STUDIES ON THE ROOT DEVELOPMENT OF HERBAGE PLANTS

Various methods of root sampling are reviewed and discussed in relation to the type of information required. The root sampling techniques at the Grassland Research Institute are described and examples of sampling errors are given. Details of a root washing machine are given.     

STUDIES ON THE ROOT DEVELOPMENT OF HERBAGE PLANTS

The influence of defoliation on the root, stubble and herbage weights of perennial ryegrass during establishment was studied on spaced plants in the greenhouse and field.
In the greenhouse trial the rate of root elongation was reduced by a single defoliation. In both the field and greenhouse, cutting reduced the number of roots and tillers per plant but increased the number of roots per tiller. A few weeks after defoliating plants in the field there was a lower root weight on the cut plants than on the uncut. Eventually the influence of a single cut disappeared, but if the cutting was in the laie summer or autumn the plants commenced the winter with a smaller amount of root and stubble, and this appeared to have a deleterious effect on the earliest spring growth.
Herbage growth in March and April was positively correlated with both root and stubble weights in the previous November.
As the number of cuts during the establishment period (March-November) was increased from 0–4 the root and stubble weight per plant progressively decreased.
The root and stubble weights decreased during the winter.     

STUDIES ON THE ROOT DEVELOPMENT OF HERBAGE PLANTS

Two cutting treatments were applied to a cocksfoot sward, and the changes in fructosan and soluble–sugar contents of the roots, stubble and herbage were studied over a complete year.
Both the soluble-sugar and fructosan contents of roots were at a low level throughout the experiment. The total soluble carbohydrate in the roots never exceeded 4%. It is concluded that cocksfoot roots are not important storage regions for soluble carbohydrates.
The total soluble carbohydrate in herbage varied with season and reached a maximum of 10%. It was not affected by cuuing treatment.
In stubble the total stubble-carbohydrate content fluctuated markedly with season and reached a maximum of 18% in October; it was generally higher on the infrequently-cut swards than on those cut frequently. The soluble-sugar content was small and changed little with season or cutting treatment; the fructosan content, however, varied from 2 to 16–6% and accounted for most of the changes in the soluble-carbohydrate content. Stubble is apparently the major storage region for soluble carbohydrates in cocksfoot.
Under sward conditions, the quantity of soluble carbohydrates in the stubble of cocksfoot may have a positive effect on the herhage growth immediately after winter defoliation. However, when swards are actively growing in spring, other factors, such as tiller size and number, may be equally important in determining the amount of herbage recovery growth.     

STUDIES IN THE DIGESTIBILITY OF HERBAGE

Data from 291 digestion trials have been used to derive regression equations relating the organic-matter digestibility of herbage to the nitrogen percentage of its dry matter and to the nitrogen percentage in the organic matter of the resulting faces.
The residual errors are very high and it is shown that the deviations from the lines are not randomly distributed but have a seasonal trend. The seasonal biases have been calculated, and the inclusion of month of cutting as a factor is found to improve the two regressions to some extent. Monthly regressions have also been calculated. Even with these, however, the errors are still too high for many practical purposes.     

STUDIES IN THE DIGESTIBILITY OF HERBAGE

This paper presents the results of 125 digestion trials with sheep fed herbage at different stages of growth from three clover-free pure grass swards. During 1958 and 1959, a study was made of the yield, leaf lamina, nitrogen, ash and digestible organic matter percentage ( D ) of first growths, of regrowths cut at monthly and two monthly intervals and of swards receiving various quantities of fertilizer nitrogen.
For first growths in the spring D remained almost constant until the ears started to protrude from the leaf sheaths and then fell rapidly at approximately 0·5 per cent per day. The D values for S 23 ryegrass were three weeks later than S 24 ryegrass, which correspond with later ear emergence of the latter. S 37 cocksfoot was always less digestible than S 24 ryegrass although both were at similar stages of growth. This difference in D also occurred in the regrowths. The D of monthly regrowths tended to fall with each successive cut, although in 1959 ryegrass values improved in the autumn.
Fertilizer nitrogen had little effect on D .
Despite the warmer spring and drier summer in 1959 and corresponding changes in production per acre there was little effect on D .     

STUDIES IN THE DIGESTIBILITY OF HERBAGE

Results are reported from six digestibility experiments in which frozen herbage was fed to groups of sheep at HIGH and Low levels of intake. The sheep on the HIGH level of intake digested the dry matter, organic matter, nitrogen and normal-acid fibre in the herbage less efficiently than those on the LOW level, confirming earlier results reported in Part VI of this series. Evidence suggests that this difference results from the higher rate of passage of food through the digestive tract at the HIGH level of intake.
These results are discussed with reference to the errors introduced into the faecal-index method for estimating the digestibility of grazed herbage.     

INVESTIGATIONS ON LOCAL STRAINS (VARIETIES) OF HERBAGE PLANTS

Data are presented to show the effect on type of multiplying seed of wild white clover obtained from permanent pastures and of seed from old pastures in different localities. The variation in type in samples of commercial wild white clover is shown.
The cause of the change in type of certain stocks of Kersey white clover is demonstrated. The steps taken to maintain the original type are described.
The value of certain botanical characters in indicating the agronomic behaviour of varieties of white clover is discussed.     

烟粉虱若虫在夏大豆植株上分布的研究

对烟粉虱若虫在223份不同结荚习性大豆品种植株上的分布进行了调查研究.结果表明烟粉虱若虫在夏大豆植株上的总体分布集中在中上部,占总数的83.1%,中部与上部之间差异不显著.不同结荚习性大豆品种上烟粉虱若虫的分布存在明显差异.有限结荚习性品种主要分布在上部,上4叶烟粉虱数占单株烟粉虱总数的57.7%;无限结荚习性品种主要分布在中上部,第11叶至第16叶上烟粉虱数占单株烟粉虱总数的53.1%;亚有限结荚习性品种中5叶烟粉虱数占单株烟粉虱总数的39.6%,上5叶烟粉虱数占单株烟粉虱总数的41.4%.由此可以看出,化学防治烟粉虱的重点部位是大豆植株的中上部叶片.     

夏大豆植株的光合性能研究

1986—1987年在田间条件下,研究早熟7号和早熟14号大豆植株的光合性能。结果表明:叶片的最高光合速率和平均光合速率,基部叶片>中部叶片>顶部叶片;叶面积、功能期和光合势,均为中上部叶片>顶部叶片>基部叶片。夏大豆植株叶片的平均光合速率,以苗期及开花期较高,随后呈下降趋势,鼓粒后期下降尤其明显。单株光合速率及叶面积随着生育进程呈单峰曲线变化,以结荚期最高。