Plants May Not Be Able To Make Use Of Nitrogen

Press, Volume XCVIII, Issue 28980, 22 August 1959, Page 9

Plants May Not Be Able To Make Use Of Nitrogen

can be present In soil in considerable amounts and yet be unavailable to plants, says Dr. Kevin O’Conner, liaison officer for tussock grassland research in the Department of Agriculture, in continuing the discussion of the mid-altitude or mountain basin country (2000 to 3000 ft) which he began on this page last week. For example, he says that in a fertile tussock grassland soil producing about 20001 b of dry matter to the acre a year in an unimproved state it was found that “available” nitrogen constituted 67 parts to the million in the uppermost three inches while total nitrogen in the same sample comprised 4570 parts to the million—nearly 70* times as much. On the unimproved terrace where the Broken river experimental area is located the corresponding figures for available and total nitrogen were found to be 81 and 2370 parts io the million. ’n contrast to the fertile site mentioned before production of herbage on the unimproved land at Broken river had been only about 4001 b of dry matter a year, less than one-fifth of that from land with as much or more available nitrogen, even if it was just a small fraction of the total nitrogen in the soil. It appeared from these analyses that the plants present in the tussock grasslands at the moment could not make use of the nitrogen that was supposedly available. Little Increase Likewise in experiments this year it had been shown that the addition of nitrolime, even at the rate of 10001 b to the acre, u> poor fescue tussock grasslands, had, on its own, produced no increase in the growth of native grasses; a little in resident grasses, such as browntop and sweet vernal, and in introduced grasses such as cocksfoot. When sulphur or gypsum had been added on its own there had been no measurable increase, but when it has been added with nitrogen there had been a measurable increase in the growth of all three groups Of grasses. When sulphur, nitrogen and phosphate had been added together on phosphate responsive soil the measured growth of fescue tussock, browntop and sweet vernal, and cocksfoot had been increased by five-fold even in a few months of a droughty season. These experiments demonstrated the importance of sulphur and phosphate to the growth of grasses

as ■well as clovers and especially important was the fact that these responses to added sulphur and phosphate had been measured as clearly and as substantially in the impoverished resident grasses such as browntop, sweet vernal and fescue tussock as in cocksfoot and similar introductions. Dr. O’Connor has this year measured yields of up to 60001 b of dry matter from well-manured resident grasses—without clover —at 3000 ft * above sea level, principally in sweet vernal, Yorkshire fog, browntop and fescue tus-sock-equivalent to about 3j tons of hay to the acre. The Future Dr. O’Connor is confident that the future will hold a much changed, more intensive, more versatile, more rewarding and more secure way of farming in the mid-altitude tussock country than there has been in the past, and he is also hopeful that the transition can be accomplished steadily and profitably. In conclusion he says: “The success of clover introduction, which has been so clearly demonstrated on an experimental and practical scale by the Department of Agriculture, runholders and others, the increased production, palatability and recovery from grazing of resident and introduced grasses, native and exotic, and the economy of manurial programmes are already combining well in practice. In this phase research is a piece of cake. The task is simply to settle arguments—to make a matter of fact out of a difference of opinion. "The real challenge is still to come—to find out the necessary limitations and modifications to existing systems or theories of intensive agriculture when applied to the mountain environment, where animals want feed for 12 months and where grass can grow like mushrooms for only four!”