Knowing exactly how much nitrogen is in the soil has enabled one Lincolnshire farming business to optimise the application of bagged nitrogen, boosting the yield and profitability of its winter barley crops in the process.
Using soil testing to calculate the level of nitrogen in the soil which will become available to the crop during the growing season, allowing application of bagged nitrogen to be tailored precisely, has enabled A.W. Smith and Sons to increase winter barley yields by 1.5 tonnes per hectare (0.6t/acre).
Farming at Home Farm, Withcall, near Louth, the business has for the last two years used the N-min test to measure soil mineral nitrogen (SMN) and additional available nitrogen (AAN).
Drew Smith says: “Until two years ago we had never done any soil nitrogen tests and relied on general figures for farms in this area.”
On just more than 1,000ha (2,470 acres) of predominantly silty clay loam over chalk, which includes 130ha (321 acres) of heavy clay, Mr Smith, together with his brothers Nik and Martyn, grow winter wheat, spring wheat, oilseed rape, winter barley, and winter oats, together with vining peas and sugar beet.
By making significant use of cattle and poultry manures and using the readily-available nitrogen they contain, the business is able to reduce the need for bagged nitrogen and optimise production.
“All manure from our herd of 200 Aberdeen-Angus cattle goes back on the land and a ‘straw for muck’ arrangement with a neighbour provides another 6,500t each year. We also buy-in 600t of poultry manure from an intensive producer, the amount we take being limited by the lack of suitable land on which to stockpile it before harvest, which is necessary so it heats up and reduces the viability of any black-grass seeds.”
Each year about 25 per cent of the farm receives an application of manure, with fields destined for cereals receiving 30t/ha (12t/acre) of cattle manure, which supplies 220kg/ha of potash. With winter wheat taking up 100kg per year, the cattle manure is sufficient to cover the crop’s requirements for at least two, and possibly three years.
Poultry manure is applied to fields destined for oilseed rape, at the rate of 7.5t/ha (3t/acre) and supplies 30kg/ha of readily-available nitrogen to promote autumn establishment, eliminating the need for a similar amount of bagged nitrogen, together with 80–90kg/ha of phosphate and potash. Crops of oilseed rape which do not receive poultry manure receive 30kg of bagged nitrogen in the autumn.
In January or February GrowHow senior farm adviser David Towse takes core samples from fields which are known to be of a consistent soil type, some fields being where manure has been applied, others not, and also from fields in which various crops have been grown.
These are analysed for SMN content and incubated to establish how much AAN will become available to the crop.
AAN, soil nitrogen supply and spring crop nitrogen are then used to calculate the optimum nitrogen input for the cereals and oilseed rape.
Mr Towse says: “The key is to fertilise the soil for what it is actually capable of producing, not what you think it can produce. Most farms which I visit are between 20kg and 30kg/ha out on their nitrogen applications, either above or below the optimum level, and farms which have never checked their soil nitrogen levels could be up to 50kg/ha either side of the optimum.
“Be realistic about the crop’s potential. Even though most farmers will say their wheats average 10t/ha the actual UK average is 8.25t/ha, so there is a considerable difference between the two. If you over-estimate yield by 1t/ha when calculating nitrogen requirement that represents a difference of 20kg to 30kg of nitrogen, which represents unnecessary additional expense.”
The Smiths’ first soil tests were done in first and second wheats, oilseed rape and winter barley. “The results clearly indicated while the amount of nitrogen we had been applying to wheats was not too far out, it was obvious our barley crops could utilise more nitrogen.
“Having access to an accurate analysis of soil nitrogen has allowed us to increase the amount applied to winter barley by 40kg/ha, from 130kg/ha up to 170kg/ha. Financially, if we take 1t of barley as being worth £150, the additional gross margin is £30/ha,” says Mr Smith, who adds the business has traditionally grown malting barley because it suits the farming situation and will continue to do so as varieties have improved significantly over the years.
The Smith’s are currently growing Nullox spring barley, or SY Venture winter barley, which receives a 50/50 split of 27:0:0 + 12SO3, with 312kg/ha of product applied at the end of tillering and the same amount at growth stage 30 or 31.
Contract nitrogen content specifications are 1.8 per cent for the SY Venture and 1.92 per cent for for the Nullox barley Cha Cha.
The Cha Cha receives 250kg/ha of 27:0:0 + 12SO3 post-drilling, then 312kg/ha at the third or fourth leaf stage, giving a total nitrogen application of 150kg/ha. “Previously we would have limited the amount of nitrogen applied to 125kg/ha just to be on the safe side, but N-min has allowed us to increase the amount substantially yet remain within the 1.92 per cent maximum level for grain nitrogen which Gleadell Agriculture specify,” says Mr Smith.
“For 2015 harvest our first wheats consist of 121ha of Alchemy, 100ha of Leeds, 80ha of Relay, together with 28ha of Skyfall for milling.
This is an initial trial of the variety and because it will be for milling we must get the nitrogen application level and grain nitrogen just right. We also grow 100ha of JB Diego in the second wheat slot.
“Our wheats receive nitrogen in three splits, the first at the beginning of March, a second dose at the end of March or beginning of April and the third at the end of April.”
The first and second applications are 312kg/ha each of 27:0:0 + 12SO3, while the final application is 34.5 per cent N with rate varied according to soil nitrogen testing results.
“Oilseed rape receives 50kg/ha N in late-February/early March, the same at the end of March and the remainder as late as we can between green bud and flowering.”
Last year the Smiths increased the number of soil test samples to six, which will generate more accurate base figures from which to calculate nitrogen applications.
“We have already been able to move from industry-standard fertiliser manual (RB209) figures for nitrogen to more precisely-tailored applications which are specific to our situation. Our aim, over time, is to build an even more comprehensive overall picture of soil nitrogen and become even more precise in our use of bagged nitrogen,” says Mr Smith.
Winter wheat: 10t/ha (4t/acre)
Spring barley: 7-7.5t/ha (2.8-3t/acre)
Winter barley: 8t/ha (3.2t/acre)
Oilseed rape: 5t/ha (2t/acre)