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

摘要

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 NH4+ and NO3- uptake by plants or simply NO3- 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 with 15N), or in separate pellets (NNa-blend), had any effect on the recovery of 15N-labelled NH4+ and NO3--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. NH4+ plus NO3--N) recovery in shoot tissue. Instead, Na, in the CCF appears to have stimulated NO3- uptake at the expense of NH4+ absorption, thereby altering the balance between NH4+ and NO3--nutrition in favour of NO3--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.