Potash for Grassland

Manures

This is often the area of greatest scope to improve grassland nutrient management and to reduce fertiliser costs.

Manures contain valuable levels of phosphate and potash; cattle slurry and FYM should provide P and K in the ideal ratio required for grass for silage or hay. A manure management strategy should in the first place use manures on crops and on grass for conservation, rather than on grazed grass, which already receives nutrient returns from the grazing animals.

Typical composition of manures is given below. The availability within the first year after application is 60% for phosphate and 90% for potash. There are however big variations in composition, particularly with differences in the dry matter content of slurries, so that occasional analysis of the nutrient contents of manures should be carried out. A slurry hydrometer can be used for a rapid check of dry matter, total nitrogen and phosphate contents. It is clearly also important to check application rates in order to calculate the quantity of nutrients applied.

			Total nutrients		Available nutrients
			(Use for soil index 2 or more)		(Use for soil index 0 or 1)
			Phosphate	Potash	Phosphate	Potash
FYM kg/t	Cattle	- fresh	3.5	8.0	2.1	7.2
		- open stored	3.5	5.5	2.1	5.0
	Pig	- fresh	7.0	5.0	4.2	4.5
		- open stored	7.0	3.5	4.2	3.2
	Poultry	- layer	13	9.0	7.8	8.1
	Broiler/Turkey	- litter	25	18	15	16
Slurry kg/m3	Dairy (6% dry matter)		1.2	3.5	0.6	3.2
	Beef (6% dry matter)		1.2	2.7	0.6	2.5
	Pig (4% dry matter)		2.0	2.5	1.0	2.3
	Strainer box (1.5% dry matter)		0.25	2.2	0.12	2.0
	Weeping wall (3% dry matter)		0.5	3.0	0.25	2.7
	Dirty water		trace	0.3	trace	0.3
Multiply kg/t x 2 = units/t			Multiply kg/m3 x 9 = units/1000 gals

The following points are important in relation to the effective use of manures:

• Slurry and poultry manures are best applied to land for silage or hay in late winter-early spring, close to the period of active grass growth and demand for nutrients, in order to reduce losses, particularly of N.
• A wider range of application times is possible for solid FYM.
• Slurry applications should not exceed 50 m3/ha to minimise risk of nutrient losses via surface run-off.
• Run-off losses may be high if there is high rainfall within 3 to 4 days of application, particularly in early winter.
• Applications for first-cut silage should be made by the end of March to reduce risk of poor silage fermentation.
• For subsequent cuts, the application should be made as soon as possible after harvest and it may be necessary to wilt heavily or apply additives for good silage fermentation.
• Manure application to land for grazing may reduce grass intake, cause nutrient imbalance and contribute to disease transfer. It is best to avoid slurry applications to grazing land in late winter/early spring. Pasture should not be grazed for one month, and preferably two months, after application or until all visible signs of slurry solids have disappeared.

Recommendations

The requirements for P and K to be supplied from fertilisers and organic manures are given below.

The recommendations are calculated to achieve full yield and maintain, improve or reduce soil P and K according to the soil index. Using these values it will take 10-20 years to raise soil fertility from the bottom of index 1 to the bottom of index 2.

Replacement values (M) are based on the average yields shown - if significantly different yields apply, the rates should be adjusted accordingly. Rates should also be adjusted if herbage analysis indicates N:K ratios outside the optimal values. The supply of nutrients from manures must be calculated and fertiliser then used to rectify any shortfall in supply; see notes in next section on 'Timing'.

	SOIL INDEX
kg/ha	0	1	2-	2+	3	4
1 cut + graze (23t/ha)
Phosphate	90	65	40M		20	nil
Potash	200	170	140M	120	30	nil
2 cuts + graze (23+15t/ha)
Phosphate	115	90	65M		20	nil
Potash	320	270	230M	180	60	nil
3 cuts + graze (23+15+9t/ha)
Phosphate	130	105	80M		20	nil
Potash	370	320	280M	190	80	nil
4 cuts + graze (23+15+9+7t/ha)
Phosphate	140	115	90M		20	nil
Potash	410	360	320M	200	110	nil
1 cut hay + graze (5t/ha)
Phosphate	80	55	30M		nil	nil
Potash	140	115	90M	65	20	nil
Grazed only
Phosphate	60	40	20M		nil	nil
Potash	60	40	20M	nil	nil	nil
Establishment These rates may be deducted from first season's phosphate & potash usage
Phosphate	120	80	50		30	nil
Potash	120	80	60	40	nil	nil