Effect of potassium fertiliser., soil magnesium status, and soil type on uptake of magnesium by pasture plants from magnesium fertilisers

Abstract

Comparisons were made between low rates of dolomite (D) and superphosphate (SP) applied separately or in a dry mixture (SP + D), dolomite-'"reverted" superphosphate (DSP), serpentine-reverted superphosphate (SSP), superphosphate plus ground serpentine rock (SR), and superphosphate plus calcined magnesite (MgO), supplying 27.5 to 55 kg total Mg/ha, in the presence and absence of K fertilise'r, as sources of Mg for uptake by pasture plants in 23 experiments on a range of soil types (pH 5.2 to 6.6) of variable Mg status (0.28 to 4.17 me. exchangeable Mg per 100 g soil). Dolomite and ground limestone (L) at 2510 kg/ha were included in 13 experiments.No consistent yield responses were obtained from any of the Mg treatments or L. but some significant K responses were found.Mg concentrations in herbage from control (no Mg) treatments ranged from 0.16 to 0.26% in spring and from 0.23 to 0.35% in autumn.At the low rates used, mean absolute increases in herbage Mg concentrations were very small, ranging from nil to 0.01% dry matter (0 to 4% increase) from one applic<:tion of 27.5 kg total Mgjha and 0.005% to 0.02% (2 to 9% increase) from two applications. Dolomite at 10 times the low Mg rate increased herbage Mg on average by 0.036% (range 0.D11 % to 0.080%) (16% mean increase) .Results differed between soil types and sites. In general, effects were greater on soils from pumice than on other soils, but the average Mg status of the pumice soils was less than half that of the non-pumice soils.The heavy rate of finely ground dolomite produced maximum effects between 4 and 9 months after application on soils from pumice, but between 10 and 14 months on other soils.Limestone slightly depressed herbage Mg levels, but significantly increased Ca levels. MgO gave greater increases than other comparable treatments.No consistent effects of the Mg or L treatments on herbage K, Na, and P concentrations were detected. K depressed Na > Mg > Ca. Larger effects of K on Na and Mg were found in grasses than in associated clovers. K effects were greater when K deficiency was corrected than when Ie was in the adequacy range.N increased herbage Mg in two experiments and decreased it in a third. Herbage Mg concentrations appeared to be better correlated with log. soil Mg values than with square root of soil Mg levels or untransformed values, but the best relationship accounted for only 46-61 % of the variation. Herbage Mg concentrations arc thus poorly predicted from soil analysis values by any of the relationships examined.

Effects of lime on the chemical composition of ryegrass and white clover grown on a yellow-brown loam

“…A decrease in plant Mg concentrations resulting from liming has also been measured in other experiments (McNaught et al 1968(McNaught et al , 1973a but the present results suggest the cause. Overall, the decrease in Mg concentration in the grass was proportional to the increase in yield (see Table 2) resulting in no change in Mg uptake.…”

“…This was associated with a decrease in herbage Mg; an effect which has been observed in other field trials (McNaught et al 1968(McNaught et al , 1973a.…”

Potassium in soil and pasture and leaching of cations on an allophanic soil in New Zealand

“…The effect of rate of K fertiliser application on pasture uptake of other cations has been reported by McNaught et al (1973) and Morton et al (2000) and the effect of dairy effluent application on pasture by Bolan et al (2000). Goff & Horst (1997) reported that addition of K to pre-calving rations for dairy cows fed indoors increased the incidence of hypocalcaemia.…”

Variation in the magnesium concentration of ryegrass plants

“…The reduction in herbage magnesium concentrations caused by adding magnesium to both the high magnesium selection and the Nui controls is almost certainly a Steenbjerg effect (Steenbjerg 1951) and does not affect the argument for genetic control. Genetic control of magnesium concentration in ryegrass may help to explain the generally poor results, in terms of tissue magnesium, when magnesium salts are applied to pasture (McNaught et al 1968(McNaught et al , 1973.…”