Plot Boundaries Research Articles

Portable Rainfall Simulator and Plot Unit for Use in Field Studies of Infiltration, Runoff and Erosion

The simulation of rainfall for studies of infiltration, surface runoff and erosion is not new. Early methods of applying rainfall used hand-operated watering cans (e.g. Duley & Hays 1932). In later work rainfall was delivered to the plots through specially designed upturned nozzles; here the spray also wets a variable area surrounding the plots and protective tents are commonly necessary to minimize wind effects. The most familiar are the Types F and FA Infiltrometers (Wilm 1943) and the Rocky Mountains Infiltrometer (Dortignac 1951). These units have proved of value in elucidating the contribution of rainfall, soil, vegetation and management effects to infiltration, runoff and soil loss (Meyer 1960), but there are several disadvantages for convenient and realistic use. The Type F Infiltrometer, for example, is bulky, due largely to the large water requirements and the need for protective tents when up-turned nozzles are used. On the other hand, the Type FA and Rocky Mountains Infiltrometers have a plot size of only 2-5 ft2, which restricts the development of surface runoff and soil erosion. Laboratory studies of the infiltration, runoff, and erosion processes generally utilize elaborate mechanical devices which are unsuitable for field use (cf. Turner 1964). The equipment described in this paper was developed progressively in the course of catchment studies in subalpine and alpine (Costin, Wimbush & Kerr 1960), forest (Gilmour 1965), and pasture (Costin & Gilmour, in preparation) areas in south-eastern Australia. Because the terrain is often rough and staff limited, the equipment had to be compact, robust and easily handled by one person. Other requirements were ease of assembly, operation and dismantling, and rapid movement from site to site enabling a large number of replicated plots (up to ten) to be examined before site conditions changed materially during any one day. A relatively large plot size (10 x 6 ft) helped to overcome problems of small scale soil variability and three-dimensional infiltration along the plot boundaries frequently encountered when small diameter infiltrometer rings are used, and to make the runoff and erosion effects more realistic. In erosion studies using simulated rainfall it is often desirable to reproduce the stress conditions most likely to be experienced in the area under investigation (Costin et al. 1960). A summer storm rainfall of about 80 points in 15 min occurs approximately every second year in the study area and was selected as the stress rain to be simulated.

A NEW PROCEDURE ALLOWING REPLICATED MINIATURE LARVICIDE TESTS IN A LARGE RIVER

AbstractDDT and DDD emulsifiable formulations were tested against aquatic invertebrates in small plots in rapids in the St. Lawrence River. Pollution was minimal; less than 0.0044% of the river discharge was treated in each rest.The weakest dosage of DDD, 0.8 p.p.m.-minutes, disabled many Trichoptera and Diptera; the strongest, 12.0 p.p.m.-minutes, did not eliminate any one Order of insects except perhaps Plecoptera. A dosage of 6.0 p.p.m.-minutes was selected for tests on a larger scale against shadfly larvae (mainly Trichoptera). Net-spinning Trichoptera were more sensitive than case-bearers. Of the non-insect organisms, amphipods were relatively sensitive but their populations were rapidly restored by immigration. Oligochaetes and molluscs were least affected.The use of small plots in a large river required special equipment and techniques: a larvicide dispenser (to be described separately), the use of concentrated milk as a dye to aid in the survey of plot boundaries, the transfer of disabled organisms to fresh water to compare recovery rates, and a formula combining data from samples of both disabled and surviving organisms to estimate per cent kill.

Results of an experiment at Rothamsted testing farmyard manure and N, P and K fertilizers on five arable crops I. Yields

1. A ‘reference plot’ rotation experiment was begun at Rothamsted in 1956 on a field where grass had grown for many years. The soil contained very little HCl-soluble P and K but much N. The soil had been acid, but was limed to pH 6·5 immediately before the experiment started; this pH has been maintained. Very small individual plots (0·00128 acre) were used and nearly all work was done by hand. The results showed that such small plots can be used to do complicated rotation experiments satisfactorily provided that all work is done carefully and movement of soil over plot boundaries is prevented.2. Responses to combinations of N, P and K fertilizers and farmyard manure (FYM) were measured on wheat, kale, barley, grass-clover ley, and potatoes grown in rotation. Two rates of N were tested. A strip of permanent grass had the same treatments as the arable crops.3. Winter wheat yielded most dry matter, but wheat yields were increased least, proportionally, by added nutrients. Potatoes gave the smallest yield without manure and responded most to nutrients, yields being increased almost sixfold by NPK fertilizer plus FYM. Kale, barley and grass-clover ley were intermediate in their unmanured yields and in their responses.4. All crops except the grass-clover ley responded to N; kale responded most and wheat least. Potatoes kale and barley responded roughly equally to P and needed this nutrient more than did wheat and the ley. Potatoes responded most to K, yields of wheat and clover ley were also small without K, but barley and kale needed K less. Interactions between nutrients were large with most crops, particularly with N on kale and K on potatoes, wheat and clover.5. FYM greatly increased yields of all crops but responses were less when fertilizers were also given. Potatoes responded most to FYM whether or not fertilizers were also used. FYM also caused large increases in yields of grass-clover ley, kale, and permanent grass.