Conservation Farming in Central Otago Restores Badly Eroded Cropland

New Zealand Journal of Agriculture, Volume 95, Issue 3, 16 September 1957, Page 273

Conservation Farming in Central Otago Restores Badly Eroded Cropland

By

G. G. Calder,

District Soil Conservator, Department of Agriculture, Dunedin

/CONTROL of erosion on a practically abandoned area of 40 acres at Gibbston in Otago and its rehabilitation into first-class pasture within 5 years are described in this article. The paddock selected to demonstrate soil conservation methods of farming that will not only restore eroded land but will stop it getting into that condition had been cropped for many years with wheat and barley; most of the topsoil was washed away and the land was deeply rilled and gullied with only scattered weed growth present. - ,

AFTER the Soil Conservation and Rivers Control Council ** became established the Council appointed two District Soil Conservators to each of the North and South Islands. Part of their duties was to stimulate interest in the need for soil conservation methods of farming and to demonstrate these methods in the problem areas of their districts. In the Gibbston, Shotover, Arrowtown, and Crown Terrace districts of Otago considerable erosion of farming land had occurred. This was brought about mainly by overcropping on a silt loam derived from loess, a soil type that is readily susceptible to sheet, rill, and gully erosion, particularly after the physical condition of the soil has been reduced or lost. Mrs. M. E. Perriam, of Gibbston, kindly agreed to cooperate with the Soil Conservation and Rivers Control Council through the Otago Catchment Board by leasing a paddock for demonstration. The lease of a 40-acre paddock was arranged from 1 January 1951 for 5 years, with the right of renewal for an extra 2 years if this were necessary to complete the work of rehabilitating the area, which was severely sheet, rill, and gully eroded and was almost depleted of vegetation except for about 7 acres of rocky outcrop and natural watercourse that had never been cropped and on which the soil was quite stable.

The paddock had been cropped for many years with wheat and then barley, until most of the topsoil was washed away and what was left had lost its physical condition. Rilling was prevalent and a number of the rills had developed into gullies up to 3ft. wide and nearly as deep. The area had been practically abandoned, as implements could no longer cross the gullies and only scattered weed growth was present. The slope varied from about 5 degrees at the bottom of the paddock to about 10 degrees at the top. At two small mounds the slope was up to 20 degrees. With the loss of its physical condition the soil became caked and impervious to rain, run-off increased, and gullies developed, and the position was continually becoming worse. Rainfall is about 20in. per year or a little less. Soil Conservation Methods These conditions appeared to offer an excellent opportunity for the Soil Conservation staff to put their training into practice as well as to demonstrate the value and use of . soil conservation methods of farming not only for rehabilitating worn-out land but to stop land getting into that condition. Conservation farming is intimately tied up with water conservation either in holding up all or part of the rainfall on the land or in disposing of surplus water in such a way that scouring and washing of the soil do not occur.

The problem on this area consisted of two parts: — 1. To stop water running off the land and make it soak in instead. 2. To bring back the physical condition of the soil so that pasture would hold on it. For the first part mechanical means could be used to slow up the run-off of water, and for the second the ploughing in of green manure and use of a straw mulch would build up the humus content and improve the physical condition of the soil. A bulldozer was hired to fill in the gullies so that a tractor and plough could cross them. The area was then ploughed on the contour. (To work land on the contour is to work it on the level instead of working up or down hill or on a slope.) This was not easy, as the contractor had difficulty in getting the plough into the dry, hard soil and then holding it in. Broad-base terraces to act as absorption banks were constructed on the contour on the gentler slopes at the bottom end of the field, and when the slope was too great for broad-base terraces graded banks were used on the contour. At the top of the field a diversion ditch was built with a fall of l|in. to 2in. per chain to drain off surplus water from the hill at the back of the 40 acres. (Broad-base terraces are built on gentle slopes and are broad and low enough to allow all cultivating and harvesting machinery to cross them if necessary. They are constructed with sufficient fall to lead surplus run-off to a natural watercourse or grassed waterway. Absorption banks can be either broad-base terraces or graded banks built on the contour to hold up and absorb all run-off.) -

A terracer was used to build the broad-base terraces and a giant disc fitted to one side of the tractor was used for the graded banks and diversion ditch. Later a Britstand grader-ditcher was used successfully for realigning the graded banks and for building two more diversion ditches. Trees were planted above the top diversion ditch to help stabilise and-hold the land. Crops A mixture of ryecorn at 1 bushel and partridge peas at 2 bushels per acre was drilled in in April with lewt. of superphosphate per acre.. All cultivation and drilling were done on the contour. By winter a good strike of ryecorn and peas was showing up. Some heavy rains had fallen and the contour drilling and harrowing of the crop, with the terraces and graded banks, had held up a considerable amount of water and soil. In some spots where the gullies had been filled the terraces had settled and sufficient soil had washed into them to block them and allow water to run over, thus causing some scouring.

By early summer the crop was much better than was expected and it was decided to harvest the best of it by direct heading instead of ploughing it in as green manure. This was done on 15 to 19 February 1952, when 183 sacks of mixed ryecorn and peas and 44 bags of peas were obtained.

The straw and remaining crop were then bush and bog disced and worked into the topsoil and because of ryecorn and peas which fell from the previous crop a good crop came away. Those terraces and banks that required attention were cleaned out and the banks were rebuilt. In October 1952 the green crop and straw from the previous crop were ploughed and harrowed on the contour, the ploughing this time being much easier than the first time.

It was then realised that all absorption banks were not practical under the conditions at Gibbston. Consequently two more diversion ditches were constructed and given an outlet into the natural watercourse on the west side of the area. Also a number of the absorption banks were filled in and rebuilt as graded banks with a fall into the watercourse. Seed Mixtures The two new diversion ditches practically divided the paddock into three blocks each of about 11 acres. During

20 to 23 January 1953 the three blocks were sown with the following mixtures per acr . - Top block, 301 b. of Certified Mother perennial ryegrass, 41b. of red clover seed, and lcwt. of superphosphate. Middle block, 301 b. of Certified Mother perennial ryegrass, 2 Jib. of Certified white clover, and lcwt. of superphosphate. _ ... „ ... Bottom block, 101 b. of subterranean clover and lcwt. of superphosphate. * v Dry conditions after sowing delayed the strike, frost lift killed a considerable portion of the red clover, and the subterranean clover was very patchy; however, the white clover and ryegrass were satisfactory. uere satisiactory. During April 147 points of rain fell in 6 hours, causing some washouts through over-topping of the terraces and graded banks with silt and water. The amount of growth gave very little protection to the soil surface. During V T _ v thp tprrncp<s and diversion ditches SL tn! were again cleaned out with the graae - ’ The ryegrass crop ripened over the Christmas period of 1953 when a header was unprocurable and most of the seed was lost. A stripper was borrowed and on 13 and 14 January 1954 12 bags of ryegrass seed were obtained. Thirty-seven bags of self-

sown ryecorn were direct headed in February. The area of subterranean clover had not developed very evenly and was worked up to scatter what subterranean clover seed was present; also 16 bushels of perennial ryegrass and 151 b. of white clover were sown. A visit during May 1954 showed a tunnel gully (underground) forming at one of the points where run-off had ponded in a depression of a graded bank. The gully was filled and the graded bank realigned and given a fall to carry water away from this point. By the summer the subterranean clover had thickened up well and the white clover and ryegrass were good, though the red clover was still, poor. In February 1955 a sack of subterranean clover was harvested experimentally and a further 13 sacks of volunteer ryecorn were also headed. The white clover was good and allowed to seed and the sack, of subterranean clover was sown on the red clover block, During winter and early spring the whole 40 acres were heavily grazed by sheep, and grazing will now be continued. Successful Rehabilitation A field day was held in October 1955, when local farmers and those from surrounding districts were present and inspected the area. It was agreed that

not only had erosion been controlled and the paddock rehabilitated into first-class pasture, but that with the system of controlling run-off there should be no risk of the paddock deteriorating again. The main lesson learnt from the area was the need to provide a fall not only for diversion ditches but also for graded banks and broad-base terraces. Also due attention must be given to . surveying the lines, particularly when gullies are being crossed, so that there is no ponding of water. The gullies were the weak spots, particularly where filling had been done. Absorption banks do not appear practicable on their own where the rainfall approaches 20in. The 5-year lease ended in December 1955. It was not necessary to exercise the renewal clause in the lease, as restoration of the land to safe, permanent production had been achieved. Cost of Work The following statement shows receipts and payments for the 5-year period: Receipts £ s. d. Sale of ryecorn, peas, and ryegrass seed . . .. .. .. . . 429 17 4 Estimated value of grazing .. .. 25 0 0 454 17 4 Payments £ s. d. Cultivation at contract rates .. 293 2 7 Seed 172 3 2 Superphosphate . ... .. .. 66 17 9 Labour . ... • . . . . .. . . 105 11 Harvesting at contract rates . . 251 8 3 Tree planting .. . .. 14 11 6 Fencing materials . . .. .. 12 6 6 Freight charges .. .. 10 9 11 926 11 2 The net cost of development on the area was £471 13s. lOd. or £ll 15s. lOd. per acre over the 5-year period. However, the cost could have been substantially reduced if the work had been done by the farmer herself and if machinery had been available to harvest the 1953-54 ryegrass seed crop. Main Objects Achieved The main objects of the project, however, were achieved. These were: To demonstrate soil conservation methods of farming that will not only rehabilitate eroded farm land but will stop land getting into that condition; and the carrying out of the soil conservation farming concept of “using each acre according to its capability and treating it according to its needs so that it may produce forever”. Applications for advice or assistance on these lines should be made to a local Catchment Board or Soil Conservation District Committee. Where neither of these bodies has been set up applications should be made to the local Soil Conservation Service of the Department of Agriculture.