Optimum phosphorus application

Johnstown research student Tim Shields investigated the interactions between different levels of nitrogen (N – 0kg/ha, 150kg/ha and 300kg/ha), phosphorus (P – 0kg/ha, 20kg/ha, 40kg/ha and 60kg/ha) and lime (0t/ha and 5t/ha) application.

The experiment was carried out on grass plots in Johnstown (P index 2, pH 5.4) and Moorepark (P index 3, pH 6.2). Tim found that a 20kg/ha application of phosphorus optimised grass growth (+5% more than the control). Application above this didn’t affect yield but would have improved soil P reserves.

Lime application in Johnstown (pH 5.4) improved grass yield by 3%, while lime application in Moorepark (pH 6.2) reduced grass yield as pH became too high. Increased N application reduced P concentration in herbage but in most cases not below the required 3.5g/kg DM. One of Tim’s main findings was the importance of P application at reseeding, even in soils in index 3 and 4 for P already.

Mole drainage

Moorepark research student Pat Tuohy is examining the durability and effectiveness of different land drainage techniques. He presented results from mole drainage trials carried out at the Solohead Research Farm.

This compared mole drainage (no stone), gravel mole drainage and a control. All drainage work was carried out in 2011 and water coming from the drains was measured between June 2012 and March 2013.

Gravel moles removed up to 60% of rainfall after installation but effectiveness deteriorated over time down to 15%. Gravel moles outperformed conventional ones by a greater proportion at the start of the experiment but this difference also decreased over time.

The mole drains had to carry water 100m to collector tanks and Pat believes this was too far.

The soil type in Solohead is not ideal for mole drainage (higher clay content needed), which also reduced the success.

Pat’s recommendations are that, in this scenario, more collector drains were needed, to mole plough in July not January and also investigate what is causing the problem before undertaking any drainage technique.

Mole drainage is used where soils are impermeable, meaning regular drainage channels are needed.

Conventional moles were installed at 0.55m depth and 1.2m spacing (cost €291/ha), while gravel moles were installed at 0.4m and 1.2m spacing (€2,816/ha).

Crop rotation and nitrogen supply

UCD research student Siobhan Walsh is looking at the effect of crop rotation and weather conditions on soil mineral nitrogen (N) supply. She carried out trials on 43 winter wheat crops across the country which received no fertilizer N to see how much N was supplied from the soil.

All fields had grown winter wheat, oilseed rape or permanent grassland the previous year. In 2012, based on crop N uptake, Siobhan found that land formerly in grass supplied the most soil N (150kg/ha on average), followed by oilseed rape (115kg/ha) and then continuous wheat (80kg/ha).

In 2013, all plots supplied significantly less N (40kgN/ha less on average). Siobhan believes this is down to the high rainfall from December 2012 to February 2013 and the colder temperatures in the spring, which would reduce soil mineralisation.

This would indicate soils being reseeded from continuous tillage back into grass will be supplied with much less N from the soil and will depend on slurry and fertilizer application.

Grass from space

Ashtown researcher Ifkthar Ali is using satellite technology to measure grass growth from space. His research project is comparing satellite data from 2001 to 2012 with grass growth information collected in Moorepark at the same time.

The satellite takes numerous images of fields each week and combines these into one image to find a best fit with minimum cloud cover. Ali reports very accurate results from the technology which analyses how green the grass plant is as one aspect of measuring growth.

This technology would help farmers identify poorest performing paddocks and quantify grass production on silage fields to decide when reseeding is needed.

Clover and stocking rate

Moorepark research student Michael Egan presented his research work on incorporating clover into a highly stocked dairy farm system (2.74LU/ha overall stocking rate). He had three treatments: (1) grass plus 250kg of N/ha; (2) grass and clover plus 150kg of N/ha; and (3) grass and clover plus 250kg of N/ha.

He found that there was no significant difference in grass grown between the three treatments (averaged 14tDM/ha). Cows on the clover treatments produced on average 30kg more milk solids per cow (+82kgMS/ha). This difference occurred in the latter half of the grazing season when there was a higher percent of clover in the sward (>30% clover). Results are from one year of the study, which is being repeated again this year. Michael’s advice on incorporating clover at reseeding was a seeding rate of at least 5kg/ha (2kg/acre) and to use a medium sized leaf variety, e.g. Chieftain or Crusader.

Utilisation and ground score

Moorepark research student Patrick Cashman investigated the utilisation of different grass varieties by dairy cows. Ten different monocultures were sown in a paddock, five of which were diploid and five were tetraploid.

Cows could choose which plots to graze in the paddock themselves over a period of 24 hours and the plots were grazed 10 times per year.

Tetraploids had a higher DMD and tended to be graxed tighter but there was significant variation between varieties.

At every grazing, cows were expected to graze to 4cm and Pat highlighted that, by the time the last variety was grazed down to 4cm, cows had grazed others down to below 3.5cm, demonstrating cow preference.

Patrick concluded that variety has a big effect on utilisation and, as a result, could be a trait used in the new pasture profit index.

Patrick also researched the relationship between ground score (density of sown grass plants in an area, scale 0-9) and yield. Ten different grass varieties were trialled under different management regimes of grazing and conservation over four years.

Dry matter production reduced on all plots (from 13.5tDM/ha to 9.9tDM/ha) as did ground score but grazing plots saw the smallest reduction. Each drop in ground score was found to reduce yield by 1.7tDM/ha.

Patrick advised backing up ground score with grass measurement yields when deciding to reseed – some tetraploids can have a low ground score but can be high yielding, while swards with weed grasses can appear dense but yield poorly, especially in spring.