IntroductionAn investigation was undertaken by one of the writers for the purpose of determining the minimum potassium requirements of the tomato plant. It was planned to use water cultures in these studies. Although the solutions contained the so-called essential elements for normal plant growth it was soon discovered that the plants failed to grow. Since attention had been recently called to the importance of boron and manganese it was thought that a possible solution to the problem lay in adding these elements to the culture medium and a special experiment was conducted to test their effects on the growth of the tomato. Manganese (1.0 ppm.) was added to the nutrient solution as manganese sulphate and boron (0.55 ppm.) as boric acid. The four groups noted in table I consisted of nine cultures, each containing a single plant in a two-quart Mason jar.
The agronomic performance of a range of perennial ryegrass cultivar-endophyte combinations was compared in 16 trials conducted at sites throughout New Zealand. Each trial was run for 3 years according to seed industry evaluation protocols, measuring variables including: dry matter (DM) yield (total annual and seasonal DM yield), ryegrass ground cover at the end of 3 years, susceptibility to plant pulling, and rust incidence. The change in DM yield over the 3-year term of each trial was also analysed. There were significant differences among cultivars in total annual DM yield, and in seasonal DM yield for each of the five periods of the year among which yield was split (winter, early spring, late spring, summer, and autumn). Mean annual yield declined between Year 1 and Year 3 in all regions except Taranaki, by between 0.8 t DM/ha (Canterbury) and 5.3 t DM/ha (Waikato). There were significant region, year, region × year, and cultivar × year interactions in yield change. Significant differences in ground cover score for perennial ryegrass at the end of 3 years were recorded among cultivars. However, these differences did not mirror on-farm observations of ryegrass persistence in the Waikato during the drought of 2007/08, suggesting that the standard trial protocols currently used do not adequately test persistence. It is recommended that industry cultivar testing needs to more accurately assess perennial ryegrass persistence, using new protocols including running trials on commercial farms, for more than 3 years, and using mixed swards. Genetic differences in persistence could be generated more quickly by choosing sites known to challenge perennial ryegrass growth and survival. Keywords: perennial ryegrass, cultivar evaluation, DM yield, persistence testing, plant pulling, rust
A question that frequently arises in connection with elements regarded necessary for plant growth is whether or not a particular element is an essential plant food or merely a stimulating substance. Is its role that of a catalyzer, or is it actually incorporated into the tissues as an integral part of the plant? These questions are more applicable to such elements as manganese, copper, zinc and boron than to nitrogen, phosphorus and potassium, which have been recognized for many years as essential nutrient units. The elements of both groups have at times been considered toxic, at others as stimulating. Here again confusion exists, for the question of toxicity seems to depend upon circumstances. Thus BRENCHLEY (1) points out that "Typical nutrient salts are toxic when they are applied singly to the plant in certain concentrations, the toxic power decreasing and the nutritive function coming into play more fully on the addition of other nutrient salts." Some elements which are toxic in high concentrations contribute to increased plant growth when their solutions are properly diluted. It is apparent then that no sharp distinction can be drawn between toxic elements, and nutrient elements, or stimulating elements if such exist. The distinction is a question rather of quantity than of kind, which should be considered in connection with other factors such as the presence of other elements. BRENCHLEY (1) has divided the class of elements that are toxic in high concentrations into two groups: " (1) Those that apparently become indifferent in high dilutions and never produce any increase in plant growth; (2) Those that are either essential for growth, or at least cause increased development, when applied in sufficiently small quantities. The former group may be legitimately regarded as toxins; the latter presents more difficulty and even now their function is not settled. It is not clear whether they stimulate the protoplasm or in some way hasten the metabolic processes in the plant, whether they help roots in their absorbent work, or whether they are simple nutrients needed only in infinitesimal quantities. "Boron without a doubt belongs in the second group. Its role in the plant is not known although several investigators have shown that its presence is essential for the normal growth of many plants. WARINGTON (7) states, "The fact that boron can be detected in the stem, leaves, and pods of the broad bean implies that the element becomes distributed throughout
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