Good detection solves lodging
Good detection solves lodging
Take one lodging prone field. Take one expert on integrated farming techniques. Put the two together and stir.
GOOD crop managers must be like good detectives, says Alastair Leake who manages the CWS/Hydro Agri/Profarma integrated farm management project in Leicestershire.
"You have to tailor inputs to meet each individual scenario," he says. "Its not always obvious which course of action is most suitable. You sometimes have to dig a bit deeper to get to the truth."
Take last year, when the arable manager on the main CWS Broadoak estate at Stoughton near Leicester asked for Mr Leakes advice on one lodging prone field. This site had gone flat for the previous four seasons and estate manager David Gardner saw it as a chance to test the Focus on Farming Practice integrated approach.
"Fundamental to the Focus project is the regular measurement of soil mineral nitrogen," explains Mr Leake. "We then plug this data into the Hydro Precision Plan computer model, together with other key variables such as drilling date, rainfall, previous cropping, soil type and so on to determine fertiliser requirements and application split. Applications are later fined tuned, in-field, using the hand-held N-Tester prior to the final nitrogen dressing.
"Soil mineral N samples had been taken at the field and showed available nitrogen at 54kgN/ha, which is not very high. On April 16 we ran the Precision Plan and it came up with a total nitrogen requirement of 183kgN/ha, which is around the estate average of 190kgN/ha. But, we knew that in previous seasons this field had regularly lodged. Instinctively, applying 180kgN didnt feel right. Precision Plan may be one of the best tools around but its designed to deal with the norm, and this was no normal situation," he says.
It took a lot of soil analysis to find out the cause of the problem. When Mr Leake walked the crop he concluded that it was well ahead of the Focus plots on the other side of the valley and in parts of the field it was particularly lush. This was strange given the soil mineral nitrogen reading and the fact that the crop had not been drilled until 12 October, so Mr Leake talked to the lab. "The sample had been taken at 0-60cm and strictly you need a 0-90cm profile. However, over the last six years Ive got to know the soil here pretty well. We usually have 50-60% of the available N in the top 0-30cms of soil, 20-25% N in the next 30-60cms and 15% in the final 60-90cms depth. So we might have been a little out but not that much."
Culprit
So why was the crop so forward? "Field history gave us our first clue," says Mr Leake. "Prior to being ploughed in 1995, the field had been in grass for many years during which time loads of muck had been applied from the old dairy close by. Fortnightly soil mineral nitrogen samples showed persistent but stable levels of nitrogen. It seemed as though there was a drip-drip supply, which was being taken up by the actively growing crop preventing reserves rising, but stimulating the extra growth. Given the field history, organic matter seemed to be the obvious culprit."
The average organic matter, however, was 3.3% compared to the usual Stoughton average of 2.2%; higher, but was it high enough to explain the crop growth differences? However, once again the average obscured what was actually happening. "Looking at the levels through the soil profile, we found that in the top 30cm of the soil in the forward parts of the field, the soil organic matter was actually 6%."
"I concluded that the different growth habit was in response to the high organic matter content of the soil in parts of the field. This was resulting in a steady mineralisation of nitrogen and improved soil structure giving rise to lusher and denser canopies than we would normally expect on this clay dominated soil type."
The inherent fertility of the field meant that yield potential was higher than the norm at Stoughton and that the potential for disease and weed pressure was also higher. Clearly in this case a growth regulator and robust fungicide programme would be needed, proving that sometimes the integrated approach can mean more inputs not less.
"Variability across the field was also an important factor. In the lushest areas the soil organic content was 6%; in the relatively backward areas it was just 2.2%. I therefore felt that precision fertiliser application was the answer," says Mr Leake.
Hydros N-Sensor was put through the crop to variably apply the second nitrogen application.
"But the N-Sensor doesnt tell you what rate to apply. You have to determine the mid-point and then the equipment works out whether to apply more or less than the average to each area of the crop," says Mr Leake. "In this case, simply applying the second split of nitrogen as determined through Precision Plan, variably across the field wouldnt have solved the lodging problem. Instead, because of all that organic matter we only needed to deliver a total of 110kg, so we set the mid-point accordingly and saved 70kgN/ha."
Mr Leake backed up his findings with the use of the hand-held N-Tester. On the 29 April, he found that in the forward parts of the crop, which at this stage had only received the first nitrogen split of 42kgN/ha, were producing readings of 661.
"I normally expect crops which have received 180kg of N to read around 700 so you can see how close the best areas of this crop were to that optimum before any further applications were made."
The variable application at a lower rate worked and the final yield came in at 0.8 t/ha above the estate average. At £68/t that contributed an extra £4,800 a 100ha worth of income, in addition to the savings in bags of nitrogen, combine time and drying.
These results show the cost-effectiveness of spending time working out exactly what you are dealing with before turning to precision technology for an answer.
"Precision farming begins with an understanding of the field and the farm rotation. Without that understanding it will never be effective," concludes Mr Leake.