A. González-Rodríguez.Centro Investigaciones Agrarias. Xunta de Galicia. Apartado 10 - 15080 La Coruña - Spain.
White clover persistence at pastures in acids soils of Galicia have problems after conservation cuts, where some N is also applied. Despite no response to K was found in the establishment of mixed sward in soils with medium levels of potash, a series of small plot experiments were set up in several places in the region, to study if potash limitations could be detected on mixed swards repetitively managed under cutting. The one made inland the region showed similar results (Mosquera and González, 1992)
The trial was located in the experimental Centre in the coast of Galicia (100 m. height) with dry summers and very mild winters. The sandy-loam soil had a level of potash of 87 ppm, and 15 ppm of phosphate and a pH of 6.0. Every winter was fertilizer with 150 k/ha P205.
Twelve treatments of an interaction of four levels of N (main plots) by three of potash, in a split plot design, were applied every year for the first and third cut.
N (kg/ha): 0, 60 (30+ 30), 60 (60+ 0) y 120 (60+ 60). K2O (kg/ha): O, 100 (50+50) y 200 (100+ 100). The first rate of N and K was applied in early march for first cut and after second cut. The first two main N rates were cut three times in spring. The second two N rates were cut for silage when the other plots had the second cut. All the trial was cut only once in autumn.
There was a significative DM response to N (p<0, 001) in cuts where N was applied, 1st and 3rd at the two first main N rates and 1st and 2nd for the next two. The clover content was very low in first year, mostly detected in the autumn cut at low N treatments. In the second and third years significative decrease in clover content were obtained as N increased, resulting in a no significative annual DM response up to 120 kg/ha of N.(Fig.1)
DM yield response to K was significative at each cut when K was applied and in the total annual in each year. The clover content in the sward showed a negative response to N and a positive to K, greater where clover was high, at lower N rates (Fig.2)
Percentage of K in the sward increased, mainly in the cuts after the K fertilization. Potash fertiliser from 0 up to 200 k/ha gave an increment of K uptake from 275 to 355 k/ha in the first year and from 160 to 250 k/ha of K in the second.
The crude protein content of the sward was not affected by potash application in any cut as mean of all N rates.
Fig. 1 DM response to N and K application
Fig. 2 Clover response to N and K
Fig. 3 Potash content per cut in response to K application, (mean of all N rates)
In schist soils with a medium level of potash, the response to this fertiliser in terms of total DM yield and clover content of the sward was found since the first years of management under cutting, either for silage, using more N and having less clover, or for frequent cutting, with less N and more clover.
The potash uptake after K fertilization has to be consider for recommending maintenance levels of potash.
MOSQUERA R, GONZALEZ-RODRIGUEZ A. 1992. Mixed sward response to N and K fertilizer in Galicia. 14th Gen. Meet. Eur. Grassld. Fed. Lathi, Finland.
