Overdrilling Pumice Pastures

New Zealand Journal of Agriculture, Volume 95, Issue 3, 16 September 1957, Page 283

Overdrilling Pumice Pastures

By

G. S. ROBINSON,

Senior Lecturer in

Field Husbandry, and M. W. CROSS, Senior Lecturer in Farm Machinery, Massey Agricultural College ’ ,

SOME of the disadvantages of having pastures with, a high proportion of clovers were commented on in the April 1956 issue of the "Journal of Agriculture" by C. R. Taylor. In particular, this report pointed out that swards lacking ryegrass give poor yields of autumn-saved pasture and do not therefore, provide their share of winter grazing. These pastures also lead to digestive disorders, the most serious of which is bloat. FOR those readers not aware of the particular problems of newly sown pumice pastures some explanation may be necessary. Each year since the war thousands of acres of pumice scrub land have been burnt, cultivated, and sown with pasture mixtures. The natural fertility of the soil is very low and consequently grasses are not prominent in the young pastures. On the other hand, clovers make remarkable progress, and if amply supplied with phosphate, dominate the pastures for the first 5 or 6 years at least. The grasses which do survive are weakened further by the smothering effect of the strongly growing clovers. As a result of the vigorous clover growth over a number of years the nitrogen status in the soil is built, up to a stage where the grasses would respond to it if they were present. Too often, however, they are very poorly represented and so cannot assume their rightful place in a high-yielding pasture. With these problems in view, and following a direct request from farmers in the Whakamaru district, the authors conducted a field day there on overdrilling grasses into the sward in the autumn of 1956. The demonstration was held on the dairy farm property of Mr. D. Tong, whose active co-operation is gratefully acknowledged. This article gives an account of the treatments used, the results obtained, and the conclusions derived from the sowings as judged from an inspection of the area 6 months later.

Preliminary Considerations ' It has been determined from numerous trials conducted by one of the authors that the successful establishment of seedlings following overdrilling or oversowing is dependent largely on the lack of competition from the plants already growing in the sward. As the latter are less competitive in autumn than in spring, and as previous trials had favoured autumn sowings, it was decided to hold the demonstration at Whakamaru on 6 March 1956, when soil conditions could be expected to he satisfactory. to oe sausiactory. Treatment of the area before sowing was designed to reduce the vigour and amount of the existing vegetation as much as possible, to assist the placement of seed and fertiliser in the soil, and ensure that the seedling growth had the minimum of competition. Unfortunately it was not possible to stock at the intensity desirable, with the result that clover competition did become a factor of importance after the seed was drilled. In a season of vigorous autumn growth hard grazing may often not be feasible on a large area,

particularly where dairy cows are the only stock available to eat it down. Consequently only the area which can be given this preliminary treatment should be overdrilled unless recourse j s made to mechanical means of removal. Overdrilling without it is not likely to be satisfactory, Experimental Sowings rp, , 0,.« . tfa tab i e below. Grass seed at “ 1 * ™ ™ „ Swl " b cet Ve conteol Anti qAnJdSI superphosphate was applied, P A desuperphosphate was applied, as detailed in the table , at 2cwt per acre on all plots. The light cultivation treatment before seeding consisted of two strokes of weighted spike tine harrows, the aim being to reduce the white clover by about 50 per cent. The heavy cultivation before seeding was done with tandem disc harrows, followed by tine harrowing, and the vegetative cover was reduced by about 90 per cent. Each plot was given one stroke with the chain harrows after seeding. Control plots were spaced among the others for later comparisons.

Machines Used The disc coulter drill (treatments 1 to 5) was a standard machine equipped with separate seed and fertiliser boxes. Separate tubes were used to guide the seed and fertiliser into the grooves left by the discs. The seed was sown in the bottom of the groove and in friable ground was covered by a little soil before the fertiliser was deposited. The disc coulters were each fitted with a depth-limiting skid (see illustration on this page) . Thus, sufficient spring pressure could be applied to the coulters to ensure constant penetration without the discs penetrating too deeply. The hoe coulter drill (treatments 6 and 7) was a standard old-pattern grain drill. “Blackmore” grassland tips were fitted to the coulters, but their real worth was masked by the poor mechanical condition of the drill. The Australian sod-seeder (treatments 8 and 9) comprised a seed and fertiliser box mounted on a tractor-mounted cultivator (see illustration on this page). Special designed furrowopening shoes were fitted to the cultivator tines, which each incorporated a stump-jump mechanism. This machine, now in production i n Australia, was the outcome of research work at Sydney University

into the problem of introducing clover into paspalum-pastures. The machine used in these sowings had been donated by the manufacturers to Massey Agricultural College for research work on overdrilling in this country. The “Wilson” tiller-seeder (treatment 10) comprised a tractor-mounted tine cultivator to which had been added a grass seed box and a pair of depth wheels (see illustration on this page). Narrow “lucerne-renovating points replaced the usual 2in.-wide chisel points. The owner, Mr. W. G. Wilson, of Tokoroa, who designed and constructed it, plans to add a fertiliser box for next season. The “White” disc-seeder (treatment 11) was based on a prototype devel-

oped at Massey College and consisted of a fertiliser distributor mounted on top of a single gang of trailed outcut discs (see illustration on page 287). Depth-limiting wheels had been fitted between the second and third blades from each end so that increased “cut” could be applied without excessive

penetration of the discs. Tubes guided the mixed seed and fertiliser into the grooves left by the discs. The machine had been designed and constructed by the joint owners, Messrs. R. White and J. Morton, of Atiamuri. Broadcast sowings (treatments 12 and 13) and all fertiliser broadcasts were made with the disc coulter drill from which the coulters and tubes had been removed. Drill settings remained unchanged. After Treatment Conditions at the time of sowing were good for establishment. The soil was moist and suitable for rapid germination and the temperature mild. These conditions were ideal for the quick recovery of the clover and it was decided x to continue grazing the plot area for 10 days after sowing. To continue grazing longer than this would have damaged the young seedlings unduly. Previous experience had shown that the new seedlings must not be defoliated until they are well established, even though it appears that the clovers and grasses of the old sward are offering strong competition. Generally the damage done by a premature grazing is greater than the weakening effect of competition. Growth on the plots was very vigorous in March and April and almost completely overtopped the sown species. The latter, however, survived quite well, but it is known now that a more severe grazing beforehand as well as a more vigorous surface cultivation would have been of advantage in this district. Results The plots were kept under observation by Mr. D. Tong and were inspected by the writers in May and October. At the first inspection the strong autumn growth masked the differences between most of the treatments, but the machines and treatments which had done most damage to the turf seemed to have given the best results at this stage. These were the “Wilson” -seeder and the Australian sod-seeder, and the heavy cultivation treatment sown with the disc drill. A more detailed inspection was made on 17 October 1956, at which stage the field had been spelled for about 3 weeks. The vigorous regrowth of the introduced ryegrass where it had become thoroughly established was quite discernible.

Short-rotation ryegrass proved more vigorous than the other grasses in the first 6 months. Perennial ryegrass was also firmly established, but because of its slower establishment and growth it was less noticeable. Cocksfoot had been well shaded by the vigorous regrowth of clover, but was still hanging on and appeared capable of becoming well established later.

The heavy cultivation treatment was disappointing because of the uneven

establishment of the short-rotation ryegrass. A heavy and vigorous regrowth of clover had occurred despite the fact that most of the old sward had been destroyed by cultivation. The light cultivation treatment in conjunction with the hoe coulter drill (treatment 6) and the sod-seeder (treatment 8) resulted in better establishment and growth of the sown species than did the sowings by the same machines on the uncultivated sward (treatments 7 and 9). Of the methods of sowing used, broadcasting the seed and fertiliser, even where a light cultivation had been given (treatment 12), resulted in the poorest establishment of grass plants. In contrast, the thickest and most uniform establishment was obtained from the “Wilson” tiller-seeder (treatment 10). This plot had been the most prominent throughout the whole period under observation. The two drills following light cultivation (treatments ■ 1 and 6) gave rather similar results, the uniformity resulting from the disc drill being slightly superior to that from the hoe coulter drill. Both, however, failed to reach the evenness of the best plot (treatment 10). Patchy development of short-rota-tion reygrass occurred in the plots sown with the Australian sod-seeder and the “White” disc-seeder. Comments and Conclusions The ability of short-rotation ryegrass to establish quickly from seed is of special value where competition in the early stages is severe. On the other hand experience has shown that it requires more favourable moisture

conditions and a higher soil fertility than perennial ryegrass. Where there is some doubt about the suitability of the area to be overdrilled, a mixture of the two grasses can be used. Cocksfoot is a useful grass on pumice soils and more information should be obtained on its performance when overdrilled. Where grass seed is drilled the sowing rate can be reduced to 61b. to 101 b. per acre because of the better placement of the seed in the soil and its restricted distribution through being sown in rows; 81b. of ryegrass seed per acre gives a seeding of between two and three seeds per inch of rows spaced 7in. apart, and, even allowing for only a 50 per cent, establishment, should still provide enough plants to give a grass-dominant sward. It is considered that time and money should not be spent on overdrilling grass seed in soils that are not in good heart. Fertility build-up on pumice soils can occur rapidly if clovers are encouraged and are well utilised by efficient grazing of the young pastures. It is advisable to delay overdrilling until the build-up has reached a stage at which the introduced grasses will be adequately fed. The time when this stage will be reached may be difficult to forecast, but is indicated by an increase in the proportion of grasses to clovers in the pasture. Cocksfoot and Yorkshire fog are usually the active grass indicators. The pre-cultivation of the sward appears to be an easy way of reducing the competition of established plants, but is not so valuable as severe grazing as a preparation for overdrilling. Cultivation still leaves the vegetation

on the ground and this interferes with seeding and establishment. The relatively poor results of the heavy cultivation were probably due to two factors. First, the discs disturbed the soil to a depth of 3in. or 4in. and left it unconsolidated. Secondly, they brought to the surface on many parts of the plot much raw pumice, and the seed was not placed ' in the black organic matter of the surface layer. Confirmation of the effect of this was obtained from small plots sown previously with different grasses. The ground was uneven. In some places the black topsoil extended the full depth of the spade; in others it was only an inch or two deep. The early growth of the grass seedlings was much greater in the former sites than in the latter. The establishment from the Australian sod-seeder was very patchy. The furrow opened by this machine is formed by the bursting of the turf and by the sideways compression of the soil rather than by removal of a strip of turf. As a result, in this, loose, friable pumice soil the furrow healed over quickly and the introduced seed was readily smothered by the vigorous clover. Also, being a rigid-framed machine it could not follow the surface irregularities, with the result that only 2 or 3 coulters were sowing at the correct depth at one —the remainder were either too deep or not touching the ground at all. Results from the “White” disc-seeder were also poor on the plot areas, though very good results were

observed where the machine had continued sowing on the way to the loading bank. Because of the construction of the ■ seed and . fertiliser delivery mechanism it is necessary to run this machine for some distance before an even flow from the seed tubes is assured. It is thought that as the machine was filled just before sowing the plot area, it would not have been sowing properly until the run was almost completed. Performance therefore could not be fairly judged from the plot area, but the good establishment noted on the trip from the field suggests that it has much merit. The performance of the two drills would have been improved had the area been more closely grazed. The addition to the disc drill of a skimmer (similar in type to that used on a plough) fitted to each disc would assist materially in leaving a wider plantfree furrow. In both cases it is thought that the unevenness of establishment was due to the competition from the established clovers which were not sufficiently repressed by the prior grazing, the light cultivation, or the action of the furrow opener. Though these machines both used independently mounted coulters, the range of vertical movement was insufficient at times to cope with the uneven ground. The need is stressed for each coulter on an overdrilling machine to have free vertical movement of up to about 12in. or more. The rate of wear of the “Blackmore” tips in abrasive soils is high, even though the points are hard faced; thus this method would be

more suited to a farmer overdrilling a small area each year than to a contractor who may overdrill upward of 2000 acres per year. Though the “Wilson” tiller-seeder is a rigid-framed machine and did not sow fertiliser with the seed, it still gave the most successful results. The reason is attributed to the following:— (a) The narrow points were set to cut about 2in. deep on level ground. Where a high spot was encountered by some of the tines they cut through at considerably increased depth without lifting the remainder of the tines out of the ground. Because of the narrow cut the seed did not fall to the bottom of the furrow but remained near the surface, where it was covered by the. chain harrowing. Some gaps in the established plants were noticed, mainly where there was a hollow and the tines had not penetrated. (b) The points, though narrow, formed their track by tearing the sward apart. This resulted in the clover being torn away in some cases up to 2in. to 3in. from each side of the coulter. There was sufficient clearance between each tine to allow the : trash free passage. The almost complete failure of the broadcast treatment (treatment 13) is in line with previous experience. An improvement was noted on the lightly cultivated plot (treatment 12), but even this was considerably poorer than the other treatments. Unless the seed can fall on to the soil it has little or no chance of survival. A more drastic harrowing or surface cultivation would assure this and provide a greater check on the established species. : 1 But this would require a considerable increase in time to prepare the field and heavier seeding rates would be required 5-to allow for the inevitably higher mortality. The cost of overdrilling, if good results are regularly obtained, is such that the operation could be repeated economically every year if necessary. On the average, seed should not cost more than 10s. per acre and contract rates for overdrilling should be about £1 per acre. The number of plants that established in the best treatments indicates that about 61b. to 81b. of ryegrass seed per acre is sufficient to ensure a desirable grass-clover balance. The observed results, of the sowings confirm the need for. overdrilling machinery designed to. cope with the requirements dictated by soil, vegetative, and climatic conditions prevailing in this country. None of the machines used fulfilled all requirements and consequently the trial sowings were not uniform. As sections of the treatments were good— some cases excellent where the requirements had been fulfilled for short lengths—seems to be no reason why uniformly good results could not be expected if such machines were available.

Treatment Fertiliser No. Method of seeding Fertiliser application Cultivation Seed mixture 1. Disc drill Light Short-rotation ryegrass . . ryegrass .. Drilled with Drilled with seed seed 0 Disc drill . Light Perennial ryegrass Drilled with seed 3. Disc drill Light ■ { i short-rotation ryegrass J perennial ryegrass Drilled with seed ,4. Disc drill Light Cocksfoot .. Drilled with seed 5. Disc drill Heavy . Short-rotation ryegrass . . ryegrass .. Drilled with Drilled with seed seed 6. Hoe coulter drill with "Blackmore” tips .. Light Short-rotation ryegrass . ryegrass .. Drilled with Drilled with seed seed 7. Hoe coulter drill with "Blackmore” tips . . . None Short-rotation ryegrass . . ryegrass .. Drilled with Drilled with seed seed 8. Australian sod-seeder .. Light Short-rotation ryegrass .. ryegrass .. Drilled with Drilled with seed seed 9. Australian sod-seeder .. None Short-rotation ryegrass . . ryegrass . . Drilled witli Drilled with seed seed 10. “Wilson” tiller-seeder Light Short-rotation ryegrass . . ryegrass .. Broadcast Broadcast 11. "White” disc-seeder .. Light Short-rotation ryegrass . . ryegrass . . Drilled with Drilled with seed seed 12. Broadcast Light Short-rotation ryegrass . ryegrass .. Broadcast Broadcast 13. Broadcast None Short-rotation ryegrass . . ryegrass . . Broadcast Broadcast 14. Control None ' None Broadcast

EXPERIMENTAL SOWINGS