Natural Fallow Research Articles

Effects of Fallowing and Nitrogen Application on Striga Infestation, Soil Fertility and Maize Performance

Striga possesses an ominous obstacle to the African continent that is struggling with food security as it affects the livelihood of more than 300 million people. The control of Striga has proved exceptionally difficult. Two fallows, namely natural fallow (NF) and A. histrix fallow (AF) were maintained in 2012, such that the field was divided into two parts and each part was further divided into three replicates. Each part was separated from one another by a strip of 2 m width and the fallow factor was randomly assigned to each part which constituted the main plot. In 2013, the inorganic N fertilizer levels (0, 60, 90 and 120 kg ha-1) were applied to the fallow plots and assigned to the sub-plot. These treatments were laid out in a split plot arrangement fitted to a randomized complete block design with three replicates. The two fallows significantly (P < 0.05) reduced Striga infestation similar to application of N at 60 – 120 kg N ha-1. The two fallows significantly (P< 0.05) increased SOC. Only natural fallow significantly (P<0.05) increased the STN by 36 %. Maize grain yield after natural fallow (1527 kg ha-1) was not significantly (P>0.05) different from that after A. histrix (1943 kg ha-1). Inorganic N application had highly significant (P<0.05) effect on grain yield. Lowest grain yield of 1253 kg ha-1 was obtained without inorganic N application, which was significantly different from those fertilized with inorganic N. Inorganic N fertilizer rate of 60 kg ha-1 seems to be optimum for maize. The Nitrogen Fertilizer Replacement Value of A. histrix was low, 13 kg N ha-1. The effect of both fallows on grain yield was due mainly to increased SOC content.

Maize and Weed Response to Legume Cover Short Fallow and Fertilizer in Port Harcourt South Eastern Nigeria

Field experiment was conducted in Faculty of Agriculture Teaching and Research Farm University of Port Harcourt, Port Harcourt, Rivers State, South Eastern Region of Nigeria between March and September 2017; to evaluate the effect of planted short fallow legume cover crop on maize performance and weed growth. The experimental design was a 5 x 2 factorial in randomized complete block design (RCBD) in a plot size of 4 m x 4 m with four replicates. The treatments consisted of four different legumes cover species fallow and a natural fallow as follows: Mucuna [Velvet bean (Mucuna pruriens (L.) DC var. utilis), Lablab (Lablab purpureus (L.) Sweet), Pigeon pea (Cajanus cajan (L.) Mill spp)], Centrosema (Centrosema pascuorum (L.) and a natural fallow (No Legume Cover) and two levels of inorganic fertilizer as NPK 15: 15: 15 (0 and 15 Kg ha-1 NPK). All legume cover growth characteristics were negatively correlated with weed cover and weed dry weight (r = -0.58 and r = -0.59 at P=0.0001). Legume dry weight had a positive correlation with all maize parameter (r =0.64 at P=0.0001) except for stem diameter (r = -0.43 at P=0.0051). Similarly, all weed attributes were negatively correlated to maize parameters. Maize height was better in plots that received short fallow legumes than natural fallow. There was increase in soil Nitrogen level after 10 weeks of fallow. Legume cover crop short fallow has the potentials for weed suppression, soil fertility and productivity improvement in maize culture.

Effect of Maize –Legume Intercrop and Fertilizer on Weed Suppression and Maize Performance in South Eastern, Nigeria

Maize is one of the most commonly cultivated arable crops in the rain forest zone of South Eastern Nigeria. Globally soil fertility and weed pressure are the most important constraints limiting increase productivity of Maize especially in Sub Saharan Africa (SSA). Unavailability and cost of inorganic fertilizer as well as cost of labour for weeding have engendered low productivity of maize. Hence this trial was conducted to evaluate the efficacy of maize-legume systems on weed suppression and maize performance. The trial was carried out at the Teaching and Research Farm of Faculty of Agriculture, University of Port Harcourt, Nigeria located within latitude 04°54’N and longitude 6°55’ E). The trial was conducted between April 4th and July 5th, 2017. The experiment was a 3 x 3 factorial arrangement fitted into a randomized complete block design (RCBD) consisting of 3 types of legume systems (Mucuna pruriens, Lablab purpurens and No legume) and three levels of NPK 15:15:15 fertilizer (0, 15, and 30 kg NPK/ha). The 9 treatment combinations were replicated thrice to give 27 plots. Data collected were on maize yield and yield components, weed and legume parameters at 4, 8 and 16 weeks after sowing (WAS). Result showed that legume significantly reduced weed biomass when compared to the natural fallow. The effect of weed biomass reduction was Mucuna 34.8% >Lablab 29.2%. The legume system significantly suppressed weed compared to natural fallow and the weed suppression ability average 56% and 30% respectively for Mucuna and Lablab whether or not they received NPK. Result of this trial also revealed that within 8 weeks after sowing legumes (8 WASL) 26% N and 22% N can be harvested by integrating this legume cover in cropping system and that NPK application has little or no effect in the performance of these legumes. Mucuna was not sensitive to fertilizer application while Lablab responded to fertilizer application. Maize was sensitive to Mucuna due to early integration; hence, it is recommended that these legumes be integrated at six weeks after sowing maize.

Aeschynomene histrix (Joint Vetch) fallow and nitrogen fertilizer effects on Striga hermonthica infestation and maize (Zea mays) productivity in southern Guinea Savanna of Nigeria

Integration of herbaceous legume Aeschynomene histrixinto the farmers’ cropping system is one viable option that can improve the nutrition of maize ( Zea mays ), increase soil physical, chemical and biological properties which can result in sustainable Striga control and crop productivity. This study was conducted to determine the effects of A. histrix fallow and N fertilizer application on Strigainfestation, growth and yield of maize. The study involved the factorial combination of fallow type: natural fallow (NF) and A. histrix fallow (AF), and inorganic N fertilizer application: 0, 30, 60 and 90 kg N ha -1 arranged in a split plot in a randomised complete block design and replicated three times. Results show that cropping/maize after A. histrix fallow significantly (P < 0.05) delayed Strigaemergence, reduced its virulence on the host crop, increased maize plant height, and grain yield compared to natural fallow. Application of 90 kg N ha -1 delayed days to Striga shoot emergence, reduced Striga damage on host crop, and increased plant height of maize. Heavier and higher grain yield of maize were significantly associated with of 60 kg N ha -1 . Integrating A. histrix fallow rotations with application of 60 kg N ha -1 can provide sustainable Strigacontrol, and A. histrix in combination with 90 kg N ha -1 modest yield of maize. This study has shown that farmers in the southern Guinea savanna location of Nigeria can effectively control Striga and obtain better maize yield by integrating A. histrix fallow with the application of N fertilizer. Keywords: Striga , Aeschynomene histrix , fallow rotation, nitrogen, maize

Effects of short-term fallow managements on soil microbial properties: A case study in China

Allowing farmland to fallow can effectively improve the self-rehabilitation of arable soil and solve agroecological problems such as biodiversity loss, soil fertility loss and over-cultivation. However, long-term fallows cannot satisfy the provisionment requirements of China; therefore, the use of short-term fallows to restore cultivated soil has become a better option. Nevertheless, few studies have compared short-term fallow managements and the influence of fallows on the soil microbial community, especially vegetation plus fertilizer management. Therefore, we periodically analyzed the soil properties, microbial biomass nitrogen and bacterial community structure of farmland soil under different treatments during one year on Yellow River Delta of China. The experiment included the following five treatments: (1) control with traditional farming and chemical fertilization (CK), (2) natural fallow without any fertilizer input (NN), (3) pasture fallow without any fertilizer (NP), (4) natural fallow with cattle manure (MN), and (5) pasture fallow with cattle manure (MP).The results made it apparent that the differences of soil physicochemical characteristics became more significant in the autumn than in the spring. In contrast to the CK treatment, the MN exerted an obvious improvement on the microbial biomass nitrogen (P < 0.05). According to the alteration in observed OTUs, the Shannon-Wiener Index and the Phylogenetic Diversity, the CK presented a significant decrease in the summer (P < 0.05). At the beginning, the microbial community showed noteworthy differences between the CK and fallow managements (P < 0.05), except for the MP. The gaps diminished in the autumn, whereas the differences between finer taxonomic groups became clearer. Compared to CK, Nitrospira and Steroidobacter were observably lower in NN and NP, whereas Chthonomonas was significantly higher (P < 0.05). Lysobacter and Sphingobacterium were notably higher in MN than CK while Geobacter and Sphingobacterium were remarkably higher in MP than CK (P < 0.05).In summary, no fertilizer input could be favorable for carbon and nitrogen retention, and the NP improved some functional microorganisms, but it may lead to soil compaction. Cattle fertilizer could promote organic matter degradation, and MN enhanced the soil microbial biomass nitrogen and soil-borne disease resistance on crops, whereas MP could reduce the nitrogen and clay content loss and improve heavy metal bioremediation. During short fallowing periods, pasture plus farmyard fertilizer could markedly promote soil micro ecosystemic function. If there was no fertilizer input, natural fallow could be a considerable choice.

Phosphorus Fertilization Increases Biomass and Nutrient Accumulation Under Improved Fallow Management in a Slash-and-Mulch System in Eastern Amazonia, Brazil

ABSTRACT Improvement of fallow vegetation can have a positive impact on the productivity of slash-and-mulch systems in eastern Amazonia. Phosphorus fertilization can increase biomass and nutrient stocks in the fallow phase, thereby improving nutrient cycling and crop productivity. Here, we compared biomass and nutrient stocks under three fallow management strategies: (1) natural fallow (regrowth vegetation) – NF; (2) NF vegetation improved with leguminous trees (Sclerolobium paniculatum Vogel and Inga edulis Mart.) – IF; and (3) NF vegetation improved with leguminous [...]

Screening Cover Crops for Soil Macrofauna Abundance and Diversity in Conservation Agriculture

Soil health is important for sustainable crop production. Frequent soil cultivation has a negative impact on soil health, resulting in loss of soil macrofauna. Conservation agriculture can be practiced to improve soil health by improving the abundance of soil macrofauna. Three leguminous cover crops were tested for soil macrofauna abundance Vigna unguiculata, (cowpea) Lablab purpureus L. (dolichos lablab) and Mucuna pruriens (L.) DC (velvet bean). The experiment was done in two contrasting experimental sites of KwaZulu-Natal (Ukulinga and Bergville) in a randomised complete block design replicated three times. Bare plot and herbicide treatments served as controls. Natural fallow was used to make a comparison to all the other treatments. Cowpea (39 species) had the highest soil macrofauna abundance in Bergville. Lablab (57 species) had the highest soil macrofauna in Ukulinga. Cowpea (0.75 species) and lablab (0.61 species) improved soil macrofauna diversity respectively in Bergville. Natural fallow (0.46 species) had the lowest soil macrofauna diversity in Bergville. Lablab (0.56 species) and velvet bean (0.74 species) had high soil macrofauna species diversity in Ukulinga. Bare plot (0.3 species) had the lowest soil macrofauna species diversity respectively. It can be concluded that cowpea and lablab can be recommended for improving soil macrofauna abundance in conservation agriculture.

Changes in soil microbial communities after 10 years of winter wheat cultivation versus fallow in an organic-poor soil in the Loess Plateau of China.

Agricultural management methods, such as cultivation or fallowing, have led to significant changes in soil fertility and hence, crop yield. Such changes may have stemmed from changes in soil microbial communities and associated biogeochemical processes. This phenomenon is particularly true in organic-poor soil in the Loess Plateau of China. In this study, we examined three existing soil management regimes as part of a 10-year field experiment and evaluated their effects on fungal and bacterial community structures by performing high-throughput 454 pyrosequencing. These management regimes were (i) fertilized winter wheat (Triticum aestivum L.) (FW), (ii) continuous natural fallow with weeds but without crop grown (NF), and (iii) continuous bare fallow without weeds or crop grown (BF). After 10 years, soil organic carbon (SOC), microbial biomass carbon (MBC), and available potassium (K) concentrations were highest in NF. Soil N behaved differently, with BF obtaining the highest nitrate nitrogen (N). Meanwhile, slight differences in total N (TN) were observed among FW, NF, and BF. Available phosphorus (P) was highest and available K was lowest in FW. Microbial communities were dominated by Ascomycota (59.1% of fungal sequences), and Acidobacteria, Actinobacteria, Bacteroidetes, Firmicutes, and Proteobacteria (75.7% of bacterial sequences) in FW, NF and BF at the phylum level. Soil management regimes did not affect the fungal and bacterial richness and diversity but significantly modified their community compositions. Compared with FW, the abundances of Ascomycota (fungi phylum) and Alternaria, Gibberella, and Emericella (fungi genus) were increased by NF, whereas the values of Chaetomium, Humicola, and Cryptococcus (fungi genus) were decreased by BF. The abundances of Verrucomicrobia (bacteria phylum), and Steroidobacter (bacteria genus) were increased by NF, and Bacteroides (bacteria genus) was increased by BF. Canonical correspondence analysis showed that SOC, available P, and TN might be the key factors in community formation. Therefore, the decadal absence of plants (BF) affected soil fertility by increased available K and nitrate N, whileas natural fallow (NF) affected soil fertility by increased SOC, available K, and MBC, and they all changed fungal and bacterial community compositions.

Spatial-temporal soil moisture dynamics under different cocoa production systems

Soil moisture has high spatial and temporal variability, depending on topography, soil texture, vegetation and meteorological conditions. It influences many processes in the soil and supplies water to the vegetation. This is often a limiting factor in agricultural production.Over an 18-month period, we measured soil moisture dynamics down to a depth of 70cm in a long-term trial in Bolivia comprising six different land-use systems, i.e. cocoa monocultures and agroforestry systems, both under organic and conventional management, successional cocoa agroforestry systems and a natural fallow. Soil was heterogeneous over the area and in depth. We identified and separated two soil groups which differed in both, texture and soil water retention capacity. Considering the two groups, we assessed the effect of the different land-use systems on soil moisture dynamics and plant available water on the one hand, and how different soil moisture conditions affect growth and production of cocoa on the other.In monocultures with shallow rooting cocoa only, soil moisture decreased mainly in the uppermost soil layer during the dry season and the lower layers kept more moisture year round. In agroforestry systems soil moisture decreased homogeneously over the soil profile, implying a complementarity in water use of cocoa and deeper rooting trees. The uppermost soil layer in the agroforestry systems had higher soil moisture than in the monoculture, demonstrating the role of shade trees to reduce water loss from top soil by evaporation and transpiration of the cocoa. Even though one soil group had continuously higher water availability than the other group, we did not find an effect on the cocoa yield.Cocoa relies on sufficient water supply, but beside information on the precipitation it is important to know the soil structure and soil water retention capacity when discussing water availability for cocoa production and to consider the heterogeneity of the soil even over small area.

Fallow associated with autumn-plough favors structure stability and storage of soil organic carbon compared to continuous maize cropping in Mollisols

Aggregate formation and stability of soil organic carbon (SOC) differ in different farming systems, probably due to differences in effects of tillage and residue management. This study used a 24-year field experiment to compare the effects of continuous maize cropping and natural fallow on aggregate formation and SOC storage in various aggregate-size classes and density fractions of a Chinese Mollisol. Soils collected from the upper 0.2-m layer were wet-sieved into four aggregate-size classes (>2, 0.25–2, 0.053–0.25 and 0.25 mm) and increased that of micro-aggregates (<0.25 mm) compared to the initial value while the opposite was observed in the natural fallow system. The fallow system generally had greater SOC concentration in the occluded fraction, higher proportion of newly-derived C as % total SOC in the light fraction and greater contribution of total residue C to new C in macro-aggregates and light fractions compared to the continuous maize system. Furthermore, the fallow system resulted in shorter turnover time of SOC than the continuous maize system. Natural fallow associated with autumn-plough improved soil structural stability and SOC storage while continuous maize cropping with residue removal decreased SOC sequestration and soil aggregate stability.

Utilization potentials of lablab (&lt;i&gt;Lablab purpureus&lt;/i&gt; (L.) Sweet) and the constraints of field pests and diseases in Nigeria

In the last one decade and half, lablab was evaluated for its crop-livestock production potentials in Samaru, Kano and Benin City in both the savanna and humid forest zones of Nigeria. Very early, early and intermediate accessions were identified that may be suitable for dry savanna and late growing season of the humid forest while late, very late and extremely late accessions were identified for moist savanna and humid forest. Vegetable-type, grain-type and dual-purpose lablab were identified. Lablab grain ranged from 600-2400 kg ha -1 with an average protein concentration of 25.3%. Huge litter of leaves and stems was recorded at the end of production period which extended far into the dry season. Short fallow of one year supported maize-cowpea intercrop with component maize having 13.7% grain yields over that of natural fallow. Following a 2-year lablab fallow, subsequent maize yield was 72.7% higher than that from natural fallow. Lablab had an average of 2600 kg ha -1 of biomass and an average of 64.1 kg N ha -1 , meaning that lablab has high potential for green manure and soil improvement. Of six herbaceous legumes, lablab was among those that had the highest soil cover. Fresh biomass of 3200 kg ha -1 was achieved at eight weeks after planting. Various insect pests, fungal diseases and parasitic plant including Ootheca mutabilis (Sahlb), Podagrica uniforma (Jac.), Nematocerus acerbus (Faust), Anoplocnemis curvipes (F.), Helicoverpa armigera (Hbn), aphids, Colletotrichum sp., Curvularia sp. and Cassytha filiformis (Linn.) were found on lablab plants, causing damage to the crop. Key words: lablab, fodder, grain yield, pest, disease

Increase in soil organic carbon in a Mollisol following simulated initial development from parent material

Better understanding of the effects of land use and agricultural management on organic carbon (C) sequestration is needed to optimize the restoration of fertility in degraded soil, maintain agricultural sustainability and mitigate emissions of greenhouse gases with C sequestration. Most current studies of C sequestration focus on mature soil, whereas there has been little research on soil development from C‐poor parent material. The aim of this study was to assess soil organic carbon (SOC) stocks and C sequestration rates during the early stages of development of a Mollisol from parent material under different types of vegetation, fertilizer application regimes and organic matter inputs, and to compare the results with C sequestration of a mature Mollisol under similar management. Carbon stocks were recorded from 2004 to 2012 in the parent material of a Mollisol under natural fallow (NatF), alfalfa (Medicago sativa L.) (Alfa) or soya beans (Glycine max (Merrill.) L.) and maize (Zea mays L.) (S–M) rotations with and without fertilizer application and crop residues returned or removed at harvest. There was a positive non‐linear relation between C inputs and SOC stocks; increases in SOC stocks decreased with larger additions of C. After 8 years of treatments, the SOC stocks at 0–20‐cm depth had increased in the order S–M + fertilizer + all residues returned (61%) &gt; Alfa (60%) &gt; S–M + fertilizer + part of residues returned (50%) &gt; NatF (30%) &gt; S–M + fertilizer without residue return (17%) &gt; S–M without fertilizer or residue return (7%). These increases in SOC stocks corresponded to annual C sequestration rates of 0.02–0.83 Mg C ha−1 year−1. In contrast, SOC stocks in the 0–20‐cm layer of the mature Mollisol changed little under similar treatments in a wheat (Triticum aestivum L.)–maize–soya bean rotation. Our results have practical implications for how vegetation and agricultural practices could be used to optimize soil restoration and C sequestration in a temperate continental monsoon climate.Highlights What management practices and vegetation lead to carbon sequestration during soil development? Use of a subsoil (parent material) to study soil development. Carbon stocks increased as much in alfalfa as in soya bean–maize rotations with residue return. Perennial legume systems sequester carbon comparable to annual systems with larger carbon inputs.

Evaluation De La Performance Des Pratiques De Gestion De La Fertilite Des Sols Dans Le Bassin De La Riviere Okpara Au Benin

A good management of agricultural land based on scientific knowledge and farmer indigenuous knowledge is necessary to ensure sustainable agricultural production. Our research aims to evaluate the performance of farmers' strategies and improved soil fertility management practices in improving level of crop yields in the basin of the Okpara River in Benin. Surveys using semi-structured questionnaire were conducted from October 11 to November 30, 2015 on a sample of 1048 farmers belonging to socio-cultural groups Tchabè, Mahi, Ditamari, Lokpa, Bariba and Fulani. Informations collected concerned farmers' soil fertility management practices and soil fertility improvement strategies introduced by the extension services. Crop rotation, long term natural fallow, fallow with perennial crops especially cashew trees, cassava "fallow" and cereal and leguminuous intercropping (respectively 91.11; 41.66; 48.53; 54.61 and 86.25% of respondents) are endogenous soil fertility management practices. However, mineral and organic fertilizers (respectively 25.45 and 20.38% of respondents) are improved soil fertility management practices introduced. Generally 42% of respondent mentioned that indigenuous soil fertility management practices could improve only by 25% crop (especially maize) yield level against 98.5% of respondents who mentioned that improved soil fertility management practices could improve by 50% of the crop yield level. Considering the efficiency of these soil fertility management practices our study suggests some issues to be taken into account for better land management in the study area.

Soil nematode community structure and metabolic footprint in the early pedogenesis of a Mollisol

Soil nematodes play an important role in soil food webs and are known to be sensitive to agricultural practices such as land use and green manure or crop residue inputs. However, such effects are largely unknown in young soil in the initial stage of soil formation. We measured nematode populations in an ongoing field experiment that was originally established to investigate the effect of agricultural practices on the early development of a Mollisol from parent material. Six field management practices were included: natural fallow (NatF), alfalfa (Alfa), and annual cropped fields without fertilization or crop residue input (F0C0), with fertilization but no crop residue input (F1C0), with fertilization and crop residue input (F1C1), and a parent material soil (PM). No nematodes were found in PM, but 37 nematode genera were identified after 8 years of soil development from PM. Management practices influenced the abundance of soil nematodes. The abundance of plant parasites was higher in Alfa than in NatF, and lowest in F0C0 and F1C1. Bacterivores were most abundant in Alfa and F1C1. In the graph of structure index vs. enrichment index, Alfa and F1C1 were located in disturbed quadrant; F1C0 was located in degraded quadrant, and NatF and F0C0 were located in maturing quadrant. The metabolic footprint of the plant parasites was larger in NatF and Alfa than in F0C0. The metabolic footprint of the bacterivores was larger in Alfa and F1C1 than in F0C0. The bacterivores and predators-omnivores were positively related to SOC in C flows. The management practices were clearly separated from each other on partial RDA bioplot; soil nematode genera were strongly related to soil properties, suggesting the soil nematode community was driven by management practices mediated via soil properties in the early stage of the Mollisol development. Our study indicates the ecosystem function of the similar eroded soils can be recovered by agricultural management practices.

Nitrogen oxides and CO2 from an Oxisol cultivated with corn in succession to cover crops

Abstract The objective of this work was to evaluate the effect of two legumes (Crotalaria juncea and Mucuna pruriens), as cover crops, and of natural fallow, as a control treatment, on the emissions of NOx, N2O, and CO2 from an Oxisol cultivated with corn, under conventional and no-tillage systems, in the Cerrado region, in Central Brazil. Variations of CO2 fluxes in the soil were explained mainly by soil humidity and, in the legumes, under conventional system, by soil NH4+-N concentration. Plots with legumes under no-tillage system had higher annual emissions of CO2, NOx, and N2O than natural fallow. Results show that the use of legumes as cover crops favors the emissions of NOx-N + N2O-N and CO2-C. However, when considering the potential for mitigation of CO2 and nitrogen oxide emissions from the soil, it is important to evaluate changes in soil carbon and nitrogen stocks.

Effects of fallow or planting wheat (Triticum aestivum L.) and fertilizing P or fertilizing P and N practices on soil carbon and nitrogen in a low-organic-matter soil

ABSTRACTSoil carbon (C) and nitrogen (N) are important for maintaining soil fertility, and they are considerably affected by soil use and management. In the present study, we conducted an 8-year field experiment on loessial dryland soil (Eum-Orthic Anthrosol, Food and Agriculture Organization of the United Nations (FAO)) in the southern Loess Plateau, China. We tested four soil management regimes—i.e., winter wheat (Triticum aestivum L.) cultivation with phosphorus (P) fertilization (WP), winter wheat cultivation with N and P fertilization (WNP), natural fallow (NF) and bare fallow (BF)—to evaluate their effects on soil C and N fractions. After 8 years, compared with the WNP treatment, the total soil organic nitrogen (SON) in the WP treatment decreased by 14.6% and 36.8%, and microbial biomass nitrogen (MBN) by 35.6% and 61.1%, at 0–20 and 20–40 cm soil depths, respectively. The soil heavy fraction nitrogen (HFN) and light fraction nitrogen (LFN) in the WP treatment also decreased by 36.6% and 39.4%, respectively. Furthermore, BF treatment decreased total soil organic carbon (SOC), heavy fraction carbon (HFC), LFN and MBN at both soil depths with average reductions of 43.4%. The NF treatment decreased light fraction carbon (LFC) by 17.0% at 0–20 cm soil depth, as well as MBN by 24.8% and 71.2%, and inorganic C by 29.1% and 23.8%, at 0–20 and 20–40 cm soil depths, respectively. There was no significant difference of microbial biomass C concentration among the WP, NF and BF treatments. These results confirmed that a lack of N fertilization decreased SON, BF reduced both SOC and SON, and NF decreased soil inorganic C. Therefore, the managements of a recommended rate of N fertilizer application and shortened time of bare fallow are critical for maintaining or increasing SON fraction sequestration, and natural fallow management is not a useful method for maintaining soil fertility in dryland in the Loess Plateau in China.Abbreviations: HFC: heavy fraction carbon; HFN: heavy fraction nitrogen; LFC: light fraction carbon; LFN: light fraction nitrogen; MBC: microbial biomass carbon; MBN: microbial biomass nitrogen; SOC: soil organic carbon; SON: soil organic nitrogen

Sediment source analysis using the fingerprinting method in a small catchment of the Loess Plateau, China

This paper aims to use the composite fingerprinting method to reconstruct the environmental history after the Grain-for-Green Project and to provide effective sediment management and soil erosion-control strategies. This study used a composite fingerprinting method based on 45 geochemical properties and a mixing model to investigate sediment core changes in the sediment source in an agricultural catchment with little native vegetation. The samples consisted of 77 source samples (i.e., gully, grassland, forest, cropland, and fallow land) and five sediment cores. Genetic algorithm (GA) optimization has been recently used to find the best optimum source contribution to sediments. The results demonstrate that gully is the main sediment source in this catchment, constituting 34.7 %, followed by cropland (28.2 %), forest (21.5 %), grassland (12.7 %), and fallow land (2.9 %). However, the relative contribution of each source type was variable in all five sediment cores. The sediment that derived from grassland was relatively stable in the five cores. The relative contribution of forest was higher in the downstream portion of the check dam and lower in the upstream portion and gradually increased in the direction of the runoff pathway. As the forest matured, the sediment that derived from the forest gradually decreased. Changes in the hydro-ecological environment would lead to the leaf litter and understory being poorly developed and the soil being bare in the forest, making it more vulnerable to erosion. Reforestation and fallow are the key ecological strategies for reducing soil erosion. However, at the beginning of the Grain-for-Green Project, the young forest contributed 21.5 % of the sediment, indicating that natural fallow may be a better-designed sediment management and soil erosion-control strategy.

Response of soil water dynamics to precipitation years under different vegetation types on the northern Loess Plateau, China

Implementation of the Grain-for-Green project has led to rapid land cover changes and resulted in a significantly increased vegetation cover on the Loess Plateau of China during the past few decades. The main objective of this study was to examine the responses of soil water dynamics under four typical vegetation types against precipitation years. Soil water contents (SWCs) were measured in 0–4.0 m profiles on a hillslope under the four vegetation types of shrub, pasture, natural fallow and crop in a re-vegetated catchment area from April to October in normal (2010), dry (2011), wet (2014) and extremely wet (2013) years. The results indicated that precipitation and vegetation types jointly controlled the soil water temporal dynamics and profile characteristics in the study region. SWCs in 0–4.0 m profiles of the four vegetation types were ranked from high to low as crop>fallow>pasture>shrub and this pattern displayed a temporal stability over the four years. In the extremely wet year, SWC changes occurred in the 0–2.0 m layer under shrub and pasture while the changes further extended to the depth of 4.0-m deep layers under fallow and crop. In the other three years, SWCs changes mainly occurred in the 0–1.0 m layer and kept relatively stable in the layers deeper than 1.0 m for all the four vegetation types. The interannual variation in soil depth of SWCs was about 0–2.0 m for shrub and pasture, about 0–3.4 m for fallow and about 0–4.0 m for crop, respectively. The dried soil layers formed at the depths of 1.0, 0.6, 1.6 and 0.7 m under shrub, and 1.0, 1.0, 2.0 and 0.9 m under pasture, respectively in 2010, 2011, 2013 and 2014. The infiltrated rainwater mostly stayed in the 0–1.0 m layer and hardly supplied to soil depth >1.0 m in normal, dry and wet years. Even in the extremely wet year of 2013, rainwater recharge depth did not exceed 2.0 m under shrub and pasture. This implied that soil desiccation was difficult to remove in normal, dry and wet years, and soil desiccation could be removed in 1.0–2.0 m soil layers even in the extremely wet year under shrub and pasture. The results indicated that the natural fallow was the best vegetation type for achieving sustainable utilization of soil water and preventing soil desiccation.

English

Improved fallows of Sesbania sesban (Sesbania) have been known to improve soil physical and chemical properties and increase crop yield compared to traditional fallows. However, the effects of soil tillage practices after improved fallows on soil properties, weeds, labour and subsequent maize crop has not been assessed in Southern Africa. This study aimed to evaluate how tillage practices affect yield of maize and affect soil properties after two years of fallow and subsequent cropping phase. In this study, done at sites in eastern Zambia, maize yield from a two-year planted Sesbania, natural fallow, continuously fertilized and unfertilized maize were compared under conventional, flat till and zero tillage practices. A split plot experiment, with improved fallow systems in the main plot and the tillage practice in the subplot, was established at the sites. The results showed that the increases in grain yield under conventional tillage over zero tillage practice were 17.8 and 28.2% during 2000/2001 and 2001/2002 seasons, respectively, at Msekera. At Chadiza, the increases in grain yield under conventional tillage over zero tillage were 66.3 and 327.4% during 2000/2001 and 2001/2002 seasons, respectively. Greater maize yields were achieved under Sesbania planted fallows compared to the natural fallow and maize monoculture without fertilizer. Overall, zero tillage practice resulted in lower maize grain yield, higher bulk density, reduced water intake, higher weed infestation and high labour demand during weeding compared to conventional tillage. Key words: Conventional tillage, flat till, grain yield, water intake, weeds, zero tillage.

Evaluation of Tillage Practices for Maize (Zea mays) Grown on Different Land-Use Systems in Eastern Zambia

&lt;p&gt;Improved fallows of &lt;em&gt;Sesbania sesban&lt;/em&gt; (Sesbania) have been known to improve soil physical and chemical properties and increase crop yield compared to traditional fallows. However, the effects of soil tillage practices after improved fallows on soil properties, weeds, labour and subsequent maize crop have not been assessed in Southern Africa. This study aimed to evaluate how tillage practices affect yield of maize and affect soil properties after two years of fallow and subsequent cropping phase. In this study, done at sites in eastern Zambia, maize yield from a two-year planted Sesbania, natural fallow, continuously fertilized and unfertilized maize were compared under conventional, flat till and zero tillage practices. A split plot experiment, with improved fallow systems in the main plot and the tillage practice in the subplot, was established at the sites. The results showed that the increases in grain yield under conventional tillage over zero tillage practice were 17.8% and 28.2% during 2000/2001 and 2001/2002 seasons, respectively, at Msekera. At Chadiza, the increases in grain yield under conventional tillage over zero tillage were 66.3% and 327.4% during 2000/2001 and 2001/2002 seasons, respectively. Greater maize yields were achieved under Sesbania planted fallows compared to the natural fallow and maize monoculture without fertilizer. Overall, zero tillage practice resulted in lower maize grain yield, higher bulk density, reduced water intake, higher weed infestation and high labour demand during weeding compared to conventional tillage.&lt;/p&gt;