Effect of tillage intensity on weed infestation in organic farming

Conservation tillage is not yet widely accepted by organic farmers because inversion tillage is considered to be necessary for weed control. Three long-term experiments were established with combinations of reduced and conventional plough tillage and stubble tillage to determine weed infestation levels in organic farming, i.e. herbicide application being excluded. Experiment 1 (with very low stocking density of perennial weeds) showed that in presence of primary tillage by mouldboard ploughing the number of annual weeds was nearly unaffected by the mode of stubble tillage. In experiment 2, however, with Canada thistle (Cirsium arvense) being artificially established, thistle density was significantly affected by stubble tillage and by a perennial grass–clover forage crop. Experiment 3 combined two levels of stubble tillage (skimmer plough, no stubble tillage = control) with four implements of primary tillage in the order of decreasing operation depth (deep mouldboard plough, double-layer plough, shallow mouldboard plough or chisel plough). Primary tillage by chisel plough resulted in significantly highest annual weed density compared to all other treatments. The natural C. arvense infestation in experiment 3 showed highest shoot density in the “skimmer plough/chisel plough” treatment compared to the lowest infestation in the “skimmer plough/double-layer plough” treatment. The poor capacity of the chisel plough for weed control was also reflected by the soil seed bank (5500 m⁻² C. arvense seeds for chisel plough, <300 seeds for all other primary tillage). A reduced operation depth of the mouldboard plough (“shallow mouldboard plough”) seemed to have an insufficient effect in controlling C. arvense infestation as well. Stubble tillage by the skimmer plough in addition to nearly any primary tillage operation largely reduced both annual weeds and thistle shoots. Most effective in controlling C. arvense was also a biennial grass–clover mixture as part of the crop rotation.Double-layer ploughing is a compromise between soil inversion and soil loosening/cutting and can be regarded as a step towards conservation tillage. In terms of controlling annual weeds and C. arvense, the double-layer plough was not inferior to a deep mouldboard plough and seems to be suitable for weed control in organic farming. Tilling the stubble shallowly after harvest can support weed control in organic farming remarkably, particularly in reducing C. arvense. If no noxious, perennial weeds occur and primary tillage is done by soil inversion, an omission of stubble tillage can be taken into consideration.     

Natural and human selection for purple-grain tetraploid wheats in the Ethiopian highlands

Summary Purple-grain tetraploid wheats (Triticum turgidum L.) are widely cultivated in the Ethiopian highlands despite the claim that they have lower industrial quality properties and market prices than the white or red/brown seed-colour types. In an attempt to find a possible explanation for this, the three seed-colour groups were compared for grain yield, other 11 agronomic traits and protein content. Five traits displayed significant differences between seed colour groups where the purple-seed was superior; earlier maturity, shorter height, and higher fertility, tillering capacity and harvest index. Most of these are important adaptive traits to waterlogging stress on dark-clay soils (pellic vertisols) where the great bulk of the Ethiopian tetraploid wheats have been grown. Furthermore, among the three seed-colour groups, purple-seed wheat has the best malting quality for the preparation of arekie, a locally distilled spirituous liquor. It, therefore, appears that both natural and human selections have been reponsible for their continued cultivation. Hence, the notion that purple-seeded wheat is the “least preferred” should be interpreted carefully not to necessarily address the whole community in Ethiopia. As to their taxonomy, all tetraploid wheat taxa (T. turgidum L. sensu lato, 2n = 4x = 28) that are found in Ethiopia, with the possible exception of T. dicoccon Shrank (locally known as Adja), may possess the purple pericarp-colour, although in varying frequencies; very low inT. polonicum L., and high inT. carthlicum Nevski andT. durum Desf.     

Soil tillage and crop productivity on a Vertisol in Ethiopian highlands

Soil quality deterioration and consequent reduced productivity characterize the Vertisols in the highlands of Ethiopia. The problem is exacerbated by lack of appropriate land preparation alternatives for the major crops in the area. A field experiment was carried out for 6 years (1998–2003) at Caffee Doonsa in the central highlands of Ethiopia to evaluate alternative land preparation methods on the performance of wheat (Triticum durum Desf.), lentil (Lens culinaries Medik L) and tef (Eragrostis tef L) grown in rotation. Four methods of land preparation (broad bed and furrow, green manure, ridge and furrow and reduced tillage) were arranged in a randomized complete block design with three replications on permanent plots of 22 m by 6 m. Broad bed and furrow significantly increased the grain yield of lentils by 59% (from 1029 to 1632 kg ha⁻¹) as compared to the control. On the other hand, reduced tillage resulted in the highest grain yield of wheat (1862 kg ha⁻¹) and tef (1378 kg ha⁻¹) as compared to 1698 kg ha⁻¹ of wheat and 1274 kg ha⁻¹ of tef for the control although the increase was not statistically significant. A gross margin analysis showed that BBF is the most profitable option for lentil with 65% increase in total gross margin. On the other hand, RT resulted in 11 and 8% increase in gross margin of wheat and tef, respectively as compared to the control. Based on the agronomic and economic performances best combinations of crop and land preparation method were: lentil sown on broad bed and furrow, and wheat and tef sown after reduced tillage.     

Influence of slope and stone cover on tillage operations in the Ethiopian highlands

Human population pressure has forced smallholder farmers in some areas of the central plateau region of the Ethiopian highlands to cultivate plots located on slopes or hillsides having varying amounts of stone cover. The objectives of this pilot study were to determine if slope and(or) stone cover influenced tillage operations on smallholder farms in the Debre Birhan area of the Ethiopian highlands, and to examine the relationship between different soil/tillage-related factors and draft of the indigenous single-tined ard (maresha). This paper also briefly describes the traditional systems of cropping and soil management, and provides data on selected physical and chemical properties of soils found in the study area. A land classification (LC) system was developed to categorize plots according to the slope and stone cover. Surface stone cover of plots was calculated and a method of estimating subsurface stones was tested. Tillage measurements included plowing frequency or number (PN) per area per annum, soil moisture tension, plowing depth, furrow “wedge” of soil moved, area plowed, contour angle, and the speed of travel and pulling force exerted by oxen. Plots were located on slopes ranging from 0% to 23%. Degree of slope was a key factor in determining the acuteness of angle of the contour at which plowing is done prior to seed covering, but had no significant effect on maresha draft. Stone cover of plots ranged up to 27%, with individual stones moved by the ard weighing up to 2.5 kg. Plowing depth ranged from 10.1–15.3 cm for all PN across LC. Oxen travelled at speeds of 0.35–0.58 m s⁻¹. Mean values for draft of the maresha across LC ranged from 0.83–1.04 kN. Farmers plowed from 0.10–0.15 ha during a 5–6 h work period, irrespective of LC or PN. Soil moisture tension (range 16–33 kPa) was found not to have a significant effect on draft, due to tillage being carried out prior to the major and minor rains. Percent stone cover explained very little of the variation in implement draft (R²=0.10). Adding stone weight to the model increased R² slightly (0.22), but significance was low (P<0.16). Furrow wedge of soil displaced by the ard head accounted for most of the variation in draft of the maresha across all LC and PN (R²=0.75, P<0.008). The design and construction of the maresha allows it to be used equally well for tillage operations on plots having minimal or high stone cover which may be located on flat or gentle sloping land, or on steep hillsides.     

Quantifying soil displacement and tillage erosion rate by different tillage systems in dryland northwestern Iran

Redistribution of soil particles by the force applied by tillage is a major factor in soil degradation of agricultural land. Decreasing tillage intensity can reduce the amount of soil displaced and the distance moved and hence may reduce rates of erosion. To understand the relative importance of erosion, we tabulated machine, soil and landform properties likely to be involved. We compared soil displacement and tillage erosion rates under different systems, including mouldboard ploughing (conventional tillage), chisel ploughing (reduced tillage), stubble cultivator (minimum tillage) and no‐tillage under dryland agriculture in northwestern Iran. The area was undulating and so all tillage took place along contours. Metallic tracers were buried in the soil at known locations and depths and their recovery after tillage provided a measure of soil displacement and tillage erosion. Conventional tillage along a contour line caused significantly greater soil displacement (≃57 cm) in the direction of tillage than reduced and minimum tillage systems (~20 and ~15 cm, respectively). Conventional tillage also caused more lateral soil displacement (downwards in the main direction of slope, the tillage erosion rate) than reduced or minimum tillage systems (48 cm or 152 kg/m vs. 5 and 4 cm or 16 and 7 kg/m, respectively). Although a range of factors contribute to the tillage systems used by farmers, our results suggest that under dryland conditions, similar to those found in our study area, adoption of noninversion, reduced tillage along the contour, for example by chisel ploughing can substantially limit tillage erosion relative to conventional tillage.     

保护性耕作对太行山前平原土壤质量的影响

保护性耕作被认为是华北平原农业可持续发展的重要措施, 但目前缺乏这些措施对土壤质量影响的系统报道。本研究以长期定位试验为基础, 探讨了太行山前平原两熟制高产农田不同耕作措施对麦田土壤质量的影响。试验始于2001 年, 设置翻耕玉米秸秆不还田(非保护性耕作对照, CK)、翻耕玉米秸秆粉碎还田(CT)、旋耕玉米秸秆粉碎还田(RT)和免耕玉米秸秆直立还田(NT)4 个处理。2007 年冬小麦收获后分层测定土壤有机碳(soil organic carbon, SOC)含量、容重(ρ_b)、水稳性团聚体、水分特征曲线、饱和导水率(K_s)和微生物量碳氮。2008 年测定了剖面SOC 含量、ρ_b 和蚯蚓数量。结果表明, 连续多年保护性耕作后土壤剖面的SOC 储量无显著变化, 但保护性耕作(RT 和NT)下SOC 的层化比率(1.74~2.04)显著高于翻耕处理(CK 和CT, 1.37~1.45); 保护性耕作显著提高了表层微生物量碳、氮含量以及单位面积土壤中的蚯蚓数量。NT 处理导致耕层(0~20 cm)土壤ρ_b 增加, 但提高了土壤团聚体的稳定性。CK 和CT 处理显著增加了0~5 cm 土层裂隙(>500 μm)和传输孔隙(500~50 μm)的比例, 而NT 处理则增加储水孔隙(50~0.5 μm)的含量。另外, 保护性耕作提高了土壤的K_s、田间持水量和有效水含量。对土壤质量指标S 的分析结果表明, 实施保护性耕作后, 太行山前平原地区土壤质量总体上得到改善。     

The prospects of reduced tillage in tef (Eragrostis tef Zucca) in Gare Arera, West Shawa Zone of Oromiya, Ethiopia

Soils in Ethiopia are traditionally ploughed repeatedly with an oxen-drawn plough before sowing. The oxen ploughing system exposes the soil to erosion and is expensive for farmers without oxen. This study was undertaken to assess agronomic and economic impacts of alternative, reduced tillage methods. Field experiments were carried out on a Vertisol and a Nitisol for 2 years to study the effect of zero tillage, minimum tillage, conventional tillage, and broad bed furrows (BBF) on the yield of tef (Eragrostis tef Zucca). No significant differences in tef biomass and grain yields were observed between the treatments on both soils in the first year. In Nitisol in the second year, yield was lower in the zero tillage treatment as compared to the other treatments. No difference in yield was observed between single plough, conventional, and BBF. On Vertisol, the yields were higher in BBF as compared to the other treatments. The yields on Vertisol were 1368, 1520, 1560 and 1768 kg ha⁻¹ for the zero tillage, minimum tillage, conventional tillage and BBF treatments respectively. More than twice as much grass weed was observed on zero tillage treatment as compared to the BBF treatment on both soils. Zero tillage gave the lowest gross margin on both soils whereas BBF gave the highest gross margin. The gross margin on Nitisols for the zero tillage and BBF treatments were −108 and 1504 Birr/ha respectively and corresponding numbers for the Vertisol were 520 and 1924 Birr ha⁻¹. On Vertisol there were no significant difference in gross margin between minimum tillage and conventional tillage. Minimum tillage is an interesting option on Vertisols, particularly for female-headed households as it reduces the tillage cost. It may also improve overall productivity of the farming system because it allows partial replacement of oxen with cows and reduces soil erosion.     

Stone bunds for soil conservation in the northern Ethiopian highlands: Impacts on soil fertility and crop yield

In the Ethiopian highlands, large-scale stone bund building programs are implemented to curb severe soil erosion. Development of soil fertility gradients is often mentioned as the major drawback of stone bund implementation, as it would result in a dramatic lowering of crop yield. Therefore, the objectives of this study are to assess soil fertility gradients on progressive terraces and their influence on crop yield, in order to evaluate the long-term sustainability of stone bunds in the Ethiopian Highlands.

The study was performed near Hagere Selam, Tigray and comprises (i) measurement of P_av, N_tot and C_org along the slope on 20 representative plots and (ii) crop response measurement on 143 plots. Results indicate that levels of P_av, N_tot and C_org in the plough layer are highly variable between plots and mainly determined by small-scale soil and environmental features, plot history and management. After correcting for this “plot effect” a significant relationship (p < 0.01) was found between the position in the plot relative to the stone bund and levels of P_av and N_tot, which are higher near the lower stone bund, especially on limestone parent material. For C_org and on basalt-derived soils in general no significant relationship was found. Although soil fertility gradients are present, they are not problematic and can be compensated by adapted soil management. Only in areas where a Calcaric or Calcic horizon is present at shallow depth, care should be taken. Crop Yields increased by 7% compared to the situation without stone bunds, if a land occupation of 8% by the structures is accounted for. Yield increased from 632 to 683 kg ha⁻¹ for cereals, from 501 to 556 kg ha⁻¹ (11%) for Eragrostis tef and from 335 to 351 kg ha⁻¹ for Cicer arietinum.

No negative effects reducing stone-bund sustainability were found in this study. Soil erosion on the other hand, poses a major threat to agricultural productivity. Stone bund implementation therefore is of vital importance in fighting desertification and establishing sustainable agriculture in the Ethiopian highlands.     

The effect of tillage systems on some microbial characteristics

Soils were sampled from plots with four variants of tillage methods: (1) conventional tillage (CT); (2) no tillage (NT); (3) minimum tillage (MTS); and (4) no tillage + mulch (NTM). Our aim was to study the influence of tillage on selected soil microbial properties. Determination of urease, dehydrogenase, invertase, arylsulphatase, potential nitrogenase activity, CFU of Azotobacter spp., and carbon microbial biomass has been conducted for time period 2002–2007. Soil samples from 0–0.1 m, 0.1–0.3 m, and 0.3–0.5 m were collected in the spring and autumn. Enzymatic activities (dehydrogenase, urease, arylsulphatase, and invertase) were significantly affected by soil depth and the tillage system employed. The statistically significant higher activity of urease was measured using the minimum tillage system (MTS), compared to the conventional tillage (CT) at soil depths of 0–0.1 m. The highest dehydrogenase activity was measured during the protective tillage treatment (NTM – no tillage with mulch). As far as other enzymatic activities (invertase and arylsulphatase) are concerned, the highest values were recorded in the protective tillage treatments. The highest counts of Azotobacter spp., as well as the highest nitrogenase activity (both statistically significant) were found in the no tillage + mulch (NTM) variant, at depths of 0.1–0.3 m. Microbial biomass (C-biomass) was the highest with the minimum tillage (MTS). The results show a positive influence of protection soil tillage on the reviving of upper layer of topsoil, especially in the variants where soil was supplied with organic matter.     

Variation of leaf esterases in some Ethiopian tetraploid wheat landraces

Summary Esterase isozymes of tetraploid wheat landraces originating from four localities in the central highlands of Ethiopia were studied using the horizontal starch gel electrophoresis. The landraces studied consisted of 60 Triticum turgidum L., one T. dicoccon Schrank, one T. polonicum L. and an improved local cultivar. One introduced durum cultivar was also included for comparison.A total of 12 esterase zymograms were detected in the landraces. Among these, the types C, A and G were found to be the most prevalent. The esterase isozymes exhibited high variation in the landraces. The esterase zymograms of the introduced durum cultivar and T. dicoccon differed from those of the landraces while the patterns attained in T. polonicum and the improved local cultivar were identical to those of the other landraces.The total number of bands detected was 10, of which 2 were rare, being displayed by only 1 pattern each. The band content of zymograms was in the range of 3–6 and the average was 4. The unique bands were observed in zymograms with both high and low prevalences in the landraces. Two zymograms, including zymogram C which had the highest frequency, occurred in all the localities. The high yielding landraces displayed 4 of the zymograms, one of which belonged to two of the zymograms with widest distribution.     

Quantitave evaluation of Ethiopian landraces of lentil (Lens culinaris)

Summary One hundred and fifty-six landrace populations of lentil (Lens culinaris Medikus) collected from 10 provinces in Ethiopia were evaluated for a set of six quantitative traits at three sites contrasting in altitude. Consistent regional differences among landraces were found for time to flower and maturity, 100-seed weight, number of seeds/pod and plant height. The regional differences were clarified by a discriminant analysis based on 100-seed weight, time to flower and plant height. The lentil of the West Highlands was early and short, that of the North Highlands was large-seeded, whereas lentils from the Central Highlands were the least distinctive group. Selection for seed size was the result of local human preferences. Humans were probably also responsible for the lack of adaptive value of plant phenology in relation to altitude. Selection for seed yield at the low and middle elevation sites gave a positive response to selection at both sites. However, selection for yield at the highland site did not give a positive response elsewhere, indicating that adaptation to highland conditions differed from that at lower elevations.     

Conservation agriculture as a sustainable option for the central Mexican highlands

Tropical highlands of the world are densely populated and intensively cropped. Agricultural sustainability problems resulting from soil erosion and fertility decline have arisen all over this agro-ecological zone. Based on selected soil quality indicators, i.e. time-to-pond, aggregate distribution and stability (expressed as the mean weight diameter (MWD) for dry and wet sieving, respectively) and soil moisture, from a representative long-term sustainability trial initiated in 1991 in Central Mexico (2240 masl; 19.31°N, 98.50°W; Cumulic Phaeozem), some insights into the feasibility of conservation agriculture (CA) as part of a sustainable production system in the tropical highlands are given. Zero tillage plots with crop residue removal showed low aggregate distribution (average MWD = 1.34 mm) and stability (average MWD = 0.99 mm) resulting in top layer slaking, increased erosion and low time-to-pond values. Retaining the residue in the field with zero tillage avoided the above-mentioned negative evolution for both aggregate distribution as stability (average MWD = 2.77 and 1.51 mm, respectively) and even improved the physical conditions of the soil as compared to conventional practice. Throughout the growing season the lowest soil moisture content was found in zero tillage without residue (average over the entire growing season = 20.5% volumetric moisture content), the highest in zero tillage with residue retention (average = 29.7%) while conventional tillage had intermediate soil moisture values (average = 27.4%). Zero tillage without residue retention had most days of soil moisture values under permanent wilting point, while zero tillage with residue retention had the least. Taking into account these results, zero tillage with residue retention can clearly be a part of an integrated watershed management scheme towards sustainable agriculture in the tropical highlands. It is clear that to develop new management practices to improve water use, reduce erosion and enhance human labor/animal power focus must be on the use of conservation agriculture both for rainfed as well as irrigated production systems and be fine tuned for each system.     

Long-term tillage system effects under moist cool conditions in Switzerland

How do different soil tillage systems influence soil quality over the years? Under moist cool conditions is it possible in the long term to reduce dramatically soil tillage intensity without experiencing reductions in yield or other problems? In 1987, the Swiss Federal Research Station for Agricultural Economics and Engineering in Tänikon initiated a long-term soil tillage trial to clarify these questions. The trial compared mouldboard plough, chisel, paraplow, shallow tillage and no-tillage systems on a well-drained Orthic Luvisol with 160 g kg⁻¹ clay, 310 g kg⁻¹ silt, and under a climate that has a mean annual precipitation of 1180 mm. The tillage treatment effects were evaluated by measuring several biological, chemical, and physical soil quality indicators. Reduced soil tillage increased earthworm populations, reduced Pseudocercosporella herpotrichoides infection in wheat (Triticum aestivum) and increased plant colonisation by arbuscular mycorrhizal fungi. Yields for no-tillage and other ploughless cultivation techniques were on par with those obtained by ploughing. An exception was direct-drilled maize (Zea mays), where no-tillage decreased yield by more than 10% over the course of 14 years. In the first 7 years of the trial, the level of soil organic carbon in all the tillage regimes was approximately 40% lower than natural grassland (initial situation 1987=75 Mg SOC ha⁻¹). The no-tillage method did not differ from the others in respect of bulk density, but it showed an increased preconsolidation stress and hence better trafficability. Under Switzerland’s moist cool climatic conditions, it is possible to reduce soil tillage intensity without substantial reductions in yield, and at the same time improve soil quality.     

Variation in gluten strength and yellow pigment in Ethiopian tetraploid wheat germplasm

Ten released varieties and one hundred and eleven tetraploid (2n = 4x = 28, AABB) wheat accessions collected from different major wheat producing regions, consisting of totally 2904 entries were characterized for content of yellow pigment, gluten strength, thousand kernel weights, grain yield, percent of yellow berry, glumes color, awn color, seed color, beak shape and spike density. The objectives were to assess variation with respect to regions of origin, species and altitudinal classes and to study the interrelationships of the qualitative traits used for the study. The accessions and/or released varieties showed significant regional variation for all the traits used in the study, but clinal variation among altitudinal classes and species were significant (P ≤ 0.01) in 6 (60%) and 9 (90%) of the studied traits, respectively. The accessions revealed consistent variation (P ≤ 0.001) within both regions and altitudinal classes for all the traits used in the study. The sedimentation volume was positively correlated with content of yellow pigment, percent of yellow berry, thousand kernel weights, glumes color, awn color, beak shape, seed color and grain yield. The contents of yellow pigment was positively correlated with awn color, beak shape and grain yield, but negatively correlated with seed color and spike density. Generally wide variation was found in the germplasm. Particularly variation was high for the content of the yellow pigment as well as the gluten strength, which provides opportunities to be utilized for genetic improvement.     

Soil structures produced by tillage as affected by soil water content and the physical quality of soil

Tillage experiments were carried out in order to study the effect of water content on the aggregate size distribution produced by tillage, and to investigate the relationship between the soil structures produced by tillage and Dexter's index of soil physical quality, S. Tillage with a mouldboard plough was done on four different soils over a range of naturally occurring water contents. The aggregate size distribution and the specific surface area produced by tillage were obtained by sieving. We define the optimum water content for tillage, θ_OPT, as the water content at which the specific surface area of the aggregates produced is maximum. This is consistent with the water content at which the amount of small aggregates produced is greatest and the proportion of clods produced is smallest. For the four investigated soils, θ_OPT was found to be close to the water content at the inflection point of the water retention curve, and in the vicinity of 0.8θ_PL (where θ_PL is the lower plastic limit). At water contents either lower or higher than θ_OPT, the specific surface area produced was smaller. The specific surface area produced at θ_OPT was found to be strongly correlated with the index of soil physical quality, S. The specific surface area produced is larger the greater S, i.e. the better the soil physical quality. Consistently, the proportion of small aggregates produced at θ_OPT is larger and the proportion of clods produced at θ_OPT smaller, the greater S. No clods (>50 mm) are produced on soils with good physical quality.     

Soil water conservation and yield of winter sorghum (Sorghum bicolor L. Moench) as influenced by tillage, organic materials and nitrogen fertilizer in semi-arid tropical India

Soil water and nutrients play an important role in increasing sorghum (Sorghum bicolor L. Moench) yields in the Vertisols of semi-arid tropics during post-rainy season. The effects of tillage practices, organic materials and nitrogen fertilizer on soil properties, water conservation and yield of sorghum were evaluated during winter seasons of 1994–1995 and 1995–1996 on deep Vertisols at Bijapur in the semi-arid tropics of Karnataka State (Zone 3) of south India. Conservation and availability of water and nutrients during different stages of crop growth were increased by deeper tillage resulting in increased grain yield of winter sorghum. Medium and deep tillage increased the grain yield by 23% (1509 kg ha⁻¹) and 57% (1919 kg ha⁻¹) during 1994–1995 and 14% (1562 kg ha⁻¹) and 34% (1835 kg ha⁻¹) during 1995–1996, respectively, over shallow tillage. Water use efficiency increased from shallow (4.90 kg ha⁻¹ mm⁻¹) to deep tillage (7.30 kg ha⁻¹ mm⁻¹). Greater water use efficiency during 1994–1995 as compared to 1995–1996 was attributed to lower consumptive use of water during 1994–1995. Among organic materials, application of Leucaena loppings conserved larger amounts of water and increased winter sorghum yield and water use efficiency. Application of Leucaena loppings increased the winter sorghum grain yield by 9% (mean of 1994–1995 and 1995–1996) as compared to vermicompost. Significantly (P < 0.05) higher water use efficiency of 6.32 kg ha⁻¹ mm⁻¹ was observed in Leucaena loppings incorporated plots compared to 5.72 kg ha⁻¹ mm⁻¹ from vermicompost. Grain yield increased by 245 kg ha⁻¹ with application of 25 kg N ha⁻¹ in 1994–1995, and a further increase in N application to 50 kg ha⁻¹ increased the grain yield by about 349 kg ha⁻¹ in 1995–1996. Deep tillage with application of 25 kg N ha⁻¹ resulted in significantly higher sorghum yield (2047 kg ha⁻¹) than control during 1994–1995. Deep tillage with integrated nutrient management (organic and inorganic N sources) conserved higher amount of soil water and resulted in increased sorghum yields especially during drought years.     

Soil fertility differences across a land-use intensification gradient in the highlands of Chiapas,Mexico

In the highlands of Chiapas, southern Mexico, soil texture and soil chemical properties were measured in 70 agricultural fields covering a range of slope positions and managements. Fields represented four corn cropping systems: long fallow, short fallow, pasture–cultivation rotation, and annual continuous cultivation, in addition to fallow at rest (forest, shrubland, and pastures). Fields were located in four slope positions (upper, middle, and lower slopes, and doline floor) in a karst landscape developed on limestone with additions of acid volcanic ashes. Distribution of clays and sands were related to the toposequence and the percentage of clay fraction increased from upper slope to doline floor. Sand presented a reverse pattern. Some soil chemical properties also vary in a characteristic way along the toposequence. Exchangeable Ca²⁺ and Mg²⁺ effective cation exchange capacity (ECEC) and pH were higher in the doline floor than in the other slope positions. Soil organic matter and total N contents were 30.4 and 35.2% higher under long fallow than under annual continuous cultivation. Soil Olsen P was greater under cultivation than under fallow (irrespective of the cropping system), with the highest values under annual continuous cultivation (16.2±8.3 mg kg⁻¹) and the lowest in the forest (5.3±2.5 mg kg⁻¹). Exchangeable K⁺ was 74 and 51% higher in cultivated plots of the long and the short fallow than under forest and shrubland, respectively. Exchangeable Ca²⁺ and Mg²⁺ and ECEC did not vary significantly among the cropping systems. Inputs of basic cations through burning of tree and shrub vegetation increased the soil pH. These results indicate that land use intensification is leading to a decline in soil organic matter and total N, whereas Olsen P increased with intensification due to the continuous application of P fertilizers and sheep manure as soil conditioners in intensively cultivated fields.     

保护性耕作对小麦玉米间作系统生产效率和可持续性的影响

农田复合系统是集约化农作的有效途径之一,在增加生物多样性和提高产量方面具有重要作用。干旱区农业生产中,温室气体减排和作物耗水减量是发展高效可持续农业的重要参考指标,研发基于作物复合生产的模式是该区节水、减排和可持续农业发展面临的重大课题。本研究以河西绿洲灌区长期规模化种植的小麦/玉米复合生产系统为对象,于2010-2012年度在甘肃农业大学校地联合绿洲农业科研教学基地（武威站）,通过集成免耕立茬（NTS）、免耕秸秆覆盖（NTM）、少耕秸秆翻压（RTS）形成不同小麦/玉米间作复合系统,并以传统间作（CTI）为对照,重点研究了不同系统的土壤碳排放量和水分利用特征,比较分析了其生产效率和可持续性。结果表明,小麦和玉米复合系统的生物热能产较单作小麦提高113%,较单作玉米提高21%,该系统基于生物热能产的土地当量比均大于1。农田复合生产系统能有效降低土壤CO₂排放,特别是集成免耕秸秆覆盖的间作系统,土壤CO₂排放量比单作玉米降低12%,比传统间作降低13%,排放效率比单作玉米提高39%,比传统间作提高31%。此外,农田复合生产系统还显著降低了作物耗水,与传统间作相比,集成免耕秸秆覆盖的间作系统的棵间蒸发量、耗水总量和单位耗水碳排放量分别降低11%、5%和9%,但单位耗水生物热能产提高19%。农田复合生产系统较传统间作具有更高的土地当量比（1.78）、碳排当量比（1.48）和耗水当量比（1.22）,三者分别提高14%、28%和20%,因而其可持续评价指数提高了13%。小麦/玉米间作集成免耕秸秆覆盖的农田复合生产系统可作为河西绿洲灌区高效可持续农作的可行模式。     

Seasonal differences in tillage draught on a sandy loam soil with long‐term additions of animal manure and mineral fertilizers

Energy requirements for soil tillage are closely linked to soil properties, such as clay, water and soil organic carbon (SOC) contents. Long‐term application of inorganic fertilizer and organic amendments affects SOC content but little is known about seasonal differences in tillage draught requirements of soils subject to contrasting nutrient management regimes. We assessed autumn and spring tillage draught following harvest of early‐sown and timely sown winter wheat grown on a sandy loam in the Askov Long‐Term Experiment on Animal Manure and Mineral Fertilizers. Draught force was related to soil texture, soil water and SOC content, shear strength and bulk density, nutrient management, and yield of the preceding winter wheat. Contents of clay and SOC ranged from 8.9 to 10.6% and from 0.98 to 1.36%, respectively. In the autumn and spring, SOC normalized by clay content explained 38 and 5% of the variation in specific draught, respectively. Specific draught did not differ significantly among individual fertilization treatments. SOC was closely correlated with clay and water contents and bulk density, and with yield of the preceding wheat. Draught force was significantly smaller in the spring than in the autumn. In the autumn when soils were drier (?700 hPa), tillage draught was correlated with several soil characteristics, whereas water content was the dominating parameter in the spring when soils were wetter (?100 hPa). The range of SOC contents observed in this study aligns with that observed in Danish sandy loams under intensive cultivation, and within this range, SOC per se had little effect on draught requirements.     

Phenotypic diversity of Ethiopian grass pea (Lathyrus sativus L.) in relation to geographical regions and altitudinal range

Fifty grass pea (Lathyrus sativus L.) populations collected from different administrative regions and altitude classes in Ethiopia, were evaluated for variations of five morphological traits. Shannon-Weaver diversity index was calculated for traits, populations and altitude classes. Monomorphism was recorded in flower color (blue) for most of the populations. Olive seed colour was dominantly distributed in all regions with mean frequency of 50% while black seed colour is rare with mean frequency of 4% in Ethiopia. Much variability was observed within populations. High diversity values for pattern of testa colour and leaflet size were recorded in populations of highland origin (>2550 m.a.s.l.). Shannon's diversity index is highest in Gondar (H = 0.65) followed by Tigray region (H = 0.64) even though there was no significant variation in H values between regions. These regions with high diversity are recommended for immediate in situ and ex situ conservation.