Cent Slope Research Articles

Land gradient and configuration effects on yield, irrigation amount and irrigation water productivity in dry direct seeded rice and non-puddle transplanted rice in cauvery delta zone

Field experiments were conducted in two different locations in the Cauvery delta zone - viz., old delta at Tamil Nadu Rice Research Institute (TRRI) Aduthurai, and new delta at Soil and Water Management Research Institute (SWMRI), Kattuthottam, Thanjavur.Laser levelling with 0% gradient significantly reduced irrigation amount and/or increased irrigation water productivity (WPi) in all crops/systems grown on the flat compared to farmer leveling practice. However, water advancement rate in farmer’s field generally very low because of flat configuration and or sub – optimal flow rate, resulting in high rates of drainage below root zone, more so at the head end of the field than tail end because of longer period of flooding of soil surface at the head end.It is hypothesized that formation of a uniform gradient from the head to tail end of the field increase the water advancement rate, reduce irrigation input and increase irrigation water productivity.Experiments were conducted during Kharif (Kuruvai) 2014, late Samba 2014 - 15 and Kharif (Kuruvai) 2015 at TRRI, Aduthurai and during early Kuruvai 2014, Samba 2014 - 15 and early Kuruvai 2015 at SWMRI, Kattuthottam, Thanjavur to evaluate the effect of land gradient on water and rice crop and water productivity. The experiments were laid out in Randomized Complete Block Design (RCBD) with three land slope treatments in which three observations are taken on each plots (16 m x 50 m) (at the head, middle and tail of the plot) and three replications (blocks) in dry direct seeded rice (DSR) and non – puddle machine transplanted rice (NPTR). The slopes studied are T1 - 0.0 per cent slope,T2 - 0.1 per cent slope (5 cm gradient in 50 m run) and T3 - 0.2 per cent slope (10 cm gradient in 50 m run) with precise leveling. Short duration (100 – 110 d) rice variety ADT (R) 45 was raised as a test variety in the field experiments conducted during early Kuruvai and Kuruvai seasons in both the experimental sites. For Samba / late Samba season, long duration (135 – 150 d) rice variety CR 1009 was used in both the experimental sites. With regard to different slope gradients, it was worked out as 2159 litres as water requirement to produce 1 kg of rice under 0.1 per cent slope as against 2566 litres in 0.0 per cent slope across the seasons which indicated a water saving of 407 litres (15.8%) of water per kg of rice at Aduthurai location, whereas it was 661 litres (20.7%) at Thanjavur experimental site. The results further suggested that the effect of land slope gradients was explicitly pronounced more in the sandy loamy soils as compared to clayey loamy soils.

Comparison of data reduction algorithms for LiDAR‐derived digital terrain model generalisation

A digital terrain model (DTM) is a three‐dimensional representation of the terrain relief created from discrete points related to each other through their elevations. New technologies such as satellite remote sensing, airborne laser scanning and radar interferometry are efficient methods for constructing high‐quality DTMs in a cost‐effective manner. The accuracy of a DTM is influenced by a number of factors, including the accuracy, density and spatial distribution of elevation points, the terrain surface characteristics, etc. In this paper, direct comparisons of absolute and relative vertical accuracies are made between data reduction algorithms for the generalisation of DTM extracted from airborne Light Detection and Ranging (LiDAR) data. The absolute vertical accuracies are presented in terms of the mean error (ME), the mean absolute error (MAE) and the root mean square error (RMSE) and the relative vertical accuracies are characterised as per cent slope over Mount St Helens in southwest Washington State. The results show that LiDAR datasets can be reduced to 50 per cent density level by a uniform data reduction algorithm using triangulation with a linear interpolation method for the generalisation of DTM while still maintaining the quality of the original data.

Slope shape effect on runoff and soil erosion under natural rainfall conditions

Abstract: Slope is often non-uniform along the hillslope, with variations describing concave and convex shapes associated with natural hillslopes. This is because runoff generations vary significantly over short distances, with changes in surface alteration during or between flow events on different slope shapes. The aim of this research is to determine the effects of slope shapes on runoff and soil erosion. A field experiment was conducted from September 2007 to September 2009 on hillside field plots located in the northern part of the city of Bartin in northwestern Turkey. The experiment focused on complex topography including uniform, concave, and convex slopes. Nine experimental field plots were established on a 30 per cent slope, including three replications of field plots per different shape treatment. Runoff and soil loss by water erosion were measured in these plots under natural rainfall conditions. A total of 158 rainy days and 69 runoff events were registered over the period of investigation. Runoff and soil loss were greater in uniform plots than in concave and convex plots. The greatest amount of runoff was measured between September 2007 and August 2008 (Period1: P1), with 211.53 mm from uniform plot1 and during September 2008 and August 2009 (Period2: P2) with 430.06 mm from uniform plot3. The lowest runoff quantities with 157.44 and 371.63 mm from concave plot3 and concave plot1, respectively, were measured at P1 and P2. The highest soil loss was recorded at 2.97 kg m-2 and 6.16 kg m-2 during P1 and P2 from uniform plot2 and uniform plot3, respectively, and soil loss was lowest from concave plot3 and concave plot1, with a total of 0.23 kg m-2 and 0.67 kg m-2, respectively. The distribution of eroded soil was separated into >2 mm (coarse) and ≤2 mm (fine) size classes, and suspended quantity in runoff was also determined. Results indicated that the majority of soil lost from the uniform plots is composed of fine particles rather than coarse and suspended material. On the other hand, both concave and convex slopes demonstrated larger variability in the size distribution of eroded particles from individual plots.

RUNOFF AND SEDIMENT FROM ORCHARD TERRACES IN SOUTHEASTERN CHINA

ABSTRACTThe severity of soil erosion is considered to vary according to the structure of the bench terrace and the ground cover conditions. Erosion losses were investigated in a field experiment based on 20 m × 5 m erosion plots on a 21 per cent slope in Southern China. Five plots were established for the present study. Rainfall, runoff and sediment yield from plots were recorded for 5 years (2001–2005) and which five different types of terraces on sloping red soil were compared. The results show that the planting of grass on the riser is the most important factor affecting runoff and sediment yield, the next most important factor was the construction of a bund built on the edge of the terrace. Although the terrace bed slope (slope < 5 degrees) does not significantly affect the runoff, it does benefit the soil. A terrace combined with vegetation measures is effective in controlling runoff and soil erosion. Among various terraces, the level terrace (i.e. grass planted on the riser and bunds built on the edge of a bench terrace) is apparently the most beneficial for soil conservation purposes, indicating that this type is an excellent choice for conserving soil and water resources in sloping red soil in Southeastern China. Copyright © 2012 John Wiley & Sons, Ltd.

Agro-topo climatological studies for crop planning- a case study for the northen hills agrocliamtic zone of Chhattisgarh state

In the Northern Hills agroclimatic zone in Chhattisgarh state (India), the soils are undulating with 15 per cent at the top to 0 per cent slope in the valley areas. Analysis of field hydrological conditions in different soils in the toposequence revealed that in the top (sandy) soils agroforestry is a better option while in the valley areas with continuously flowing water from Mid July to November, tall varieties of rice are only suitable. In the clay loam soils rice is the best suited crop while in sandy loam soils maize is an alternative crop for diversifying rice.
 Local climate analysis indicated that it varies from near arid type climate at the top of the topo-sequence to near moist sub-humid conditions in the valley areas. Thus, the farmers in the zone need to plan from arid climate crops to moist sub-humid type crops like rice.

Measurement and prediction of sediment production from unpaved roads, St John, US Virgin Islands

AbstractExcess delivery of land‐based sediments is an important control on the overall condition of nearshore coral reef ecosystems. Unpaved roads have been identified as a dominant sediment source on St John in the US Virgin Islands. An improved understanding of road sediment production rates is needed to guide future development and erosion control efforts. The main objectives of this study were to: (1) measure sediment production rates at the road segment scale; (2) evaluate the importance of precipitation, slope, contributing area, traffic, and grading on road sediment production; (3) develop an empirical road erosion predictive model; and (4) compare our measured erosion rates to other published data. Sediment production from 21 road segments was monitored with sediment traps from July 1998 to November 2001. The selected road segments had varying slopes, contributing areas, and traffic loads. Precipitation was measured by four recording rain gauges.Sediment production was related to total precipitation and road segment slope. After normalizing by precipitation and slope, the mean sediment production rate for roads that had been graded within the last two years was 0·96 kg m−2 cm−1 m m−1 or approximately 11 kg m−2 a−1 for a typical road with a 10 per cent slope and an annual rainfall of 115 cm a−1. The mean erosion rate for ungraded roads was 42 per cent lower, or 0·56 kg m−2 cm−1 m m−1. The normalized mean sediment production rate for road segments that had been abandoned for over fifteen years was only about 10 per cent of the mean value for ungraded roads. Sediment production was not related to traffic loads. Multiple regression analysis led to the development of an empirical model based on precipitation, slope to the 1·5 power, and a categorical grading variable.The measured and predicted erosion rates indicate that roads are capable of increasing hillslope‐scale sediment production rates by up to four orders of magnitude relative to undisturbed conditions. The values from St John are at the high end of reported road erosion rates, a finding that is consistent with the high rainfall erosivities and steep slopes of many of the unpaved roads on St John. Other than paving, the most practical methods to reduce current erosion rates are to minimize the frequency of grading and improve road drainage. Copyright © 2005 John Wiley & Sons, Ltd.

Soil erosion and runoff response to plant‐cover strips on semiarid slopes (SE Spain)

AbstractOver a four‐year period (1997–2000), soil loss and surface‐runoff patterns were monitored in hillside erosion plots with almond trees under different plant‐cover strips (thyme, barley and lentils) on the south flank of the Sierra Nevada (Lanjaron) in south‐eastern Spain. The erosion plots (580 m a.s.l.), located on a 35 per cent slope, were 144 m2 (24 m×6 m) in area. The plant‐cover strips, 3 m wide, ran across the slope. The most effective plant cover proved to be thyme, reducing soil loss by 97 per cent and runoff by 91 per cent, compared to bare soil. Barley reduced soil loss by 87 per cent and runoff by 59 per cent, compared to bare soil, while these percentages were 58 per cent and 18 per cent for lentils. Thyme proved 77 per cent more effective than barley and 93 per cent more effective than lentils in reducing soil loss; thyme was also 79 per cent more effective than barley and 90 per cent more than lentil in blocking runoff. The present study demonstrates the effectiveness of plant‐cover strips in controlling soil erosion and runoff on sloping agricultural land. Copyright © 2005 John Wiley & Sons, Ltd.

Runoff and losses by erosion in soils amended with sewage sludge

AbstractIn order to promote the transformation of a burnt Mediterranean forest area into a dehesa system, 10 t ha−1 of dry matter of the same sewage sludge in three different forms: fresh, composted and thermally‐dried, were added superficially to field plots of loam and sandy soils located on a 16 per cent slope. This application is equivalent to 13ċ8 t ha−1 of composted sludge, 50 t ha−1 of fresh sludge and 11ċ3 t ha−1 of thermally‐dried sludge. The surface addition of a single application of thermally‐dried sludge resulted in a decrease in runoff and erosion in both kinds of soil. Runoff in thermally‐dried sludge plots was lower than in the control treatment (32 per cent for the loam soil and 26 per cent for the sandy soil). The addition of any type of sludge to both soil types also reduces sediment production. Significant differences between the control and sludge treatments indicate that the rapid development of plant cover and the direct protective effect of sludge on the soil are the main agents that influence soil erosion rates. Results suggest that the surface application of thermally‐dried sludge is the most efficient way to enhance soil infiltration. Copyright © 2003 John Wiley & Sons, Ltd.

Cropping systems and bed width effects on runoff, erosion and soil properties in a rainfed Vertisol

AbstractThe effects of two bed widths (1 and 2 m) and four rainfed cotton‐based cropping systems on soil properties, runoff and erosion were evaluated in a Vertisol (1 per cent slope; 21 g per 100 g sand, 12 g per 100 g silt, 67 g per 100 g clay) in subtropical central Queensland, Australia. The cropping systems were: early cotton (Gossypium hirsutum L.) sown between August and October; wheat (Triticum aestivum L.) sown in May, sprayed out and followed by early cotton; wheat allowed to mature, harvested and followed by late cotton sown between October and December; and grain sorghum (Sorghum bicolor (L.) Moench.) followed by cotton. Land preparation was by minimum tillage and traffic was restricted to the furrows between the beds. Rainfall runoff and soil erosion were monitored with water‐height recorders, flumes and troughs. Soil structure was evaluated as air‐filled porosity of oven‐dried soil in the 0–0.15, 0.15–0.30, 0.30–0.45 and 0.45–0.60 m depths. Soil chemical properties measured in the 0–0.15 m depth were organic carbon, pH (in 0.01 M CaCl2), electrical conductivity (EC1:5) of a 1 : 5 soil : water suspension and exchangeable Ca, Mg, K and Na. In comparison with 1 m beds, 2 m beds resulted in lower runoff and soil erosion, lower exchangeable Na, exchangeable sodium percentage and higher EC1:5/exchangeable Na, higher rate of soil organic matter decrease and better soil structure in the 0–0.15 m depth. Runoff and erosion were reduced, and cotton lint yields increased either by cropping systems sown early to intercept most of the seasonal rainfall or by those which produced a high level of ground cover. Soil physical and chemical properties were best, and runoff and erosion lowest with 2 m beds and cropping systems producing a high level of ground cover. Copyright © 2002 John Wiley & Sons, Ltd.

Sediment transport capacity and erosion processes: model concepts and reality

Sediment transport capacity, Tc, defined as the maximum amount of sediment that a flow can carry, is the basic concept in determining detachment and deposition processes in current process-based erosion models. Although defined conceptually and used extensively in modelling erosion, Tc was rarely measured. Recently, a series of laboratory studies designed to quantify effects of surface hydrologic conditions on erosion processes produced data sets feasible to evaluate the concept of Tc. A dual-box system, consisting of 1·8 m long sediment feeder box and a 5 m long test box, was used. Depending on the relative magnitudes of sediment delivery from feeder and test boxes, five scenarios are proposed ranging from deposition-dominated to transport-dominated sediment regimes. Results showed that at 5 per cent slope under seepage or 10 per cent slope under drainage conditions, the runoff from the feeder box caused in the additional sediment transport in the test box, indicating a transport-dominated sediment regime. At 5 per cent slope under drainage conditions, deposition occurred at low rainfall intensities. Increases in slope steepness, rainfall intensity and soil erodibility shifted the dominant erosion process from deposition to transport. Erosion process concepts from the Meyer–Wishmeier, Foster–Meyer and Rose models were compared with the experimental data, and the Rose model was found to best describe processes occurring during rain. A process-based erosion model needs to have components that can represent surface conditions and physical processes and their dynamic interactions. Copyright © 1999 John Wiley & Sons, Ltd.

Sediment transport capacity and erosion processes: model concepts and reality

Sediment transport capacity, Tc, defined as the maximum amount of sediment that a flow can carry, is the basic concept in determining detachment and deposition processes in current process-based erosion models. Although defined conceptually and used extensively in modelling erosion, Tc was rarely measured. Recently, a series of laboratory studies designed to quantify effects of surface hydrologic conditions on erosion processes produced data sets feasible to evaluate the concept of Tc. A dual-box system, consisting of 1·8 m long sediment feeder box and a 5 m long test box, was used. Depending on the relative magnitudes of sediment delivery from feeder and test boxes, five scenarios are proposed ranging from deposition-dominated to transport-dominated sediment regimes. Results showed that at 5 per cent slope under seepage or 10 per cent slope under drainage conditions, the runoff from the feeder box caused in the additional sediment transport in the test box, indicating a transport-dominated sediment regime. At 5 per cent slope under drainage conditions, deposition occurred at low rainfall intensities. Increases in slope steepness, rainfall intensity and soil erodibility shifted the dominant erosion process from deposition to transport. Erosion process concepts from the Meyer–Wishmeier, Foster–Meyer and Rose models were compared with the experimental data, and the Rose model was found to best describe processes occurring during rain. A process-based erosion model needs to have components that can represent surface conditions and physical processes and their dynamic interactions. Copyright © 1999 John Wiley & Sons, Ltd.

Soil degradative effects of slope length on alfisols in western Nigeria. IV plots of equal land area

Field experiments were conducted to evaluate effects of four slope lengths (20 m, 10 m, 6·7 m and 5 m) and four slope gradients (0·9–1·8 per cent, 4·7–5·7 per cent, 9·3–9·9 per cent, and 14·2–14·9 per cent) on interrill erosion. Plot width was appropriately adjusted to keep the plot area constant at 20 m2. These experiments were conducted on natural slopes and rainfall conditions for four consecutive years from 1984–1987 for maize (Zea mays)–cowpeas (Vigna unguiculata) or soybean (Glycine max)–cowpeas rotation. Runoff per unit area decreased with increase in slope length especially for steep slope gradients and erosive rains. Mean annual runoff per unit area was 3·2 per cent, 3·7 per cent, 4·6 per cent, and 8·1 per cent of the annual rainfall amount for 20 m, 10 m, 6·7 m and 5 m slope length, respectively. Similarly, interrill erosion per unit area also decreased with increase in slope length, and was 893 kg ha−1, 588 kg ha−1, 845 kg ha−1 and 1979 kg ha−1 for 20 m, 10 m, 6·7 m and 5 m slope length, respectively. For the steep slope gradient of 14·2–14·9 per cent, mean sediment concentration was 0·15 g l−1 for 20 m, 0·19 g l−1 from 10 m, 0·56 g l−1 for 6·7 m and 0·92 g l−1 for 5 m slope length. Highest grain yield was obtained for slope gradient of 4·7–5·7 per cent for maize, and for 0·9–1·8 per cent slope for cowpeas. High soybean yield was obtained on the steep slope gradient. Crop yields were related to clay content of the surface horizon and the soil's susceptibility to crusting, but not to slope length. These results show that surface detention capacity, for runoff and sediments, play an important role in runoff rate and amount and on interrill erosion. © 1997 John Wiley & Sons, Ltd.

Soil degradation by Erosion of a typic hapludalf in central Ohio and its rehabilitation

ABSTRACTSoil erosion and runoff were monitored from 1988 to 1990 on a Miamian soil (Typic Hapludalf) of 5‐6 per cent slope using field runoff plots. Four treatments were studied: (i) disk‐plough up and down the slope to 0.3 m depth (DP); (ii) disk‐plough up and down the slope followed by a protective netting (PN); (iii) uncultivated fallow without any vegetation followed by surface soil removal (R); (iv) uncultivated fallow with natural vegetation followed by ploughing (F). Mean annual runoff losses were 6, 114 and 128 mm, or 4, 20 and 18 per cent of the rainfall, and mean annual soil losses were 1.2, 85.0 and 64.0 Mg ha−1 in 1988, 1989 and 1990, respectively. Mean runoff amounts were 26, 69, 116 and 118mm and mean annual soil losses were 0.4, 23.2, 58.6 and 118 Mg ha−1 for the F, PN, DP and R treatments, respectively. In comparison with DP, PN decreased annual runoff by 40.3 per cent and annual soil loss by 79.5 per cent. The high mean soil loss for the R treatment was due to erosion following soil removal. An additional 2920 Mg ha−1 of surface soil was removed from the R treatment in May 1990. The F treatment reduced runoff by 78, 77 and 62 per cent and reduced soil loss by 99.7, 99.4 and 98.4 per cent compared with the R, DP and PN treatments, respectively. Mean losses of K, Ca, Mg and P were 1.3, 4, 1 and 01 kg ha−1, respectively for F, 3, 16, 5 and 0.3kg ha−1, respectively, for PN, 5, 31, 1 and 0.6kg ha−1, respectively, for DP, and 3, 32, 12 and 0.4 kg ha−1, respectively, for R. Soil and nutrient losses for each treatment were in the order R > DP > PN > F. The soil organic carbon (SOC) content was significantly affected by soil erosion and management treatments, and ranged from 0.98 per cent for the R treatment to 2.3 per cent for the F treatment. Soil surface removal for the R treatment in 1990 reduced water‐stable aggregates (WSA) by 9.0 per cent, SOC by 0.6 per cent, and clay content of the uppermost 0‐50 mm depth by about 7.0 per cent. Mean total porosity (ft) ranged from 0.43 for the F to 0.52 for the DP treatment. Cumulative infiltration for 3h ranged from 13 cm for R to 34cm for PN, with corresponding infiltration rates of 4 cm h−1 and 13 cm h−1, respectively. Regardless of the treatment, there were also temporal changes in soil properties. In comparison with 1988, measurements made in 1990 showed a significant decrease in WSA of 21.3 per cent, an increase in clay content of 2.8 per cent, and a decrease in SOC of 0.39 per cent. Runoff and soil losses were significantly correlated with the mean weight diameter (MWD), SOC, bulk density (pb) and available water capacity (AWC). Plant height measured 8 weeks after planting (WAP) for the R treatment was reduced by 33.3 per cent, 33.0 per cent and 29.0 per cent compared withh DP, PN and F, respectively. Nitrogen uptake by maize plants (Zea mays L.) 10 WAP for the R treatment was lower by 15 per cent, 8 per cent, and 6 per cent compared with the DP, PN and F treatments, respectively, while P uptake was lower by 33 per cent, 32 per cent and 29 per cent, respectively, compared with the same treatments. Grain yield was 9.78 Mg ha−1 for PN, 9.76 Mg ha−1 for DP, 8.64 Mg ha−1 for F and 6.60 Mg ha−1 for R during the 1990 crop season. Grain yield was reduced by about 32.4 per cent in the R treatment compared with the PN treatment, representing a maize grain yield reduction of 158 kg ha−1 for each centimeter of soil lost.

Study of the importance of splash and wash on cultivated loamy soils of Hesbaye (Belgium)

During 1974 and 1975, measurements of splash and wash were carried out in the cultivated area, in a station installed on 6·5 per cent slope covered with a loess in which a grey-brown podzolic soil has developed. Splash has been measured using an apparatus prepared for this purpose and wash has been measured on plots of standard length (22·13m). The splash is some tens t/ha.year but the splash loss calculated using the results of the measurements of splash is only a few tens kg/ha.year. Splash is positively correlated with the erosion index of the rains and with the structural stability but negatively with the crop cover. As splash, wash is positively correlated with the erosion index of the rains and negatively with the crop cover, but unlike splash it is negatively correlated with structural stability. The mean value of the wash loss is a few t/ha.year but very important differences are observed from one plot to another with regard to the structural stability. However, on a given plot wash loss and splash are positively correlated because the particles of soil detached by splash are easily carried off by runoff, but the relation between wash loss and splash is very different from one plot to another because splash is positively and wash loss negatively correlated with the structural stability of soils.

Pulmonary arterial oxygen saturation during treadmill exercise. A discriminative index of functional class

Six patients in functional class II and 11 in functional class III underwent graded treadmill exercise, with severe fatigue as their limiting symptom. During exercise, none of the patients developed chest pain, or significant arrhythmia. Our data suggest that at a treadmill workload of 2 mph and 7 per cent slope, with an oxygen consumption four times that a rest, measurement of the pulmonary arterial oxygen saturation permits clear separation of functional class II from functional class III. Although there was a significant difference in the heart rate response, mean pulmonary arterial pressure, and percentage change in pulmonary arterial end-diastolic pressure, considerable overlap occurred. The use of pulmonary arterial oxygen saturation may prove to be of value in instances in which the functional cardiac status is not reasonably clear from the clinical interview or routine exercise testing. It requires less than maximal effort on the part of the patient, and provides an objective end point to distinguish between two important groups of patients.

Runoff and soil loss on a sandveld in Rhodesia

Abstract Runoff and soil loss from veld treated in various ways was measured over a ten‐year period on a sandy soil with a 4 per cent slope in south‐western Rhodesia. The runoff as a percentage of the mean annual rainfall varied from 3.8, where the veld was left undisturbed, to 30.3, where the soil was kept bare artificially. The corresponding mean annual soil losses were 0.228 and 4.482 tons per acre (0.511 and 10.047 tonnes per hectare). The data for certain treatments were used to derive regression equations which allow for the estimation of runoff from, records of the amount and intensity of rainfall.

Moisture and energy conditions within a sloping soil mass during drainage

In an effort to explain the source of nonstorm streamflow in deep-soiled areas of the southern Appalachians, a 3×3× 45-foot inclining concrete trough was constructed on a 40 per cent slope. The structure was packed with a natural sandy-loam soil to a bulk density of 1.3, and after thorough soaking was covered with plastic to prevent evaporation. Outflow was measured at the base, and soil moisture tension and content were recorded for 145 days. As shown by piezometers, the larger pores were substantially emptied in 1.5 days, during which outflow occurred according to the expression, Q = a1T−b1 where T is time in days since day zero and a1 and b1 are constants. After a 5-day transition period, the logarithm of drainage for the next 80 days was again linearly related to the logarithm of time, but with new constants,a2 and b2, expressing unsaturated flow from the entire soil mass. An additional 60 days of flow occurred, deviating more and more from the log-log relation as the limits of drainage were approached. Soil moisture content and tension substantiated the theory that the entire unsaturated soil mass was contributing to outflow throughout the experiment. It is concluded that unsaturated flow in the earth mantle of steep watersheds cannot be ignored in hydrograph analysis, since it may well be a primary mechanism for sustaining baseflow.

Factors affecting sheet and rill erosion

This paper discusses the two principal processes by which sheet erosion occurs and the six factors which effect the magnitude of the losses. The processes are raindrop impact and transportation of soil particles by flowing water. The factors are length and per cent slope, cropping, soil, management and rainfall. The relative effectiveness of each of the three main conservation practices in control of erosion, contour farming, strip cropping, and terracing is presented. The factors and practices are combined in a rational erosion equation for calculating field soil loss for use in application of conservation practices and in assessing land program benefits.

Studies on the soil erosion Control in the apple orchards II

1 Run off soil caused by melting snow was measured on the tillage apple orchards in Yamagata Village, Minamitsugaru-County, Aomori Prefecture during January to March in 1951. 2. Special three plots, 7.2 feet wide and 30 feet long, were established on the 28 per cent Slope. The side and upper ends of three plots were formed by wood borders projecting 25 ems. above the sur-face of the soil and extending 25 cms. into the soil, At the lower ends of each plot a concrete tank to catch everything that run off were built. 3. First melting snow were caught in January 31 and last one in March 25. Melting snow water which were caught into the tank was 12.4 per cent of total water in snowdrift on March 15 and a larger part of the run off soil was caused during 15 to 25 in March. 4. Entire loss of soil by melting snow was 184 kgs. in air dry matter per acre in 1951.

Comparative rain measurements and rain‐gage performances on a steep slope adjacent to a pine stand

In this study, measurements from two rows of rain gages, extending outward along contours from the edge of a pine plantation on a steep slope, showed that the 45 foot‐high trees influenced the amount of rain reaching the ground for a distance not exceeding 34 ft from the edge of the plantation.Seven types of rain‐gaging installations were tested for accuracy on a windy, 40 per cent slope, including three types of shielding, gages exposed with the orifice horizontal and with orifice tilted parallel to the slope. Best results were obtained with tilted, shielded gages, but tilted, unshielded gages were only slightly less accurate for the conditions encountered. Shielding of untilted gages proved much less effective than tilting unshielded gages, although superior to a conventionally exposed gage, unshielded and with orifice horizontal. It was demonstrated again that the conventional installation is unsuitable for accurate rain gaging on windy slopes.