EVALUATION OF A CAPACITANCE METER FOR ESTIMATING HERBAGE PRODUCTION OF OAT CULTIVARS

An electronic pasture-meter was found to be of limited use for the routine estimation of DM production of oat cultivars for the reason that the relationship between the meter reading and DM varied with different cultivars.     

USES AND CAPABILITIES OF ELECTRONIC CAPACITANCE INSTRUMENTS FOR ESTIMATING STANDING HERBAGE

An electronic capacitance meter was used to estimate herbage yield from sown ranges in western USA. On an area in Arizona where the grass stand had heen sown broadcast, an r² of 0.47 was obtained between the meter value and oven-dry weigbt estimate. Excluding tbose plots with very large amounts of standing dead organic matter (OM), or very succulent plants which had not been sown, improved yield estimates. Tests on pastures in Colorado in whicb seed had been drilled and tbe meter tested to evaluate performance in relation to drill rows showed that a common regression could be used for estimating yield. Metbods of placing the meter in relation to row directions are described which avoid a biased estimate of total pasture yield. Cutting the herbage in a 3-dimensional manner improved the r² values over those obtained by the usual 2-dimensional cutting procedure. Separation of dead OM from living plant material did not significantly change the r² values and showed that dead OM bad very little influence on the meter reading. This dead OM can contribute significantly to variation of the estimate about the regression line, however, and if differences in dead OM are substantial, sample sizes may need to be increased or sampling stratified to obtain an accurate yield estimate. Pertinent literature on the evolution of electronic capacitance instruments for estimating herbage yields has been presented in Part 1 of this series (3). Tbe present evaluation is restricted to the herbage yield estimates from mechanically sown pastures. The Neal Electronics Model 18–612 meter was used to make the yield estimates.     

USES AND CAPABILITIES OF ELECTRONIC CAPACITANCE INSTRUMENTS FOR ESTIMATING STANDING HERBAGE

A meter using electronic capacitance to estimate weight of standing vegetation was first tested in 1949. It proved to be faster and more accurate than most indirect methods of measurement. Since then, other similar instruments have been built and several problems have become apparent. Short or dry vegetation, non-homogeneous distribution of vegetation, non-homogeneous phenology, and electronic circuit instability were the major problems. The chief steps in the development of capacitance instruments for estimating vegetation weight are discussed. The significance of each of the major problems has been greatly reduced by improvements in instrumentation. The technique of using electronic capacitance has now proved itself useful under a wide variety of range conditions.     

A NOTE ON THE USE OF THE POWER-DRIVEN SHEEP-SHEARING HEAD FOR MEASURING HERBAGE YIELDS

3-inch sheep shears powered by various motors have been used extensively for sampling in grazing experiments at Hurley since 1958. General observations on their use are made and the results obtained in comparisons of sampling methods made in 1958 and 1959 are discussed.     

THE ELECTRONIC MEASUREMENT OF THE YIELD OF RAPE (Brassica napus)

The application of an electronic pasture probe to the measurement of rape is described. Measurements taken over two years demonstrated that good relationships could be established between probe readings and parameters of crop yield. Crop height, spatial distribution of crop profile, crop density and percentage DM were found to he significant factors in obtaining meaningful results.     

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.     

THE DIGESTIBILITY AND PRODUCTIVITY OF SELECTED HERBAGE VARIETIES

Much of the published digestibility data refer to swards grown in the south of Britain. In order to study digestibility curves in a more northerly latitude, several pure swards were established in the west of Scotland in 1962 and 1963. Varieties included S22 and Tetila Italian ryegrass, S37 cocksfoot, S170 tall fescue, S215 meadow fescue, Scots timothy, English broad red clover, and SI00 white clover. In addition to primary growth in vitro digestibility, the effect of various cutting managements on digestibility and productivity was measured. Flowerhead emergence was delayed, with the result that the digestibility curve was later than is reported from southern Britain. Highest yields of digestible organic matter were obtained from the less frequent cutting regimes, but the mean digestibility of the herbage was lower. Pre-dictibility of herbage digestibility is desirable as the basis of a reliable and planned herbage utilization programme, particularly for conservation.     

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

Herbage, stubble and root weights were recorded for thirteen months on various leys subjected to two treatments differing in frequency of cutting.
The root-weight per unit area of a ryegrass/white-clover ley was not affected by the frequency of cutting, but the less frequently cut plots had fewer tillers per unit area; the root- and stubble-weight per tiller was, therefore, higher on the less frequently cut plots, On a cocksfoot ley the root-weight was not affected by the cutting treatment, but in late summer and early autumn the stubble-weight was considerably higher on the less frequently cut plots.
When cocksfoot was grown in rows 2 feet apart, the more frequent cutting decreased both the root- and stubble-weight.
On grass leys root-weights were heaviest in the summer and thereafter decreased until the following spring.
The root-weight of lucerne decreased from May to July, increased to a maximum in December and then decreased in weight. The changes in root-weight under lucerne leys were mainly due to changes in the weight of the tap-roots.
The vertical distribution of roots was recorded, and, in the case of the cocksfoot in rows, the lateral distribution of roots is also given.     

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.