Contributions of soil biota to C sequestration varied with aggregate fractions under different tillage systems

It is increasingly believed that substantial soil organic carbon (SOC) can be sequestered in conservation tillage system by manipulating the functional groups of soil biota. Soil aggregates of different size provide diverse microhabitats for soil biota and consequently influence C sequestration. Our objective was to evaluate the contributions of soil biota induced by tillage systems to C sequestration among different aggregate size fractions. Soil microbial and nematode communities were examined within four aggregate fractions: large macroaggregates (>2 mm), macroaggregates (2–1 mm), small macroaggregates (1–0.25 mm) and microaggregates (<0.25 mm) isolated from three tillage systems: no tillage (NT), ridge tillage (RT) and conventional tillage (CT) in Northeast China. Soil microbial and nematode communities varied across both tillage systems and aggregate fractions. The activity and abundance of microbes and nematodes were generally higher under NT and RT than under CT. Among the four aggregate fractions, soil microbial biomass and diversity were higher in microaggregates, while soil nematode abundance and diversity were higher in large macroaggregates. Structural equation modelling (SEM) revealed that the linkage between microbial and nematode communities and their contributions to soil C accumulation in >1 mm aggregate fractions were different from those in <1 mm aggregate fractions. Higher abundance of arbuscular mycorrhizal fungi (AMF) could enhance C retention within >1 mm aggregates, while more gram-positive bacteria and plant-parasitic nematodes might increase C accumulation within <1 mm aggregates. Our findings suggested that the increase in microbial biomass and nematode abundance and the alteration in their community composition at the micro-niche within aggregates could contribute to the higher C sequestration in conservation tillage systems (NT and RT).     

Soil compressibility and penetrability of an Oxisol from southern Brazil, as affected by long-term tillage systems

The precompression stress value defines the transition from the reloading curve to the virgin compression line in the stress–strain curve, which can be used to quantify the highest load or the most intense predrying previously applied to the soil. Thus, in soils with well-defined structured soil horizons, each layer can be characterized by such mechanical strength. Penetration resistance measurements, on the other hand, can be used to determine total soil strength profiles in the field. The effect of long-term tillage systems on physical and mechanical properties was determined in undisturbed and remolded samples collected at 5 and 15 cm depth, 6 months after applying no-till (NT), chisel plow (CP), and conventional tillage (CT) treatments, along with the application of mineral fertilizer and poultry litter. The compressibility tests were performed under confined conditions, with normal loads varying from 10 to 400 kPa after a defined predrying to −6 or −30 kPa. Penetration resistance was determined in the field, after seeding, in three positions: seeding row (SR), untrafficked interrow (UI), and recently trafficked interrow (TI). No-till system showed greater soil resistance to deformation than tilled treatments, as determined by the higher precompression stress and lower coefficient of compressibility. When original soil structure was destroyed (remolded samples), smaller differences were found. The application of extra organic matter (poultry litter) resulted in a reduction of precompression stress in undisturbed samples. Penetration resistance profiles showed greater differences among tillage treatments in the upper layer of the untrafficked interrow, where NT system showed the higher values. Smaller differences were found in the seeding row (with lower values) and in recently trafficked interrow (with higher values), showing that even traffic with a light tractor after soil tillage reduced drastically the effect of previous tillage by loosening up the soil. On the other hand, the tool used to cut the soil and to open the furrow for seeding, incorporated in the direct seeding machine, was sufficient to realleviate surface soil compaction.     

The effects of ryegrass roots and shoots on loess erosion under simulated rainfall

Numerous studies have demonstrated that vegetation coverage is very important to control soil erosion by water. However, the combined impacts of plant roots and shoots on soil erosion by water and the relative contributions of the roots and shoots are not clearly understood. Four rainfall simulation experiments with the rainfall intensity at 1.5 mm min^− 1 were conducted at an interval of 5 weeks to investigate the effects of ryegrass (Lolium perenne L.) shoots and roots on soil erosion and runoff reductions. Ten ryegrass planted pans and four fallow pans were prepared for the experiments. The first rainfall simulation experiment was conducted after ryegrass had been planted for 12 weeks. It showed that compared with the runoffs in the fallow pans, the runoff in the planted pans decreased 25% and 70% in the 12th week and the 27th week, respectively; and the sediment decrements amounted up to 95% in the 27th week. The results also indicated that the shoot effect on runoff reduction, accounting for over 50% except in the 27th week when the shoot affect also accounted for 44%, was relatively greater than the root effect. However, the roots contributed more to soil loss reduction than the shoots, and in particular accounted for 90% of soil loss reduction at the 27th week. Both the soil erosion rate and average infiltration rate were linearly correlated with root surface area density in cm² root surface area per unit soil volume. Ryegrass planting could improve soil physical properties, especially soil aggregate stability, which increased from 33.1% in the 12th week to 38.5% in the 27th week. The study results are probably useful in evaluating the effects of plant shoots and roots on soil erosion control.     

Effects of N fertilizer treatments on biologically active N pools in soils under plow and no tillage

Studies assessing the effects of different tillage and N fertilizer management practices on distributions and amounts of various C and N pools in soil can provide information about the influence of such management on the quality of organic matter in agricultural soils. To assess the influence of management on soil quality, we characterized the organic matter by measurements of total N, organic C, microbial biomass N and active N in the 0–20cm profiles of soil from long-term field experiments containing plots under treatments of plow or no tillage and 0, 135, or 270kgNha^–1 fertilizer. Previous work had established that on the basis of the crop growth requirement of maize, these application rates of fertilizer N provide amounts of N that are deficient, sufficient, and excessive, respectively. The studies reported provide evidence that the sufficient amount of fertilizer N stimulated formation of the biologically active pools of N (biomass N and active N) in soils under no tillage treatments, but the excessive amount of fertilizer N tended to suppress these pools. The results demonstrated that these influences of excessive N fertilization were not reflected in distributions of total N or total organic C in soil profiles but became evident with the measurements of biologically active N. This suggests that such measurements can provide information related to the influence of different management practices on soil quality. Received: 30 November 1995     

Soil pH decline in relation to rotation, tillage, stubble retention and nitrogen fertilizer in S.E. Australia

Abstract. The decline in topsoil (0–0.1 m) pH (CaCl₂) over 11 years (1979–90) was measured in a rotation, tillage, stubble and nitrogen fertilizer experiment on a Chromic Luvisol at Wagga Wagga in S.E. Australia. The rotations consisted of annual wheat cropping (WW) with and without nitrogen fertilizer (100 kg N/ha/year), alternating lupin-wheat (LW) and subterranean clover-wheat (CW). The initial mean pH at the site was 4.9 and the experiment was preceded by subterranean clover-based pasture for most of the previous 19 years. An initial rapid decline in soil pH under all treatments over the first 8–9 years was followed by a 2–3 year period when no further decline was detected. The annual rate of pH decline over the first 8–9 years varied from 0.06 for WW to 0.09 units for WW with added N fertilizer. Apparent steady-state for WW after 11 years was approximately 0.5 pH units higher than for WW with added N fertilizer. There was no difference between CW and LW in the rate of decline or in the apparent steady-state reached. Six years' stubble burning in a LW rotation promoted a slightly higher pH than where stubble was retained. However, there was no significant effect of tillage in either LW or CW rotations. By 1990 the addition of N fertilizer to WW had increased the concentration of exchangeable aluminium by 100% and of manganese by 24%. The inclusion of a legume in the rotation increased the concentration of aluminium but did not affect manganese. However, burning stubble in the LW rotation slightly decreased manganese concentrations.     

Soil physical responses to cattle grazing cover crops under conventional and no tillage in the Southern Piedmont USA

Grazing of cover crops in grain cropping systems can increase economic return and diversify agricultural production systems, but the environmental consequences of this intensified management have not been well documented, especially under different tillage systems. We conducted a multiple-year investigation of how cover crop management (grazed and ungrazed) and tillage system [conventional (CT; initial moldboard plowing and thereafter disk tillage) and no tillage (NT)] affected soil physical properties (bulk density, aggregation, infiltration, and penetration resistance) on a Typic Kanhapludult in Georgia. Responses were determined in two cropping systems: summer grain/winter cover crop and winter grain/summer cover crop. Soil bulk density was reduced (P = 0.02) with CT compared with NT to a depth of 30 cm at the end of 0.5 year, but only to a depth of 12 cm at the end of 2, 2.5, and 4.5 years. Grazing of cover crops had little effect on soil bulk density, except eventually with 4.5 years of management. Water-stable macroaggregation was reduced (P ≤ 0.01) with CT compared with NT to a depth of 12 cm at all sampling times during the first 2.5 years of evaluation. Stability of macroaggregates in water was unaffected by grazing of cover crops in both tillage systems. Across 7 sampling events during the first 4 years, there was a tendency (P = 0.07) for water infiltration rate to be lower with grazing of cover crops (5.6 mm min⁻¹) than when ungrazed (6.9 mm min⁻¹), irrespective of tillage system. Across 10 sampling events, soil penetration resistance was greater under NT than under CT at a depth of 0–10 cm (P = 0.001) and the difference was greater in ungrazed than in grazed systems (P = 0.06). Biannual CT operations may have alleviated any surface degradation with animal traffic, but the initially high level of soil organic matter following long-term pasture and conversion to cropland with NT may have buffered the soil from any detrimental effects of animal traffic. Overall, the introduction of cattle to consume the high-quality cover crop forage did not cause substantial damage to the soil.     

人工模拟降雨条件下花岗岩红壤坡面侵蚀过程与特征分析简

通过室内人工模拟降雨试验,研究降雨强度、坡度及地表覆盖3因素对花岗岩红壤坡面侵蚀过程的影响.结果表明：1）起始产流时间随降雨强度和坡度的增加而有所提前,而地表覆盖能延缓起始产流时间;2）在不同降雨强度和坡度条件下,径流率从产流初期开始都快速增加,7 ～ 10 min后达到稳定,且随着降雨强度和坡度增加,径流率也显著增加;3）随着降雨强度的增大,产沙率明显增大,且降雨强度越大,坡度对产沙率的影响越明显;4）降雨强度和径流总量、产沙总量之间相关性极显著,其相关系数分别为0.892和0.799;5）地表覆盖具有良好的减沙作用,其减沙效益超过90％.     

The erosion threshold for a sustainable agriculture in cultures of bean (Phaseolus vulgaris L.) under conventional tillage and no‐tillage in Northern Nicaragua

Soil erosion by water is one of the main environmental problems of the tropical mountains of Central America. The fragility of these areas, the significant degree of human population pressure exerted and changes in traditional farming systems all contribute to the current state of degradation. In this study, we compare two types of agricultural management (conventional tillage with traditional ploughing and no‐tillage with a digging stick) and analyse the influence of land slope, the management of vegetation cover, and various soil features and properties related to erosion in fields dedicated to the cultivation of beans (Phaseolus vulgaris L.) to determine the erosion thresholds. The study area was located in the hills around El Cuá, in northern Nicaragua. The results showed the system of no‐tillage (NT) to be more effective at controlling erosion than conventional tillage (CT), such that 28.7% less land was affected by erosion. Erosion in plots under CT did not present any statistically significant relationship with the factors analysed. Conversely, the erosion in the plots under NT was significantly related to the coverage of vegetation residues, and we calculated an erosion threshold of 40% of the level of vegetation coverage, which significantly reduces erosion.     

Relationship of percolation stability of soil aggregates to land use, selected properties, structural indices and simulated rainfall erosion

Simple tests of structural stability are needed for evaluating the ease with which soils slake and erode when in contact with water. In a laboratory study, we related the percolation stability (PS) of 22 Nigerian soils to land use, soil properties, structural stability indices and simulated rainfall erosion. All measurements were carried out with the 1–2 mm diameter air-dry aggregates. Land use influenced PS more than the type of soil. Forest soils, bush fallows, mulched, minimally tilled plots and pasture lands had rapid PS (>250 ml/10 min) values, whereas mulched conventionally tilled plots, bare fallows and continuously cultivated plots from where residues were removed by burning had relatively slow to moderate PS values (34–241 ml/10 min). The single most important soil property that correlated positively with PS is organic matter (OM) (r = 0.55^*) followed by total Fe + Al (r = 0.52^*). The significant inverse relationship (r = −0.49^*) between log (PS) and log (pH/OM) indicates a decrease in PS of these acidic, low-OM soils with increasing pH levels. The percent water-stable aggregate (WSA) >0.20 mm diameter, aggregated clay index (AC) and clay dispersion ratio (CDR) correlated weakly with PS. Conversely, the sealing index (SI) (i.e. the ratio of saturated hydraulic conductivity of an uncrusted to that of a crusted soil) had a strong, inverse relationship with PS (r = −0.97^***). These relationships indicate that PS measures the slakability (and not dispersibility) of soils. The relationship between PS and erosion (E) was an exponential decay form, E = 102 e^−0.0043PS (r² = 0.98) and showed that high interrill erosion rates would be expected on soils with PS < 250 ml/10 min. The PS which is simple to measure, is, therefore, a good indicator of structural stability for assessing the potential of these soils to erode.     

呼伦湖流域不同利用方式草场水土和氮磷流失

摘 要：为了研究不同利用方式草场水土和氮磷流失规律及原因,在呼伦湖流域选择传统放牧草场、草库伦草场、不放牧草场三种利用方式草场,用模拟降雨的方法进行了水土及氮磷随径流流失试验。结果表明：两种雨强下,传统放牧草场水土流失最严重。相同雨强下,总氮流失量：草库伦草场>传统放牧草场>不放牧草场;总磷流失量：传统放牧草场>草库伦草场>不放牧草场。同一种利用方式草场径流中总氮、总磷浓度与降雨强度关系不显著。草库伦草场可有效防止水土流失。传统放牧草场和草库伦草场的氮磷排放负荷与累积径流量之间存在线性关系,而不放牧草场的存在指数关系。该研究可为探讨呼伦湖流域草场合理利用、水环境的保护和面源污染的治理提供参考。     

保护性耕作下大豆农田土壤呼吸及影响因素分析

为了探讨保护性耕作对旱作农田土壤呼吸的影响,采用LI6400-09仪器(LI6400便携式光合作用系统连接6400-09呼吸室)在重庆北碚西南大学试验农场对平作(T)、垄作(R)、平作+覆盖(TS)、垄作+覆盖(RS)、平作+覆盖+秸秆速腐剂(TSD)、垄作+覆盖+秸秆速腐剂(RSD)6种处理下的西南紫色土丘陵区小麦/玉米/大豆套作体系中大豆生长季节的土壤呼吸及其水、热、生物因子进行测定和分析,探讨西南丘陵区保护性耕作下大豆农田土壤呼吸及其影响因素。结果表明,大豆整个生育期内土壤呼吸先缓慢增强,到开花期开始增长迅速,成熟期明显下降。不同处理土壤呼吸速率存在差异,表现为TTSD>TS、R>RSD>RS,土壤呼吸的土温敏感指标Q10值排序为TS>TSD>RS=R>T>RSD。秸秆覆盖处理的土壤呼吸对于土壤温度敏感性较高,垄作则降低了土壤温度敏感性。5 cm土层的土壤含水量高低排序为TSD>RSD>TS>RS>T>R。本研究中土壤呼吸与土壤水分呈抛物线函数关系,垄作处理下土壤呼吸与土壤水分正相关,达到显著水平;其他处理均表现负相关,其中TS达到极显著水平。在大豆农田生态系统中优势类群有弹尾目、螨目和双翅目,干漏斗法、陷阱法捕获的土壤动物与土壤呼吸均没有显著的相关关系,两种方法所得土壤动物数量加总与土壤呼吸进行相关分析,发现处理T相关系数达到显著水平,r=0.901,P=0.037。     

Short-term soil CO2 emission after conventional and reduced tillage of a no-till sugar cane area in southern Brazil

The impact of tillage systems on soil CO₂ emission is a complex issue as different soil types are managed in various ways, from no-till to intensive land preparation. In southern Brazil, the adoption of a new management option has arisen most recently, with no-tillage as well as no burning of crops residues left on soil surface after harvesting, especially in sugar cane areas. Although such practice has helped to restore soil carbon, the tillage impact on soil carbon loss in such areas has not been widely investigated. This study evaluated the effect of moldboard plowing followed by offset disk harrow and chisel plowing on clay oxisol CO₂ emission in a sugar cane field treated with no-tillage and high crop residues input in the last 6 years. Emissions after tillage were compared to undisturbed soil CO₂ emissions during a 4-week period by using an LI-6400 system coupled to a portable soil chamber. Conventional tillage caused the highest emission during almost the whole period studied, except for the efflux immediately following tillage, when the reduced plot produced the highest peak. The lowest emissions were recorded 7 days after tillage, at the end of a dry period, when soil moisture reached its lowest rate. A linear regression between soil CO₂ effluxes and soil moisture in the no-till and conventional plots corroborate the fact that moisture, and not soil temperature, was a controlling factor. Total soil CO₂ loss was huge and indicates that the adoption of reduced tillage would considerably decrease soil carbon dioxide emission in our region, particularly during the summer season and when growers leave large amounts of crop residues on the soil surface. Although it is known that crop residues are important for restoring soil carbon, our result indicates that an amount equivalent to approximately 30% of annual crop carbon residues could be transferred to the atmosphere, in a period of 4 weeks only, when conventional tillage is applied on no-tilled soils.     

Effects of tillage practices combined with mucuna fallow on soil erosion and water dynamics on Ishigaki Island,Japan

Abstract

This study was conducted on a sloping field at the Japan International Research Center for Agricultural Sciences, Okinawa Subtropical Station, Ishigaki Island, Okinawa Prefecture, Japan, to evaluate the effects of zero tillage farming combined with mucuna fallow as a cover crop on soil erosion and water dynamics. Two fallow systems (natural and mucuna) in combination with two soil tillage treatments (zero tillage and conventional tillage) were imposed on three sloping fields (2.0°, 3.5° and 5.0°). A sorghum crop (Sorghum bicolor (L) moench) was planted after the soil tillage treatment. Soil loss for zero tillage farming combined with mucuna fallow was equivalent to only 3% of that for the conventional tillage farming with natural fallow. Runoff water was also reduced by between 74% and 77% when compared with the conventional tillage system with natural fallow. These results indicate that zero tillage with mucuna fallow is a very effective measure for the control of soil erosion and water runoff. Moreover, this farming system improved water infiltration during both the fallow and the sorghum cropping periods. For the zero tillage plot, water loss as deep percolation increased 1.6-fold compared with that for the conventional farming under heavy rainfall conditions. It is expected that under less rainfall areas or seasons, the effects of zero tillage farming combined with the mucuna cover crop may be more pronounced on water runoff control and, therefore, may greatly improve soil water conditions.     

Hydraulic conductivity, residue cover and soil surface roughness under different tillage systems in semiarid conditions

The objective of this study was to investigate the effect of tillage and cropping system on near-saturated hydraulic conductivity, residue cover and surface roughness to improve soil management for moisture conservation under semiarid Mediterranean conditions. Three tillage systems were compared (subsoil tillage, minimum tillage and no-tillage) under three field situations (continuous crop, fallow and crop after fallow) on two soils (Fluventic Xerochrept and Lithic Xeric Torriorthent). Soil under no-tillage had lower hydraulic conductivity (5.0 cm day⁻¹) than under subsoil tillage (15.5 cm day⁻¹) or minimum tillage (14.3 cm day⁻¹) during 1 of 2 years in continuous crop due to a reduction of soil porosity. Residue cover at sowing was greater under no-tillage (60%) than under subsoil or minimum tillage (<10%) in continuous crop. Under fallow, residue cover was low (10%) at sowing of the following crop for all tillage systems in both soils. Surface roughness increased with tillage, with a high value of 16% and decreasing following rainfall. Under no-tillage, surface roughness was relatively low (3–4%). Greater surface residue cover under no-tillage helped conserve water, despite indications of lower hydraulic conductivity. To overcome the condition of low infiltration and high evaporation when no-till fallow is expected in a cropping sequence, either greater residue production should be planed prior to fallow (e.g. no residue harvest) or surface tillage may be needed during fallow.     

紫色土丘陵区保护性耕作下旱地土壤呼吸及影响因素

为了探讨保护性耕作对旱作农田土壤呼吸的影响,采用LI6400XT便携式光合作用测量系统自带的土壤呼吸室(6400-09)在重庆北碚西南大学试验农场对传统耕作(T,traditional farming)、垄作(R,ridge planting)、传统耕作+秸秆覆盖(TS,traditional farming+straw mulching)、垄作+秸秆覆盖(RS,ridge planting+straw mulching)、传统耕作+秸秆覆盖+秸秆速腐剂(TSD,traditional farming+straw mulching+decomposing agent)、垄作+秸秆覆盖+秸秆速腐剂(RSD,ridge planting+straw mulching+decomposing agent)6种处理下的西南紫色土丘陵区小麦/玉米/大豆套作体系中作物生长季节的土壤呼吸及其水热因子进行了测定和分析。结果表明,6种处理中土壤呼吸速率的季节变化明显,各处理日均土壤呼吸速率差异显著。其中在小麦-大豆条带,小麦土壤呼吸速率均值为1.53μmol m-2s-1,大豆土壤呼吸速率日均值为4.10μmol m-2s-1,各处理日平均土壤呼吸速率大小排序为TRTSTSDRSRSD。在空地-玉米-空地条带,玉米土壤呼吸日均值为2.56μmol m-2s-1,介于小麦和大豆土壤呼吸速率之间,各处理日平均土壤呼吸大小排序为RTRSTSRSDTSD。整个套作体系土壤呼吸总量C为1 543~2 134 g m-2,表现为TRRSTSTSDRSD。研究结果还显示土壤温度和土壤水分是影响旱地农田土壤呼吸的主要因素,二者分别解释了土壤呼吸季节变化的28.9%~53.7%和13.7%~42.0%。水热因子与土壤呼吸速率的回归分析表明,指数方程较好地模拟了土壤呼吸与10 cm土温的关系,土壤呼吸的温度敏感性指标Q10值在2.25~2.69之间;而土壤呼吸与5 cm土壤水分的关系以抛物线型函数模拟最优。土壤呼吸对土壤水分的响应阈值为14.94%。该研究为明确农田生态系统土壤呼吸变化规律及影响因素的控制机理提高参考,对估算全球碳平衡、评估区域碳源汇具有重要意义。     

Stratification of soil aggregation and organic matter under conservation tillage systems in Africa

Soil degradation due to tillage has been reported Africa-wide. Other main causes of soil degradation are overgrazing, extensive cultivation of marginal lands, widespread clearing of vegetation for agriculture, deforestation, exploitation of unsuitable agricultural technologies, mis-management of arable lands, and frequent drought. Hence, declining soil fertility and increasing population pressure on lands are fragile bases on which to build expectations for improved crop production. This paper recognizes conservation tillage systems as one means for preventing food shortages and natural resources degradation throughout the continent. Conservation tillage has the potential for increasing soil organic matter content and enhancing soil aggregation. Conservation tillage systems can create an aggregated, fertile surface layer that is important from a soil erosion reduction perspective and thus for a sustainable agriculture in Africa. Some indigenous tillage systems in Africa can be adapted to meet objectives of conservation tillage systems. Further, recent technological developments in tillage and seeding machinery will certainly enhance the rate of farmer’s acceptance and adoption of conservation tillage.     

Management of a previously eroded tropical Alfisol with herbaceous legumes: Soil loss and physical properties under mound tillage

A study was carried out on a previously eroded Oxic Paleustalf in Ibadan, southwestern Nigeria to determine the extent of soil degradation under mound tillage with some herbaceous legumes and residue management methods. A series of factorial experiments was carried out on 12 existing runoff plots. The study commenced in 1996 after a 5-year natural fallow. Mound tillage was introduced in 1997 till 1999. The legumes – Vigna unguiculata (cowpea), Mucuna pruriens and Pueraria phaseoloides – were intercropped with maize in 1996 and 1998 while yam was planted alone in 1997 and 1999. This paper covers 1997–1999. At the end of each year, residues were either burned or mulched on respective plots. Soil loss, runoff, variations in mound height, bulk density, soil water retention and sorptivity were measured. Cumulative runoff was similar among interactions of legume and residue management in 1997 (57–151 mm) and 1999 (206–397 mm). However, in 1998, cumulative runoff of 95 mm observed for Mucuna-burned residue was significantly greater than the 46 mm observed for cowpea-burned residue and the 39–51 mm observed for mulched residues of cowpea, Mucuna and Pueraria. Cumulative soil loss of 7.6 Mg ha⁻¹ observed for Mucuna-burned residue in 1997 was significantly greater than those for Pueraria-mulched (0.9 Mg ha⁻¹) and Mucuna-mulched (1.4 Mg ha⁻¹) residues whereas in 1999 it was similar to soil loss from cowpea treatments and Pueraria-burned residue (2.3–5.3 Mg ha⁻¹). There were no significant differences in soil loss in 1998 (1–3.2 Mg ha⁻¹) whereas Mucuna-burned residue had a greater soil loss (28.6 Mg ha⁻¹) than mulched cowpea (6.9 Mg ha⁻¹) and Pueraria (5.4 Mg ha⁻¹). Mound heights (23 cm average) decreased non-linearly with cumulative rainfall. A cumulative rainfall of 500 mm removed 0.3–2.3 cm of soil from mounds in 1997, 3.5–6.9 cm in 1998 and 2.3–4.6 cm in 1999, indicating that (detached but less transported) soil from mounds was far higher than observed soil loss in each year. Soil water retention was improved at potentials ranging from −1 to −1500 kPa by Mucuna-mulched residue compared to the various burned-residue treatments. Also, mound sorptivity at −1 cm water head (14.3 cm h^−1/2) was higher than furrow sorptivity (8.5 cm h^−1/2), indicating differences in hydraulic characteristics between mound and furrow. Pueraria-mulched residues for mounds had the highest sorptivity of 17.24 cm h^−1/2, whereas the least value of 6.96 cm h^−1/2 was observed in furrow of Mucuna-burned residue. Pueraria phas eoloides was considered the best option for soil conservation on the previously eroded soil, cultivated with mound tillage.     

Influence of tillage on crop residue cover, soil properties and yield components of cowpea in derived savannah ectones of Nigeria

The effects of five tillage treatments: no tillage (NT), disc harrowing (DH), mouldboard ploughing followed by disc harrowing (MPH), disc ploughing followed by disc harrowing (DPH), and disc ploughing followed by two passes of disc harrowing (DPHH) on crop residue cover, soil properties and some yield parameters of cowpea were investigated for a derived savannah ectone soil. The residue left on the soil surface for NT, DH, and MPH is not significantly different. The NT left 32.1 and 44.3% more residue on the soil surface than the DPH and DPHH treatments, respectively. The NT treatment had least average value of soil bulk density of 1.01 g/cm³. The mean soil bulk densities for the DH, MPH, DPH and DPHH vary between 1.20 and 1.35 g/cm³. The soil moisture content decreased with increasing soil depth. At the soil depth of 10–30 cm, the cone penetration resistance at NT was 1.18 MPa compared with 0.92 MPa for the DH treatment, although these were not significant (p≤0.05). The tillage treatments had a significant effect on grain yield, mass of leaves and stems, root length density, and number of pods per plant of cowpea except on the germination count. DH and NT treatments gave different grain yield and number of pods per plant but these values were not statistically different and represent the highest grain yield and number of pods per plant among the other treatments were considered. The root zone exploration revealed highest root density at shallow depths with the DH and MPH treatments.     

耕作与施肥对旱地玉米田土壤耗水量和水分利用效率的影响

为探究保护性耕作与施肥对渭北旱地春玉米田土壤耗水量和水分利用效率的影响,达到高效生产的目的。于2013—2015年在渭北旱塬实施了春玉米耕作与施肥田间试验,共设置6种耕作与施肥处理:翻耕+低肥(A1)、免耕+高肥(A2)、深松+平衡施肥(A3)、翻耕+无肥(B1)、免耕+无肥(B2)和深松+无肥(B3),测定了春玉米休闲期与生育时期0~200 cm土层土壤蓄水量和收获时籽粒产量。结果表明:1)保护性耕作能显著提高旱地玉米田土壤蓄水保墒能力。与传统翻耕处理B1相比,休闲期,B2和B3播前土壤蓄水量分别提高23.39 mm和27.73 mm(P0.05);耕作处理区,B2和B3全生育期土壤蓄水量平均提高13.41 mm和15.70 mm;耕作施肥处理区,A2、A3土壤蓄水量较A1分别提高13.15 mm、19.54 mm。2)平衡施肥能有效提高玉米全生育期平均土壤蓄水量,与不施肥处理相比,全生育期土壤蓄水量平均提高6.79 mm(P0.05)。3)保护性耕作与施肥能提高玉米籽粒产量与水分利用效率。耕作无肥处理区,与B1比较,B3处理产量提高212~576 kg×hm~(-2),水分利用效率提高0.83~2.21 kg×hm~(-2)×mm~(-1);耕作施肥处理区,A3产量与水分利用效率提高最为显著,产量较A1提高659~1 495 kg×hm~(-2),水分利用效率提高0.65~3.82 kg×hm~(-2)×mm~(-1)(P0.05)。3种施肥方式下以氮、磷、钾平衡施肥产量与水分利用效率提高幅度最大。4)对耗水量与产量进行相关性分析发现,抽雄—灌浆生育阶段土壤耗水量与产量呈显著正相关,保护性耕作提高玉米生长初期土壤蓄水保墒能力,提高春玉米抽雄—灌浆期土壤水分,增加作物生长关键时期对水分的利用效率,利于玉米籽粒产量的提高。因此在渭北旱地春玉米田,深松与平衡施肥组合能提高春玉米产量与水分利用效率,是该地区玉米高效生产较为适宜的种植模式。