Runoff Water Losses Research Articles

Biotic pump of atmospheric moisture as driver of the hydrological cycle on land

Abstract. In this paper the basic geophysical and ecological principles are jointly analyzed that allow the landmasses of Earth to remain moistened sufficiently for terrestrial life to be possible. 1. Under gravity, land inevitably loses water to the ocean. To keep land moistened, the gravitational water runoff must be continuously compensated by the atmospheric ocean-to-land moisture transport. Using data for five terrestrial transects of the International Geosphere Biosphere Program we show that the mean distance to which air fluxes can transport moisture over non-forested areas, does not exceed several hundred kilometers; precipitation decreases exponentially with distance from the ocean. 2. In contrast, precipitation over extensive natural forests does not depend on the distance from the ocean along several thousand kilometers, as illustrated for the Amazon and Yenisey river basins and Equatorial Africa. This points to the existence of an active biotic pump transporting atmospheric moisture inland from the ocean. 3. Physical principles of the biotic moisture pump are investigated based on the previously unstudied properties of atmospheric water vapor, which can be either in or out of aerostatic equilibrium depending on the lapse rate of air temperature. A novel physical principle is formulated according to which the low-level air moves from areas with weak evaporation to areas with more intensive evaporation. Due to the high leaf area index, natural forests maintain high evaporation fluxes, which support the ascending air motion over the forest and "suck in" moist air from the ocean, which is the essence of the biotic pump of atmospheric moisture. In the result, the gravitational runoff water losses from the optimally moistened forest soil can be fully compensated by the biotically enhanced precipitation at any distance from the ocean. 4. It is discussed how a continent-scale biotic water pump mechanism could be produced by natural selection acting on individual trees. 5. Replacement of the natural forest cover by a low leaf index vegetation leads to an up to tenfold reduction in the mean continental precipitation and runoff, in contrast to the previously available estimates made without accounting for the biotic moisture pump. The analyzed body of evidence testifies that the long-term stability of an intense terrestrial water cycle is unachievable without the recovery of natural, self-sustaining forests on continent-wide areas.

Aspectos financeiros relacionados às perdas de nutrientes por erosão hídrica em diferentes sistemas de manejo do solo

A erosão hídrica é a forma mais séria de degradação do solo, pois, além de reduzir a capacidade produtiva deste para as culturas, causa prejuízos financeiros e ambientais em razão da perda de nutrientes a ela associada. A presente pesquisa foi realizada com o objetivo de quantificar as perdas de água e solo, de P, K, Ca e Mg na água e de P disponível e K, Ca e Mg trocáveis nos sedimentos da enxurrada perdida por erosão hídrica, em um experimento realizado sob chuva natural, entre novembro de 1992 e outubro de 2003, no sul do Planalto Catarinense. Calculou-se o custo financeiro desses nutrientes, expressos na forma de superfosfato triplo (P), cloreto de potássio (K) e de calcário (Ca e Mg), perdidos na erosão hídrica, para um Cambissolo Húmico alumínico léptico com declividade média de 0,10 m m-1, em três sistemas de manejo do solo, com duas repetições: preparo convencional (PC), preparo mínimo (PM) e semeadura direta (SD). Em uma das repetições dos tratamentos foram cultivados soja, trigo, milho, ervilhaca, feijão, aveia, soja e nabo forrageiro, em sistema de rotação de culturas, enquanto na outra se cultivaram soja, trigo, soja, trigo, soja, trigo, soja e trigo, em sistema de sucessão de culturas. Para efeito de realização deste trabalho, as duas parcelas experimentais com o mesmo tipo de manejo do solo foram consideradas como repetição, embora com diferentes espécies culturais (em rotação e em sucessão de culturas). As perdas de solo foram fortemente influenciadas pelo sistema de manejo e variaram com os anos de cultivo, enquanto as perdas de água variaram menos do que as de solo, tanto nos sistemas de manejo do solo quanto nos anos de cultivo. O valor monetário das perdas anuais de P expresso na forma de superfosfato triplo, de K expresso como cloreto de potássio e de Ca e Mg expressos na forma de calcário, por erosão hídrica, foi relativamente elevado, independentemente do sistema de manejo do solo. A SD e o PM comportaram-se de modo semelhante em termos de valor monetário das referidas perdas, em cujos tratamentos as perdas de água e solo foram expressivamente menores que no preparo convencional. O valor monetário da perda anual por hectare de K expresso na forma de cloreto de potássio, por erosão hídrica, foi equivalente a 2,6 vezes aquele representado pelo somatório das perdas de P na forma de superfosfato triplo e de Ca e Mg na forma de calcário, na média dos sistemas de manejo do solo. Na SD, essas perdas foram de US$ 14,83 por hectare por ano, enquanto no PM foram de US$ 16,33 e, no PC, de US$ 24,94. Na média destes sistemas de manejo do solo, o valor monetário total anual por hectare das perdas de P expresso na forma de superfosfato triplo correspondeu a 8,6 %, enquanto de K na forma de cloreto de potássio e de Ca e Mg expressos na forma de calcário o valor correspondeu a 76,8 e 14,6 %, respectivamente.

Measurement and modelling of runoff and phosphate movement from seasonally dry hill‐country pastures

In seasonally dry hill pastures on a Waipawa stony loam (Pallic Soil) in Hawke's Bay, a range of methods was used to measure phosphorus (P) movement and losses in runoff water. Measurements with a rainfall simulator and micro‐plots showed that dissolved reactive P (DRP) and total dissolved P (TDP) concentrations in surface runoff were directly related to soil Olsen P (R2= 0.93 and R2 = 0.90 respectively) status. The distance that surface runoff travelled, as measured by P fertiliser transport, was about 5 m when rainfall in autumn had not occurred for 12–22 days, but decreased sharply in subsequent rainstorms. Over a 12‐month period most natural surface runoff occurred mostly during early summer to late autumn and was inversely related to soil moisture content (R2= ‐0.38 for all data). Most (55–84%) of total P (TP) losses occurred in three of 12 storms measured, with the majority as DRP from low P (60–85%) and high P (70–93%) soils. Continuous flows from twin catchments of 12.6 ha (north, with low soil P status), and 12.8 ha (south, with a moderate to high soil P status) were recorded. For the north catchment, total flow ranged from 18 to 26% of annual rainfall, and for the south catchment from 18 to 21%, over 2000 to 2002. About half of this occurred in July‐August. Over a 7‐month period, surface runoff was equivalent to only about 3% of rainfall. The difference in soil P status of the two catchments provided an approximate index of the difference in TP export. The DRP and TDP concentrations in catchment flow were about 10‐fold less than those recorded in surface runoff from associated pastures. The TOPMODEL runoff simulation model accurately estimated total flow from two catchments (R = 0.89 and 0.87 for north and south catchments respectively), but not the contribution by surface runoff.

Sorption of Inorganic and Total Phosphorus from Dairy and Swine Slurries to Soil

Understanding P sorption from animal manures is essential to formulate best management practices with regard to land application of manure from the standpoint of crop production and environmental quality. Little research has focused on the construction of P sorption isotherms where the P source is manure. The objectives of this study were to: (i) develop a procedure to characterize how inorganic P (P(i)) and total P (P(t)) from dairy slurry and swine slurry sorbs to soil; and (ii) compare the sorption characteristics of P(i) and P(t) where the P source was dairy slurry, swine slurry, or potassium phosphate (KH2PO4). Sorption solutions were prepared in 0.1 M KCl at pH 6 and equilibrated with soils at a 1:25 (w/v) soil/solution ratio for 24 h. Inorganic P, P(t), Al, and Fe in the equilibrated solutions were measured. For all soils, P(i) and P(t) sorption capacity of dairy slurry was greater than KH2PO4. Total P sorption capacity of swine slurry was greater than KH2PO4, while P(i) sorption capacity was less than KH2PO4. Overall, P(i) and P(t) sorption strengths of the manure slurries were less than or equal to KH2PO4. Increased P(i) sorption from dairy slurry was correlated with Fe and Al desorption. Reduction of P(i) sorption capacity from swine slurry was related to preferential sorption of organic P. Additional studies need to be conducted to determine how differences in P sorption between manures and fertilizer impact in-field P availability to a crop and potential for losses in runoff water.

Cattle treading effects on plant growth and soil stability in the mountain grassland of Japan

AbstractExperiments were conducted in two types of Japanese mountain pastures to quantify the effects of cattle treading on plant growth, and on soil loss with runoff water. Duplicate plots (10 m × 10 m) were trodden with zero, three, or six cows of approximately 300 kg body weight for 15 minutes on moderately‐sloping and steep pastures on 8 July and 27 September, 2003. A similar treatment was repeated on the steep pasture only on 14 June and 30 September 2004. Measurements included herbage growth, tiller density, soil loss in runoff water, hydraulic conductivity, soil hardness and soil surface roughness.Trampling damage to pasture resulted in a significant decrease in herbage growth, greater soil loss with runoff water, decreased hydraulic conductivity, and increased soil hardness and soil surface runoff. The reduction in the herbage growth rate was mainly due to decreased tiller density. Increased soil loss with runoff water mainly resulted from soil disturbance caused by the animals' hooves. There was a strong negative relationship between tiller density and soil surface roughness. The effect of treading on plants and soils increased with treading intensity. Moderately‐sloping pasture was less seriously affected than steep pastures for soil loss, indicating that steep terrains are more susceptible to treading impacts. Copyright © 2006 John Wiley & Sons, Ltd.

Runoff, sediment, nitrogen, and phosphorus losses from agricultural land converted to sweetgum and switchgrass bioenergy feedstock production in north Alabama

Abstract Renewable energy sources such as bioenergy crops have significant potential as alternatives to fossil fuels. Potential environmental problems arising from soil sediment and nutrient losses in runoff water from bioenergy crops need to be evaluated in order to determine the sustainability and overall feasibility of implementing bioenergy development strategies. This paper discusses runoff, sediment, N, and total P losses from agricultural land (continuous cotton (Gossypium hirsutum L.)) converted to short-rotation sweetgum (Liquidamber styraciflua L.) plantations with and without fescue (Festuca elatior L.) and switchgrass (Panicum virgatum L.) bioenergy crops, compared to corn (Zea mays L.), on a Decatur silt loam soil in north Alabama, from 1995 to 1999. Runoff volume was significantly correlated to total rainfall and sediment yield in each year, but treatment differences were not significant. Sweetgum plots produced the highest mean sediment yield of up to 800 kg ha−1compared to corn and switchgrass plots, which averaged less than 200 kg ha−1. Runoff NH4+ N losses averaged over treatments and years for spring season (3.1 kg ha−1) were three to five times those for summer, fall, and winter seasons. Runoff NO3− N for no-till corn and switchgrass plots in spring and summer were five to ten times that for sweetgum plots. No-till corn and switchgrass treatments had 2.4 and 2.1 kg ha−1 average runoff total P, respectively, which were two to three times that for sweetgum treatments. Growing sweetgum with a fescue cover crop provides significantly lower risk of water pollution from sediment, runoff NH4+ N, and NO3− N.

NUTRIENT AND ?17-ESTRADIOL LOSS IN RUNOFF WATER FROM POULTRY LITTERS

A main water quality concern is accelerated eutrophi- cation of fresh waters from nonpoint source pollution, particularly nutrient transport in surface runoff from agricultural areas and confined animal feeding operations. This study examined nutrient and β17-estradiol concentrations in runoff from small plots where six poultry litters were applied at a rate of about 67 kg/ha of total phosphorus (TP). The six poultry litter treatments included pellet- ed compost, pelleted litter, raw litter, alum (treated) litter, pelleted alum litter, and normal litter (no alum). Four replicates of the six poultry litter treatments and a control (plots without poultry litter application) were used in this study. Rainfall simulations at inten- sity of 50 mm/hr were conducted immediately following poultry lit- ter application to the plots and again 30 days later. Composite runoff samples were analyzed for soluble reactive phosphorus (SRP), ammonia (NH4), nitrate (NO3), TP, total nitrogen (TN) and β17-estradiol concentrations. In general, poultry litter applications increased nutrient and β17-estradiol concentrations in runoff water. Ammonia and P concentrations in runoff water from the first simu- lation were correlated to application rates of water extractable NH4 (R2 = 0.70) and P (R2 = 0.68) in the manure. Results suggest that alum applications to poultry litter in houses inbetween flocks is an effective best management practice for reducing phosphorus (P) and β17-estradiol concentrations in runoff and that pelleted poultry litters may increase the potential for P and β17-estradiol loss in runoff water. Inferences regarding pelleted poultry litters should be viewed cautiously, because the environmental consequence of pelleting poultry litters needs additional investigation. (KEY TERMS: water quality; poultry litter; nonpoint source pollu- tion; nutrients; estradiol; best management practices.)

Phosphorus loss to runoff water twenty-four hours after application of liquid swine manure or fertilizer.

Phosphorus (P) added to soil from fertilizer or manure application could pose a threat to water quality due to its role in eutrophication of fresh water resources. Incorporating such amendments into the soil is an established best management practice (BMP) for reducing soluble P losses in runoff water, but could also lead to higher erosion. The objective of this study was to test whether incorporation of manure or fertilizer 24 h before an intense rain could also reduce sediment-bound and total phosphorus (TP) losses in runoff. A rainfall simulation study was conducted on field plots (sandy loam with 6-7% slope, little surface residue, recently cultivated) that received two application rates of liquid swine manure or liquid ammonium polyphosphate fertilizer, using either surface-broadcast or incorporated methods of application. Incorporation increased the total suspended solids (TSS) concentrations in runoff but mass losses were not affected. Incorporation also reduced flow-weighted concentrations and losses of dissolved reactive phosphorus (DRP) and TP by as much as 30 to 60% depending on source (fertilizer vs. manure) and application rate. Phosphorus is moved below the mixing zone of interaction on incorporation, and thus the effect of the amount and availability of P in this zone is more important than cultivation on subsequent P losses in runoff. Incorporating manure or fertilizer in areas of intense erosive rain, recent extensive tillage, and with little or no surface residue is therefore a best management practice that should be adhered to in order to minimize contamination of surface water. Results also show comparatively lower P losses from manure than fertilizer.

Endosulfan Losses through Runoff and Leaching from Calcareous Gravelly or Marl Soils

The non‐point loss of a pesticide through runoff and leaching from agricultural fields depends not only on its chemical properties but also on environmental factors such as soil type, rainfall intensity, and water table level. Two major agricultural calcareous soils in South Florida, Krome (loamy‐skeletal, carbonatic, hyperthermic Lithic Udorthents) very gravelly loam (Krome) and Biscayne (loamy, carbonatic, hyperthermic, shallow Typic Fluvaquents) marl (marl), were packed in tilted stainless‐steel runoff–leaching chambers for measuring the transport of endosulfan (6,7,8,9,10,10‐hexachloro‐1,5,5a,6,9,9a‐hexahydro‐6,9‐methano‐2,4,3‐benzadioxathiepin 3‐oxide) isomers in leachates and surface runoff. Endosulfan loss was the greatest in runoff sediment, followed by loss in runoff water, and finally in the leachate. At a rainfall intensity of 75 mm h−1, the infiltration rate in the Krome soil was higher than in the marl soil. Endosulfan movement with infiltration water in Krome soil is a nonequilibrium process. Increasing rainfall intensity to 150 mm h−1 significantly decreased endosulfan leaching and increased runoff. High rainfall intensity and/or water table dramatically increased the endosulfan loss through the sediments in runoff. Marl soil has a higher endosulfan runoff potential than Krome soil. Endosulfan α had a lower average experimental distribution coefficient, KD, than endosulfan β (265 vs. 472). Loss of endosulfan α dissolved in runoff water and through leaching was higher than that of endosulfan β, while loss of endosulfan α from runoff sediments was lower than that of endosulfan β. Endosulfan concentrations in runoff water decreased exponentially with cumulative rainfall and runoff sediment.

Off-site movement of surface-applied simazine from a citrus orchard as affected by irrigation incorporation

Abstract In the San Joaquin Valley of California the presence of preemergence herbicides in runoff water from citrus orchards during winter rainfall can cause surface water and groundwater contamination. In 1999 and 2000 this study was conducted in a citrus orchard to evaluate the effect of irrigation incorporation with rotor sprinklers on simazine losses in runoff water. Four treatments included the application of simazine at 2.0 kg ai ha−1 without irrigation incorporation and the application of simazine at 2.0 kg ai ha−1 with three levels of irrigation incorporation (0.5, 1.25, and 1.75 cm of water). Simulated rainfall with 3.5 cm of water was then applied on the plots to generate surface runoff. Simazine concentrations in runoff water from the first simulated rainfall event averaged 0.85, 0.77, 0.45, and 0.30 mg L−1 for treatments without irrigation incorporation and for those receiving 0.5, 1.25, and 1.75 cm of water incorporation, respectively; simazine concentration in runoff water from the second e...

Effects of tillage and phosphorus placement on phosphorus runoff losses in a grain sorghum-soybean rotation.

Phosphorus enhances eutrophication of fresh water bodies. This study was conducted to determine the influence of tillage and P placement on P losses in runoff water from a somewhat poorly drained soil (Woodson silt loam [fine, smectitic, thermic Abruptic Argiaquoll], 1.0-1.5% slope) in a grain sorghum [Sorghum bicolor (L.) Moenchl-soybean [Glycine mar (L.) Merr] rotation. Chisel-disk-field cultivate (ChT), ridge-till (RT), and no-till (NT) in combination with 0 kg P ha(-1) or 24 kg P ha(-1) broadcast or knifed (applied prior to planting grain sorghum) were studied. Runoff volume and losses of sediment and P were summed over the growing season. Significant interactions between tillage and P placement for soluble P losses were found. For example, soluble P loss in 1999 for NT-broadcast in grain sorghum was 358 g ha(-1); significantly greater than 31 g ha(-1) for NT-knife or 23 g ha(-1) for NT-check. Similar results were found for RT but no such differences were found for ChT. Bioavailable P losses were generally highest with broadcast P placement and for NT and RT. Total P losses were significantly higher at 959 g ha(-1) with broadcast P on grain sorghum in 1998, compared with 521 g ha(-1) for the check and 659 g ha(-1) for the knifed P applications. Total P losses in 1999 for soybeans were only 18 g ha(-1) for NT, which was significantly lower than 75 g ha(-1) for ChT and 66 g ha(-1) for RT. The results indicate that broadcast P applications on RT and NT will increase P losses, but the influence of tillage was not consistent.

Irrigation and drainage needs of transplanted rice in diked rice fields of rainfed medium lands

An experiment was conducted in diked rice fields with various weir heights (6 cm to 30 cm at an interval of 4 cm) for three consecutive years in the sub-humid climate of eastern India. The results reveal that about 56.75% and 99.5% of the seasonal rainfall can be stored in 6 cm and 30 cm weir height plots, respectively. Sediment losses of 347.8 kg/ha and 3.3 kg/ha have been recorded in runoff water coming out of 6 cm and 30 cm weir height plots, respectively in a cropping season. Similarly, total Kjeldahl nitrogen loss in runoff water from rice fields ranged from 4.23 kg/ha (6 cm weir height plots) to 0.17 kg/ha (26 cm weir height plots). The available K loss ranged from 2.20 kg/ha (6 cm weir height plots) to 0.04 kg/ha (30 cm weir height plots). Keeping in mind the aspects of conserving rainwater, sediment and nutrient and minimizing irrigation requirement, 22–26 cm of dike height is considered to be suitable for rice fields of the Bhubaneswar region during the Kharif (rainy) season. A lumped water balance model for diked rice field was developed and used for the present investigation. The computed values of runoff obtained from the simulation model are in close agreement with the observed values obtained in an experiment using higher weir heights (22 cm and above). The temporal distribution of runoff and irrigation requirement at fortnight intervals reveal that highest irrigation requirement is found during the first half of November followed by the second half of October and the first half of October. Rice fields up to a weir height of 18 cm produced about 20% of the total runoff in each of the first three fortnights. A gradual reduction in runoff was observed in the remaining fortnights. The least runoff was noticed in the month of November (during the first fortnight).

Runoff and leaching of atrazine and alachlor on a sandy soil as affected by application in sprinkler irrigation

Rainfall simulation was used with small packed boxes of soil to compare runoff of herbicides applied by conventional spray and injection into sprinkler‐irrigation (chemigation), under severe rainfall conditions. It was hypothesized that the larger water volumes used in chemigation would leach some of the chemicals out of the soil surface rainfall interaction zone, and thus reduce the amounts of herbicides available for runoff. A 47‐mm rain falling in a 2‐hour event 24 hours after application of alachlor (2‐chloro‐N‐(2,6‐diethylphenyl)‐N‐(methoxymethyl)‐acetamide) and atrazine (6‐chloro‐N‐ethyl‐N‐(1‐methylethyl)‐1,3,5‐triazine‐2,4‐diamine) was simulated. The design of the boxes allowed a measurement of pesticide concentrations in splash water throughout the rainfall event. Initial atrazine concentrations exceeding its’ solubility were observed. When the herbicides were applied in 64000 L/ha of water (simulating chemigation in 6.4 mm irrigation water) to the surface of a Tifton loamy sand, subsequent herbicide losses in runoff water were decreased by 90% for atrazine and 91% for alachlor, as compared to losses from applications in typical carrier water volumes of 187 L/ha. However, this difference was not due to an herbicide leaching effect but to a 96% decrease in the amount of runoff from the chemigated plots. Only 0.3 mm of runoff occurred from the chemigated boxes while 7.4 mm runoff occurred from the conventionally‐treated boxes, even though antecedent moisture was higher in the former. Two possible explanations for this unexpected result are (a) increased aggregate stability in the more moist condition, leading to less surface sealing during subsequent rainfall, or (b) a hydrophobic effect in the drier boxes. In the majority of these pans herbicide loss was much less in runoff than in leachate water. Thus, in this soil, application of these herbicides by chemigation would decrease their potential for pollution only in situations where runoff is a greater potential threat than leaching.

Rainwater, soil and nutrient conservation in rainfed rice lands in Eastern India

In rainfed rice ecosystem, conservation of rainwater to maximum extent can reduce the supplemental irrigation water requirement of the crop and drainage need of the catchment. The results of 3 years of experimental study on the above stated aspects in diked rice fields with various weir heights (6–30 cm at an interval of 4 cm) revealed that about 56.75% and 99.5% of the rainfall can be stored in 6 and 30 cm weir height plots, respectively. Sediment losses of 347.8 kg/ha and 3.3 kg/ha have been recorded in runoff water coming out of 6 cm and 30 cm weir height plots, respectively in a cropping season. Similarly, total Kjeldahl nitrogen (TKN) loss in runoff water from rice field ranged from 4.23 kg/ha (6 cm weir height plots) to 0.17 kg/ha (26 cm weir height plots) and available potassium loss ranged from 2.20 kg/ha (6 cm weir height plots) to 0.04 kg/ha (30 cm weir height plots). Conservation of rainwater in rice fields with various weir heights could not create any significant impact on grain yield differences, leaf area index and other biometric characters. Irrigation requirement of 18 cm and above weir height plots was found to be half of the requirement of 6 cm weir height plots. Keeping in view the aspects of conserving rainwater, sediment and nutrient and minimizing irrigation requirement, 22–26 cm of dike height is considered to be suitable for rice fields of Bhubaneswar region.

Soil degradative effects of slope length and tillage method on alfisols in Western Nigeria II. Soil chemical properties, plant nutrient loss and water quality

Effects of erosion-induced degradation on soil chemical quality, plant nutrient loss in runoff water and water quality were related to slope length for a 5-year study from 1984 through 1988 conducted on tropical Alfisols under maize (Zea mays)–cowpeas (Vigna unguiculata) rotation. A total of 13 field runoff plots involved six slope lengths (i.e. 60 m, 50 m, 40 m, 30 m, 20 m, and 10 m), two tillage methods (i.e. conventional till and no-till), and an uncropped control of 25 m length. Slope length effects on soil chemical quality differed among tillage methods. Decrease in slope length had a favorable effect on soil chemical quality in the conventional till treatment for exchangeable Ca+, cation exchange capacity (CEC) and Bray-P. The soil organic carbon (SOC) increased with decrease in slope length at the rate of 0·007 per cent m−1 for 0–5 cm depth and 0·015 per cent m−1 for 5–10 cm depth, and soil pH decreased with increase in slope length. Soil concentration of Bray-1 P generally increased with decrease in slope length. For the no-till treatment, however, there were no consistent trends in soil chemical quality with regard to slope length. Further, soil chemical quality was superior under no-till than conventional till treatment for 0–5 cm and 5–10 cm depths. All soil chemical properties declined with cultivation duration, with the rate of decline being more in conventional till compared with the no-till treatment. The rate of decline for the conventional till treatment was 0·396 per cent year−1 for SOC, 0·21 unit year−1 for pH, 0·053 per cent year−1 for total soil N, 0·375 cmol kg−1 year−1 for Ca+, and 0·41 cmol kg−1 year−1 for CEC. The rate of decline in soil quality with cultivation duration was consistently more for longer than for shorter slope lengths especially for SOC and soil pH. Temporal changes in soil chemical quality for the no-till treatment were not well defined. The total loss of plant nutrients in runoff ranged from 8·4 kg ha−1 to 17·8 kg ha−1 for season 1, and, in general, the nutrient loss decreased with decrease in slope length. The total loss of plant nutrients in season 2 was lower than that in season 1, and lower with no-till compared with conventional till treatment. Total nutrient loss in runoff decreased with increase in slope length for conventional tillage, and increased with decrease in slope length for the no-till treatment. Concentration of plant nutrient in runoff differed among elements, tillage methods and slope length treatments. Concentration of bases and NO3-N in runoff followed a U-shape response over time during the year, with relatively high concentrations toward the beginning and end of the rains. The concentration of PO4-P in runoff generally decreased with time after application of fertilizer. For the conventional till treatment, the concentration of PO4-P, K, and Fe decreased with decrease in slope length. © 1997 John Wiley & Sons, Ltd.

Factors affecting soil erosion hazards and conservation needs for tropical steeplands

Understanding the basic processes and factors that are responsible for inducing land degradation, particularly soil erosion and associated phenomena is critical to the conceptualization, design, and implementation of productive, stable, and sustainable agricultural systems. This is particularly so on steeplands where the potential for soil erosion and runoff water losses is high. The productivity and degradation hazards on these lands are determined by the site's climate, soil and topography. However, their uniqueness lies more with their topographic constraints than with other factors. Use of steeplands is an increasingly common situation in the tropics because of high population pressures and continuing encroachment on hilly lands. Erosion potential and actual erosion in these settings may exceed tens or even hundreds of tons of soil loss per hectare per year; thus the selection and design of cropping systems, land management systems, and water management systems must be tailored to attain effective runoff and erosion control in order to avoid their detrimental impacts both on-site and off-site. Contrary to the customary arguments for the ‘long-term’ nature of erosion impacts; enhancing the conservation-effectiveness of rainfed farming on tropical steeplands can be shown to provide both short- and long-term benefits to the farming system, the overall economy, and the environment. Productivity-enhancing crop and soil and water conservation management approaches (biological measures) may be more important than structural measures in imparting long-term sustainability. Incorporating indigenous knowledge into project design should be emphasized to assure the farmer's involvement and cooperation in planning, implementing, and maintaining conservation measures.

Clay minerals and soil fertility loss on Petric Calcisol under a semiarid Mediterranean environment

The authors study clay mineral and main nutrient element losses in runoff water generated by rainfall events in 1990–1991 from five field plots on a Petric Calcisol or Xerollic Paleorthid. Illite is the main layer silicate in the clay Ap horizon, with a smaller proportion of kaolinite and a minor amount of chlorite and smectite. Soil samples taken in different seasons show that plots under shrub vegetation are very much alike and, with the exception of available Fe, Cu, Mn and Zn, they are markedly different from arable soil plots, being much richer in organic C, total N and available K, but poorer in available P. Annual and seasonal losses of the main nutrient elements are small, with the highest amounts in the plots cultivated for barley and with cut shrub; losses are extremely low for the plot with shrub cover.

Fate of Azinphosmethyl in a Sugarcane Field: Distributions in Canopy, Soil, and Runoff

Azinphosmethyl (O,O-dimethyl S-[4-oxo-1,2,3-benzotriazin-3(4H)-yl)methyl] phosphorodithioate) dynamics in surface soils, on canopy leaves and in runoff waters was studied on six 0.2-ha sugarcane (Saccharum sp. Hyb.) plots of a Commerce silt loam (fine-silty, mixed, nonacid, thermic Aeric Fluvaquent) during three growing seasons (1993-1995). Three applications of azinphosmethyl was made yearly (at 0.82 kg/ha) as a mixed emulsifiable concentrate with a water carrier. We found only 1 to 2% of applied azinphosmethyl remained within the canopy and the soil surface 10 to 12 d following application. Azinphosmethyl on leaf surfaces diminished sharply following rainfalls with subsequent increases in amounts in surface soil. Azinphosmethyl losses in runoff water decreased with time and maximum concentration was 10 to 21.9 μg/L. Concentrations were <2 μg/L in runoff waters 30 d after application. Based on first-order decay estimates, azinphosmethyl half-lives on canopy leaves ranged from 2 to 8 d whereas in surface soil it ranged from 6 to 66 d. A compartmental model also was used to estimate azinphosmethyl disappearance and transfer from leaves to soil based on rain conditions. Such an approach provided poor description of peak concentrations and predicted a much faster rate of disappearance than that measured.

Role of some riparian wetland plants in reducing erosion of organic carbon and selected cations

Five riparian herbaceous plants, Leonotis nepetaefolia, Cassia tora, Ageratum conyzoides, Parthenium hysterophorus and Sida acuta, dominant on the banks of the Rihand river at Renukoot (India), were selected to assess experimentally their quantitative role in conserving organic-C, Na, K and Ca. Young seedlings from the river bank were planted on sloping experimental plots made of alluvial soil. Simulated rainfall totalling 42.5 mm was applied at 300 mm h −1 on five vegetated and one bare plots. Runoff water and eroded soil were collected from each experimental plot in artificial reservoirs and their quantities were measured. The soil conservation value of the five selected species ranged between 33 and 84% while the water conservation value varied between 19 and 50%. The overall nutrient conservation value, based on the losses in runoff water and eroded soil taken together, varied from 30 to 83% for organic-C, 19 to 78% for Na, 13 to 72% for K and 29 to 52% for Ca under different species. Loss of these four nutrients in response to 42.5 mm simulated rainfall was much higher than their input through rainfall. Loss value for the nutrients were in following order: organic-C > Ca > K > Na. The fraction of organic-C transported down the slope was higher in eroded soil (averaging 73%) and of exchangeable bases in runoff water (averaging 86% for Na, 82% for K and 90% for Ca). Flow-weighted concentrations of all the studied nutrients were consistently greater from bare stands. Number of fine roots was found to play greater role in the case of organic-C (92%; p < 0.01) and Na (70%; p < 0.05) runoff and their conservation by different plant species but canopy cover played greater role for K (58%; p < 0.08) and Ca (90%; p < 0.01).

Nutrient losses in runoff water following application of different fertilisers to grassland cut for silage

Studies were made to assess the losses of nutrients in runoff from pastures, and to ascertain whether application of N as NH 4 rather than NO 3 both reduced N losses and enhanced yields of herbage. Two experiments were conducted during consecutive springs in which surface lysimeter plots were established on sloping grassland with soils of low permeability, and different forms of fertiliser applied for first-cut silage. Despite weather conditions conducive to large nutrient losses, less than 10% of the N applied was found in runoff. However, the peak concentrations of nutrients were large relative to standards for good water quality. The concentrations of NO 3-N were greater in water from plots that received NH 4 NO 3 than from those that received either (NH 4) 3 PO 4 or urea. Large concentrations of NH 4-N were measured in runoff in response to all treatments, with the largest in water from plots that received urea. The mechanisms that may account for the observed resistance to loss in runoff are discussed. In the first experiment there was no advantage (or disadvantage) in applying an (NH 4) 3 PO 4 formulation 2 weeks earlier than applying either NH 4 NO 3 or urea. In the second experiment, where all treatments were applied on the same dates, herbage mass accumulated more slowly on plots that received NH 4 NO 3 compared to those that received more NH 4-rich forms. However, in neither experiment did the fertiliser treatments influence the yields of herbage cut for silage.