Phosphate

[DB67]

How important is this to the grass in the spring?

Last year we put soft rock phosphate on a bit later than normal fert.

This year the grass just isn't getting away (although it's been cold and wet for a while now and ground is well stocked) so I wonder if not putting P on at usual time has effected this?

 

[clemmo]

Depends on several factors, what are your indices? And ph?

 

[DB67]

PH is slightly low but we limed it. Had a lot of soil analysis done and Guy recommended soft rock phosphate rather than the conventional stuff you get in normal fert bags.

 

[Global ovine]

Several important factors can play an important part in phosphate requirements;

1. Soil type. Most soils in Scotland (apart from recent soils very near rivers) are very old and extensively weathered. These soils have about double the phosphate retention of recent soils. That means to attain the same biological optimum (economically sustainable plant growth....max growth without losses into waterways etc) you will need double the rates to achieve the same plant growth as recent soils.
2. pH also affect P availability by stimulating soil organisms which drive the P cycling in the organic matter.
3. Soft rock phosphate requires much longer to break down and get into the P cycle compared to Super phosphate (soft phosphate rock treated with Sulphuric acid) which is in plant ready form for absorption through the root hairs. Therefore, if the soil was already marginal for P it may have become quite limiting to plant growth until later in the season when rock breakdown delivered the necessary P.
4. Weathered soils have high aluminium levels that are toxic to plant root development. Shallow rooting means plants feed from a restricted part of the soil profile. Al concentration can be reduced with burnt lime, or extremely fine ground soft limestone lime. Hard limestone lime is useless.

If you wish to learn a heap more about soils, look out for the Easyrams Industry Good meeting where international soil scientist/consultant Dr. Rex Dolby will be present talking about "Knowing your soils" for pastoral farming. This will be held in the Borders region on the 4th July along with "yours truly" speaking about sheep farming business management and rotational grazing.

 

[JD-Kid]

Rex is worth going along to hear talk

intresting if P levels not bad and lacking clovers that are working N will be the biggest thing slowing your growth down not P

 

[Wastexprt]

PH is slightly low but we limed it. Had a lot of soil analysis done and Guy recommended soft rock phosphate rather than the conventional stuff you get in normal fert bags.

I would say it's more down to the prolonged cool weather slowing things down. Some sources say that soft rock P is more available than other sources, but as is often the case soil type, pH, weather etc etc dictates availability.