Nitrogen-sodium concentrated complex fertilisers (CCF’s)versus nitrogen-sodium blends: Effects on ammonium and nitrate uptake by perennial ryegrass plants replete with potassium

Abstract

There is ample experimental evidence that, Na, if supplied in separate fertiliser granules or crystals to N, i.e., in blended fertiliser form, can improve both the yield and the recovery of fertiliser N by grassland swards in situations of limited K supply, but not in situations of K abundance. There is some evidence, though, that in K-replete situations, Na, if supplied in the same fertiliser granule as N, i.e. in concentrated complex fertiliser (CCF) form, also improves dry matter production and N recovery by swards whilst lowering the risk of grass tetany in grazing animals. However, the mechanism for the latter effect of Na on N uptake has never been elucidated, nor has it been clarified whether Na stimulates NH 4 + and NO 3 − uptake by plants or simply NO 3 − uptake alone. The aim of the present study was to see if supplying Na in the same fertiliser pellets (NNa-CCF) as NH4NO3 (differentially labelled with15N), or in separate pellets (NNa-blend), had any effect on the recovery of15N-labelled NH 4 + and NO 3 − -N by perennial ryegrass plants growing in a glasshouse under K-replete conditions. The results of the experiment confirmed that using an NNa-CCF was more beneficial to shoot production than using an NNa-blend. However, the differential in shoot production occurred without any corresponding difference in total N (i.e. NH 4 + plus NO 3 − -N) recovery in shoot tissue. Instead, Na, in the CCF appears to have stimulated NO 3 − uptake at the expense of NH 4 + absorption, thereby altering the balance between NH 4 + and NO 3 − -nutrition in favour of NO 3 − -nutrition, and stimulating shoot production as a consequence. It was concluded that if grassland is already well supplied with K it would be more beneficial in terms of sward production to apply a Na and N-containing CCF than a blend of separate Na and N-containing granules or crystals.