Stabilizing steep slopes with soil conditioners and plants

The approach in this study of runoff and erosion control on steep slopes was to combine soil stabilizers with the planting of drought-resistant, perennial plants.The effect of 10 t ha⁻¹ phosphogypsum (PG) + 70 kg ha⁻¹ polysaccharide (PS), 10 t ha⁻¹ PG and 20 kg ha⁻¹ polyacrylamide (PAM), and 200 kg ha⁻¹ PS on the erosion of steep slopes (30–60%) was studied in plots 2 m in width and of different lengths (12–20 m), at three of different sites in Israel (semiarid conditions), and under natural rainfall conditions. Likewise, observations on the establishment and development of nonirrigated, drought-resistant, perennial plants on steep slopes (40–60%), combined with 10 t ha⁻¹ PG + 70 kg ha⁻¹ PS, were conducted at two sites in Israel.PS + PG and PAM + PG treatments were very efficient in erosion control in a wide range of soil types, ESP, CaCO₃ level, and weather conditions. These treatments reduced erosion six- to eleven-fold in comparison with the control. No significant difference was found between PS + PG and PAM + PG treatments. However, the application of PAM was problematic due to its very low dissulution rate and its high viscosity in water. Two-hundred kg PS without PG was found efficient only at one experimental site with calcic haploxeralf soil and 300 mm average annual rainfall.The combination of PS + PG, and drought-resistant, perennial plants was very sucessful. The plants developed very well without irrigation throughout the long, dry summer. Only one year later, the creeper plant canopy covered an area of 0.75–1.5 m, and the bushes were 0.8–1.2 m in height.     

Stabilizing steep slopes with geomembranes

The effects of five types of geomembranes, placed at the soil surface, on runoff and erosion on steep earth slopes were studied under laboratory and field conditions. In the laboratory, the soil samples were packed in boxes held at a 50% slope and subjected to three consecutive simulated rainstorms of 120 mm each. The membranes dissipated the drops' impact and reduced runoff significantly compared with the control. There was no significant difference among the membranes regarding their effect on the runoff. In the field, the membranes lined earth dikes of 33–60% slope and 12–20 m length, during 2 years. There was no runoff and erosion from the lined plots compared with 80–125 tonne ha⁻¹ of erosion in the control plots. No considerable wear and tear of the membranes was observed.     

Restoration of eroded soil with conservation tillage

Eroded Kandhapludult soils occupy more than 40% of the Southern Piedmont region of the USA. The humid-thermic climate associated with the Ultisols permits double crop residue production ranging from 10 to 14 Mg ha⁻¹ yr⁻¹. Long-term conservation tillage into these crop residues is beneficial in ameliorating the effects of soil erosion. During the course of a five-year study, decomposition of these residues increased soil carbon significantly. Restoration processes were initiated by increasing average soil carbon, representing slight, moderate and severe soil erosion classes, from 0.97 to 2.37% in the 0 to 1.5-cm depth. Accompanying soil carbon responses were increases in soil N, water-stable aggregation and infiltration. Runoff coefficients on conservation tilled restored soils was only 6%, compared to 35% for those conventionally tilled. Rill and interrill soil loss rates were also reduced significantly with surface residue provided with conservation tillage.Restoring Ultisol landscapes with variable levels of soil erosion requires differential fertilization. All fertilizer requirements for severely eroded plots were 1.43 to 2.30-fold higher than those of moderately eroded plots. Because biological N fixation by the crimson clover (Trifolium incarnatum L.) cover crop appeared to be retarded on the severely eroded site, observed plant N stress developed on the irrigated/conservation tillage treatment. Cumulative grain yields of severely eroded site, ranged from 15.4 to 30.3 Mg ha⁻¹ 5yr⁻¹, and were statistically equal to or exceeded those of the slightly eroded site. Conservation tillage grain yields were best optimized on the rainfed-moderately eroded site, probably because of the more desirable texture-organic properties of the 13-cm thick Ap horizon. Management of cool-season cover crops with conservation tillage appears essential to restore and sustain crop productivity on eroded Ultisols.     

Severe erosion on agricultural land in east Sussex,UK October 1987

Severe erosion occurred as a result of heavy rainfall on 7 October 1987 and subsequent storms. Rates of erosion were highest on land drilled with winter cereals in the previous three weeks but erosion also occurred on ploughed land. In an area of c36 km² some erosion was recorded on all cereal fields. Several fields suffered losses >50 m³ ha⁻¹ and rates reached>200 m³ ha⁻¹ on one field. This is the most serious erosion on agricultural land recorded in Britain.In autumn months heavy rain on erodible, silt-rich soils prone to crusting inevitably leads to runoff and high rates of soil loss but a number of factors contributed to the severity of this event: the amount of bare, recently drilled land; the timing of drilling; the size of fields, steepness and length of slopes; the rolling of drilled fields, and the prevalence of wheelings.     

Effect of water quality and amendments on the hydraulic properties and erosion from several mediterranean soils

The response of six sandy-loam soils from Portugal and Israel to leaching with sodic and saline water and to simulated rain was studied. The dominant clay mineral in the soils from Portugal was kaolinite, whereas smectite predominates in the soils from Israel. The permeability of the soils depended on the soil texture: it decreased with an increase in the silt and clay content. The response of the soils to sodicity depended on the electrolyte concentration; salt concentrations exceeding 10 mmol_c·L⁻¹ was enough to prevent the deleterious effect of exchangeable sodium (≤20%). When leaching with distilled water (stimulating rain water), the presence of primary minerals and lime determine the susceptibility of the soils to sodicity. The calcareous loess from Israel was the least susceptibility to sodicity.The six soils were susceptible to sealing, high runoff and erosion when exposed to rain. The soil surface was particularly vulnerable to sealing due to both the mechanical impact of raindrops and the low concentration of electrolytes in the rainwater. Seal formation was due to two mechanisms:

• 1.(i) physical disruption of aggregates at the soil surface which depended on the impact energy of raindrops and the inherent aggregate stability; and
• 2.(ii) chemical dispersion which depended on the mineralogy of the clay, the ESP, and the electrolyte concentration.

When the impact of the drops was prevented, or when the anionic polymer was sprayed at the soil surface, physical breakdown of the aggregates was reduced and runoff and erosion were slight. When the electrolyte concentration was high, the chemical dispersion was small and runoff and erosion decreased, compard with the control. The smectite soils from Israel were more susceptible to sealing than the kaolinitic soils from Portugal.     

Effect of soil-N and urine-N on nitrate leaching under pure grass,pure clover and mixed grass/clover swards

During six annual drainage periods (DP_O to DP₅), the drainage water, the NO₃ concentration of the drainage water and the total leached N were compared under bare soils and under ryegrass/white clover, pure ryegrass and pure white clover stands in 80 deep lysimeters with 3m² area. For each soil cover, the sensitivity of the variables to the soil N supplying capacity at sowing was measured, using a set up of 32 lysimeters. This initial capacity to supply mineral N (SoilN) varied from 90 to 230 kg N ha⁻¹ year⁻¹. The stands were managed in a simulated rotational grazing system, without addition of fertilizer N. During the first drainage period after sowing (DP₀), N leaching increased significantly with the initial SoilN under the bare soils, the pure grass and the mixture, but was not influenced under the pure clover. In the following drainage periods, N leaching increased according to the sequence pure grass (1–5 kg N ha⁻¹ year⁻¹), mixed swards (1–19 kg N), pure white clover (28–140 kg N) and bare soils (84–149 kgN ha⁻¹ year⁻¹). It was only slightly greater under the mixture than under the pure grass, despite the N harvest and the N animal returns were much higher. Under the mixed stands, N leaching became independent of the initial SoilN in DP₁ and DP₂ and decreased with increasing initial SoilN in DP₃, DP₄ and DP₅. This inversion of the SoilN effect in time and the limited amounts of leached N demonstrated that adaptations in the ecosystem tend to counteract the SoilN effect on the N losses. In the mixed stands, the accumulated N leaching represented 12 and 21% of the accumulated N at harvest for the initially rich and poor soils, respectively and 32% of the accumulated N harvest in the mixed clover, whatever the initial SoilN. N leaching also represented 13% of the urine-N above 80 kgN ha⁻¹ year⁻¹. The low values of N leaching under the mixed swards make them sustainable for environment quality. Mechanisms which regulate the N fluxes are discussed, using published data on the soil and some results concerning the harvests in the same experiment.     

Reduction in soil loss from erosion-susceptible soils amended with humic substances from oxidized coal

Soils that pose high risk of erosion require amendment with either natural or synthetic soil conditioners to reduce soil loss hazards. The objective of this study was to evaluate the potential of using coal-derived humic substances (as soil conditioners) to reduce runoff erosion on erosion-susceptible soils. Surface (0–20 cm) samples of severely degraded soils from Principina in Tuscany (Orthic Xerofluvent) and Bovolone in Venice (Udic Ustochrept) in Italy were used to assess the effects of five rates (0, 0.05, 0.10, 0.50 and 1.00 g/kg) of humic acids (HA) on soil loss and other hydrological parameters. A rainfall simulator was used to apply approximately 40 mm/h intensity rain for 1 h on soil beds of dimensions 2 m × 0.5 m × 0.01 m, packed at a bulk density of 1.20 Mg/m³ and inclined at a slope of 15%. The amount of soil eroded (E) and the time to initiate runoff (Rt) and drainage (Dt) were related to changes in the water-holding capacity and aggregate stability of the soils following the HA treatments. In the control treatments, the values of E, Rt and Dt were higher in the Principina than Bovolone soil. Increasing HA rates generally delayed Rt, accelerated Dt and reduced E substantially on both soils. On the Principina soil a reduction of about 36% in soil loss was obtained by adding only 0.05 g/kg of HA (equivalent to 100 kg/ha). On the sandier Bovolone soil, the same magnitude of reduction was achieved with 0.10 g/kg (200 kg/ha) of HA. Improvements in Rt and Dt from the HA amendments explained between 58 and 81% of the variation in E from both soils. Furthermore, improvements in the water retention capacity more than in the aggregate stability of these soils accounted for the reduced runoff erosion. These results show that amending erosion-susceptible soils with low rates of coal-derived humic substances is a potentially effective soil management practice for reducing erosion rates.     

Environmental impact of soil erosion under different cover and management systems

Runoff, soil loss and physical chemical composition of surface soil, runoff water and eroded sediment were measured for three erosive rainstorms of the 1988 Autumn-Winter season, on clay soil slopes (Typic Chromoxeret) under different cover and management systems in a locality of Sicily.Four years reconsolidated natural grass-sod (Avena fatua and Lolium tumulentum), natural grass-sod with implanted forage shrubs (Atriplex halimus) and natural grass-rod afforested with Pine trees (Pinus halepensis), reduced significantly runoff and soil loss in comparison with tilled fallow following four years durum wheat cultivation.While differences in runoff and soil loss between reconsolidated systems were not significant, the higher biomass yield (Stringi et al. 1991) and the better soil cover (Chisci et al. 1991) of the Atriplex system, increased O.M. content of the soil and prevented soil erosion under very intense rainstroms of the semiarid Mediterranean area.The comparison of textural and aggregate grain-size composition of surface soil and sediment confirmed that physico-mechanical composition of sediment detached and transported by over-land flow on clayey soils is better estimated by pseudo-textural grain-size composition of surface soil (Chisci et al. 1989) than from textural composition.Soil loss amounts, and O.M., N and P enrichment ratios, combined in a specifically devised Environmental Impact Index (EI), demonstrated the excellent environmental protection value of reconsolidation of arable soils. However, Pinus system was somewhat less efficient than Atriplex and good natural grass-sod systems.     

Soil carbon and nitrogen changes after 28 years of no-tillage management under Mediterranean conditions

Mouldboard ploughing is known to accelerate soil organic matter (SOM) mineralization rate in Mediterranean regions. Long-term reduced tillage intensity potentially diminishes soil organic carbon (SOC) and total nitrogen (STN) depletions. Here, we compared long-term no-tillage (NT) and conventional tillage (CT) impact on SOC and STN sequestration rates at different depths ranging from 0 to 30 cm. The long-term experiment started in 1986 on a Typic Xerofluvent soil in Central Italy using a randomized complete block design with four replications. Ten years after the experiment began, SOC and STN concentrations in the 0–30 cm soil layer were already higher under NT compared to CT. The shallow layer (0–10 cm) showed the highest SOC and STN concentration increments. However, no differences between tillage systems were observed in the deeper layers. After 28 years, continuous NT increased SOC and STN content in the 30 cm soil depth by 22% compared to initial values. In the same period, continuous CT decreased SOC and STN content by 3% and 5%, respectively. On average, the total SOC and STN gains under NT may be attributed to the shallow layer increments. In the 10–20 and 20–30 cm soil layers, SOC accumulation over time was negligible also under NT. In the whole profile (0–30 cm), the mean annual SOC variation was +0.40 Mg ha⁻¹ yr⁻¹ and −0.06 Mg ha⁻¹ yr⁻¹ under NT and CT, respectively. Under NT, SOC content increased rapidly in the first ten years (+0.75 Mg ha⁻¹yr⁻¹); later on, SOC increments were slower indicating the reaching of a new equilibrium. Data show that NT is a useful alternative management practice increasing carbon sequestration and soil health in Mediterranean conditions.     

Chemical changes in a saline-sodic soil after gypsum application and cropping

Reclamation is needed on three million ha of slowly permeable saline-sodic soils in the Indus Plain of Pakistan. Previous studies measured an increased field-saturated hydraulic conductivity (K_fs) in the soil under study with cropping and gypsum application. This field experiment was conducted on a low permeability, saline-sodic soil (a fine-loamy, mixed thermic Typic Natrustalf) to compare the leaching of sodium and soluble salts and changes in chemical properties after various treatments. Treatments were: (i) perennial alfalfa (Madicago sativa L.), (ii) a rotation of sesbania [Sesbania bispinosa (Jacq.)W.F. Wright]-wheat (Triticum aestivum L.)-sesbania, (iii) incorporated wheat straw at 7.5 Mg ha⁻¹ and (iv) a fallow control. These four treatments were each combined with and without 25 Mg ha⁻¹ of gypsum and open-ditch drainage. Electrical conductivity (EC), pH, Na⁺, Ca²⁺, Mg²⁺ and Cl⁻ of the soil in the saturated paste extract under each treatment were measured in each 20 cm increment to 120 cm after 6 month and 1 yr. Gypsum application increased the soluble Na⁺ in the top 20 cm soil. Poor internal drainage of the soil caused the exchanged Na⁺ to remain in the soil solution. However, one year after the treatments, the crop rotation with gypsum significantly decreased SAR, EC, pH and Cl⁻ in the top 20 cm of soil. Alfalfa decreased these same parameters when compared to fallow in the top 80 cm of soil in gypsum-treated plots. The open-ditch drainage was not helpful in reclamation of this soil. In general, for surface soil improvement, a combination of added gypsum plus crop rotation was the best. For improvement of the deeper soil profile, gypsum plus alfalfa was the most effective of the treatments used.     

Effect of antecedent soil water content and rainfall regime on microrelief changes

Surface microrelief substantially affects surface sealing, runoff, and soil erosion processes on bare soils. Yet, the stability of microrelief for different antecedent soil water contents and rainstorms is not well understood. This study investigates the effect of surface microrelief and antecedent water content on the decay of microrelief under different rainstorm regimes. Two different rainstorm regimes were studied in laboratory experiments: continuous rainfall for a total amount of 60 mm applied at 30 mm/h intensity, and intermittent rainfall consisting of five successive rainstorms of 12 mm each, again with an intensity of 30 mm/h and separated by one week drying cycles. Rough, medium, and fine microrelief surface conditions representing different degrees of seedbed preparation were studied for three soils at antecedent soil water contents of 2–4% and 14–20%. Before and after rainfall, digital elevation models determining the surface microrelief were developed using a laser scanner with 2 mm grid spacing. The specific surface area calculated from microrelief data was used as an index to characterize microrelief. Microrelief stability increased with increasing initial roughness and was much higher for the antecedent wet soils than for the dry soils. Microrelief stability for the continuous rainstorm regime was higher than for intermittent rainfall. Differences in microrelief stability were mostly attributed to different aggregate stabilities. Additionally, the higher stability for the rougher microrelief surfaces was attributed to the lower drop impact density and splash density on the surfaces with larger specific surface area. Aggregate slaking due to air escape and rapid wetting was found to be responsible for the low microrelief stability at initially dry conditions.     

Tillage,cover crops,and nitrogen fertilization effects on soil nitrogen and cotton and sorghum yields

Sustainable soil and crop management practices that reduce soil erosion and nitrogen (N) leaching, conserve soil organic matter, and optimize cotton and sorghum yields still remain a challenge. We examined the influence of three tillage practices (no-till, strip till and chisel till), four cover crops {legume [hairy vetch (Vicia villosa Roth)], nonlegume [rye (Secaele cereale L.)], vetch/rye biculture and winter weeds or no cover crop}, and three N fertilization rates (0, 60–65 and 120–130 kg N ha⁻¹) on soil inorganic N content at the 0–30 cm depth and yields and N uptake of cotton (Gossypium hirsutum L.) and sorghum [Sorghum bicolor (L.) Moench]. A field experiment was conducted on Dothan sandy loam (fine-loamy, siliceous, thermic, Plinthic Paleudults) from 1999 to 2002 in Georgia, USA. Nitrogen supplied by cover crops was greater with vetch and vetch/rye biculture than with rye and weeds. Soil inorganic N at the 0–10 and 10–30 cm depths increased with increasing N rate and were greater with vetch than with rye and weeds in April 2000 and 2002. Inorganic N at 0–10 cm was also greater with vetch than with rye in no-till, greater with vetch/rye than with rye and weeds in strip till, and greater with vetch than with rye and weeds in chisel till. In 2000, cotton lint yield and N uptake were greater in no-till with rye or 60 kg N ha⁻¹ than in other treatments, but biomass (stems + leaves) yield and N uptake were greater with vetch and vetch/rye than with rye or weeds, and greater with 60 and 120 than with 0 kg N ha⁻¹. In 2001, sorghum grain yield, biomass yield, and N uptake were greater in strip till and chisel till than in no-till, and greater in vetch and vetch/rye with or without N than in rye and weeds with 0 or 65 kg N ha⁻¹. In 2002, cotton lint yield and N uptake were greater in chisel till, rye and weeds with 0 or 60 kg N ha⁻¹ than in other treatments, but biomass N uptake was greater in vetch/rye with 60 kg N ha⁻¹ than in rye and weeds with 0 or 60 kg N ha⁻¹. Increased N supplied by hairy vetch or 120–130 kg N ha⁻¹ increased soil N availability, sorghum grain yield, cotton and sorghum biomass yields, and N uptake but decreased cotton lint yield and lint N uptake compared with rye, weeds or 0 kg N ha⁻¹. Cotton and sorghum yields and N uptake can be optimized and potentials for soil erosion and N leaching can be reduced by using conservation tillage, such as no-till or strip till, with vetch/rye biculture cover crop and 60–65 kg N ha⁻¹. The results can be applied in regions where cover crops can be grown in the winter to reduce soil erosion and N leaching and where tillage intensity and N fertilization rates can be minimized to reduce the costs of energy requirement for tillage and N fertilization while optimizing crop production.     

Evaluation of long-term conservation agriculture and crop intensification in rice-wheat rotation of Indo-Gangetic Plains of South Asia: Carbon dynamics and productivity

In the context of deteriorating soil health, stagnation of yield in rice-wheat cropping system (RWCS) across Indo- Gangetic plains (IGP) and environmental pollution, a long term field experiment was conducted during 2009–2016 taking four crop scenarios with conservation agriculture (CA), crop intensification and diversified cropping as intervening technology aiming to evaluate the sustainability of the systems. Scenario 1 (S1) represented conventional farmers’ practice of growing rice and wheat with summer fallow. In scenario 2 (S2) and scenario 3 (S3), legume crop was taken along with rice and wheat with partial CA and full CA, respectively. Conventional RWCS was replaced with rice-potato + maize- cowpea cropping system with partial CA in scenario 4 (S4). The S3 scenario registered highest total organic carbon (TOC) stock of 47.71 Mg C ha⁻¹ and resulted in significant increase of 14.57% over S1 (Farmer’s practice) in 0–30 cm soil depth after 7 years of field trial. The S4 scenario having intensified cropping systems recorded lowest TOC of 39.33 Mg C ha⁻¹ and resulted in significant depletion of 17.56% in C stock with respect to S3 in 0–30 cm soil depth. The TOC enrichment was higher in S2, S3 and S4 scenario in the surface soil (0–10 cm) compared to S1. At lower depth (20–30 cm), the TOC enrichment was significantly higher in S2 (12.82 Mg C ha⁻¹) and S3 (13.10 Mg C ha⁻¹ soil) over S1 scenario. The S2 and S3 scenario recorded highest increased allocation of TOC (3.55 and 6.13 Mg C ha⁻¹) to passive pool over S1. The S2 (15.72 t ha⁻¹), S3 (16.08 t ha⁻¹) and S4 (16.39 t ha⁻¹) scenarios recorded significantly higher system rice equivalent yield over S1 (10.30 t ha⁻¹). Among the scenarios, S3 scenario had greater amount of total soil organic carbon, passive pool of carbon and higher system rice equivalent yield, thus, is considered the best cropping management practice to maintain soil health and food security in the middle IGP.     

Estimation of past and recent carbon input by crops into agricultural soils of southeast Germany

In agricultural soils, the formation of soil organic matter largely depends on the carbon (C) input by crop residues and rhizodeposition, which is thus of decisive importance for the management and prediction of soil organic carbon (SOC) stocks in cropland and grassland. However, there is a remarkable lack of reliable, crop-specific C input data. We used a plant C allocation approach to estimate the C input of major crops and grassland into agricultural soils of Bavaria in southeast Germany. Historic and recent plant C allocation coefficients were estimated and C inputs were calculated for a 60-year period (1951–2010) using long-term agricultural statistics. The spatial distribution of C inputs within Bavaria was derived from county-specific statistical data. The results revealed increases of the C input by 107–139% for cereals, 173–188% for root, forage and leguminous crops and 34% for grassland in the last 60 years. This increase was related to linear yield increases until 1995 despite significant changes of plant C allocation. However, from 1995 onwards, crop yields and related C inputs stagnated, which allowed a robust estimation of recent crop-specific C input values. A total C input of 3.8–6.7 t ha⁻¹ yr⁻¹ was estimated for cereals, 5.2–6.3 t ha⁻¹ yr⁻¹ for root, forage and leguminous crops and 2.4 t ha⁻¹ yr⁻¹ for grassland. These amounts were partly higher compared to estimations in the literature. A generally high spatial variability of C inputs was detected within Bavaria with differences of up to 40% between adjacent counties. The results of this study could be used to optimize the C input of crop rotations and thus promote the formation of soil organic matter and C sequestration in agricultural soils on the basis of a soil carbon model. Moreover, recent estimations of C inputs could be used to model the future development of agricultural SOC stocks. A further stagnation of crop yields and the related C input under an ongoing temperature increase bears the risk of a future decrease of SOC stocks in cropland soils of Bavaria.     

Maize yield and water balance is affected by nitrogen application in a film-mulching ridge–furrow system in a semiarid region of China

Poor soil and drought stress are common in semiarid areas of China, but maize has a high demand for nitrogen (N) and water. Maize production using the technique of double ridges and furrows mulched with plastic film are being rapidly adopted due to significant increases in yield and water use efficiency (WUE) in these areas. This paper studied N use and water balance of maize crops under double ridges and furrows mulched with plastic-film systems in a semiarid environment over four growing seasons from 2007 to 2010. To improve precipitation storage in the non-growing season, the whole-year plastic-film mulching technique was used. There were six treatments which had 0, 70, 140, 280, 420 or 560 kg N ha⁻¹ applied in every year for maize. In April 2011, spring wheat was planted in flat plots without fertilizer or mulch following four years of maize cultivation. After four years, all treatments not only maintained soil water balance in the 0–200 cm soil layer but soil water content also increased in the 0–160 cm soil layer compared to values before maize sowing in April 2007. However, under similar precipitation and only one season of spring wheat, soil water content in the 0–160 cm soil layer sharply decreased in all treatments compared to values before sowing in April 2011. Over the four years of maize cultivation, average yield in all treatments ranged from 4071 to 6676 kg ha⁻¹ and WUE ranged from 18.2 to 28.2 kg ha⁻¹ mm⁻¹. In 2011, the yield of spring wheat in all treatments ranged from 763 to 1260 kg ha⁻¹ and WUE from 3.5 to 6.5 kg ha⁻¹ mm⁻¹. The potential maximum grain yield for maize was 6784 kg ha⁻¹ with 360 kg N ha⁻¹ applied for four years, but considerable NO₃N accumulated in the soil profile. A lesser application (110 kg N ha⁻¹) to this tillage system yielded in 82% of the maximum, increased nitrogen use efficiency and mitigated the risk of nitrogen loss from the system. This study suggests that double ridge–furrow and whole-year plastic-film mulching could sustain high grain yields in maize with approximately 110 kg N ha⁻¹ and maintain soil water balance when annual precipitation is >273 mm in this semiarid environment.     

Optimized single irrigation can achieve high corn yield and water use efficiency in the Corn Belt of Northeast China

Decreasing the corn (Zea mays L.) gap between the potential yield and farm yield and reducing the risk of grain yield of drought are very important for corn production in the Corn Belt of Northeast China (CBNC). To achieve a high and stable corn yield, the effects of supplementary irrigation on yield, water use efficiency (WUE) and irrigation water use efficiency (IWUE) were studied using a modelling approach. The Root Zone Water Quality Model 2 was parameterized and evaluated using two years of experimental data in aeolian sandy soil and black soil. The evaluated model was then used to investigate responses to various irrigation strategies (rainfed, full irrigation and 12 single irrigation scenarios) using long-term weather data from 1980 to 2012. Full irrigation guarantees a high and stable corn grain yield (12.92 Mg ha⁻¹ and has a coefficient of variation (CV) of 14.8% in aeolian sandy soil; 12.30 kg Ma⁻¹ and CV of 11.1% in black soil), but has a low water use efficiency (19.92 and 21.81 kg ha⁻¹ mm⁻¹) and a low irrigation water use efficiency (10.01 and 11.03 kg ha⁻¹ mm⁻¹). A single irrigation can increase corn yields by 3–35% for aeolian sandy soil and 5–35% for black soil over different irrigation dates compared with no irrigation. The most suitable single irrigation date was during late June to early July for aeolian sandy soil (yield = 10.73 Mg ha⁻¹ and WUE = 27.94 kg ha⁻¹ mm⁻¹) and early to mid-July for black soil (yield = 11.20 Mg ha⁻¹ and WUE = 27.70 kg ha⁻¹ mm⁻¹). The lowest yield risk of falling short of the yield goal of 8, 9, and 10 Mg ha⁻¹ were 9.1%, 18.2%, and 33.33% in aeolian sandy soil and 3.0%, 15.25, and 21.2% in black soil when an optimized single irrigation was applied in late June or early July, respectively. Therefore, an optimized single irrigation should be applied in late June to early July with the irrigation amount to refill soil water storage of root zone to field capacity in CBNC.     

Evaporation from soil in relation to residue rate,mixing depth,soil texture and evaporativity

The role of crop residues as a surface mulch on evaporation has been widely studied. But information on evaporation and its reduction by crop residues mixed in surface soil to different depths particularly in relation to soil texture and evaporativity (E_o) is lacking. We studied the effect of four rates of paddy straw, viz. 0, 2, 4 and 8 Mg ha⁻¹ used as mulch and mixed in top soil layer to two depths (2 and 5 cm) under two evaporativities (E_o's) viz. 2.0 ± 0.5 and 8.7 ± 1.5 mm day⁻¹ in silty clay loam and sandy loam soil columns of 0.95 m length and 0.1 m diameter. Cumulative evaporation was predicted from water transmission properties of the soil and E_o as influenced by these variables. The otherwise short-lived benefit of evaporation reduction with mulch per se, which peaked after a few days, plateaued when residue was mixed with soil at peak reduction, and as a result the benefit was prolonged. The maximum reduction achieved was more and sustained for a longer period in finer textured soil, and a higher rate of mulch mixed to a greater depth. Mixing of residue in the surface soil layer not only reduced evaporation but also resulted in higher water content in the near surface soil after drying.     

Changes in microrelief and their effects on infiltration and erosion during simulated rainfall

The erosivity of soils under a given rainfall energy appears to vary greatly among soil orders, probably reflecting differences in clay composition and organic matter content. This study was conducted to quantify microrelief, infiltration, and sediment yield changes during three consecutive simulated rain events on a Udic Haploboroll and a Typic Hapludalf from Minnesota, and a Mollic Kandiudalf, and Typic Palehumult from Uganda. Air dry aggregates (< 5 mm) were packed in 19 1 containers tilted to a 5% slope and were subjected to three consecutive high energy rain storms (63 mm h⁻¹) for a duration of 1 h. Runoff and sediment were continuously monitored during a storm. Infiltration was measured by continued weighing of the soil and containers. An automated non-contact laser relief meter was used to measure changes in soil roughness initially and after each storm. Soil surface roughness decreased during the rain events indicating that aggregate breakdown was the dominant process in seal formation. For example, random roughness decreased form 5.9 to 4.0 mm on Barnes loam and from 9.7 to 6.9 mm on Renova silt loam with cumulative rainfall of 0 and 126 mm. These infiltration rates indicated that the Barnes Loam (Haploboroll) and Kabanyolo clay (Kandiudalf) were unstable soils while Kachwekano clay (Palehumult) and Renova silt loam (Hapludalf) were quite stable. Final infiltration rates after 3 consecutive rainfalls on Kachwekano clay (15 mm h⁻¹) and Renova silt loam (13 mm h⁻¹) [the stable aggregate soils] were significantly higher than those of Barnes loam (4 mm h⁻¹) and Kabanyolo clay (3 mm h⁻¹). For the two stable soils a high infiltration rate on a rough surface was maintained until aggregate breakdown occurred and runoff began. Sediment yield from Barnes loam (29 kg m⁻²) and Kabanyolo clay (28 kg m⁻²) was significantly greater than soil loss from Kachwekano clay (0 kg m⁻²) and Renova silt loam (6 kg m⁻²). The microrelief method to quantify aggregate stability is an improvement over wet sieving and other related measurements because of its rapidity and because the statistical quantification can be linked to physical processes.     

Reed Canarygrass Forage Yield and Nutrient Uptake on a Year-round Wastewater Application Site

Reed canarygrass (Phalaris arundinacea L.) is often planted at wastewater treatment sites to provide ground cover and remove nutrients. Our overall objective was to determine the forage yield and nutrient uptake under year-round potato wastewater application in northern latitudes. Specifically, we determined the effect of N fertilization rate on forage dry matter yield and N and P uptake by reed canarygrass, and compared the forage yield, persistence and nutrient uptake of reed canarygrass relative to those of orchardgrass (Dactylis glomerata L.), smooth bromegrass (Bromis inermis Leyss), timothy (Phleum pratense L.) and quackgrass [Elytrigia repens (L.) Nevski]. With only wastewater application, reed canarygrass had a forage yield of 5.8 Mg ha⁻¹, with N and P uptake of 113 and 30 kg ha⁻¹, respectively. Forage dry matter yield, N uptake and P uptake increased to 14.5 Mg ha⁻¹, 383 kg ha⁻¹ and 64 kg ha⁻¹, respectively, with an N fertilization rate of 224 kg ha⁻¹. Forage yield and N uptake of reed canarygrass, orchardgrass, timothy and smooth bromegrass were similar and exceeded those of quackgrass. Reed canarygrass P uptake exceeded that of the other grasses. Reed canarygrass was less persistent than quackgrass or smooth bromegrass.