Most oilseed rape growers see crop nutrition as the prime factor limiting the potential of today’s crops. To help drive yields and deliver more consistent results, Mark Tucker of Yara, gives his ideas and options for this season’s crop – and a look at the latest thinking that will manage crops more effectively and efficiently in the future.
Small crops set spring N challenge
Mark Tucker, Yara Technical Manager This season’s small oilseed rape plants will benefit greatly from an early foliar N application as soon as they want to start growing this spring, as a kick-start to get crops growing as quickly as possible. The small crop canopies mean that most plants have very little N biomass reserves to utilise and, after the heavy rains reducing soil reserves, most of the nutrients are going to have to come from fertiliser inputs. In fact, and somewhat counter-intuitively, crops are likely to need higher N inputs to optimise yield than in previous seasons.
The situation this year is even more extreme than in 2010, when crops were also small, with GAIs of just ¼ (0.25 per m2) going into the spring, Trials then showed that over 300kg/ha of N was required to optimise yield from the backward plants, compared to a more typical 200kg in seasons with good autumn growth. In addition to the low canopy N, small roots of this season’s crops could exacerbate problems by limiting fertiliser uptake. Good oilseed rape root structures may capture up to 60% of applied N for the plant; with lower efficiency from small roots only 20 to 30% of the N
may be taken up - so growers may need to apply relatively more to get the required amount into the crop.
A small amount of foliar N in the early spring will encourage the plants to develop essential roots that will improve their efficiency to capture and utilise following applications. The season suggests that crops will respond well to split N applications, within the practical limits of a farm’s application capability. At the very least the main N applications should be split in two, after the early foliar treatment; with growers also assessing the positive potential for a post flowering foliar application. Once the crops get going they will be drawing up to 4kgN per day. It is essential that they have sufficient nutrient available so as not to cause any further check in growth or reduction in healthy green leaf that will be vital to capture sunlight and build yield.
We have found that oilseed rape nutrition has responded incredibly well to the potential of variable rate N application, including use of the Yara N Sensor technology. A new version of the technique, launched in 2009, enables absolute variability in the way the crop is assessed and the amount for fertiliser applied, compared to working within set parameters that is retained for treating cereal crops. Our experience is that with small crops in the spring the N Sensor is looking to put on higher rates, and it has reliably proven to be right. In practice it is very accurate in picking up smaller crops, where the differentiation is even greater than with leafier plants; which could make it especially effective this season. The company has also introduced a new smartphone app - ImageIT - to help growers assess crop growth and appropriate fertiliser inputs.
Trials have shown there is a far better correlation between canopy N and plant reserves in calculating spring N requirements, compared to assessments of soil nitrogen reserves. Results with the variable N rate application are very consistent across oilseed rape types, varieties and individual crops, which gives the confidence that it is the right approach to be using to improve efficiency and increase yields.
Sulphur supplement Sulphur is now widely acknowledged to be a limiting factor for oilseed rape yields, but some growers may be over compensating and applying too much. Most UK OSR crops will respond positively to 75-100kg/ha of SO3. The first 50kg/ha of SO3 will give by far the greatest responses, but once applications get above 75kg/ha further yield increases are a marginal response. This season growers will face a challenge in balancing N and S application at appropriate times for plant growth. Sulphur is a key building block of proteins in OSR, so it is required all the way through the growing season. Unfortunately the plant partitions S into cells as it grows and cannot move into new areas of growth. Ideally, it should be applied at the end of February, in March and again in April and May. Also be warned that at higher rates Sulphur can affect the uptake of other nutrients, especially molybdenum. Growers can differentiate Sulphur deficiency that typically shows as yellowing of the youngest leaves, compared to Nitrogen deficiency that shows as yellowing of the oldest leaf.
Feeding canopy extension Maintaining the green leaf area of oilseed rape crops for as long as possible will be more important than ever this season, to build yield from backward plants. The last few weeks before harvest are critical for yield. Pre-flowering and flowering Amistar fungicide applications will help to minimise disease leaf loss and retain green leaf to absorb sunlight that will build oil yield and content.
Furthermore, recent research by HGCA, Agrii, Yara and others have all shown a potential yield boost from late N foliar feeds at around the flowering timing. The principle is that during
seed development, the plant extracts the N it requires from the leaf and pod walls, which leads to a reduction in photosynthetic activity - and consequently limits yield potential. Applying late N has, in most seasons, given a valuable yield increase averaging around 0.2 t/ha and worth around £65/ha. With the exception of 2011, when yields were suppressed with the late N, the average from trials would have been over 0.3t/ha, reported Mark Tucker of Yara. Reports that oil content had been lower in some HGCA trials had not been seen in the company’s own work, he added. It would appear that the timing of application is key to achieving successful uptake and utilisation of the N. New research suggests that if it is applied too early the plants fail to remobilise existing N resources and overall results may suffer. The latest recommendation is to wait until plants just start to remobilise N from the leaf and the first signs of N stress are being seen; and then feed it so that it takes in the foliar N and optimises its use.
Spring Phosphate requirement Wet, cold soils that will restrict the availability of phosphate could put further pressure of oilseed rape crops recovering quickly this spring. Phosphate is essential for the movement of energy within the plant, with trials showing good responses to spring applications. Even fields with an Index 4 have shown a high response.
Spring treatment, when the plant can take up the nutrient, appears to be an efficient timing for application. Once it is in the plant, it will remobilise around to where it is required; so loading in the early spring is useful. Up to 70% of the plants’ requirement will be taken up in the spring as it starts to grow, most significantly from February to early April. There is risk of Phosphate lock-up on some soils, but it does remain water soluble for the first few weeks after application, so plants can take up the required amount before it may be bound in the soil. This season, with small plants and limited root systems, growers will have to make sure that there is sufficient growth to take up the nutrient. Potash is also required at high levels during periods of active plant growth, taking up to 10kg/ha K2O per day during stem extension to flowering. Spring applications of up to 50kg/ha of K are increasingly being applied in oilseed rape to satisfy the demand.
Although the cost is attributable to the crop, it will largely be available for following crops when put back into the soil through the straw, he added. Potash availability is less affected by soil conditions, compared to other nutrients, but it is important that the cation exchange capability is not limited.
Autumn N The number of oilseed rape crops that receive autumn N has declined hugely over recent years – with significant cut backs in the rate at which it has been applied. In 1985 over 80% of crops received a treatment, with average rates at 80-90kg/ha; by 2010 only 30% of crops were being treated, with an average application of 30kg/ha. Whilst growers have responded positively to messages to avoid wasteful over application, trials suggest that autumn establishment and overall yield may be restricted by insufficient N in the autumn. With the higher yield responses of current agronomy techniques and varieties, autumn N applications of 40 to 60kg/ha may be more appropriate. With lower seed rates, you can afford to create stronger plants in the autumn without risk of competition compromising yield. If you capture N in the canopy in the autumn, it drives down the requirement for spring N. Within the current legislative restrictions on autumn N application, Lincolnshire grower, Andrew Ward, believes there are opportunities to get better results with precision placement of fertiliser close to the seed when drilling. Applying liquid fertiliser on the farm’s Elita LD drill at 43cm row spacing has enabled him to focus applications of 30kg/ha in a band, which makes the equivalent of 60 to 90kg/ha available to the seedling.
Results of trials on the farm with (above right, left plant) and without fertiliser have certainly shown the benefits of faster, more consistent establishment – with stronger early growth, thicker stems and significantly greater root mass.