Biosolids were applied with urea to produce a granulated organo-mineral fertiliser (OMF) for application by farm fertiliser equipment to a range of agricultural crops. The recommended rates of nitrogen, phosphate and potash were calculated for the test crops using “The Fertiliser Manual”, which assesses the nutrient requirement based on previous cropping, rainfall and soil index. The OMF produced similar crop yields compared to ammonium nitrate fertiliser when applied as a top-dressing to winter wheat, forage maize and grass cut for silage in the cropping years 2010 to 2014. In 2012 the grain yield of spring barley top-dressed with OMF was significantly lower than the conventional fertiliser treatment, due to dry conditions following application. For this reason it is recommended that OMF is incorporated into the seedbed for spring sown crops and The Safe Sludge Matrix guidelines followed. The experimental work presented shows that OMF can be used in sustainable crop production systems as a source of nitrogen and phosphorus for a range of agricultural crops.
Biosolids is the term for sewage sludge that has been treated to reduce the level of pathogens. The production of biosolids is approximately 2 million tonnes per annum in the UK and 10 million tonnes per annum in the EU expressed on a dry solids basis. These levels are increasing due to population growth and also because more households are being connected to sewage systems in the EU. Current disposal methods include anaerobic digestion, incineration and application to land. In the UK the application of biosolids to agricultural land is seen as the “Best Practicable Environmental Option” in most circumstances [
The main concerns with adding biosolids to agricultural land have been the impact of pathogens on the food chain and heavy metals on the soil [
The application of biosolids to agricultural crops, such as winter wheat and grass cut for silage, has given significant yield responses [
This research has developed an organo-mineral fertiliser (OMF) created by adding urea to treated biosolids for use on a range of agricultural crops. Previous research reported that initial experiments comparing OMF with ammonium nitrate fertilisers gave similar crop responses [
The crop experiments were carried out on a mixed farm in Broxton, Cheshire (Grid ref: SJ 4770054400) by the Crop and Environment Research Centre, Harper Adams University (HAU). The site consists of slowly permeable clay loam soil which is seasonally waterlogged and the annual rainfall is approximately 1250 - 1500 mm. A detailed description of the site and experiment is given by [
The experimental site consisted of a 5 ha silage grass field (perennial rye grass), with a centralised 1.6 ha arable block. This block was split into four blocks of 12 plots (48 plots in total), allowing for up to four different arable crops to be grown in one season (
The experimental design consisted of two fertiliser treatments applied as a topdressing;
・ Conventional fertiliser (Ammonium Nitrate, Triple Super Phosphate (TSP) and Muriate of Potash (MOP) for all cereals and silage grass and a 19:40:0 NPK fertiliser for forage maize).
・ OMF (Thermally dried biosolids, Urea and MOP).
Ammonium nitrate was applied as the conventional treatment in 2010-2011 because soil analysis results indicated that there were sufficient phosphate and potash in the soil for crops to reach their potential yield. However, in the following three years ammonium nitrate, TSP and MOP were applied to provide the quantities of nutrients based on the recommendation obtained using The Fertiliser Manual [
All arable crops were harvested using a Wintersteiger Nursery Master combine, the silage grass using a Haldrup grass harvester and the forage maize using a front mounted Champion 1200 forage harvester. The tramlines, running in an east to west direction, were harvested first, allowing the plots to be harvested in a north to south direction. Plot lengths were measured at the time of harvest, allowing for a yield per hectare to be calculated. Moisture content of the cereals and OSR were analysed using a Sinar moisture meter. Maize and grass silage were dried in an oven at 60˚C for 24 hours to obtain their dry matter content.
Statistical analysis was performed using Genstat 16th edition. All data sets were analysed using One-way ANOVA to test for statistical significance at 95% confidence.
The winter wheat grain yields for OMF and conventional fertiliser treatments of 7.0 and 7.3 t for ha−1 respectively for the 2010-2011 cropping season and 6.12 and 6.59 t∙ha−1 respectively for 2011-2012 were not significantly different (
The spring barley grain yield of 4.5 t∙ha−1 for the conventional fertiliser treatment was significantly higher than that of 3.6 t∙ha−1 for the OMF treatment in 2012 (
The forage maize grown in 2010-2011 and 2012-2013 produced crop yields ranging from 11.3 to 11.97 t∙ha−1 (
The grass sward was sown in 2008 with a perennial ryegrass mixture and had been cut for silage in 2009 and 2010. A total grass fresh yield of 45 t∙ha−1 is typical in a three cut silage system [
Year | Crop | Sowing date | 1st application | 2nd application | 3rd application | Harvest date | Treatment | Mean yield (t/ha) | Standard error means | Significance | d.f. |
---|---|---|---|---|---|---|---|---|---|---|---|
2010-2011 | Winter wheat | 04.10.10 | 06.04.11 | 10.05.11 | - | 03.09.11 | Conventional | 7.3 | 0.7714 | 0.427 | 11 |
OMF | 7 | 0.3115 | |||||||||
2011-2012 | Winter wheat | 08.10.11 | 28.03.12 | 05.04.12 | 24.05.12 | 07.09.12 | Conventional | 6.12 | 0.258 | 0.114 | 23 |
OMF | 6.59 | 0.317 | |||||||||
2012-2013 | Spring barley | 06.04.13 | 24.04.13 | 18.06.13 | - | 03.09.13 | Conventional | 4.5 | 0.276 | 0.002 | 23 |
OMF | 3.6 | 0.215 | |||||||||
2013-2014 | Spring barley | 01.04.14 | 02.04.14 | - | - | 04.09.14 | Conventional | 2.98 | 0.197 | 0.13 | 11 |
OMF | 2.67 | 0.235 | |||||||||
2011 | Forage maize | 05.05.11 | 05.05.11 | 27.07.11 | - | 20.10.11 | Conventional | 11.94 | 0.245 | 0.261 | 55 |
OMF | 11.54 | 0.275 | |||||||||
2013 | Forage maize | 23.05.13 | 27.05.13 | 23.06.13 | - | 30.10.13 | Conventional | 11.97 | 0.662 | 0.332 | 10 |
OMF | 11.33 | 0.409 |
Year | Crop | Treatment | Sowing data | Cut number | Fertiliser application date | Harvest date | Mean dry yield (t/ha) | S.E.M. | Significance | d.f. |
---|---|---|---|---|---|---|---|---|---|---|
2011 | Silage grass | Conventional | 2008 | 1st | 06.04.11 | 10.05.11 | 4.7 | 0.199 | 0.729 | 5 |
OMF | 4.9 | 0.229 | ||||||||
2011 | Silage grass | Conventional | 2008 | 2nd | 11.05.11 | 13.07.11 | 3.1 | 0.193 | 0.025 | 5 |
OMF | 4.7 | 0.051 | ||||||||
2011 | Silage grass | Conventional | 2008 | 3rd | 06.08.11 | 14.10.11 | 0.1 | 0.016 | 0.255 | 5 |
0.1 | 0.005 | |||||||||
2012 | Silage grass | Conventional | 2008 | 1st | 28.03.12 | 13.06.12 | 8.0 | 0.104 | 0.875 | 5 |
OMF | 8.2 | 0.707 | ||||||||
2012 | Silage grass | Conventional | 2008 | 2nd | 05.07.12 | 14.08.12 | 1.8 | 0.088 | 0.499 | 5 |
OMF | 2.0 | 0.282 | ||||||||
2012 | Silage grass | Conventional | 2008 | 3rd | 30.08.12 | 09.10.12 | 1.1 | 0.057 | 0.74 | 5 |
1.2 | 0.156 | |||||||||
2013 | Silage grass | Conventional | 2008 | 1st | 25.04.13 | 10.06.13 | 8.1 | 0.552 | 0.181 | 5 |
OMF | 6.8 | 1.072 | ||||||||
2013 | Silage grass | Conventional | 2008 | 2nd | 26.06.13 | 01.08.13 | 5.1 | 0.297 | 0.147 | 5 |
OMF | 3.8 | 0.423 | ||||||||
2013 | Silage grass | Conventional | 2008 | 3rd | 09.08.13 | 20.09.13 | 2.0 | 0.034 | 0.998 | 5 |
2.0 | 0.195 |
The concept of this research was to develop a new fertiliser material based on the addition of urea to biosolids
that could be used in sustainable crop production systems. The resultant mixture was dried and granulated to produce particles in the size range of 2 - 5 mm which were capable of being spread accurately with farm fertiliser application equipment. This would utilise the nitrogen and phosphorus from human waste as a valuable plant nutrient rather than continuing to utilise phosphate minerals which are a finite resource of our planet. The results presented are a continuation of the initial experiments reported by where OMF was applied to arable crops [
Overall the results presented demonstrate that OMF gave comparable crop yields to ammonium nitrate fertiliser when applied as a top-dressing to winter wheat and forage maize.
This indicates that the organic nitrogen applied in the biosolids is released for uptake by the growing crop and in combination with the inorganic nitrogen applied as urea is sufficient to provide the requirements of the growing crop. It was also interesting to find that the grain size of the winter wheat measured by the weight of a thousand grains (TGW) or plumpness of the grain (SW) was not influenced by the addition of OMF. Grain size is an important quality indicator of winter wheat, especially for the variety Solstice which is a milling or bread making variety. Currently, the use of OMF for the production of bread making wheat is not be approved by milling organisations in the UK, but further data to support their potential as a suitable fertiliser would be needed prior to them being considered appropriate.
The NPK analysis of 3:4:0 or 3:8:0 make OMF particularly attractive for the basal dressing for forage maize as a replacement for mono ammonium phosphate (11:52:0) or diammonium phosphate (18:45:0) fertiliser. In these experiments OMF applied as a surface topdressing gave similar yields to the conventional fertiliser (19:40:0) fertiliser treatment. The application of OMF incorporated into the seedbed or preferably placed close to the seed would be a better option in commercial farming systems.
Spring barley was the one arable crop where the conventional fertiliser treatment produced a higher yield in 2012-2013 compared with that of the OMF. In 2013 there was no rain for the month following topdressing with the OMF making it very unlikely that the nutrients applied became available to the crop. In the more typical growing conditions experienced in 2013-14, with rainfall following application of the OMF, there was no significant difference in grain yield between the two fertiliser treatments. From these findings it is recommended that OMF should be incorporated into the seedbed for spring sown crops to ensure that the nutrients in the biosolids are in contact with moisture and become available to the growing crop.
The three cut grass silage system produced its highest yield under both treatments at the first cut and the lowest at the third cut, as expected. Only one cut showed a significant difference, the second cut of 2010-2011, with OMF producing the higher grass matter yield (
The disposal of biosolids to land is considered the Best Environmentally Practical Option, but their potential to produce crops needs to be understood in order for them to be used effectively. The data presented here indicates that OMF can produce similar yields to conventional fertilisers, but their nutrient release may be influenced by environmental and meteorological factors. For this reason, it is recommended that OMF is incorporated into the seedbed of spring crops (such as spring barley or forage maize) to ensure that nutrient release is optimised. The effects of biosolids on crop quality need to be studied in order to assess what end markets OMF may be appropriate for and the products need to be applied in accordance with The Safe Sludge Matrix [
This research was funded by the European Union Seventh Framework Programme (FP7-ENV.2010.3.1.1-2 ENV) under grant agreement No. 265269. The authors would like to thank the farmers who allowed the experiments to be conducted on their land.