Weaver Discussion Group - Managing forage crops

Monday 14 May 2012

Report of the group meeting Held at Reaseheath College on Thursday 3rd May 2012, covering nitrate leaching, nutrient management, cropping policy and water testing.

1. Nitrate Leaching:

The first field we visited had been in continuous forage maize. The soil type of the field is a medium to light loam and the field does have a drain running through it. Last year (2011 harvest) the field was drilled to forage maize and under sown with grass to ensure the farm had sufficient grassland to meet the NVZ grassland derogation. The field has recently been drilled with barley/pea mix and Lucerne.

Sam Grundy has been sampling the outflow drain from this field since early February and nitrate levels have been consistently high. It was expected that the grass ley would utilise more of the nitrogen once the forage maize crop had been harvested, after all this is one of the environmental reasons for under sowing maize with grass.

The group discussed the reasons for these high nitrate levels which were as follows:-

Dry summer of last year and low winter rainfall may be the reason for concentrated levels of nitrate since early February. The recent heavy rainfall will have contributed to higher levels than normal being leached from the soil.
The ploughing up of the under sown grass ley post three weeks ago to establish the current crop may now be starting to release nitrate which is contributing to the high water levels.
The previous cropping of continuous maize has meant that maximum application of manures has been applied and this will have led to high soil nitrogen supply levels. This was confirmed by the excessive P & K indices which were in excess of 4.
Nutrient management during the planning of the maize crop in the spring of 2011 may have underestimated the soil nitrogen supply and actual availability from the organic manures resulting in an unnecessary application of inorganic nitrogen application (e.g. could a saving of 40 units of N been saved without a reduction in dry matter yield?).

It was agreed that the sampling of water from this field should continue to see if there are any improvements in nitrate levels following a change from maize cropping to Lucerne. This sampling may need to continue for a number of years as soil nitrogen levels should fall.

2. Nutrient Management:

The second field looked at a three year grass ley field which had recently received manure, been ploughed, rolled and then received slurry/dirty water on top of the rolled ploughing. The field is then to be power harrowed and drilled with maize.

The first observation was that since the heavy rainfall the field has become surface compacted and that the dirty water/slurry may have caused runoff. Secondly the subsoil may have become compacted due to the spreading of slurry/dirty water on top of the rolled ploughing. The field was being power harrowed whilst the group were in discussion and it was observed that the soil profile was compacted at around five inches just below the power harrow cultivation depth.

The field had received the maximum amount of organic manure to meet the 250kg N limit. It was suggested by Andrew Nicholas that water samples should be taken from this field over the next 12 months to see if nitrate levels increase. It is quite possible that the ploughing up of the permanent pasture and applying the maximum slurry application to meet the field N limit may well result in a surplus nitrate requirement for the maize crop and that no or little inorganic N application would be required.

3. Cropping Policy:

The policy of the farm is to provide a crop rotation that will provide an energy dense dairy ration to support the current milk yields (in excess of 40 litres per cow per day). The introduction of peas and Lucerne to the ration is to reduce the reliance on purchased protein.

A schedule of the growing costs for the Lucerne/Barley/Pea crop was produced which indicates a total cost of £534 per hectare (£216 per acre). The crop is to be monitored to see how this compares with alternatives.

The group discussed the environmental implications of growing peas and Lucerne in the rotation and generally agreed that a rotation of maize, winter beans followed by wheat could be an option.

Given the increasing demand and value of land it was suggested by Andrew Nicholas that growing proteins on farm is not financially attractive when compared to purchased rape or soya meal. The cost of growing say winter beans is around £320 per tonne of dry matter when all costs including rental value on the land is included. This equates to around 18 pence/DCP when compared with oilseed rape meal at 8 pence/DCP.

Farmers should consider maximising dry matter production by concentrating on growing energy crops. Sam Grundy produced a cost of production schedule (see attached) for grazed grass, grass silage, forage maize and whole crop cereals which indicates cost per tonne of dry matter of £45, £94, £74 and £90 respectively.

Although forage maize is cheaper than growing whole crop it was agreed that whole crop wheat is likely to have a more consistent yield over time than maize which can be vulnerable and challenging to grow particularly on heavier soils. Whole crop wheat particularly autumn sown is more likely to have a positive impact on the environment as there should be less runoff than bare maize stubbles and wheat should utilise available N during the autumn and early spring months.

4. Nutrient Management Plan:

Sam Grundy produced a good example of a nutrient plan for field 19 which was going from long term grass to winter wheat.

Sam pointed out that despite a high soil nitrogen index following the ploughing out of grass the crop requirement for the winter wheat crop is 160 kg N per hectare (128 units/acre). The field received 40 tonnes per hectare of FYM in the seedbed followed by 250 kg/ha of 27:0:0:12s and 120 kg/ha 34.5% N. After the application of FYM and bagged fertiliser the crop needs will have been met for P & K with N being short by around 40 kg/ha (32 units/acre). It was agreed that the shortfall in N will be made up from the release of N following the ploughing out of grass and that in practice more of the N will be available from the FYM than 5% as recommended by RB209.

The management plan for the field is a good example of how to plan and monitor nutrient input for both an environmental/financial benefit whilst also vital for NVZ compliance. Unfortunately many farmers are not operating nutrient management plans as these plans are simply seen as more paperwork and or current recording systems on the market are too complicated.

5. Water Testing:

With the recent heavy rainfall it has been very encouraging to see that group members are sampling water to see if their previous and current management is affecting water quality.

Data produced from other farms in the group suggests that nitrate levels have fallen on some of the permanent pasture land which is less intensive whereas the intensively farmed land is remaining constantly high.

At another farm in the group nitrate levels in the Weaver are around 30 mg/litre which was encouraging although this could be due to the increased water levels causing a dilution effect.

Another farm reported levels of nitrate above 50 mg/litre and one field outlet was in excess of 250 mg/litre.

The water results are just starting to provide some trends and it will be important for the group to continue monitoring these for at least the next 12 months. The monitoring is vital if we as a group want to be at the forefront of making management decisions that may give us the ability to reduce nutrient inputs, have a positive impact on the Environment and prevent further regulation.