不同机械深耕的改土及促进作物生长和增产效果

长期不合理耕作导致土壤结构性能恶化、土壤耕性变差,限制作物根系下扎、影响土壤生产潜力发挥。为了改善土壤耕层构造,该试验采用自主研发的改土机械ES-210型深松犁和前置式心土(亚表层)耕作犁进行深耕,以灭茬旋耕(常规耕作)为对照,进行大区耕作对比试验。结果表明:1)深松、亚表层耕作处理与对照相比,耕层土壤固相率分别降低1.6%~3.3%、2.8%~4.5%,液相、汽相相对增加,三相比更趋于合理化;打破犁底层,降低耕层土壤硬度,其中20~35 cm土层效果更为明显;耕层土壤有效水含量上升1.1%~1.2%、0.9%,束缚水(无效水)含量下降0.4%~1.1%、0.5%~0.9%。2)深松、亚表层耕作处理比对照根长增长,其中甜菜增长5.1%、2.9%,大豆增长11.5%、13.2%;干物质积累量增加,其中甜菜增加2.3%~4.1%、3.1%~4.8%,大豆增加7.8%~10.0%、10.4%~13.6%;3)深松、亚表层耕作处理与对照相比,其中甜菜增产8.5%、12.6%;大豆增产5.0%、6.1%;深松及亚表层耕作改土处理分别比对照增收1003.3、1454.4元/hm2,其中收益大小为亚表层耕作处理深松处理对照。可见,采用ES-210深松犁及心土耕作犁深耕改土,改变了土壤耕层构造,起到扩库增容的效果;改善了作物根系生长环境,提高了作物产量,为今后农业耕作机械的发展提供了技术支撑。     

Subsoil loosening in a crop rotation for organic farming eliminated plough pan with mixed effects on crop yield

Compacted subsoil may reduce plant root growth with resulting effects on plant uptake of water and nutrients. In organic farming systems subsoil loosening may therefore be considered an option to increase nutrient use. We investigated the effect of subsoil loosening with a paraplow to ca. 35 cm depth within a four-crop rotation in an organic farming experiment at Foulum (loamy sand) and Flakkebjerg (sandy loam) in Denmark. In each of the years 2000–2003, half of four plots per site were loosened in the autumn bearing a young grass-clover crop (mixture of Lolium perenne L., Trifolium repens L. and Trifolium pratense L.) established by undersowing in spring barley (Hordeum vulgare L.). The grass-clover was grown for another year as a green manure crop and was followed by winter wheat (Triticum aestivum L.), lupin (Lupinus angustifolius L.):barley and spring barley in the following 3 years. On-land ploughing was used for all cereal and pulse crops. Penetration resistance was recorded in all crops, and the results clearly showed that subsoil loosening had effectively reduced the plough pan and that the effect lasted at least for 3.5 years. Measurements of wheat root growth using minirhizotrons at Foulum in 2002/2003 did not show marked effects of subsoil loosening on root frequency in the subsoil. Subsoil loosening resulted in reduced growth and less N uptake of the grass-clover crop in which the subsoil loosening was carried out, probably due to a reduced biological nitrogen (N) fixation resulting from a smaller clover proportion. This had a marked effect on the growth of the succeeding winter wheat. Negative effect of subsoil loosening on yield of winter wheat and spring barley was observed without manure application, whereas small positive yield effect of subsoil loosening was observed in crops with a higher N supply from manure. Yield decrease in winter wheat was observed in years with high winter rainfall. There was no significant effect of subsoiling on grain yield of the lupin:barley crops, although subsoiling had a tendency to increase crop growth and yield during dry summers. Our results suggest that subsoil loosening should not be recommended in general under Danish conditions as a measure to ameliorate subsoil compaction.     

Short‐term effects of in‐row subsoiling and simultaneous admixing of organic material on growth of spring barley (H. vulgare)

Previous studies have shown that deep tillage, so‐called subsoiling, is beneficial for yield development, and that tillage of deeper soil layers can promote water and nutrient availability during dry periods. The application of composts to the topsoil has been widely studied and evaluated, and it has been shown to improve soil stability and plant N uptake. These effects can differ over time depending on the compost type. Since dry periods have become more frequent, sustainable soil tillage and fertilizer practices must be developed. A combination of deep soil tillage and compost application might be a way to ensure proper plant supply during dry periods. Therefore, a field experiment on spring barley growth was carried out to evaluate the short‐term effects of in‐row subsoiling with simultaneous admixing of compost. Two types of composts and one organic fertilizer (Bio: decomposed organic waste, Green: decomposed green cuttings and CM: cattle manure) were admixed into the subsoil, and a control treatment received single deep loosening (DL) to a depth of 0.6 m. Yield development, yield parameters and grain quality were analysed and showed that the DL and Bio treatments resulted in the highest yields, and a significantly increased ear density and number of kernels. The TKW (100‐kernel weight) of the CM treatment was significantly lower than the other treatments. In all treatments, a clear trend of decreasing yields with increasing distance from the subsoil tillage was observed. Thus a subsoil tillage every meter can increase overall yield development and offers a new perspective for sustainable crop production.     

Crop and soil response to subsoil loosening, deep incorporation of phosphorus and potassium fertilizer and subsequent soil management on a range of soil types.: Part 1: Response of arable crops

Abstract. Between 1978 and 1985 16 experiments tested crop response to subsoil loosening by either the Wye Double Digger or a winged subsoiler. Additionally, response to incorporation of 350 kg ha of P₂O₅and K₂O into the subsoil was tested. Soil types were mainly well-drained light-and medium-textured soils in arable rotations. Subsoil loosening increased the yield of spring-sown crops on sandy soils in years of moderate to severe drought. Response was associated with deeper rooting and improved water extraction from the subsoil. No yield increases were recorded with autumn-sown crops which were largely grown on the medium and heavy textured soils. There was a trend towards yield reductions on deep silty soils in wetter years. At one site only did the response to phosphorus and potassium fertilizer incorporated into the subsoil exceed that of fertilizer applied to the topsoil.     

The effect of subsoiling on soil resistance and cotton yield

Soil compaction occurs due to heavy wheeling or repetitive tillage in the field. Soil compaction changes the soil physical parameters and water infiltration that cause reduction in the crop yield. Proper subsoiling alleviates the negative effect of soil compaction. The objectives of the research was to examine the effects of subsoiling on the resistance of the soil and to find out deep tillage effects on the cotton yield and the convenient time for applying subsoil treatment for reducing the soil compaction. One-pass (B) and two-passes (C) subsoil treatments were applied in the fields where wheat, silage maize (Zea mays L.) and cotton (Gossypium hirsutum L.) crops were grown by 2 years rotation. The experiment was started in 1998 and carried out for 4 years. Soil penetrations were measured during the experiments years at thaw conditions of silty-clay soil (43% clay, 50% silt, 7% sand) before seedbed preparation in autumn seasons. According to the results, the subsoiling treatments created statistically significant effects on the soil resistance (P<0.05) comparing the control plots (A). The initial disruption in subsoiled plots has almost disappeared after 2 and 4 years in B and C plots, respectively. The soil resistance in C plots was lower than in B plot. The percentage of decrease in the soil resistance from A to B and A to C plots was calculated as 13.3 and 26.2%, respectively, in the first year. In the effective subsoiling area from 0.20 to 0.50 m depth, the ratio of penetration decrease in both plots was about 7–8% per year. The difference of penetration decrease between B and C plots was found to be about 15.8% level. Cotton yields at each subsoiled plots increased slightly comparing with control plots (A) where subsoiling was not applied. However, these increments were found to be statistically insignificant. It may be concluded that the subsoiling treatments does not affect the crop yield in intensive and fully irrigated field conditions.     

Crop and soil response to subsoil loosening, deep incorporation of phosphorus and potassium fertilizer and subsequent soil management on a range of soil types.: Part 2: Soil structural conditions

Abstract. In a series of experiments on 16 sites both a power-driven rotary-tine Wye Double Digger and a rigid tine winged subsoiler produced significant subsoil loosening and fissuring. The Double Digger consistently produced the greatest clod breakdown together with the least soil bulk densities and cone penetration resistances. Management strategies after loosening had an important influence on the longevity of the loosening effect. The rate of recompaction was least with controlled traffic and bed systems and increased with random traffic and with the growing of root crops. No significant differences in crop response were monitored between the two loosening treatments, yield response depending largely on the extent of moisture stress experienced by the crop. Loosening on silty soils reduced yields in wet seasons and this was associated with soil structural instability. Visual soil profile examination is necessary to support bulk density and cone penetration resistance measurements when assessing soil compaction.     

Kemink subsoiling before and after planting

The Kemink exact soil management system is a non-inversion soil management system based on subsoiling, ridges and controlled traffic. Previous studies have documented benefits of the Kemink system used in its entirety, but the isolated effect of Kemink subsoiling has not been investigated before. To determine the isolated effect of Kemink subsoiling before and after planting two field experiments in sugar beet and barley were conducted in 1999 and 2000 under low nutrient input conditions in a conventional soil management system without recognized compaction problems. Kemink subsoiling after planting generally showed a negative effect on the growth and yield of both crops, whereas subsoiling before planting increased sugar beet yield from 8.4 to 9.5 t ha⁻¹ and sugar beet nitrogen uptake from 48.5 to 57.4 kg ha⁻¹. There was no effect of subsoiling before planting on the grain yield of barley. The negative effect of subsoiling after planting was more pronounced in 1999 than in 2000, and more pronounced in spring barley. The study shows that Kemink subsoiling after planting involves a significant risk of crop damage and cannot be expected to improve crop performance in conventional soil management systems in its current form, whereas Kemink subsoiling before planting may have potential as a measure to increase yield of sugar beet and possibly other row crops too, under low nutrient input conditions.     

Deep tillage and traffic effects on subsoil compaction and sunflower (Helianthus annus L.) yields

The main function of deep tillage is to alleviate subsoil compaction, but how long do the benefits of this technique remain? Traffic on loose soil causes a significant increase in soil compaction. Subsoiling and chisel plowing were carried out at 450 and 280 mm depth, respectively on a compacted soil in the west Rolling Pampas region of Argentina. The draft required, physical soil properties, root growth, sunflower (Helianthus annus L. Merr.) yield and traffic compaction over the subsequent two growing seasons were measured. Cone penetrometer resistance was reduced and sunflower yields increased following deep tillage operations. Subsoil compaction caused changes to the root system of sunflower that affected shoot growth and crop yields. Although subsoiling and chiseling had an immediate loosening effect, it was evident that after just 2 years, when traffic intensity was >95 mg km ha⁻¹, re-compaction and settling had occurred in the 300–600 mm depth range.     

耕作方式对土壤水动态变化及夏玉米产量的影响

一个连续２年的田间耕作试验在夏玉米生长期内完成,分析对比３种不同耕作方式对土壤水动态变化过程及对作物产量的影响。耕作扰动对土壤水动态变化的影响是明显的,夏玉米生长初期免耕下的表层土壤持有较高的水分,这归因于土壤非耕扰动、冬小麦残茬覆盖以及耕层土壤孔隙尺度分布的变化;另一方面,深松土壤受到耕作活动的强烈干扰,苗期耕层土壤蓄水明显小于传统耕作。耕作方式对土壤水差异的影响伴随着作物的生长发育过程显著减弱。深松耕作对作物根系生长发育状况及作物增产效果的作用是十分显见的。     

耕作措施对土壤特性及作物产量的影响

通过夏玉米田间试验研究了不同耕作措施及秸秆覆盖对土壤特性、水分状况、作物产量及水分利用效率的影响。试验处理包括常规耕作、深松、秸秆覆盖、垄作、浅坑及免耕。结果表明,秸秆覆盖可显著提高土壤蓄水量、作物产量及水分利用效率。其保水增产效果在干旱年份更加明显。深松可有效打破犁底层降低其密度,可增加作物根深、根长及根重,提高作物产量和水分利用效率。免耕可提高夏玉米早期田间土壤含水率,保持相同产量。     

Properties,degradation risks and rehabilitation possibilities of heavy soils in Bulgaria

The objective of this study was to determine soil properties, limiting site deficiencies for agricultural production and degradation risks of some major soil groups of Bulgaria. Vertisols, Planosols, Chernozems and Luvisols were characterised based on soil analyses. Temporal waterlogging in combination with water erosion, soil compaction and chemical degradation limit the fertility of Vertisols and Planosols. Chernozems and Luvisols are partly compacted. To ensure soil productivity for coining generations and to protect soil and water resources, the evident soil degradation must be halted. Long‐term field studies of soil rehabilitation variants were conducted. Soil parameters and crop yield were the main indicators used to estimate soil quality. Pipe drainage in combination with subsoiling and the application of gypsum and limestone, respectively, are effective measures for site rehabilitation of degraded Vertisols and Planosols. Degraded Luvisols and Chernozems characterised by distinct and persistent subsoil compaction can be regenerated by subsoil loosening and following site‐adapted soil management practices.     

Remediation of subsoil compaction and compaction effects on corn N availability by deep tillage and application of poultry manure in a sandy-textured soil

Subsoil compaction may reduce the availability and uptake of water and plant nutrients thereby lowering crop yields. Among the management options for remediating subsoil compaction are deep tillage and the selection of crop rotations with deep-rooted crops, but little is known of the effects of applications of organic amendments on subsoil compaction. The objectives of this study were to determine the effects of subsoil compaction on corn yield and N availability in a sandy-textured soil and to evaluate the use of deep tillage and surface applications of poultry manure to remediate subsoil compaction. A field experiment planted to corn (Zea mays L.) was conducted from 2000 to 2001 on a Reelfoot fine sandy loam (fine-silty, mixed thermic Aquic Argiudolls) formed in silty alluvium located in southeast Missouri near the Mississippi River. Treatments were arranged in a factorial design with three levels of subsoil compaction and subsoiling and four rates (averaging 0, 6, 11 and 18 Mg ha⁻¹) of poultry manure. Subsoil tillage to a depth of 30 cm had multiple effects, including overcoming a natural or tillage-induced dense layer or pan and increasing volumetric soil water content and crop N uptake, especially in the 2001 cropping year with low early season precipitation. N recovery efficiency (NRE) was significantly higher in the subsoil treatment compared to the highest compaction treatment in 2001. No significant interactions between manure rates and compaction and subsoiling treatments were observed for corn grain and silage yields, N uptake and NRE. Average increases in corn grain yields over all manure rates due to subsoil tillage of compacted soil were 2002 kg ha⁻¹ in 2000 and 3504 kg ha⁻¹ in 2001. Application of poultry manure had a consistent positive effect on increasing grain yields and N uptake in 2000 and 2001 but did not significantly alter measured soil physical properties. The results of this study suggest that deep tillage and applications of organic amendments are management tools that may overcome restrictions in both N and soil water availability due to subsoil compaction in sandy-textured soils.     

Subsoil loosening does little to enhance the transition to no-tillage on a structurally degraded soil

Long-term cropping with conventional cultivation on New Zealand’s easily compacted soil causes soil structure degradation. The objective of this study was to ascertain if soil physical properties, and crop establishment and yield could be improved by subsoil loosening in the first year of conversion from conventional tillage to no-tillage. Plots on a Milson silt loam (Argillic Perch-Gley Pallic Soil, Typic Ochraqualf) were Paraplowed (PP), straight-legged subsoiler (SL), mole ploughed (M), or left as non-loosened controls (C) in the autumn of 1997. Forage brassica was sown with a Cross-Slot™ no-tillage drill. Wheat was established on the plots in the spring of 1997. Subsoil loosening resulted in some transient improvements in measured soil physical properties. Initially, subsoil loosening significantly reduced soil strength. Shortly after subsoil loosening, cone indices showed disruption to 300 mm with PP, 350 mm with SL and 100 mm with M. About 80% of profile cone indices from the PP and SL treatments were less than the critical value of 2 MPa compared to 48% for C and M. At 267 days after subsoil loosening, PP continued to have significantly lower cone index values than C and M. In May, the bulk density of PP plots was significantly lower than SL, M and C although reconsolidation in all plots was observed 9 months later after the wheat was harvested. Air permeability for PP, SL and M was significantly greater than C in June. Subsoil loosening did not increase plant populations or yield of the brassica or wheat crops. Vertical rooting depth was greater in the PP treatment. Few significant differences in wheat rooting patterns were found at depth.     

耕作方式对麦–玉轮作农田固碳、保水性能及产量的影响

【目的】 农田固碳保水性能是影响作物产量的关键因素,研究耕作方式对耕层 (0—20 cm) 土壤碳、水含量和产量的影响,为选择适宜该地区的最佳耕作措施提供参考。 【方法】 保护性耕作长期定位试验始于2002年,种植制度为冬小麦–夏玉米一年两熟,两季秸秆全量粉碎 (3～5 cm) 还田,试验设传统翻耕、深松、旋耕和免耕4种耕作方式。对2015—2016年作物生长各时期土壤有机碳含量、土壤含水量、碳水储量、产量和等价产量等进行了测定。 【结果】 不同处理麦–玉轮作农田0—20 cm土层有机碳含量有所不同。耕作措施对土壤有机碳含量有显著 (P < 0.05) 影响,表现为深松和免耕能显著增加0—10 cm土层有机碳含量,且以深松效果最为显著 ( P < 0.05)。与传统翻耕相比,免耕和旋耕降低了10—20 cm土层土壤有机碳含量;深松比传统翻耕显著 ( P < 0.05) 增加了小麦季土壤有机碳含量,玉米季没有显著性差异 ( P < 0.05)。0—10 cm土层,玉米季旋耕和免耕处理的土壤含水量高于深松和传统翻耕;在10—20 cm土层小麦季免耕处理土壤含水量高于其他三种耕作方式。产量结果表明,深松能有效增加作物的有效穗数、穗粒数和千粒重,进而增加籽粒产量和周年等价产量;免耕显著 ( P < 0.05) 降低了亚表层 (10—20 cm) 有机碳含量,降低穗粒数和千粒重,不利于作物增产。两年小麦玉米单作产量和周年等价产量均表现为深松 > 传统翻耕 > 旋耕 > 免耕。 【结论】 深松能有效促进耕层土壤有机碳积累和保水性能提高,增加作物的有效穗数、穗粒数和千粒重,从而增加产量;免耕显著 (P < 0.05) 提高了表土层 (0—10 cm) 碳储量,有助于增强耕层土壤的保水性能。      

Mitigation of subsoil recompaction by light traffic and on-land ploughing: II. Root and yield response

Plough pans have been shown to severely hamper root development, limit rooting depth and reduce crop yields. We evaluated the effect of plough pan re-compaction on root and yield response for winter wheat in a field trial conducted in two neighbouring fields on a sandy loam. Plots were mechanically loosened by a subsoiler to a depth of 35 cm in 1997 and 1998. In 2 years following the loosening operation, perennial grass/clover was grown with limited traffic intensity. Subsequently oats were established and followed by winter wheat. On-land ploughing was compared with traditional mouldboard ploughing. In addition, the plots were either heavy-trafficked (10–18 Mg axle load and ∼200 kPa inflation pressure) or light-trafficked (<6 Mg axle load and <100 kPa inflation pressure). The loosened treatments were referenced by non-loosened soil. Root growth of winter wheat was followed applying the minirhizotron technique. In one of the fields, these measurements were supplemented with core sampling for root length determination approximately at anthesis. Soil water content was followed in one of the fields using time domain reflectometry (TDR). Grain yield and nitrogen content in grain were determined. The adjoining study showed that the combination of heavy traffic and traditional ploughing caused strong recompaction of loosened soil, whereas the combination of light traffic and on-land ploughing produced moderate recompaction. For the loosened plots in one field, the strongly recompacted soil produced 7% lower yield than moderately recompacted soil, whereas no clear difference was found for the other field. No clear difference between the loosened treatments on root growth was observed. Surprisingly, the non-loosened soil performed similar or even better than the loosened and moderately compacted soil. The non-loosened soil facilitated higher root intensity at depth and produced similar yield and N-uptake. Our results suggest that mechanical subsoil loosening of humid sandy loams only is recommendable in case of very severe subsoil compaction. Natural alleviation of subsoil structure induced by changes in soil management may comprise a favourable alternative to mechanical subsoil loosening.     

Traffic and residue management systems: effects on fate of fertilizer N in corn

Soil compaction has been recognized as a problem limiting crop production, especially in the Southern Coastal Plain of the USA. Development of tillage and residue management systems is needed to alleviate soil compaction problems in these soils. Fertilizer nitrogen (N) management is also an important factor in these management systems. In 1988, a study was initiated with a wide-frame (6.3 m) vehicle to determine the interactive effects of traffic, deep tillage, and surface residue management on the fate of fertilizer N applied to corn (Zea mays L.) grown on a Norfork loamy sand (fine-loamy, siliceous, Thermic, Typic Kandiudults). Corn was planted into a winter cover crop of ‘Tibbee’ crimson clover (Trifolium incarnatum L.). Treatments included: traffic (conventional equipment or no traffic); deep tillage (no deep tillage, annual in-row subsoiling, or one-time only complete disruption); residue management (no surface tillage or disk and field cultivation). The one-time only complete disruption was accomplished by subsoiling at a depth of 43 cm on 25 cm centers in spring 1988. In 1990–1991, fertilizer applications were made as ¹⁵N-depleted NH₄NO₃ to microplots inside each treatment plot. The 1990 and 1991 data are reported here. In 1990 an extreme drought resulted in an average grain yield of 1.8 Mg grain ha⁻¹, whereas abundant rainfall in 1991 resulted in 9.4 Mg grain ha⁻¹. Deep tillage increased corn dry matter production in both years. In 1991, grain yields indicated that corn was susceptible to recompaction of soil owing to traffic when residues were incorporated with surface tillage. In the dry year, plant N uptake was increased 27% with deep tillage and decreased 10% with traffic. In the wet year, a surface tillage × deep tillage × traffic interaction was observed for total N uptake, fertilizer N uptake, and total fertilizer N recovery in the plant-soil system. When combined with traffic, plant N uptake was reduced with the highest intensity tillage treatment (135 kg N ha⁻¹) because of rootrestricting soil compaction, and with the lowest intensity tillage treatment (129 kg N ha⁻¹) because of increased N losses. In these soils, leaving residues on the soil surface can reduce the detrimental effect of traffic on corn production, but if no surface tillage is performed, deep tillage is needed.     

不同土壤耕作方式对东北风沙土区玉米田土壤质量及产量的影响

[目的]研究黑龙江省西部不同土壤耕作方式对玉米产量及土壤性状的影响,为该地区农业生产提供参考。[方法]比较常规耕作、旋耕、翻耕、深翻和超深翻耕作对玉米产量和土壤物理特性的影响。[结果]翻耕和超深翻耕作增加了土壤含水量和田间持水量,降低了耕层土壤渗透速率、土壤容重和土壤紧实度,但是增加犁底层土壤渗透速率、土壤容重和土壤紧实度。翻耕、深翻和超深翻处理耕层土壤三相结构距离(STPSD)和土壤结构指数(GSSI)较好;翻耕、深翻和超深翻处理显著降低犁底层土壤的GSSI,增加STPSD;旋耕处理没有显著影响犁底层土壤GSSI和STPSD。与常规耕作处理相比,翻耕和超深翻分别增加玉米产量7.6%和6.0%。翻耕比超深翻玉米产量高10.9%。深翻处理玉米产量为5.58t/hm2,比常规耕作减产8.1%。[结论]在不完全打破犁底层情况下,在黑龙江西部地区翻耕是比较理想的耕作方式。     

休闲期不同耕作方式对洛阳冬小麦农田土壤水分的影响

采用连续5a的田间定位试验资料，研究了洛阳地区休闲期4种不同耕作方式对冬小麦农田土壤水分变化、水分利用效率及作物产量的影响。结果表明：休闲期不同耕作方式对冬小麦播种前底墒具有明显的影响，与传统耕作方式相比，免耕和深松覆盖处理可以显著增加土壤含水率，具有良好的保墒作用；各处理以深松覆盖作物产量和水分利用效率最高，其次为免耕处理，深翻处理效果较差。因此，洛阳地区采用深松覆盖保护性耕作方式比较有利。     

Effects of subsoil compaction on yield and yield attributes of wheat in the sub-humid region of Pakistan

The prolonged use of vehicular traffic for farming creates subsoil compaction, which reduces crop yield and deteriorates the physical conditions of the soil. Field experiments were conducted during 2002–2003 and 2003–2004 in Pakistan to study subsoil compaction effects on soil bulk density, total porosity, yield and yield components of wheat. Soil compaction was artificially created at the start of the experiment using 7.0 t roller having length of 1.5 m and diameter of 1.22 m. Treatments consisted of T₁ = control (no compaction), T₂ = two passes of roller, T₃ = four passes of roller, T₄ = six passes of roller. The experiments were arranged in randomised complete block with four replications. Results indicated that subsoil compaction adversely affected the bulk density, total porosity of soil and root length during both the years. Soil compaction increased the bulk density (BD) from 1.37 for T₁ to 1.57, 1.61 and 1.72 Mg m⁻³ whereas decreased the total porosity from 47.3% for T₁ to 40.0, 37.4 and 34.5% for T₂, T₃ and T_4, respectively. Similarly grain yield decreased from 4141.7 for T₁ to 3912.8, 3364.5 and 3010.3 kg ha⁻¹ for T₂, T₃ and T_4, respectively. The deteriorating effect of compaction depended upon the degree of compaction. Subsoil compaction adversely affected the yield and yield attributes of wheat during both years of experiments. The subsoil compaction adversely affected soil physical conditions, which substantially decreased the yield of wheat. Therefore, appropriate measures of periodic chiselling, controlled traffic, conservation tillage, and incorporating of crops with deep tap root system in rotation cycle is necessary to minimize the risks of subsoil compaction.     

Tillage systems and soil compaction in Africa

Introduction of mechanized agriculture induces profound changes in soil characteristics. Soil compaction originating from mechanical land clearing, mechanized cultivation, and continuous cropping is aggravated by crusting and hard-setting phenomena of soils, and widespread occurrence of naturally compacted upland soils and subsoil gravel horizons. Natural and anthropogenically induced soil compaction has detrimental effects on growth and yields of a wide range of crops. Furthermore, compaction can persist for a long time if no adequate measures are taken to minimize or alleviate it.

In humid and subhumid regions of Africa, the no-tillage system with crop residue mulch is an important method of controlling soil compaction, followed in significance, by biological and mechanical loosening where motorized land clearing is the causative agent. Biological methods involve cover crops and alley cropping or agroforestry. Where new land areas need to be opened up, land clearing should be done by the slash-and-burn method, so that most of the nutrients in the vegetation are returned to the soil. Where mechanical land clearing is inevitable, forest removal should be done by the use of shear blade, whereby most of the roots and stumps are left in the ground intact, and the forest litter is not removed.

In semi-arid and arid regions of Africa, alleviation of soil compaction can be done by two methods. One method is to use the controlled traffic tillage system. Controlled traffic results in both a loose-rooting zone and a firmed traffic lane, thereby providing good plant growth and trafficability for timely field operations. The second method is to use mechanical loosening techniques, i.e. ploughing by animal traction or tractor power, chiseling, deep ripping, subsoiling, and tied-ride system. The effect of mechanical loosening, however, tends to be of short duration if the ensuing field traffic is not controlled.