Sewage products add to N benefits
DIGESTED sewage products are best used to augment bag nitrogen rather than replace it.
That is the main finding of two years of field trials with cake and granular products on Southern Waters demonstration farm north of Horsham, West Sussex.
The 1999 results confirm findings from the first year, showing that even when the bag nitrogen dressing for winter wheat on Weald clay is as high as 240kg/ha (192 units/acre), an extra 40kg/ha (32 units/acre) in organic form still improves yield and quality, without raising lodging risk.
One field of Abbott first wheat yielded 2.7t/ha (1.1t/acre) extra, with better quality, after receiving 7t/ha (2.8t/acre) of SWs digested sewage granules. Such a result more than covers the delivered and spread cost of £105/ha (£42/acre).
The whole 9ha (22-acre) field benefited from 21t/ha (8.5t/acre) of Bioproduct cake applied to the preceding spring barley. That supplied 15kg/ha (12 units/acre) of nitrogen to the wheat, says SW.
The northern half of the field also had 7t/ha (2.8t/acre) of Bioproduct granules pre-ploughing, supplying a further 26kg/ha (21 units/acre) of N. Bagged N use was 240kg/ha (192 units/acre), taking total N supply to 281kg/ha (225 units/acre). The southern half of the field missed out on the pre-ploughing granules and had bagged N rate reduced in line with the organic supply from the cake.
Yield in the north half of the field, measured on-combine by an independent contractor, was a huge 2.72t/ha (1.1t/acre) ahead of the 7.1t/ha (2.9t/acre), recorded in the southern half.
Quality was also better at 79.2kg/hl specific weight, 323 Hagberg and 13.6% protein, compared with 76.7, 273 and 13.4, respectively, in the south.
Furthermore, neither half lodged, despite missing their first PGR dose, because the crop raced through early extension so fast, says Guy Gagen, part of ADASs team supplying agronomy and management advice. Both areas received 1.5 litres/ha of Terpal (2-chloroethylphosphoric acid + mepiquat chloride) at GS32.
That raises questions about the normal practice of reducing bag N use according to organic nitrogens contribution, adds Bill Griffiths, SWs Bioproduct sales manager. Not only does the higher total N availability increase yield, it also improves grain quality, a point substantiated by results from other growers, he claims.
"On the basis of our results so far, we might well have to rewrite the fertiliser recommendations for crops receiving digested sewage products," Mr Griffiths reckons.
Another top crop on the Horsham farm was 7ha (17.3 acres) of Espace peas. The field had received 21t/ha of cake for the two preceding years, making 41kg/ha (33 units/acre) of nitrogen available to the crop.
The crop yielded 5.1t/ha (2.1t/acre) compared with 4.1t/ha for a control crop that received no bag fertiliser or cake.
"The crop receiving Bioproduct had about 75% less pea and bean weevil damage than the control peas," adds Mr Griffiths. "This effect has also been reported by other growers using digested sewage products." *
• Heavy Weald clay.
• 2.4t/ha more wheat.
• Better quality too.
• No lodging.
• Add N contribution to usual rates?
Believe us… Digested sewage applications boosted wheat yield by 2.4t/ha and quality too on this Weald clay, say Southern Waters Bill Griffiths (left) and ADASs Guy Gagen.