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Jul 2012

We lifted and spread over 90 hectares of seaweed across the machair this winter to provide vital organic nutriants for the growing of crops. This work has been very popular with crofters and in support of this we commissioned SAC to run tests on the nutritive value of seaweed as an organic fertiliser so that we can advise crofters on appropriate application rates to obtain quality yields from their crops.

We have commissioned two tests in 2012 to test the qualities of seaweed as an organic fertiliser.  SAC has been commissioned to carry out tests on the nutritative qualities of seaweed so that we can share this information with crofters.  One test is measuring the effect of seaweed on the nutritative quality of soil by taking soil tests before and after the application of seaweed followed by tests on crop yields from areas which have either been established with seaweed or artifisial fertiliser. We have also commissioned tests on the nutritative quality of seaweed at various stages of decomposition. Results from this has shown that as the seaweed becomes more decomposed the levels of phosphate increases while the levels of potasium decreases. Nitrogen content is more sporadic. Based on an average of all three stages of decomposition (fresh, semi-fresh, rotten) the average nutritative quality of seaweed in terms of Nitrogen, Phosphate and Potasium is: 0.55: 0.17: 1.05. From these results recommendations from SAC on the required application rates of seaweed which was at an avearge stage of decomposition would be at a rate of 11000kg/ha (11 tonnes/ha). This would satisfy the levels of potasium required to promote crop growth. However, the levels of nitrogen and phospahte at this rate of application would be below those recommended. Recommendation is therefore to increase nitrogen levels through ensuring that a good proportion of clover is availble in fallow years.  An addition of farmyard manure or another organic phosphate additative would also be advisable.

Seaweed Fresh Semi-rotten Rotten Average
Total Nitrogen0.38%0.016%0.79%0.55%
Total Phosphate0.14%0.17%0.20%0.17%
Total Potasium1.35%1.06%0.74%1.05%