W. J. Ridgman

A physiological analysis of the growth of oilseed rape

For seed crops other than cereals there have been comparatively few comprehensive field studies which have analysed the physiological basis of the effects of genotype and agronomic treatments on growth, development and yield. Milbourn & Hardwick (1968), working on vining peas ( Pisum sativum L.), have recently shown that pod growth rate and the yield of seeds are not simple functions of leaf area index and that sourc es of materials other than the leaves are important in affecting the yields of pods and seeds. Furthermore, Flinn & Pato (1970) have shown that the pods themselves can contribute to assimilation in the field pea ( Pisum arvense L.). Field experiments carried out at Cambridge in 1968 and 1969 have produced evidence on the relative importance of leaves and other photosynthetic tissues in determining the yields of pods and seeds in another seed crop, namely oilseed rape. The experiment in 1969 is described and discussed below.

The effects of fertilizers on the bulking of Majestic potatoes

1. Four experiments designed to investigate the effect of fertilizers on the rate of bulking of Majestic potatoes are described and the results discussed. 2. Irrespective of fertilizer application yield increased until the haulm died and then decreased slightly. 3. Sulphate of ammonia increased the yield by increasing the number of tubers and increasing the yield in all size-grades. Thus its effect was seen throughout the season, no matter what grades yield was based on. It also increased dry-matter percentage.

Studies on lucerne and lucerne-grass leys II. The nitrogenous manuring of a lucerne-cocksfoot ley

An experiment, carried out to determine the effect of dressings of sulphate of ammonia on an established lucerne-cocksfoot ley grown in narrow rows on heavy gault clay soil, is described and the results discussed. The experiment was carried out over 3 full years (1948–50) and the first crop of the following year. The results suggest that it is possible to increase the yields of grass and total produce without decreasing the yield of lucerne but that no marked increase in the yield of nitrogen per acre is to be expected. Of the times of application tested February proved the most effective.

The effects of leys and their management on the yield of succeeding wheat crops on heavy land

1. One long-term experiment comparing the effects of leys and arable cropping on the yield of arable crops and three experiments on the effect of management of lucerne/grass leys on the following arable crops, all conducted on heavy clay land, are described and the results discussed. 2. In the first two years after breaking a ley yields of wheat were higher than on plots which had had all-arable cropping and it is suggested that this effect could be due to a combination of disease and weed control and the nitrogen status of the soil.

Results from three cycles of six-course rotations on light land

A rotation experiment comparing the effects of length, type and management of leys on three test crops in six-course rotations during three cycles is described and the results discussed. Although the yields of the test crops varied from cycle to cycle there were no clear-out trends to suggest that the yield improves or deteriorates as time goes on with these particular rotations; the full benefit of the leys was obtained in the first cycle. The yield of potatoes immediately following the leys was no greater than the yield in an all-arable rotation receiving adequate nitrogen fertilizer, but the yields of two, barley crops following the potatoes were less in the all-arable rotation than in ley rotations even when 58 kg N/ha/year and 38t dung/ha/cycle had been applied and trefoil ploughed-in in the all-arable rotation. Rotations containing lucerne or lucernecocksfoot leys gave their greatest yields of potatoes and of barley following potatoes without any applied nitrogen fertilizer, but in the second barley crop showed the same sort of nitrogen responses as the all-arable rotation. Yield data were also obtained on the leys themselves in each cycle. These showed a decline from the first to third cycle in yield of broad red clover grown as 1-year leys and in that of 3-year leys which contained lucerne, both of which could be explained by the build-up of specific diseases. There were also changes in the effect of grazing compared with mowing on the yield of some leys but little change in the effects on leys of applying nitrogen to them. However there was no suggestion that these changes affected the arable crops that followed.

Some effects of rate of application of nitrogenous fertilizer to wheat grown continuously compared with wheat in a four-course rotation

An experiment comparing continuous winter wheat with the two wheat crops in a rotation of beans, oats, wheat, wheat, with four rates of application of N fertilizer, is described and the results discussed. The wheat following wheat in the rotation consistently outyielded the wheat following oats, but the continuous wheat yielded on average less. Response to N fertilizer was not affected by sequence of cropping and since there was practically no response to the highest increment of N, it is clear that additional N could not have brought the yield of the continuous wheat up to the level of the wheat in rotation.

A comparison of growing wheat continuously with growing wheat in a four-course rotation

The design and analysis of an experiment to compare the yield of wheat grown continuously with that of wheat grown in two phases of a four-course rotation is described and the results discussed. A method of analysis which avoids making assumptions about the covariance structure of the errors derived from repeated observations on the same plots, which could be appropriate to other sorts of rotation experiments, is given. There were no differences between yields of the first and second wheat crops which followed oats after beans in a four-course rotation, but the average of these two crops was 0·75 t/ha greater than the yield of wheat grown continuously. The response to N was the same in the two systems of cropping. The only yield component affected by the system of cropping was grain mass.

The long-term effects of applying high rates of N fertilizer to winter wheat

An experiment in which all combinations of four rates of N fertilizer soon after sowing, four in early spring and nine in late spring were applied to the same plots of winter wheat for 6 years is described and the effects discussed. It was found that although the yield varied considerably from year to year the regime leading to greatest yield was fairly consistent. If the farmer had used the regime which gave the greatest average yield (0, 90, 180 kg N/ha in autumn, early spring and late spring, respectively) he would have averaged only 0·12 t/ha less than the maximum attainable each year. Application of N increased protein concentration in the grain more or less linearly but the latest application increased it most. Since the regime which gave greatest yield on average produced grain which qualified for bread-making premium from the protein point of view in all years except 1981, adopting the regime which gave maximum yield would reduce the potential maximum gross margin by only £30/ha. Analysis of the soil showed a reduction in pH down to 15 cm and of available P 2 O 5 down to 10 cm.

The effect of date of winter grazing on the yield of a lucerne-grass ley

It has been shown that lucerne/grass mixtures, especially those containing a high proportion of cocksfoot, can make a valuable contribution to the winter feeding of livestock when the autumn growth is allowed to stand in the field until the winter. For instance, Hughes (1954) showed that it was possible to carry store cattle right through the winter on such herbage with little supplementary feeding. Other experimental work (Barker, Hanley & Ridgman, 1955) has shown that mowing or grazing this autumn growth in September may lead to poorer production in subsequent years than October defoliation. It therefore seemed desirable to determine the effect of date of grazing in the winter on the subsequent yield of a lucerne/grass ley and two experiments for this purpose were carried out at Cambridge from 1953 to 1957.