nitrogen (N) mineralisation from the organic fraction of farm manures so that the long-term effects of manure application on soil N supply could be predicted.The mineralisation of manure organic N was measured from April 1998 to March 1999 following earlier measurements over a c. 22 month period (May/June 1996 to March 1998) at 3 field experimental sites with contrasting soil types and climatic conditions (ADAS Gleadthorpe, IGER North Wyke and ADAS Rosemaund). At each site, 9 ammonium-N ‘stripped’ manures (2 cattle slurries, 2 cattle FYMs, 2 pig FYMs, a pig slurry, layer manure and broiler litter) were applied in summer 1996 (3 replicates of each manure type in a randomised block design). The experiments were sown with perennial ryegrass (Lolium perenne) which was cut periodically to quantify plant N uptake and porous ceramic cups installed to measure nitrate leaching losses. Net N mineralisation was calculated by subtracting the sum of plant N uptake and nitrate leaching loss measurements on the individual manure treatments from the untreated control. Soil temperatures were measured continually at each site (10 cm depth) and manure organic N decay curves calculated using cumulative day degrees above 5C (CDD).
The field study results showed that manure organic N mineralisation rates varied with manure type and were in broad agreement with those from the laboratory incubation studies undertaken as part of MAFF project NT1501- ‘Fate of Manure Organic N’. The incubation studies showed that the amount of N mineralised was inversely proportional to the C:organic N ratio of the applied manures, with the largest amounts of N mineralised from the layer manure and pig slurry treatments, and least from the cattle slurry and cattle/pig FYM treatments.
There was a good relationship (P<0.01, r2 = 77%) between the mineralisation measurements made at ADAS Gleadthorpe and IGER North Wyke in the c. 13 month period following application. The greatest amounts of organic N mineralisation occurred following the pig slurry (52% and 67% at Gleadthorpe and North Wyke, respectively) and layer manure (36% Gleadthorpe and 60% North Wyke) applications, and lower amounts following the cattle slurry (mean 18% at Gleadthorpe and 20% at North Wyke) and FYM (mean 10% at Gleadthorpe and 29% at North Wyke) additions. There were good relationships between the amount of manure organic N mineralised and thermal time (cumulative day degrees above 5C) for 8 out of 9 manure types at ADAS Gleadthorpe (P<0.05, r2>70%) and all manures at IGER North Wyke (P<0.01, r2>80%). At North Wyke, mineralisation ceased c. 13 months after the manures were applied. At Gleadthorpe, movement of the experimental topsoils (akin to a topsoil cultivation) in July 1997, c.13 months after the initial manure applications, stimulated further mineralisation with a mean of 7% (range 2-17%) of the applied organic N mineralising between July 1997 and July 1998.
Utilising the manure organic N decay curves to evaluate the impact of manure application timing on crop N availability and leaching losses, showed that delaying manure applications from September to November/ February had little effect on the amount of N taken up by winter cereal crops, although the timecourse of N leaching was delayed. Comparison of the field mineralisation measurements with published model predictions, showed that the models tested were not sufficiently developed to accurately quantify manure organic N mineralisation.
The study has provided a much improved understanding of manure organic N mineralisation and has derived organic N decay curves based on thermal time, enabling the contribution of mineralised organic N to nitrate leaching and crop N supply to be estimated for different manure application timings. This information will be of great value in the development of mineralisation models and fertiliser recommendation systems (e.g. MANNER,
NCYCLE), better enabling farmers and their advisers to take account of mineralised organic N in their inorganic
fertiliser N policies. The information will help MAFF to fulfil its policy objectives of reducing nitrate pollution
from agriculture and improving nutrient utilisation from livestock manures as part of sustainable farming systems.
CSG 13 (1/97)1
Section 5 : Scientific reportCSG 13 (1/97)1
ROAME B: SCIENTIFIC OBJECTIVES AND PRIMARY MILESTONES TO BE ADDRESSEDObjective
- To fully quantify nitrogen (N) mineralisation from the organic fraction of farm manures following land application.
Data from the field experiments undertaken in this project have shown that manure type and soil temperature are important factors controlling the mineralisation of manure organic nitrogen, and have enabled the contribution of mineralised organic N to nitrate leaching and crop N supply to be predicted. The field measurements of manure organic N mineralisation were compared with model predictions and generally there was poor agreement. The findings of this work will assist MAFF in achieving its policy objectives of reducing nitrate losses from agriculture and improving manure nitrogen utilisation as part of sustainable farming systems.
II BACKGROUND
In the UK, applications of farm manures to agricultural land supply c. 450,000 tonnes of total nitrogen per annum, of which c. 300,000 tonnes are estimated to be present as organic N and c. 150,000 tonnes as readily available N (principally ammonium and uric acid-N). Typically, 75-90% of the total N content of straw-based farmyard manures (FYM) is present as organic N, 50-60% for poultry manures and 40-50% for slurries (MAFF, 1994).
Research in the UK has largely focused on manure readily available N forms because in the short-term these have the greatest influence on crop N supply, ammonia volatilisation and nitrate leaching losses (Jarvis and Pain, 1990; Unwin et al., 1991; Chambers et al., 1997). However, in the longer-term manure organic N mineralisation will have an increasingly important effect on soil N supply, particularly in situations where repeated manure applications are made to land. If mineralisation of the organic N occurs during periods of crop growth (spring-summer) fertiliser N requirements will be reduced, but if mineralisation occurs during the autumn-winter period, nitrate leaching and denitrification losses are likely to be increased.
Quantifying N mineralisation from the organic fraction of farm manures is complicated by the presence of several N forms which differ between manure types, namely: (i) mineral N (principally ammonium-N), (ii) readily mineralisable N (uric acid and urea) and (iii) more slowly mineralised organic compounds. Previous studies have not accounted for these different N fractions when assessing manure organic N mineralisation.
Previous work carried out under MAFF project NT1501 - ‘Fate of Manure Organic Nitrogen’ (Chambers et al. 1998) characterised the N fractions present in fifty contrasting manure types (20 slurries, 20 farmyard manures and 10 poultry manures). The work showed that the organic N content of the different manure types varied considerably, with cattle slurry and FYM typically containing 29% and 71% of their total N content in organic forms, pig slurry and FYM 35% and 71%, and broiler litter and layer manure 71% and 54%, respectively. The work also identified differences in the C:organic N ratio of the contrasting manure types, with cattle FYM typically having the highest ratio at 17:1, followed by cattle slurry and pig FYM at 14:1, pig slurry at 11:1, broiler litter at 9:1 and layer manure at 6:1. Generally, organic materials with low C:N ratios breakdown (mineralise) more rapidly, than those with higher C:N ratios (Aleef and Nannipieri, 1995; Floate, 1970; Serna and Pomares, 1991). Thus, organic N mineralisation is likely to vary according to manure type and C:organic N ratio.
This report describes the results of field experimental measurements undertaken to quantify manure organic N mineralisation between April 1998 and March 1999, and compares the data with laboratory incubation results from the earlier NT1501 project.
III SCIENTIFIC PROGRESS
1. Laboratory Incubation Study
1.1. Ammonium-N ‘stripping’
In order to quantify mineralisation from the organic N content of farm manures it was necessary to remove the mineral N content (principally ammonium-N) before the mineralisation measurements were carried out. The following methodologies were developed for ‘stripping’ the ammonium-N content of the solid and liquid manures used in the laboratory incubation studies. The procedures were undertaken as quickly as practically possible, to minimise organic N mineralisation during the ‘stripping’ process. The procedures reduced the ammonium-N content of cattle manures to less than 1% of the total N content, pig manures to less than 2 % and poultry manures to less than 3%, respectively.
(i) Farmyard manures
10 kg of farmyard manure was spread to a maximum thickness of between 4 and 10 cm depending on the dry matter content. To speed drying and to enhance ammonia volatilisation losses, the manures were turned by hand every three days. After three weeks, the dried material was cut into “chunks” no bigger than 3 cm3 to increase the surface area and further speed drying and ammonia loss. The manure was left for a further week, before being re-wetted using a watering can. The wetting and turning was repeated weekly until laboratory analysis showed that the ammonium-N content was reduced to less than 5% of the total N. The process took 8 weeks with ambient temperatures of 16C (five wetting and drying cycles).
(ii) Poultry manures
The procedure used for the poultry manures was similar to that for the farmyard manures, although rewetting started after one week of drying because of the higher initial dry matter content of the poultry manures. After rewetting, the manures were dried in an oven for between 2 and 3 hours at 35C to speed drying. The temperature was kept below 40C to ensure that proteins and other organic nitrogen compounds were not denatured. The wetting and drying cycles were repeated seven times.
(iii) Slurries
For the higher dry matter slurries (>4%), approximately 400 ml of slurry was dried at 40C for 4 days. To complete the ammonium-N ‘stripping’, the partially dried slurry was cut into 10 cm³ chunks and dried for a further 3 days.
For the lower dry matter slurries (<4%), equal volumes of slurry and deionised water were mixed together and shaken for 1 hour. The mixture was centrifuged at 13 000 rpm for 10 minutes. The supernatant, which contained most of the ammonium-N was discarded, and the remaining solid material recovered. The process was repeated several times with each slurry to provide sufficient quantities of manure organic matter. The drying procedures used for the higher dry matter slurries above were then followed.
1.2. Methodology
Organic N mineralisation from seventeen ammonium-N ‘stripped’ manures (3 cattle FYM, 4 pig FYM, 3 cattle slurries, 3 pig slurries and 4 poultry manures) was measured in a controlled environment. The manures, which had contrasting C:organic N ratios (Table 1), were each mixed with 5 kg of a low mineral N status loamy sand textured soil from ADAS Gleadthorpe in pots 16.5 cm x 16.5 cm x 20 cm deep. Target total N applications for each treatment were 200 kg/ha N.
The pots were sown with perennial ryegrass (Lolium perenne) and kept under uniform conditions of light (16 hours photo-period), temperature (18C days and 12C nights) and moisture status (60% of moisture holding capacity) for six months in a controlled environment room. Additional P, K, S and other micronutrients were applied to the pots in solution to ensure that grass growth was not limited by an inadequate supply of major nutrients, other than nitrogen.
Ryegrass N uptakes were used to quantify manure organic N mineralisation and were corrected for the small quantities of mineral N initially present in the manures. The first harvest was 30 days after sowing with subsequent harvests made 44, 65, 118, 155 and 199 days after sowing. At each harvest, the grass was cut to a height of 2 cm and the cut grass analysed for total N and dry matter content.
1.3. Results
There were differences in the amounts of organic N mineralised (i.e. treatment N offtakes subtracted from the untreated control, and expressed as a percentage of the organic N applied) between the manure treatments, with the greatest amounts mineralising on layer manure (56% of organic N) and pig slurry (37% of organic N) treatments, and least on cattle slurry (2% of organic N) and beef FYM (6% of organic N) treatments (Figure 1). The amount of organic N mineralised was inversely related to the C:organic N ratio of the ‘stripped’ manures (P <0.01, r2=40%), Figure 2 (Chadwick et al., in press).
Table 1. Organic N, organic C and C:organic N ratios of the ‘stripped’ manures used in the laboratory incubation study.
Manure / Organic N(%DM) / Organic C
(%DM) / C:organic N
ratio
Dairy slurry 1 / 2.29 / 35.1 / 15.3
Dairy slurry 2 / 3.59 / 35.5 / 9.9
Dairy FYM 1 / 2.85 / 35.0 / 12.3
Beef slurry 1 / 2.56 / 38.4 / 15.0
Beef FYM 1 / 2.66 / 34.0 / 12.8
Beef FYM 2 / 2.35 / 34.5 / 14.7
Pig slurry 1 / 4.26 / 38.3 / 9.0
Pig slurry 2 / 3.71 / 28.8 / 7.8
Pig slurry 3 / 2.86 / 37.0 / 12.9
Pig FYM 1 / 3.43 / 34.8 / 10.1
Pig FYM 2 / 2.35 / 25.6 / 10.9
Pig FYM 3 / 3.40 / 33.6 / 9.9
Pig FYM 4 / 2.38 / 34.1 / 14.3
Broiler litter 1 / 5.09 / 40.0 / 7.8
Broiler litter 2 / 3.85 / 35.9 / 9.3
Broiler litter 3 / 3.55 / 25.5 / 7.2
Layer manure / 3.17 / 25.4 / 8.0
2. Field experiments
In spring 1996, nine manures (two cattle slurries, a pig slurry, two cattle FYM’s, 2 pig FYM’s, a broiler litter and a layer manure) were collected from commercial farms across England and Wales and delivered to ADAS Gleadthorpe. Between 5 and 15 tonnes of solid manure and 25m3 of slurry were collected. The manures were selected to provide contrasting carbon:organic N ratios.
2.1 Ammonium-N ‘stripping’
The manures were ‘stripped’ of their ammonium-N content by cycles of wetting and drying over a period of 8 weeks. The solid manures were spread on plastic sheets to depths of between 5 and 15 cm. After initial drying, the manures were re-wetted and turned periodically to encourage ammonia volatilisation. The slurries were held in lagoons constructed using straw bales and a butyl liner. The slurries were allowed to settle and the supernatant removed by pumping until only c. 50 cm of semi-solid manure remained. The dry matter of the supernatant was tested to ensure that solid manure organic matter was not being lost; in all cases the dry matter of the discarded liquid was < 1%. The semi-solid material was then spread out onto plastic sheets and treated in the same manner as the solid manures to encourage ammonia losses. The procedures were undertaken as quickly as practically possible to minimise organic N mineralisation during the ‘stripping’ process. The ‘stripping’ techniques were effective at reducing the readily available N content (mineral N plus uric acid N) of the cattle, pig and poultry manures to < 5%, <10% and < 10% of the manure total N content, respectively.
2.2 Methodology
In May/June 1996, batches of each ammonium-N ‘stripped’ manure were transported from ADAS Gleadthorpe to ADAS Rosemaund and IGER North Wyke (Table 2). Field experiments with an untreated control (no N applied), five inorganic fertiliser N treatments (range 30-150 kg/ha) and nine ‘stripped’ manure treatments (Table 3) were established at each site.
Table 2. Soil type, cropping and average annual rainfall
Site / Topsoil texture / Average annual rainfall (mm) / Topsoil total N (%) / Topsoil organic matter (%) / TopsoilC: N ratio
ADAS Gleadthorpe / Loamy sand / 650 / 0.04 / 1.7 / 25:1
ADAS Rosemaund / Silty clay loam / 800 / 0.20 / 2.9 / 8:1
IGER North Wyke / Sandy loam / 1000 / 0.08 / 1.8 / 13:1
Table 3. Total N loadings and C: organic N ratios of the manures applied at each field site