Polyacrylamide coated Milorganite™ and gypsum for controlling sediment and phosphorus loads

The application of polymer for controlling erosion and the associated nutrient transport has been well documented. However, comparatively less information is available on the effect of polymer application together with soil amendments. In this study, the effect of polyacrylamide (PAM) in combination with surface application of gypsum and Milorganite™ (MILwaukee ORGAnic NITtrogEn) biosolid for reducing sediment and phosphorus transport under laboratory rainfall simulations was investigated. The treatments considered were bare soil, gypsum, Milorganite™, gypsum + Milorganite™, PAM-coated gypsum and PAM-coated Milorganite™. Application rates for gypsum and Milorganite™ were 392 kg ha⁻¹ (350 lb/acre) and 726 kg ha⁻¹ (650 lb/acre), respectively. The PAM was coated on gypsum and Milorganite™ at an application rate of 11.2 kg ha⁻¹ (10 lb/acre) and 22.4 kg ha⁻¹ (20 lb/acre), respectively. Rain simulation experiments were conducted using a rainfall intensity of 6.0 cm h⁻¹ for 1 h on a 10% slope. Surface runoff was collected continuously from each soil box over 10 min intervals and leachate was collected continuously over the 60 min simulation. The reduction in runoff or in leachate for all treatments was not significantly different from the bare soil control. The sediment loss for PAM coated Milorganite™ was reduced by 77%, when compared to bare soil. However, the sediment loss was not significantly reduced for any other treatment compared to bare soil. The PAM-coated gypsum was not effective for erosion control in our study, and there appears to be a correlation between effectiveness and prill size. However, the gypsum (coated and uncoated) contributed about half of the dissolved reactive phosphorus (DRP) export (in the runoff) compared to bare soil. The PAM-coated Milorgante™ reduced the DRP and total phosphorus (TP) export to 0.3-0.5 times that of Milorganite™ and to levels similar to bare soil. The decreased sediment and phosphorus export for the PAM-coated Milorganite™ treatment is a signal for a potential management practice for controlling erosion and nutrient transport in fertilized agricultural landscapes.     

Controlling factors of sheet erosion under degraded grasslands in the sloping lands of KwaZulu-Natal, South Africa

The current increase in the global demand for food and fresh water and the associated land use changes or misuses exacerbate water erosion which has become a major threat to the sustainability of the soil and water resources. Soil erosion by rainfall and runoff is a natural and geologic phenomenon, and one of the most important components of the global geochemical cycle.Despite numerous studies on crop lands, there is still a need to quantify soil sheet erosion (an erosion form that uniformly removes fertile upper soil horizons) under grasslands and to assess the factors of the environment that control its spatial variation. For that purpose, fifteen 1 m² micro-plots installed within a 23 ha catchment under pasture in the sloping lands of KwaZulu-Natal (South Africa) were monitored during the 2007-2008 rainy season to evaluate runoff (R) and sediment losses (SL). Soil losses computed from the 37 rainfall events with soil erosion averaged 6.45 ton ha⁻¹ year⁻¹with values from 3 to 13 ton ha⁻¹ year⁻¹. SL were significantly correlated with the proportion of soil surface coverage by the vegetation (P < 0.01) whereas the slope gradient, and soil characteristics such as bulk density or clay content were not correlated. R and SL increased as the proportion of soil surface coverage decreased and this trend was used to predict the spatial variations of sheet erosion over the 23 ha catchment. Greater sheet erosion occurred at the catchment plateau and at the vicinity of gully head cuts probably in relation to regressive erosion. Mitigating sheet erosion would require an appropriate management of the soil cover through appropriate management of cattle grazing, especially at places where “natural” erosion is likely to occur.     

模拟降雨下PAM对砂黄土养分迁移影响实验研究

利用室内人工模拟降雨试验,研究了砂黄土施用不同量PAM在降雨条件下入渗-径流、土壤侵蚀和养分迁移特征。研究结果表明,砂黄土在不同PAM用量下均较对照表现出降低入渗增加径流,并能有效减少土壤侵蚀,其侵蚀量随PAM用量增加而减少。径流的增加造成硝态氮,水溶性磷和水溶性钾累积流失量增加,通过径流和泥沙流失的养分很少,硝态氮主要通过淋溶损失,磷和钾移动性弱,土壤固定性强,损失不大。PAM适宜用量在1~3 g/m2之间。     

Field evaluation of sand-ditch water harvesting technique in Jordan

Water harvesting is viable alternatives for rainfed agricultural production in semiarid lands. A field experiment was conducted to evaluate the efficiency of a relatively new water harvesting technique, called sand ditch, for moisture and soil conservation. Twelve field plots of 10 m × 2 m were constructed in two adjacent fields having silt loam soils but varied in soil depth, 0.75 m and 2 m, and slope of 10% and 12%. A 130 L barrel was installed at the downslope end of the plots to collect water and sediments at the end of each rainstorm along the rainy season. Three types of treatments were used in duplicates (12 plots in total); sand-ditch plots in which a ditch of 2-m long, 1 m wide and 0.8 m deep was constructed in the middle of plots across the slope (2 in each field), two compacted plots and two plots covered with plastic mulch in addition to four control plots, 2 in each field. The total amount of runoff, sediment concentration, total infiltration and sediment loss for the experimental plots were measured or calculated after each storm during the winter season 2004/2005. Experimental results showed that sand-ditch technique significantly reduced runoff and sediment loss and increased infiltration and soil moisture compared to control or compacted plots. The overall average runoff and sediment reductions in the sand-ditch plots were 46% and 61% compared to control plots. Sediment losses from compacted plots were about 2.2 and 6 folds higher than control and sand-ditch plots, respectively making soil compaction unsuitable technique for rainfall harvesting under the current experimental and climatic conditions. Construction of sand ditch also increased the dry matter yield of native grass by an average of 62% and 40% in the two experimental fields compared to control.     

Impact of modified tillage on runoff and nutrient loads from potato fields in Prince Edward Island

Potato production accounts for ∼24% of the cultivated land-use in Prince Edward Island, Canada. The island often experiences prolonged dry periods interspersed with excessive rainfall events throughout the growing season. Thus, water retention is important for maximum crop production while sediment and nutrient loading to surface water systems are also concerns. Therefore, agronomic practices that reduce the environmental impact of potato production are being sought. Basin tillage (BT) is a potential option in which small dams are created in the furrows (row middles), resulting in basins that enhance infiltration, reduce runoff, minimize contaminant loads, and increase yields.This on-farm study compared BT against two types of ‘conventional’ hilling treatments with replicated plots on four field sites over two growing seasons. Field sites had sandy loam soils with topography slopes ranging from 3% to 5%. Within each field, nine 25 m long and 3.66 m wide (4 rows) plots were established, including three plots of each hilling treatment (CT = conventional tillage; RS = row shaper tillage; BT = basin tillage). Runoff volume, nutrient (phosphate, ammonium, nitrate) and suspended solids loads were measured using collection barrels on the down slope end of each furrow.Basin tillage had 78% and 75% less runoff than CT and RS, respectively (P < 0.05). Runoff differences between BT and CT were significant at all sites while runoff differences between BT and RS were significant at three of four sites. Reductions for each parameter (on a mass basis) averaged across all sites were: sediment 89%, nitrate 45%, ammonium 38%, and phosphate 15%; although, treatment effect was not significant for some mass loads in some fields. No significant effect on marketable potato yield was observed at any site; soil water was not limiting in either growing season. Overall, basin tillage was effective at reducing runoff and nutrient losses without affecting yield and appears to be an effective tool for decreasing environmental risks.     

The effect of polyacrylamide on runoff,erosion, and cotton yield from fields irrigated with moving sprinkler systems

Summary Irrigation with self-propelled moving sprinkler irrigation system (MSIS) enhances seal formation at the soil surface and results in large amounts of runoff and erosion which are aggravated by the MSIS high water application rate and reflected in lower yields. The effect of polyacrylamide (PAM) application (at the equivalent rate of 20 kg ha^-1), prior to the irrigation season, on runoff and erosion from bare soil and soil covered with a crop, as well as on cotton yield was studied in a clay loam vertisol (Typic Chromoxert) and a silt loam loess (Calcic Haploxeralf). A center pivot and a lateral MSIS were used in the vertisol and loess, respectively. Vegetative growth of cotton plants in the vertisol was inversely related to water application intensity, which in turn affects runoff. PAM significantly reduced runoff in both the bare and crop-covered soils. The runoff level from the PAM treatments was 50–70% of that of the control. PAM also reduced erosion especially in the vertisol soil. However, the amount of eroded material carried by a unit runoff was similar in both treatments for both soils, indicating that PAM influences erosion by reducing runoff levels. A trend whereby PAM increased yield of cotton (Gossypium hirsutum L., cv. Pima S5) compared with the control was observed. Our results suggest that, under irrigation with a MSIS, reducing runoff is essential for obtaining higher yields. PAM is suggested as an effective tool to attain this target.Contribution from the Agricultural Research Organization, The Volcani Center, Bet Dagan, Israel. No. 2866-E, 1989 series     

PAM和SAP交并施用对旱区坡地固土截水的影响

对PAM和SAP交并施用对旱区坡地固土截水的影响进行初步测定。PAM和SAP都是很好的土壤改良剂。使用PAM可以显著降低土壤结皮,减少地表径流和土壤侵蚀。SAP可以提高土壤的保水性,改善土壤结构。采用两种SAP施用方式:SAP(0~20cm)混施和SAP(20cm)层施。土槽装填好后,将PAM均匀撒施在土壤表层。将土槽置于调整好角度的支架上。降雨10min,湿润土壤。静置1d后再进行试验。试验结果表明PAM和SAP交并施用可以明显增强土壤的固土截水能力。当SAP混施时,PAM施用量的影响比SAP显著。而SAP层施时,SAP施用量的变化对土壤的固土截水能力没有影响,但PAM依然影响很大。相同PAM和SAP施用量的情况下,SAP混施比层施时减少水土流失量、土壤侵蚀量、地表径流量更大。     

Runoff estimation in southern Brazil based on Smith's modified model and the Curve Number method

The objective of this work was to measure and model the runoff for different soils classes at different rainfall intensities (30, 60 and 120 mm h⁻¹) in Southern Brazil. A portable rainfall simulator with multiple nozzles was used to simulate these rainfall intensities. For each soil, the initial time and runoff rate, rainfall characteristics (total, duration and intensities), surface slope, crop residue amount and cover percentage, soil densities (bulk and particle), soil porosity (bulk, macro and micro), textural fractions (clay, silt and sand), and the initial and saturated soil water content were measured. The runoff measured was compared to Smith's modified and Curve Number (USDA-SCS) models. The cumulative runoff losses were 67, 45 and 27% of the total rainfall, for a Rhodic Paleudalf, Typic Quartzipsamment and Rhodic Hapludox, respectively. An inverse relationship was observed between initial runoff and the runoff rate, independently of the soil surface and rainfall conditions. Increasing rainfall intensity decreased the time to runoff and increased runoff rate. The Smith's modified model overestimated the cumulative runoff by about 4%. The Smith's modified model presented a better estimate for both higher and lower rainfall intensities (120 and 30 mm h⁻¹). The SCS Curve Number model overestimated the cumulative runoff by about 34%. This large overestimate is probably due to that the model did not take into account the soil tillage system used in the field by farmers, particularly for irrigated conditions. The combination of high porosity, low bulk density and presence of crop residue on soil surface decreased runoff losses, independently of the soil texture class. Smith's modified model better estimated the surface runoff for soil with a high soil water content, and it was considered satisfactory for Southern Brazil runoff estimations. The SCS Curve Number model overestimated the cumulative runoff and its use needs adjustments particularly for no-tillage management system.     

Polymer effects on runoff and soil erosion from sodic soils

High levels of soil sodicity, resulting from intensive irrigation with saline-sodic waters, lead to an increased soil susceptibility to seal formation and to severe problems of runoff and soil erosion. The objective of this study was to investigate the efficacy of the addition of small amounts of an anionic polyacrylamide (PAM) to the irrigation water in controlling seal formation, runoff and soil erosion. Two predominantly montmorillonitic soils were studied, a grumusol (Typic Haploxerert) and a loess (Calcic Haploxeralf), having naturally occurring exchangeable sodium percentage (ESP)>12. The soils were exposed to 60 mm of simulated irrigation with commonly used tap water (TW, electrical conductivity=0.8 dS m^–1; sodium adsorption ratio (SAR)=2), or saline water (SW, electrical conductivity=5.0 dS m^–1; SAR>12). PAM effectiveness in controlling runoff and erosion from the sodic soils was compared with runoff and erosion levels obtained from untreated soils having low ESPs (<4). For both soils and for both water qualities and polymer concentrations in the irrigation water, PAM was efficient in controlling runoff at low ESP levels and inefficient at high ESP levels. At moderate ESP levels, PAM's efficacy in controlling runoff was inconsistent and varied with water quality and polymer concentration. Conversely, in general, soil loss originating from rill erosion, was significantly and effectively reduced in moderate and high ESP soils by addition of PAM to the irrigation water, irrespective of water quality and polymer concentration. PAM was more effective in reducing rill erosion than in reducing runoff in the moderate and high ESP samples, because the energy involved in generating runoff is much higher than that involved in rill erosion. PAM treated surface aggregates were not stable against the distructive forces leading to seal formation and runoff production; but they were stable enough to resist the hydraulic shear exerted by the runoff flow.     

Micro-catchment water harvesting potential of an arid environment

Micro-catchment water harvesting (MCWH) requires development of small structures across mild land slopes, which capture overland flow and store it in soil profile for subsequent plant uses. Water availability to plants depends on the micro-catchment runoff yield and water storage capacity of both the plant basin and the soil profile in the plant root zone. This study assessed the MCWH potential of a Mediterranean arid environment by using runoff micro-catchment and soil water balance approaches. Average annual rainfall and evapotranspiration of the studied environment were estimated as 111 and 1671 mm, respectively. This environment hardly supports vegetation without supplementary water. During the study period, the annual rain was 158 mm in year 2004/2005, 45 mm in year 2005/2006 and 127 mm in year 2006/2007. About 5000 MCWH basins were developed for shrub raising on a land slope between 2 and 5% by using three different techniques. Runoff at the outlets of 26 micro-catchments with catchment areas between 13 and 50 m² was measured. Also the runoff was indirectly assessed for another 40 micro-catchments by using soil water balance in the micro-catchments and the plant basins. Results show that runoff yield varied between 5 and 187 m³ ha⁻¹ for various rainfall events. It was between 5 and 85% of the incidental rainfall with an average value of 30%. The rainfall threshold for runoff generation was estimated about 4 mm. Overall; the soil water balance approach predicted 38-57% less water than micro-catchment runoff approach. This difference was due to the reason that the micro-catchment runoff approach accounted for entire event runoff in the tanks; thus showed a maximum water harvesting potential of the micro-catchments. Soil water balance approach estimated water storage in soil profile and did not incorporate water losses through spillage from plant basins and deep percolation. Therefore, this method depicted water storage capacity of the plant basins and the root zone soil profile. The different between maximum water harvesting potential and soil-water storage capacity is surplus runoff that can be better utilized through appropriate MCWH planning.     

Runoff, erosion, and water quality of agricultural watersheds in central Navarre (Spain)

Two experimental watersheds, La Tejería (1.69 km²) and Latxaga (2.07 km²), appointed by the Government of Navarre (Spain) for assessing the effect of agricultural activities on the environment, were monitored during 10 years (1996-2005). Both watersheds are roughly similar with regard to soils, climate (humid sub Mediterranean) and land use (almost completely cultivated with winter grain crops). The first results for both sites on runoff, exported sediment, nitrate and phosphate are presented.Most runoff, sediment, nitrate and phosphate yields were generated during winter, when variability was also the highest of the whole year.La Tejería had much higher sediment concentrations and sediment yield than Latxaga. Nitrate concentrations were also significantly higher at La Tejería, with values constantly over the critical threshold (>50 mg NO₃ l⁻¹). However, phosphate concentrations were similar in both watersheds and corresponded to water with a significant risk of eutrophication. Differences in watershed behaviour could be mainly due to differences in morphology, topography, and amount of stream channel vegetation between both sites.This is an unprecedented research for the region and the generated dataset is of paramount importance for research issues such as hydrology, erosion and water quality. The results highlight the complexity of Mediterranean agricultural landscapes and the need for further analyses to better ascertain the processes behind them.     

Modelling of water and nitrogen balances in the ponded water and soil profile of rice fields in Northern Greece

This paper presents a water and nitrogen balance model for the surface ponded water and soil profile system of rice (Oryza sativa L.) fields. The model estimates the daily water balance components, as well as, the daily losses and transformations of nitrogen. Data from two neighbouring rice fields during the growing season of 2005 in the Thessaloniki plain of Northern Greece were used for the application of the model. The data set of field A was used for the calibration of the model, while the data set from the field B for validation of model. Simulation results of total inorganic nitrogen in the soil and runoff water exhibited reasonable agreement with the measured data during calibration and verification of the model. Significant amounts of applied irrigation water were lost through surface runoff and deep percolation into the groundwater. The sum of nitrogen inputs from fertilization, mineralization and irrigation water were 292.7 and 280.4 kg ha⁻¹ for field A and B, respectively. Nitrogen uptake by algae in ponding water and plants was one of the main processes of nitrogen reduction in the rice field systems with an amount of 125.7 and 131.8 kg ha⁻¹ for field A and B, respectively. Leaching through percolated water was the other significant process with 118.3 and 120.8 kg ha⁻¹, respectively. Gaseous losses of nitrogen (via volatilization and denitrification) were also substantial processes of nitrogen reduction in the flooded compartment. The study showed that the simple model presents important results for the water and nitrogen management in rice fields. This information can be used for irrigation water saving and prevention of water resources contamination in rice-based agroecosystems.     

黑土区坡耕地几种耕作措施水土保持效益研究

我国东北黑土区作为全国水土流失重点区域,其坡耕地的水土流失问题早已备受关注。【目的】采取保护性耕作措施可以大大降低坡耕地的水土流失强度,起到保水保肥的作用。【方法】在10°坡径流小区上,对比分析了黑土区不同耕作措施对坡耕地坡面产流、土壤侵蚀以及土壤养分的影响。【结果】竹节垄Ⅱ与横坡耕作相比,产流起始时间延长38 min,单次降雨径流量减少57.1%,产沙量减少51.9%;0～20 cm土层土壤有机质、碱解氮、速效磷、速效钾平均质量分数分别提高5.89%、11.48%、16.54%、21.75%。【结论】在相同降雨条件下,横坡耕作、竹节垄Ⅰ、竹节垄Ⅱ较顺坡耕作均有不同程度的减流减沙作用,竹节垄Ⅱ效果最为明显。     

Rainfall simulation to identify the storm-scale mechanisms of gully bank retreat

Gully erosion is one of the main causes of soil loss in drylands. Understanding the dominant mechanisms of erosion is important to achieve effective erosion control, thus in this study our main objective was to quantify the mechanisms involved in gully bank retreat as a result of three processes, falling of entire soil aggregates, transport of soil material by splash and by water running along gully banks (runoff), during rainfall events. The study was conducted in the sloping lands of the KwaZulu-Natal province, a region that is highly affected by gully erosion. Artificial rain was applied at 60 mm h⁻¹ for 45 min at the vertical wall of a gully bank typical to the area. The splash material was collected by using a network of 0.045 m² buckets. The sediments in the running water were assessed by sampling the runoff collected from a microplot inserted within the base of the bank, and collecting the fallen aggregates after the rainfall simulation was complete. Results indicated that the overall erosion for the simulation was 721 g m⁻² h⁻¹. Runoff erosion proved to be the dominant mechanism and amounted to 450 g m⁻² h⁻¹, followed by splash and fall down of aggregates (about 170 g m⁻² h⁻¹). Gully bank retreat occurred at a rate of 0.55 mm h⁻¹ and assuming that the soil bulk density is 1.3 g cm⁻³, this corresponds to a retreat of 8.8 mm y⁻¹. Extrapolations to the watershed level, where about 500 m² of gully bank are observed per hectare, would lead to an erosion rate of 4.8 t ha⁻¹ y⁻¹. These limited results based on a simulated storm show that the three main mechanisms (runoff, splash and fall down of aggregates) are responsible for the retreat of gully banks and that to mitigate gully erosion, appropriate measures are required to control all three mechanisms. Further research studies are needed to confirm and to scale up, both in time and space, as these data are obtained at one location and from a single artificial storm.     

Antecedent water content effects on runoff and sediment yields from two Coastal Plain Ultisols

The highly weathered, low-carbon, intensively cropped, drought-prone Coastal Plain soils of Georgia are susceptible to runoff and soil loss, especially at certain times of the year when soil water contents are elevated. We quantified the effects of antecedent water content (AWC) on runoff (R) and sediment (E) losses from two loamy sands managed under conventional- (CT), strip- (ST), and/or no-till (NT) systems. Two AWC treatments were evaluated: field moist (FM) and pre-wet (PW), created with and without post pesticide application irrigations (∼12 mm of water added with the rainfall simulated over 30 min) for incorporation. Treatments (5) evaluated were: CT + FM, CT + PW, ST + FM, ST + PW, and NT + PW. Field plots, each 2-m × -3 m, were established on each treatment. Each 6-m² field plot received simulated rainfall at a variable rainfall intensity (I_v) pattern for 70 min (site 1) or a constant rainfall intensity (I_c) pattern for 60 min (site 2; I_c = 50.8 mm h⁻¹). Adding ∼12 mm of water as herbicide incorporation increased AWCs of the 0-2 (3-9-fold) and 2-15 (23-117%) cm soil depths of PW plots compared to existing field moist soil conditions. Increase in AWC increased R (as much as 60%) and maximum R rates (as much as 62%), and decreased E (at least 59%) and maximum E rates (as much as 2.1-fold) for corresponding tillage treatments. Compared to CT plots, ST and NT plots decreased R (at least 2.6-fold) and maximum R rates (as much as 3-fold), and decreased E (at least 2.7-fold) and maximum E rates (at least 3.2-fold). Runoff curves for pre-wetted CT and ST plots were always higher than corresponding FM curves, whereas E curves for field moist CT and ST plots were always higher than corresponding PW curves. Changes in AWC and tillage affected detachment and transport processes controlling runoff and sediment yields. A more accurate measure of rainfall partitioning and detachment and transport processes affecting R and E losses was obtained when commonly occurring field conditions (increased AWC with irrigation; I_v pattern derived from natural rainfall; commonly used tillage systems) were created and evaluated.     

非硬化路面侵蚀产沙规律野外模拟试验

为了科学治理非硬化路面水土流失,采用野外放水冲刷试验,对非硬化路面侵蚀产沙规律进行了试验研究。结果表明,同一坡度不同放水流量与同一放水流量不同坡度条件下,非硬化路面产沙随时间的变化形式均有3种,分别为平缓型、多峰型和单峰型。对同一路面不同观测断面的产沙量分析发现,产沙量沿坡面的空间变化形式分别为波动式减小、逐渐式减小和先增大后减小。、得出平均含沙量与放水流量呈对数相关,产沙率与放水流量、平均含沙量与坡度、产沙率与坡度均呈直线相关。以期为非硬化路面的水土流失预测和治理提供科学依据。     

Modeling soil carbon sequestration in agricultural lands of Mali

Agriculture in sub-Saharan Africa is a low-input low-output system primarily for subsistence. Some of these areas are becoming less able to feed the people because of land degradation and erosion. The aim of this study is to characterize the potential for increasing levels of soil carbon for improving soil quality and carbon sequestration. A combination of high- and low-resolution imagery was used to develop a land use classification for an area of 64 km² near Omarobougou, Mali. Field sizes were generally small (10–50 ha), and the primary cultivation systems are conventional tillage and ridge tillage, where tillage is performed by a combination of hand tools and animal-drawn plows. Based on land use classification, climate variables, soil texture, in situ soil carbon concentrations, and crop growth characteristics, the EPIC-Century model was used to project the amounts of soil carbon sequestered for the region. Under the usual management practices in Mali, mean crop yield reported (1985–2000) for maize is 1.53 T ha⁻¹, cotton is 1.2 T ha⁻¹, millet is 0.95 T ha⁻¹, and for sorghum is 0.95 T ha⁻¹. Year-to-year variations can be attributed to primarily rainfall, the amount of plant available water, and the amount of fertilizer applied. Under continuous conventional cultivation, with minimal fertilization and no residue management, the soil top layer was continuously lost due to erosion, losing between 1.1 and 1.7 Mg C ha⁻¹ over 25 years. The model projections suggest that soil erosion is controlled and that soil carbon sequestration is enhanced with a ridge tillage system, because of increased water infiltration. The combination of modeling with the land use classification was used to calculate that about 54 kg C ha⁻¹ year⁻¹ may be sequestered for the study area with ridge tillage, increased application of fertilizers, and residue management. This is about one-third the proposed rate used in large-scale estimates of carbon sequestration potential in West Africa, because of the mixture of land use practices.     

InfoCrop: A dynamic simulation model for the assessment of crop yields,losses due to pests,and environmental impact of agro-ecosystems in tropical environments. II. Performance of the model

InfoCrop, a generic crop model, simulates the effects of weather, soils, agronomic management (planting, nitrogen, residues and irrigation) and major pests on crop growth, yield, soil carbon, nitrogen and water, and greenhouse gas emissions. This paper presents results of its evaluation in terms of its validation for rice and wheat crops in contrasting agro-environments of tropics, sensitivity to the key inputs, and also illustrates two typical applications of the model. Eleven diverse field experiments, having treatments of location, seasons, varieties, nitrogen management, organic matter, irrigation, and multiple pest incidences were used for validation. Grain yields in these experiments varied from 2.8 to 7.2 ton ha⁻¹ in rice and from 3.6 to 5.5 ton ha⁻¹ in wheat. The results indicated that the model was generally able to explain the differences in biomass, grain yield, emissions of carbon dioxide, methane and nitrous oxides, and long-term trends in soil organic carbon, in diverse agro-environments. The losses in dry matter and grain yield due to different pests and their populations were also explained satisfactorily. There were some discrepancies in the simulated emission of these gases during first few days after sowing/transplanting possibly because of the absence of tillage effects in the model. The sensitivity of the model to change in ambient temperature, crop duration and pest incidence was similar to the available field knowledge. The application of the model to quantify multiple pests damage through iso-loss curves is demonstrated. Another application illustrated is the use of InfoCrop for analyzing the trade-offs between increasing crop production, agronomic management strategies, and their global warming potential.     

Annual carbon and nitrogen loadings for a furrow-irrigated field

Evaluations of agricultural management practices for soil C sequestration have largely focused on practices, such as reduced tillage or compost/manure applications, that minimize soil respiration and/or maximize C input, thereby enhancing soil C stabilization. Other management practices that impact carbon cycling in agricultural systems, such as irrigation, are much less understood. As part of a larger C sequestration project that focused on potential of C sequestration for standard and minimum tillage systems of irrigated crops, the effects of furrow irrigation on the field C and N loading were evaluated. Experiments were conducted on a laser-leveled 30 ha grower's field in the Sacramento valley near Winters, CA. For the 2005 calendar year, water inflow and runoff was measured for all rainfall and irrigation events. Samples were analyzed for C and N associated with both sediment and dissolved fractions. Total C and N loads in the sediment were always higher in the incoming irrigation water than field runoff. Winter storms moved little sediment, but removed substantial amounts of dissolved organic carbon (DOC), or about one-third of the total C balance. Despite high DOC loads in runoff, the large volumes of applied irrigation water with sediment and DOC resulted in a net increase in total C for most irrigation events. The combined net C input and N loss to the field, as computed from the field water balance, was 30.8 kg C ha⁻¹ yr⁻¹ and 5.4 kg N ha⁻¹ yr⁻¹ for the 2005 calendar year. It is concluded that transport of C and N by irrigation and runoff water should be considered when estimating the annual C field balance and sequestration potential of irrigated agro-ecosystems.     

A regional soil survey approach for upgrading from flood to sprinkler irrigation in a semi-arid environment

Increasing pressure on water resources in Spain is forcing farmers to move from flood to pressurized water application. Initial recommendations for this upgrading require soil survey information, especially in areas prone to soil salinity. In this article a 3158 ha soil survey at a scale of 1:25,000 is presented. Soil series are split in phases based on the texture of the surface layer, slope, and salinity. Available water holding capacity (AWHC), to a depth of 1.5 m or to a lithic or paralithic contact, texture and coarse components in the surface horizons, and salinity mapped as discrete soil units are combined to develop a regional soil suitability map for irrigation upgrade. To minimize soil erosion and salt mobilization in the soils, our recommendations are: (i) maintain and improve flood irrigation on 296 ha, (ii) develop standard sprinkler irrigation on 2261 ha, and (iii) move to high frequency sprinkler irrigation on 601 ha. This research demonstrates the importance of soil survey as part of the decision making process for upgrading the regional irrigation systems.