Tillage, mulch and irrigation effects on corn (Zea mays L.) in relation to evaporative demand

The effects of deep tillage, straw mulching, and irrigation on corn (Zea mays L.) yield on a loamy sand (mixed, hyperthermic, Typic Ustipsamment) were studied for early (high evaporativity) and normally sown (relatively low evaporativity) crop for 3 years in a semi-arid sub-tropical monsoon region at Punjab Agricultural University, Ludhiana, India. Treatments included all combinations of two tillage systems (conventional tillage — harrowing the soil to a 10-cm depth; deep tillage — chiselling 40 cm deep, 35–40 cm apart), two irrigation regimes (75 mm irrigation when net open pan evaporation accumulated to 75 mm or 50 mm), and two straw mulch rates (0 and 6 Mg ha⁻¹).

Deep tillage significantly reduced soil strength (cone index) and caused deeper and denser rooting than conventional tillage, more so in the dry season and with the infrequent irrigation regime than in the wet season and frequent irrigation regime. Mulch also improved rooting by influencing the hydrothermal regime of the soil. Better rooting with deep tillage and/or mulch helped the crop to extract stored soil water more efficiently, which was reflected in a favourable plant water status (indicated by canopy temperature). Averaged across years, irrigation, and mulch, deep tillage increased grain yield by 1.6 Mg ha⁻¹ for the early season and 0.5 Mg ha⁻¹ for the normal season crop over the yield of 2.0 Mg ha⁻¹ achieved with conventional tillage regardless of season. Yield increase with mulching was also greater for the early season crop. Crop response to deep tillage and mulching was generally linked to the interplay between water supply (rain + irrigation) and demand (seasonal evaporativity) during the growing season. Increasing irrigation frequency increased crop yield when evaporativity exceeded rainfall early in the growing season. The results show that higher corn yields on coarse-textured soils in these regions may be achieved by advancing the seeding time and by using a proper combination of deep tillage, mulch, and irrigation.     

Soil carbon and nitrogen accumulation with long-term no-till versus moldboard plowing overestimated with tilled-zone sampling depths

Numerous investigators of tillage system impacts on soil organic carbon (OC) or total nitrogen (N) have limited their soil sampling to depths either at or just below the deepest tillage treatment in their experiments. This has resulted in an over-emphasis on OC and N changes in the near-surface zones and limited knowledge of crop and tillage system impacts below the maximum depth of soil disturbance by tillage implements. The objective of this study was to assess impacts of long-term (28 years) tillage and crop rotation on OC and N content and depth distribution together with bulk density and pH on a dark-colored Chalmers silty clay loam in Indiana. Soil samples were taken to 1 m depth in six depth increments from moldboard plow and no-till treatments in continuous corn and soybean–corn rotation. Rotation systems had little impact on the measured soil properties; OC content under continuous corn was not superior to the soybean–corn rotation in either no-till or moldboard plow systems. The increase in OC (on a mass per unit area basis) with no-till relative to moldboard plow averaged 23 t ha⁻¹ to a constant 30 cm sampling depth, but only 10 t ha⁻¹ to a constant 1.0 m sampling depth. Similarly, the increase in N with no-till was 1.9 t ha⁻¹ to a constant 30 cm sampling depth, but only 1.4 t ha⁻¹ to a constant 1.0 m sampling depth. Tillage treatments also had significant effects on soil bulk density and pH. Distribution of OC and N with soil depth differed dramatically under the different tillage systems. While no-till clearly resulted in more OC and N accumulation in the surface 15 cm than moldboard plow, the relative no-till advantage declined sharply with depth. Indeed, moldboard plowing resulted in substantially more OC and N, relative to no-till, in the 30–50 cm depth interval despite moldboard plowing consistently to less than a 25 cm depth. Our results suggest that conclusions about OC or N gains under long-term no-till are highly dependent on sampling depth and, therefore, tillage comparisons should be based on samples taken well beyond the deepest tillage depth.     

Assessment of tillage erosion rates on steepland Oxisols in the humid tropics using granite rocks

Soil translocation by tillage may be an important factor in land degradation in the humid tropics. The objective of this study was to evaluate tillage-induced soil translocation on an Oxisol with 25% and 36% slopes in Claveria, Philippines for three tillage systems: contour moldboard plowing (CMP), moldboard plowing up and downslope (UMP), and contour ridge tillage (CRT). Small rocks 3–4 cm in “diameter” were used as soil movement detection units (SMDU). The SMDUs were placed at 10 cm intervals in a narrow 5-cm-deep trench near the upper boundary of each plot, the position of each rock recorded, and the trench backfilled. Five tillage operations used to produce one corn crop were performed during a one month period: two moldboard plowing operations for land preparation (except for CRT), one moldboard plowing for corn planting, and two inter-culture (inter-row cultivation) operations. After these operations, over 95% of the SMDU were recovered manually and their exact locations recorded. Mean annual soil flux for the 25% slope was 365 and 306 kg m⁻¹ y⁻¹ for UMP and CMP, respectively. For the 36% slope, comparable values were 481 and 478 kg m⁻¹ y⁻¹. Estimated tillage erosion rates for the 25% slope were 456 and 382 Mg ha⁻¹ y⁻¹ for UMP and CMP, respectively, and increased to 601 and 598 Mg ha⁻¹ y⁻¹, respectively, for the 36% slope. The mean displacement distance, mean annual soil flux, and mean annual tillage-induced soil loss for both slopes were reduced by approximately 70% using CRT compared to CMP and UMP.     

Alternative tillage and crop residue management in wheat after rice in sandy loam soils of Indo-Gangetic plains

A 3-year field study was conducted to evaluate the effect of three tillage practices (conventional, zero and reduced/strip) with two nitrogen levels (120 and 150 kg N ha⁻¹) applied in primary strips and three crop residue management practices (removal, burning and incorporation) in secondary strips in wheat after rice. Reduced tillage resulted in significantly higher overall mean wheat yield (5.10 Mg ha⁻¹) compared to conventional (4.60 Mg ha⁻¹) and zero tillage (4.75 Mg ha⁻¹). Residue incorporation resulted in highest mean yield (5.86 Mg ha⁻¹) during third year. Maximum mean yield (6.1 Mg ha⁻¹) was obtained in reduced tillage followed by conventional tillage (5.8 Mg ha⁻¹) under residue incorporation in third year. The weed dry weight recorded at 30 days after sowing was highest (0.3 Mg ha⁻¹) under zero tillage and lowest under conventional tillage (0.16 Mg ha⁻¹). Among crop residue management practices, the highest dry weight of weeds (0.22 Mg ha⁻¹) was recorded under residue incorporation. The highest infiltration rate (1.50 cm h⁻¹) was recorded in residue incorporation followed by residue burning (1.44 cm h⁻¹) whereas; the lowest (0.75 cm h⁻¹) in zero tillage. Soil bulk density was the highest (1.69 Mg m⁻³) under zero tillage and the lowest in residue incorporation (1.59 Mg m⁻³). There were no changes in soil available P and K after each crop sequence in relation to tillage practices during first 2 years. Higher organic carbon (5.1–5.4 g kg⁻¹) was measured under zero tillage compared to other treatments. Residue incorporation increased soil organic carbon and available P while higher available K was monitored in burning treatment during the third year. These results suggest that reduced tillage and in situ incorporation of crop residues at 5 Mg ha⁻¹ along with 150 kg N ha⁻¹ were optimum to achieve higher yield of wheat after rice in sandy loam soils of Indo-Gangetic plains of India.     

The impact of tillage and residual nitrogen on wheat

Wheat (Triticum aestivum L.) yield and quality is influenced by management of the previous crop but is highly dependent on current year management. The objective of this study was to evaluate the response of winter wheat seeded in two tillage systems [conventional tillage (CT) and no-till (NT)] to four N rates applied to a previous cotton (Gossypium hirsutum L.) crop (0, 67, 134, and 202 kg ha⁻¹). The experiment with wheat was conducted on a Dothan sandy loam (fine, loamy siliceous, thermic Plinthic Kandiudults) at the University of Florida North Florida Research and Education Center near Quincy, FL from 1995 to 1997. For most plant characteristics, there was a tillage x N x year interaction. Greater plant emergence (79.4 vs. 65.3%) and grain N (23.5 vs. 21.5 g kg⁻¹), and lower grain moisture (139 vs. 142 g kg⁻¹) were obtained under NT than CT, respectively, in one out of two years. Nitrogen applied to a previous cotton crop increased wheat grain yields, plant height and seed number under NT in 1995–1996 and CT in 1996–1997, head density under NT in both years, harvest index under CT in 1996–1997, and grain N concentration in 1995–1996 and 1996–1997 due to residual plant and soil N. With every 1 kg N applied to a previous cotton crop, wheat grain yields increased by 5.38 kg ha⁻¹ under NT, whereas grain yield under CT was not influenced by N application to cotton in 1995–1996. In 1996–1997, grain yields increased by 4.96 and 4.23 kg ha⁻¹ for wheat grown in NT and CT, respectively. Generally, wheat seeded in NT following cotton did not decrease stand or yields compared to CT and wheat grain yields and grain N content increased with N fertilization of the previous crop. However, we would have to apply about 134 kg N ha⁻¹ to a previous cotton crop to maximize wheat production under NT and CT.     

Long-term effects of tillage systems and rotations on soil structural stability and organic carbon stratification in semiarid central Spain

Under semiarid Mediterranean climatic conditions, soils typically have low organic matter content and weak structure resulting in low infiltration rates. Aggregate stability is a quality indicator directly related to soil organic matter, which can be redistributed within soil by tillage. Long-term effects (1983–1996) of tillage systems on water stability of pre-wetted and air dried aggregates, soil organic carbon (SOC) stratification and crop production were studied in a Vertic Luvisol with a loam texture. Tillage treatments included conventional tillage (CT), minimum tillage (MT) and zero tillage (ZT) under winter wheat (Triticum aestivum L.) and vetch (Vicia sativa L.) rotation (W–V), and under continuous monoculture of winter wheat or winter barley (Hordeum vulgare L.) (CM). Aggregate stability of soil at a depth of 0–5 cm was much greater when 1–2 mm aggregates were vacuum wetted prior to sieving (83%) than when slaked (6%). However, slaking resulted in tillage effects that were consistent with changes in SOC. Aggregate stability of slaked aggregates was greater under ZT than under CT or MT in both crop rotations (i.e., 11% vs. 3%, respectively).

SOC under ZT tended to accumulate in the surface soil layer (0–5 and 5–10 cm) at the expense of deeper ones. At depths of 10–20 and 20–30 cm no differences in SOC were encountered among tillage systems, but CT exhibited the highest concentration at 30–40 cm depth. Nevertheless, when comparisons were made on mass basis (Mg ha⁻¹), significant differences in stocked SOC were observed at depths of 0–10 and 0–20 cm, where ZT had the highest SOC content in both rotations. The stock of SOC to a depth of 40 cm, averaged across crop rotations, was greater under ZT (43 Mg ha⁻¹) than under CT (41 Mg ha⁻¹) and MT (40 Mg ha⁻¹) although these figures were not significantly different. Likewise, no significant differences were encountered in the stock of SOC to a depth of 40 cm among crop rotations (i.e., 42 Mg ha⁻¹ for W–V vs. 40 Mg ha⁻¹ for CM).

Crop production with wheat–vetch and continuous cereal showed no differences among tillage systems. Yields were strongly limited by the environmental conditions, particularly the amount of rainfall received in the crop growth season and its distribution. Similar yield and improved soil properties under ZT suggests that it is a more sustainable system for the semiarid Mediterranean region of Spain.     

Effects of farmyard manure and tillage systems on soil physical properties and corn yield in central Iran

Tillage management and manure application are among the important factors affecting soil physical properties and crop yield. A 2-year field experiment was conducted on a silty clay loam soil (fine-loamy, mixed, thermic Typic Haplargids). Effects of two tillage systems (moldboard plowing as conventional tillage (T₁) and disk harrowing as reduced tillage (T₂)) at three farmyard manure rates (zero (M₁), 30 (M₂), 60 (M₃) Mg ha⁻¹) were studied on the soil physical properties and corn (Zea mays L.) yield. The experiment was carried out in split block design with three replications. Organic matter (OM) content, bulk density (BD), saturated hydraulic conductivity (K_S), aggregate mean weight diameter (MWD) and dry biomass yield (DBY) were measured after harvesting in the second year. Manure application increased OM on both the row and inter-row tracks significantly. Manure application rate of 60 Mg ha⁻¹ increased MWD (0.33, 0.40 and 0.75 mm for M₁, M₂ and M₃, respectively) at the 0–5 cm soil layer, but the effect was not significant below 5 cm depth. Adding manure significantly decreased soil BD on the row tracks (1.39, 1.22 and 1.17 Mg m⁻³ for M₁, M₂ and M₃ treatments, respectively), but did not have any significant effect on the inter-row tracks. Hydraulic conductivity was improved by manure applications both on the row and inter-row positions. Manure treatments M₂ and M₃ increased DBY compared to the M₁ treatment. Although moldboard plowing increased the depth of root penetration significantly (43 cm for T₁ and 30 cm for T₂), the effect of tillage systems on yield and soil physical properties was not significant.     

Land configuration and soil nutrient management options for sustainable crop production on Alfisols and Vertisols of southern peninsular India

Land configuration in combination with nutrient management has the potential to improve the productivity of Alfisols and Vertisols in the semi-arid tropics. A four year (1989–1990 and 1992–1993) field experiment was conducted at Coimbatore, India on Alfisols (Chromic Cambisol) to compare the effect of land configuration and nutrient management practices on yield of rainfed sorghum (Sorghum bicolor (L.) Moench). The land configuration treatments were flat bed (FB, the traditional practice), open ridging (OR, ridges, 45 cm apart and 30 cm high) and tied ridging (TR, same as OR plus ridges were tied randomly). The manure and fertilisers were farm yard manure (FYM, livestock excreta plus litter at 5 Mg ha⁻¹) and coir dust (CD, by-product after the extraction of coir from the coconut (Cocos nucifera L.) husk at 12.5 Mg ha⁻¹) in combination with nitrogen (N) and phosphorus (P) fertiliser levels. Tied ridges stored 14% more soil water and produced 14% and 11% more grain and straw yields of sorghum, respectively, than did flat bed. However, crop yield in TR was comparable with OR. Application of CD at 12.5 Mg ha⁻¹ combined with 40 kg N ha⁻¹ and 9 kg P ha⁻¹ was beneficial for more soil water storage and increased yield of sorghum by 7% over FYM at 5 Mg ha⁻¹ + 40 kg N ha⁻¹ and 9 kg P ha⁻¹. In Vertisols (Vertic Cambisols), experiments were conducted for two years (1991–1992 and 1992–1993) to evaluate land configuration practices. The treatments were broad bed furrow (BBF, 120 cm wide bed with 30 cm wide and 15 cm deep furrows on both sides), compartmental bunding (CB, bunds of 15 cm height formed in all the four sides to form a check basin of 6 m × 5 m size), ridging (RD, ridges were formed for each and every row of the crop manually at four weeks after sowing) and FB under sorghum + pigeonpea (Cajanus cajan (L.) Millsp) and pearl millet (Pennisetum glacum (L.) Stuntz) + cowpea (Vigna unguiculata (L.) Walp) intercropping separately. Compartmental bunding stored 22% more soil moisture and increased the yield of sorghum + pigeonpea intercropping than did FB in a low rainfall year. In a high rainfall year, BBF produced 34% and 33% more grain yield of sorghum and pearl millet base crops, respectively, over FB. However, BBF and CB were comparable. Pigeonpea intercrop under sorghum followed the same trend as its base crop, whereas, yield of cowpea differed compared to the pearl millet base crop. Tied ridging and application of manures (CD or FYM) in combination with inorganic N and P fertiliser can increase the soil water storage and yield of crops compared to traditional flat bed cultivation in rainfed Alfisol and related soils of semi-arid tropics. Similarly BBF and CB land configuration practices could be adopted on Vertisols for better water conservation to increase the soil fertility and productivity of intercropping systems.     

Wheat yield and weed population as influenced by three tillage systems on a clay soil in temperate continental climate

The potential benefits of conservation tillage practices depend mainly on the soil and climatic conditions of the site. A study was conducted to determine the effects of three tillage systems (conventional, CT; reduced, RT; zero, ZT) on spring wheat (Triticum aestivum L.) and weed growth on a clay soil in temperate continental climate, northern Alberta (55°43′N, 118°41′W), Canada. A medium duty cultivator with 25 cm sweeps spaced 22 cm apart and a working depth of 8–10 cm was used for tillage in the CT (once in fall and twice in spring) and RT (once in spring) plots. The ZT plots received a harrowing to spread straw and a preseeding application of Roundup (glyphosate) to control weeds. Experimental design was a randomized complete block with four replications and the tillage systems were fixed in space for the 1989, 1990 and 1991 seasons. The RT treatment resulted in higher yields than the CT or ZT treatments. However, the differences were not always significant. The ZT treatment produced higher yields than CT in 1989 and 1991, whereas its yields were lower than CT in 1990. The 3 year means of total dry matter (TDM) were 3899 kg ha⁻¹, 3640 kg ha⁻¹ and 3331 kg ha⁻¹ for the RT, ZT and CT treatments, respectively. The corresponding grain yields were 1728 kg ha⁻¹, 1573 kg ha⁻¹ and 1530 kg ha⁻¹. The concentration of total N in plants and grains of wheat, amounts of extractable NO₃-N, NH₄-N and P in soil and soil moisture and bulk density were not significantly affected by tillage. The mean weight diameter of aggregates in surface soil was significantly greater under ZT than under the other systems. Wild buckwheat (Polygonum convolvulus L.) was more abundant under CT, but common groundsel (Senecio vulgaris L.), dandelion (Taraxacum officinale Weber), hemp nettle (Galeopsis tetrahit L.), field horsetail (Equisetum arvense L.) and smartweed (Polygonum scabrum Moench) tended to have higher populations under the ZT system. The populations of foxtail barley (Hordeum jubatum L.) wild rose (Rosa sp.), stinkweed (Thlaspi arvense L.) and wild oats (Avena fatua L.) showed no consistent effect of tillage. Tillage or preseeding application of glyphosate did not provide an effective control of all weed species. The spring tillage of the RT system improved crop yields and weed control relative to ZT, whereas the fall tillage of the CT system (in addition to spring tillage) reduced crop yields and had no significant effect on weed population relative to RT. The overall results showed that tillage intensity could be reduced to the level of RT without any adverse influence on crop yields, soil properties or weed populations. The RT system is also economical and environmentally desirable owing to lower tillage and herbicide requirements.     

Effect of fall tillage following soybeans on organic matter losses in snowmelt

In a corn–soybean rotation, maintaining crop residue on the soil surface is a challenge following soybeans. Often farmers are encouraged not to till the soil following a soybean crop in order to maximize the amount of residue at the soil surface. In this study we evaluated the effect of this practice compared to fall moldboard plowing on snowmelt runoff and losses of total solids (TS) and organic carbon (using oxygen demand in runoff as a surrogate). A paired watershed approach was used to evaluate the effect of these management practices. Individual hydrographs were compared and contaminant losses in runoff calculated. Results show that snowmelt runoff and the associated losses of total solids, chemical oxygen demand (COD), and biochemical oxygen demand (BOD) were less with fall moldboard plowing compared to no fall tillage following soybean (0.22 cm, 1.9 kg ha⁻¹, 0.81 kg ha⁻¹, 74 g ha⁻¹, reduction in median value per melt cycle, respectively). In areas where snowmelt runoff is an important component of annual runoff, some tillage in the fall would be preferable to no-tillage in order to reduce snowmelt runoff losses.     

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.     

Crop yield and rooting as affected by fragipan depth in loess soils in the southeast USA

The combination of soil erosion and restrictive subsurface features can adversely influence root growth and crop productivity. The effects of depth to a restrictive layer on yield and root development were determined for soybean (Glycine max (L.) Merr.) and corn (Zea mays L.) grown on Grenada silt loam (Oxyaquic Fraglossudalfs) in West Tennessee. Seven sites were selected in a cropped field where depth to the fragipan ranged from 0 to 107 cm below the soil surface. Across-the-site comparisons involving bulk density, soil color, exchangeable acidity and organic carbon indicated that at the sites that were shallow to the fragipan, profile modification had occurred as a result of soil erosion. Soils were sampled to 120 cm depths in 15 cm increments within the row and 25 and 51 cm from the row. Roots were extracted and total root lengths were determined by the line-intercept method. Greater total root lengths were observed with increasing depth to the fragipan. Crop yields decreased significantly as depth to the fragipan decreased. Soybean yields ranged from 0.5 Mg ha⁻¹ on the 0 cm depth site to 2.8 Mg ha⁻¹ on the 107 cm depth site, whereas corn yields ranged from 5.5 Mg ha⁻¹ on the 0 cm depth site to 10.0 Mg ha⁻¹ on the 107 cm depth site. Erosion was not measured directly; however, the reduced soil depth due to erosion caused an easily demonstrated reduction in root growth and yield in both corn and soybean.     

Conservation tillage for maize production in the U.S. southeastern coastal plain

Eight conservation tillage methods were evaluated for maize (Zea mays L.) production and were related to water conserved, soil strength, plant stand, plant nutrient status, and methods of managing crop residues on Norfolk loamy sands (Typic Paleudults) in the U.S. southeastern coastal plain. This study summarizes 10 site-years of data collected from 1978 through 1982.

Seasonal soil-water balance and crop residue management largely determined the success of maize production under conservation tillage. Autumn subsoiling increased winter forage and maize production under both conventional and conservation tillage. When early-season rainfall was limited, water extraction by a winter cover crop or winter weeds often reduced early-season growth and yield of maize under conservation tillage. For adequate stands, increased seeding rates and effective weed-, rodent-, bird- and insect-control were all necessary.

Under adequate water regimes, conventional tillage resulted in greater yields at low levels of nitrogen, but maximum yields occurred regardless of tillage system, when 200 kg ha⁻¹ were applied. Conventionally-tilled maize generally resulted in higher yields than conservation tillage production. The only significant increase for conservation tillage occurred under non-irrigated conditions in 1981 during severe drought. The interactive soil and climatic factors which have impact on conservation tillage in this physiographic region were identified.     

氮肥施用对冬小麦籽粒产量和氮素表观损失的影响

Excessive nitrogen （N） fertilizer application to winter wheat is a common problem on the North China Plain. To determine the optimum fertilizer N rate for winter wheat production while minimizing N losses, field experiments were conducted for two growing seasons at eight sites, in Huimin County, Shandong Province, from 2001 to 2003. The optimum N rate for maximum grain yield was inversely related to the initial soil mineral N content （Nmin） in the top 90 cm of the soil profile before sowing. There was no yield response to the applied N at the three sites with high initial soil mineral N levels （average 212 kg N ha^-1）. The average optimum N rate was 96 kg N ha^-1 for the five sites with low initial soil Nmin （average 155 kg N ha^-1） before sowing. Residual nitrate N in the top 90 cm of the soil profile after harvest increased with increasing fertilizer N application rate. The apparent N losses during the wheat-growing season also increased with increasing N application rate. The average apparent N losses with the optimum N rates were less than 15 kg N ha^-1, whereas the farmers＇ conventional N application rate resulted in losses of more than 100 kg N ha^-1. Therefore, optimizing N use for winter wheat considerably reduced N losses to the environment without compromising crop yields.     

Tillage, crop residue and N fertilizer effects on crop yield, nutrient uptake, soil quality and nitrous oxide gas emissions in a second 4-yr rotation cycle

An 8-yr (1998–2005) field experiment was conducted on a Gray Luvisol (Boralf) soil near Star City, Saskatchewan, Canada, to determine the effects of tillage (no-tillage – NT and conventional tillage – CT), straw management (straw retained – R and straw not retained – NR) and N fertilizer (0, 40, 80 and 120 kg N ha⁻¹, except no N to pea (Pisum sativum L.) phase of the rotation) on seed and straw yield, mass of N and C in crop, organic C and N, inorganic N and aggregation in soil, and nitrous oxide (N₂O) emissions for a second 4-yr rotation cycle (2002–2005). The plots were seeded to barley (Hordeum vulgare L.) in 2002, pea in 2003, wheat (Triticum aestivum L.) in 2004 and canola (Brassica napus L.) in 2005. Seed, straw and chaff yield, root mass, and mass of N and C in crop increased with increasing N rate for barley in 2002, wheat in 2004 and canola in 2005. No-till produced greater seed (by 51%), straw (23%) and chaff (13%) yield of barley than CT in 2002, but seed yield for wheat in 2004, and seed and straw yield for canola in 2005 were greater under CT than NT. Straw retention increased seed (by 62%), straw (by 43%) and chaff (by 12%) yield, and root mass (by 11%) compared to straw removal for barley in 2002, wheat in 2004, and seed and straw yield for pea in 2003. No-till resulted in greater mass of N in seed, and mass of C in seed, straw, chaff and root than CT for barley in 2002, but mass of N and C were greater under CT than NT for wheat in 2004 and for canola in 2005 in many cases. Straw retention had greater mass of N and C in seed, straw, chaff and root in most cases compared to straw removal for barley in 2002, pea in 2003 and wheat in 2004. Soil moisture content in spring was higher under NT than CT and with R than NR in the 0–15 cm depth, with the highest moisture content in the NT + R treatment in many cases. After eight crop seasons, tillage and straw management had no effect on total organic C (TOC) and N (TON) in the 0–15 cm soil, but light fraction organic C (LFOC) and N (LFON), respectively, were greater by 1.275 Mg C ha⁻¹ and 0.031 Mg N ha⁻¹ with R than NR, and also greater by 0.563 Mg C ha⁻¹ and 0.044 Mg N ha⁻¹ under NT than CT. There was no effect of tillage, straw and N fertilization on the NH₄-N in soil in most cases, but R treatment had higher NO₃-N concentration in the 0–15 cm soil than NR. The NO₃-N concentration in the 0–15, 15–30 and 30–60 cm soil layers increased (though small) with increasing N rate. The R treatment had 6.7% lower proportion of fine (<0.83 mm diameter) and 8.6% greater proportion of large (>38.0 mm) dry aggregates, and 4.5 mm larger mean weight diameter (MWD) compared to NR treatment. This suggests a lower potential for soil erosion when crop residues are retained. There was no beneficial effect of elimination of tillage on soil aggregation. The amount of N lost as N₂O was higher from N-fertilized (580 g N ha⁻¹) than from zero-N (155 g N ha⁻¹) plots, and also higher in CT (398 g N ha⁻¹) than NT (340 g N ha⁻¹) in some cases. In conclusion, retaining crop residues along with no-tillage improved some soil properties and may also be better for the environment and the sustainability of high crop production. Nitrogen fertilization improved crop production and some soil quality attributes, but also increased the potential for NO₃-N leaching and N₂O-N emissions, especially when applied in excess of crop requirements.     

Response of conservation tillage sorghum to growing season precipitation

In earlier crop rotation studies in which grain sorghum (Sorghum bicolor (L.) Moench) followed winter wheat (Triticum aestivum L.) after a 10- to 11-month fallow period during which the wheat residues were managed by different tillage methods, sorghum yields increased in response to increases in soil water content at sorghum planting time. Similar results were obtained when residues were placed on the surface at the start of the fallow period. The soil water contents at planting time were positively correlated with amounts of wheat residue maintained on the soil surface during fallow.

The studies also suggested that sorghum responded positively to growing season precipitation when increasing of residue remained on the soil during the growing season. The objective of this study was to evaluate this response to growing season precipitation through statistical analyses of data from five earlier tillage and residue placement studies. Regression analyses of data from the studies showed that sorghum grain yields increased with increasing amounts of surface residues at planting time. Differences in response of grain yield to precipitation were greatest in the vegetative period. For the period, grain yields increased 0.014 Mg ha⁻¹ per mm of precipitation when residue amounts ranged from 0 to 0.4 Mg ha⁻¹ per mm of precipitation when residue amounts ranged from 0 to 0.4 Mg ha⁻¹, and 0.027 Mg ha⁻¹ per mm of precipitation when residue amounts were 3.2 Mg ha⁻¹.

Differences in response to rainfall in the heading and grain filling period were lower or negligible. High responses for the vegetative period were attributed to the residues which increased infiltration and reduced evaporation before canopy development. Lower responses during heading and lack of responses during grain filling were attributed to: (1) canopy development, which minimized the effect of residues on imfiltration and evaporation; (2) soil cracking, which resulted in similar infiltration with all treatments; and (3) residue decomposition, which minimized differences among residue amounts on the soil with different treatments.     

Soil and residue management effects on arable cropping conditions and nitrous oxide fluxes under controlled traffic in Scotland 1. Soil and crop responses

Soil compaction can affect crop growth and greenhouse gas emission and information is required of how both these aspects are affected by compaction intensity and weather. In this paper we describe treatments of compaction intensity and their effects on soil physical conditions and crop growth in loam to sandy loam cambisol soils. Soil conditions and crop performance were measured over three seasons in a field experiment on soil compacted by wheels on freshly ploughed seedbeds. Ploughing buried the chopped residues of the previous crop. After ploughing, traffic was controlled such that the experimental plots received wheel traffic only as treatments. The overall objective was to discover how the intensity and distribution of soil compaction just before sowing influenced crop performance, soil conditions and emissions of nitrous oxide. Compaction treatments were zero, light compaction by roller (up to 1 Mg m⁻¹) and heavy compaction by loaded tractor, (up to 4.2 Mg). The experiment was located at Boghall, near Edinburgh (860 mm average annual rainfall) for the first two seasons under spring and winter barley (Hordeum vulgare L.) and in a drier area at North Berwick (610 mm average annual rainfall) for the third season under winter oil-seed rape (Brassica napus L.). Heavy compaction in dry soil conditions had little effect on crop growth. However, in wet conditions heavy compaction reduced air porosity, air permeability and gas diffusivity, increased cone resistance and limited winter barley growth and grain yield. Heavy compaction in wet conditions reduced winter barley yields to 7.1 Mg ha⁻¹, in comparison to 8.8 Mg ha⁻¹ in the zero compaction treatment. The compaction status of the top 15 cm of soil seemed to be particularly important. Loosening of the top 10 cm of soil immediately after heavy compaction restored soil conditions for crop growth. However, zero seed bed compaction gave patchy and uneven crop emergence in dry conditions. Both zero and light compaction to a target depth of 10 cm gave similar crop productivity. Maintenance of a correct compaction level near the soil surface is particularly important for establishment and overwintering of barley and oil seed rape.     

Influence of long-term tillage, straw and N fertilizer on barley yield, plant-N uptake and soil-N balance

Long-term influence of N fertilizer, tillage and straw on crop production and soil properties are not well known in central Alberta. Field experiments were established in autumn 1979, on a Black Chernozemic soil and on a Gray Luvisolic soil in north-central Alberta to determine the long-term effect of tillage, straw and N fertilizer on yield and N uptake of barley (Hordeum vulgare L.). Fertilizer N was applied annually at 56 kg ha⁻¹. The 11 year averages of barley yields and N uptake under zero tillage were lower than under conventional tillage. Retention rather than removal of straw tended to reduce barley yield for the initial 6 years and 2 year at Site 1 and Site 2, respectively. A simple mathematical model of average annual plant N uptake and grain yield could account for most of the variation in the data observed at both sites (R² = 0.907; P < 0.01). Final values of soil N, calculated using a mass balance approach, agree closely with values measured at the end of the eleventh year. Conventional tillage and zero tillage, with addition of fertilizer N and retention of straw, were the only treatments with apparent but small net addition of N to soil at Site 1 (40 kg ha⁻¹ and 117 kg ha⁻¹, respectively). At Site 2, only the zero tillage treatment with addition of fertilizer and retention of straw gained soil N (29 kg ha⁻¹). In conclusion, soil ecosystems functioning in subhumid environments with slight to moderate heat limitations such as those in central Alberta can adapt, within a few years, to zero tillage practices with full retention of straw.     

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.     

Effect of tillage and field condition on soil physical properties, cane and sugar yields in Vertisols of Kenana Sugar Estate, Sudan

An experiment was conducted to study the effect of heavy disc harrowing in combination with chisel ploughing to depths of 10, 20, and 30 cm, on soil physical properties, cane yield, and sugar yield. The experiment was executed in two non-fallow, two semi-fallow and one fallow field conditions, in Kenana Sugar Estate, Sudan.

Results showed that the final surfaces for all tillage treatments were clean and smooth. Percent residue cover ranged from 4.2 to 5.4. After seedbed preparation percent clods greater than 1 cm in diameter ranged from 31.1 to 35.8, while gravimetric moisture content in the tillage zone ranged from 29.9 to 30.5. No significant differences were observed between treatments in residue cover, clod size and moisture content.

Soil penetration resistance in the five sites measured after the last irrigation showed no significant differences. Cone index ranged from 802 to 934 kPa. Bulk density measurements also showed no significant differences between tillage treatments.

Yield data showed that chisel ploughing to depths of 20 and 30 cm before disc harrowing, significantly increased cane and sugar yields than conventional tillage at Kenana. The highest field productivity (105.27 Mg ha⁻¹) was obtained with the combined disc harrowing and 20 cm chisel ploughing. Yield of cane per hectare under this method was 8.38 Mg ha⁻¹ higher than that under the conventional method. Sugar yield per hectare increased by 1 metric ton, which was 8.6% higher than that of the conventional method.

The relation between tillage depth (x) and cane yield (Y), in tons of cane per hectare, for average Kenana field condition could be expressed by the third-order polynomial:

Y=158.141−7.725x+0.293x²−0.003x³

The fallow, semi-fallow and non-fallow sites were not significantly different in cane yield.

All tillage methods studied were more intensive than adequate levels for soil conservation practices found in the reviewed literature; it is suggested to omit the re-harrowing operation of Kenana conventional tillage.