Stubble Mulch Research Articles

Fallow soil evaporation and water storage as affected by stubble in sub-humid (Argentina) and semi-arid (Australia) environments

The effect of stubble mulch on soil water storage during fallow is highly variable. In environments with low rainfall and coarse-textured soil, contribution of stubble to gains in water storage is often smaller than in wetter environments with heavier soil. While this pattern is recognised, the effect of rainfall, evaporative demand and soil remains confounded. This paper investigates the effect of stubble on soil evaporation and soil water storage during fallow in contrasting environments at Balcarce (Argentina) and Walpeup (Australia). Field and modelling experiments were combined to quantify stubble effects on soil evaporation and water storage for loam (Balcarce) and sandy loam soils (Walpeup). Simulations with the CropSyst model and long-term weather records included reference evapotranspiration from 185 to 240 mm, and rainfall from 108 to 471 mm for the winter fallow period at Balcarce, and reference evapotranspiration from 595 to 686 mm, and rainfall from 46 to 305 mm for the summer fallow period at Walpeup. The effect of size of rainfall events, quantified with power laws, was emphasised. Amount of rainfall during fallow accounted for most of the variation in soil evaporation, irrespective of reference evapotranspiration and soil type. For bare soil, evaporation was lower than expected in years with higher frequency of large rainfall events, but no relationship between soil evaporation and size of rainfall event was found for soil with stubble. The response of soil evaporation and soil water storage to rainfall comprised three phases. In the first phase, all the rainfall was evaporated irrespective of soil cover; hence, there were no benefits of stubble in terms of water storage. In the second phase, stubble reduced soil evaporation with respect to bare soil, with a subsequent gain in soil water. In the third phase, the benefit of stubble declines up to the point in which rainfall is high enough to meet evaporative and storage demands irrespectively of soil cover. It is proposed that gains in stored soil water due to stubble could be estimated as a function of rainfall using a non-linear model with locally adjusted parameters.

Nutrient Leaching in Oxisols Under Native and Managed Vegetation in Brazil

Brazilian savanna Oxisols are prone to nutrient leaching because of low nutrient retention and high water conductivity. We determined downward and upward fluxes of Ca, Mg, K, NH4–N, and NO3–N at 0.3‐, 0.8‐, and 2.0‐m soil depths under native savanna vegetation (Cerrado), Pinus caribaea Morelet plantation, managed productive Brachiaria decumbens Stapf pasture, degraded B. decumbens pasture, conventional tillage, and no‐till corn (Zea mays L.)–soybean [Glycine max (L.) Merr.] cropping using exchange resin cores, and set up a nutrient budget using previously published input data. At each of the study depths, we installed three to six PVC tubes (0.10 m in diameter, 0.11 m in length) filled with a mixture of field‐fresh soil and HBr‐washed ion exchange resin (Amberlite MB‐20, 10:1 v/v), which were removed and extracted after 2 yr. Downward fluxes at 2‐m soil depth ranged from 0.22 to 2.3 g Ca, 0.02 to 0.71 g Mg, 0.08 to 1.17 g K, not detected (n.d.) to 0.96 g NH4–N, and n.d. to 4.4 g NO3–N m−2 yr−1 Upward fluxes, because of capillary rise, frequently amounted to 30 to 50% of downward fluxes. At 0.3‐m depth, net leaching fluxes of Ca in the cropping systems and productive pasture (2.3–4.9 g m−2 yr−1) and of K and NO3–N in the cropping systems (K: 0.73–0.85, NO3–N: 2.3) were significantly higher than in all other systems except for NO3–N in Pinus (Ca: 0.02–0.18, K: 0.09–0.15; NO3–N: n.d.–0.70). In forests and pastures, all nutrients accumulated on balance while in cropping systems budgets were balanced or negative except for N. To reduce these losses, timing of fertilizer amendments should be optimized and in the no‐till system evaporation and fast water fluxes reduced for example, by stubble mulching.

English

A study was conducted to examine the impacts of land reclamation and management practices on the saturated infiltration rates (Ks) and bulk densities (BD) of soils in reclaimed surface coal mines of Wyoming. The use of direct- hauled topsoil vs. stockpiled topsoil, hay mulch vs. stubble mulch, grazing vs. no- grazing, and standard seed mixes (grass seeding) vs. shrub mosaic seed mixes as surface coal mineland reclamation practices were studied in five coal mines of the Powder River Basin, the Green River Coal Region and the Hanna Coal Field in Wyoming. Results from the reclaimed sites with the above listed management practices were compared to each other and with representative soils from adjacent native undisturbed sites. In all the study sites, native undisturbed soils had the lowest BD and the highest Ks compared to reclaimed soils. At Jim Bridger mine, results indicated no differences in BD and Ks between stockpiled and directly hauled soils. At the Belle Ayre mine, there was no significant difference in Ks between reclaimed soils and native undisturbed soil. At Seminoe mine, reclaimed stubble mulched soil had greater Ks (9.208 mm/min) than native undisturbed soil Ks (6.042 mm/min). At Jacob's Ranch, ungrazed soils had greater Ks (6.958 mm/min) than grazed soils Ks (3.350 mm/min) and native undisturbed soils (3.833 mm/min). BD at 0-5 cm for grazed soils was also greater (1.462 g/cm 3 ) than for ungrazed soils (1.255 g/cm 3 ) . Native undisturbed soils had the lowest BD (1.116 g/cm 3 ) averaged over all depths. Although native undisturbed BDs were generally lower, their Ks were not always greater. These results suggest that removal and manipulation of soil during mining accompanied by heavy machinery traffic over reapplied topsoil during reclamation may cause some degree of soil compaction relative to undisturbed sites. However, it can be concluded that land reclamation and management measures taken during and after mining may help to improve infiltration rates.

Soil Water Depletion and Root Distribution of Three Dryland Crops

Characterization of plant uptake of soil water at different points in time and space are important in evaluating seasonal water use as well as rotational dryland cropping strategies. The objective of this study was to characterize root length density (RLD) and soil water depletion patterns of cowpea [Vigna unguiculata (L.) Walp.], grain sorghum [Sorghum bicolor (L.) Moench], and sunflower (Halianthus annuus (L.)] under no tillage (NT) and stubble mulch tillage (SMT) systems in a Torrertic Paleustoll. Root length density of crops was measured from scanned images of washed root samples obtained from soil cores extracted several times during each of two growing seasons. Soil water contents were measured with a neutron moisture meter to a depth of 2.3 m at weekly intervals throughout each growing season. The RLDs of sorghum and sunflower near the soil surface increased rapidly after planting but thereafter declined whereas subsoil RLD increased throughout the growing season. Residual water contents at harvest were 28 to 93 mm greater (P < 0.05) under cowpea as compared to sorghum. As compared to the other crops, most of the additional residual water under cowpea was confined to soil depths between 0.5 and 1.7 m. Soil depths of 1.0 to 1.8 m were the most important source of stored water for sorghum and sunflower towards the end of the season. Deeper rooting and greater soil water extraction below 1.2 m depth were observed for NT as compared to SMT (P < 0.05). Results suggest that a rotation of cowpea with sorghum or sunflower would permit the stratified use of soil water and that the storage and crop use of water deep in the profile would be optimized under NT.

Tillage Intensity and Tillage-Induced CO2Loss

Field experiments were done to measure the effect of different primary tillage methods on the CO2 flux from soil and to evaluate the effect of conservation tillage tools on short-term CO2 emissions. The experiments were conducted on a clay loam soil winter wheat field and a corn field. The three tillage treatments included stubble mulching (disc harrow, mulch tiller, chisel plough), primary tillage (disc harrow, moldboard plough, and chisel plough) and secondary tillage (combined seedbed maker). The control treatment was no-till with soil and residues left by the harvester. The CO2 flux from the tilled soil surface was measured by a portable closed-chamber tester. Moldboard ploughing produced the roughest soil surface and the highest initial CO2 flux and maintained the highest flux throughout the experiment. The moldboard ploughing caused higher CO2 loss than less intensive tillage such as chisel ploughing, mulch cultivating, or disc harrowing. Primary tillage caused higher CO2 emission in the fall than s...

Productivity and economic of on-farm rainfed rabi crops in rice based croping system under different moisture conservation practies

On-farm field experiments were carried out in midland rainfed rice based cropping system during rabi seasons of 1999-00 and 2000-01 at village Khatti, district Mahasamund (C.G.) under National Agricultural Technology Project, RRPS-3 to explore the possibility of rabi crops (Safflower, Gram, Lentil, Lathyrus and Greengram) using moisture conservation practices (no mulch, soil and stubble mulch and rice straw mulch) in rainfed rice area. Among the crops, safflower produced significantly higher gram equivalent yield (13.50 q ha') and net profit (Rs. 10142 ha) than that of gram during 1999-00, while it was at par during 2000-01. Among the mulches, application of rice straw mulch recorded significantly higher grain yield (6.49 q ha¹) and net return (Rs. 10142 ha) and it was on par with that of soil and stubble mulch. Regarding interaction effect safflower with rice straw mulch gave significantly higher grain yield (12.29 q ha¹), which was at par with that of soil stubble mulch.

Factors affecting runoff and soil loss under simulated rainfall on a sandy Bainsvlei Amalia soil

This study was conducted on a long-term tillage experiment that was designed to evaluate appropriate tillage practices for sustainable dryland crop production. Measurements of runoff and soil loss were conducted on a sandy Bainsvlei Amalia soil (88.0% sand, 3.6% silt, and 8.4% clay) with a rainfall simulator on three tillage practices, namely no-tillage (NT), stubble mulch (ST) and conventional tillage (CT), each combined with four levels of wheat residue cover. The measurements were replicated twice for each of the three tillage practices on 1 m2 area plots. The simulator used for the study produced raindrops at a constant intensity of 60 mm h-1 with a veejet type nozzle, which had kinetic energy comparable to natural rainfall. A sharp decline in runoff and soil loss occurred with an increase in residue ground cover from bare to about 70%, above which the effect was less dramatic. Generally, runoff and soil loss was higher on NT plots compared with ST and CT plots. It is recommended that a crop residue covering at least 70% should be maintained on the soil surface when conservation tillage is practiced to ensure higher infiltration and lower runoff on this type of soil. Tilling the soil to a depth of at least 150 to 250 mm below the mulch gave the lowest runoff and soil loss.

Tillage System and Crop Rotation Effects on Dryland Crop Yields and Soil Carbon in the Central Great Plains

Winter wheat (Triticum aestivum L.)–fallow (WF) using conventional stubble mulch tillage (CT) is the predominant production practice in the central Great Plains and has resulted in high erosion potential and decreased soil organic C (SOC) contents. This study, conducted from 1990 through 1994 on a Weld silt loam (Aridic Argiustoll) near Akron, CO, evaluated the effect of WF tillage system with varying degrees of soil disturbance [no‐till (NT), reduced till (RT), CT, and bare fallow (BF)] and crop rotation [WF, NT wheat–corn (Zea mays L.)–fallow (WCF), and NT continuous corn (CC)] on winter wheat and corn yields, aboveground residue additions to the soil at harvest, surface residue amounts at planting, and SOC. Neither tillage nor crop rotation affected winter wheat yields, which averaged 2930 kg ha−1. Corn grain yields for the CC (NT) and WCF (NT) rotations averaged 1980 and 3520 kg ha−1, respectively. The WCF (NT) rotation returned 8870 kg ha−1 residue to the soil in each 3‐yr cycle, which is 2960 kg ha−1 on an annualized basis. Annualized residue return in WF averaged 2520 kg ha−1, which was 15% less than WCF (NT). Annualized corn residue returned to the soil was 3190 kg ha−1 for the CC (NT) rotation. At wheat planting, surface crop residues varied with year, tillage, and rotation, averaging WCF (NT) (5120 kg ha−1) &gt; WF (NT) (3380 kg ha−1) &gt; WF (RT) (2140 kg ha−1) &gt; WF (CT) (1420 kg ha−1) &gt; WF (BF) (50 kg ha−1). Soil erosion potential was lessened with WCF (NT), CC (NT), and WF (NT) systems because of the large amounts of residue cover. Levels of SOC in descending order in 1994 were CC (NT) ≥ WCF (NT) ≥ WF (NT) = WF (RT) = WF (CT) &gt; WF (BF). Although not statistically significant, the CC (NT) treatment appeared to be accumulating more SOC than any of the rotations that included a fallow period, even more rapidly than WCF (NT), which had a similar amount of annualized C addition. Reduced tillage and intensified cropping increased SOC and reduced soil erosion potential.

Management of &lt;i&gt;Oxalis latifolia&lt;/i&gt; and &lt;i&gt;Calystegia sepium&lt;/i&gt; in maize

Fishtail oxalis (Oxalis latifolia) and pink bindweed (Calystegia sepium) are problem perennial weeds in maize crops Four field trials were conducted over two growing seasons to evaluate both cultural and chemical control methods The postemergence application of nicosulfuron provided good control of fishtail oxalis as did imazethapyr/imazapyr in imidazolinonetolerant maize Use of maize cultivars with strong early season growth or long staygreen attributes did not provide the expected reduction in oxalis bulb production Two trials with pink bindweed showed that the postemergence herbicides nicosulfuron dicamba and imazethapyr/imazapyr gave good control of this weed Postharvest crop management with stubble mulching cultivation or glyphosate treatment had little effect on pink bindweed but use of glyphosate as close as possible to maize planting significantly reduced the bindweed population

Effect of methods of planting of rice (Oryza sativa) weed and nutrient management practices on growth and productivity of succeeding crops and system productivity of rice (Oryza sativa)-based cropping systems

A field experiment was conducted at the Instructional farm, College of Agriculture, Vellayani, Kerala, India, during 201314, to study the effect of methods of planting, weed and nutrient management on rice (Oryza sativa L.) and effect on the succeeding cassava (Manihot esculenta Crantz.) intercropped with groundnut (Arachis hypogaea L.) and cowpea [Vigna unguiculata (L.) Walp.] in uplands. The experiment was laid out in split-plot design, comprising 3 main plot shaving methods of planting [broadcasting of sprouted seeds, dibbling (sprouted seeds with drum seeder along with weeding by power weeder) and dibbling (sprouted seeds with drum seeder along with stubble mulching)] and 5 subplots with methods of nutrient application [broadcasting (60, 30 and 30 kg N, P and K/ ha), band placement (60, 30 and 30 kg N, P and K/ha), foliar spray of complex foliar fertilizer 19-19-19 @ 0.5%, foliar spray of diammonium phosphate (DAP) and sulphate of potash (SoP) each @ 2%, control] with 5 replications. For cassava intercropped with groundnut and cowpea recommended dose of fertilizer along with 0.5% foliar spray of 19-19-19 was applied at 30 and 14 days interval respectively. The results revealed that, the yield of succeeding crops as well as rice-equivalent yield of the cropping system (29.71 t/ha) was significantly increased by the method of planting of rice using drum seeder + stubble mulching @ 3 t/ha along with either broadcasting of 60, 30 and 30 kg N, P and K/ha or foliar spray of diammonium phosphate (DAP) and sulphate of potash (SoP) each @ 2% applied to rice. Residual effect of stubble mulching, basal application of nutrients along with foliar spray of DAP and SoP each @ 2% applied to rice enhanced the residual nutrients, yield and better profitability of rice-based sequential cropping system in uplands

Long-term effects of wheat residue management on some fertility indicators of a semi-arid Plinthosol

This study was done to establish how soil fertility indicators such as pH, Ca, Mg, K, Na, P and Zn were influenced by the application of different residue management practices in a field trial near Bethlehem in South Africa. The trial consisted of 36 treatments, including all combinations of straw burning (burnt or unburnt), three primary tillage methods (ploughing, stubble mulch or no tillage), two weed control methods (mechanical or chemical) and three levels of nitrogen fertilization (20, 30 and 40 kg N ha −1). Representative soil samples were collected at 0–50, 50–150, 150–250, 250–450 and 450–650 mm depth intervals from the 30 kg N ha −1 plots for analysis, reducing the number of treatments to 12. After 11–12 years, only pH, K, P and Zn were significantly influenced by the residue management practices. Straw burning and conservational tillage increased the levels of those four indicators when compared with no burning and conventional tillage. The prominence of these effects declined with depth and phased out below 250 mm, viz. ploughing depth. A thorough investigation into the plant availability of the K, P and Zn that accumulated in the upper 50 mm soil as a result of either straw burning or conservational tillage is suggested.

Sensitivity of Wheat Genotypes to a Toxic Fraction Produced by Cephalosporium gramineum and Correlation with Disease Susceptibility

ABSTRACT Cephalosporium stripe is an important disease of winter wheat (Triticum aestivum) in several areas of the world, especially where stubble mulch and early seeding are practiced to maintain soil moisture and prevent erosion. We developed a procedure to mass-produce a toxic fraction produced by Cephalosporium gramineum through a modification of the method of Kobayashi and Ui. Exposure of excised wheat leaves to a concentration of 60 mul/ml of the toxic fraction for 72 h produced distinct wilting symptoms that allowed us to distinguish toxin-sensitive wheat genotypes in a repeatable manner. Twenty wheat genotypes belonging to four distinct germ plasm groups (common, club, durum, and synthetic) were evaluated. Variation in toxin sensitivity of wheat genotypes was mostly at the level of the germ plasm group, and all differences among the four germ plasm groups were highly significant (P < 0.001) based on linear contrasts. Seventeen winter wheat genotypes representing the common, club, and durum germ plasm groups were planted in C. gramineum-infested fields at two locations. The logarithm of the percentage of tillers showing whitehead symptoms at each of the two locations was significantly (P < 0.0001) correlated with wilting symptoms measured by the toxin assay (r = 0.80 and 0.84). The common wheat genotypes were all sensitive to the toxic fraction, but showed a substantial range of disease reactions in the field. However, we found no case of a toxin-insensitive genotype being susceptible in the field. These results suggest that toxin insensitivity may be an important mechanism of resistance to Cephalosporium stripe, but that other mechanisms are operative as well. The toxin assay may be useful as an initial screening procedure to reduce the number of genotypes to be tested in the field.

Tillage and traffic effects on runoff

Traffic and tillage effects on runoff and crop performance on a heavy clay soil were investigated over a period of 4 years. Tillage treatments and the cropping program were representative of broadacre grain production practice in northern Australia, and a split-plot design used to isolate traffic effects. Treatments subject to zero, minimum, and stubble mulch tillage each comprised pairs of 90-m 2 plots, from which runoff was recorded. A 3-m-wide controlled traffic system allowed one of each pair to be maintained as a non-wheeled plot, while the total surface area of the other received a single annual wheeling treatment from a working 100-kW tractor. Rainfall/runoff hydrographs demonstrate that wheeling produced a large and consistent increase in runoff, whereas tillage produced a smaller increase. Treatment effects were greater on dry soil, but were still maintained in large and intense rainfall events on wet soil. Mean annual runoff from wheeled plots was 63 mm (44%) greater than that from controlled traffic plots, whereas runoff from stubble mulch tillage plots was 38 mm (24%) greater than that from zero tillage plots. Traffic and tillage effects appeared to be cumulative, so the mean annual runoff from wheeled stubble mulch tilled plots, representing conventional cropping practice, was more than 100 mm greater than that from controlled traffic zero tilled plots, representing best practice. This increased infiltration was reflected in an increased yield of 16% compared with wheeled stubble mulch. Minimum tilled plots demonstrated a characteristic midway between that of zero and stubble mulch tillage. The results confirm that unnecessary energy dissipation in the soil during the traction process that normally accompanies tillage has a major negative effect on infiltration and crop productivity. Controlled traffic farming systems appear to be the only practicable solution to this problem.

Nitrates in soil after long‐term management for dryland grain sorghum and winter wheat

Long‐term cropping with clean and stubble mulch tillage (SMT) resulted in soil organic carbon and total nitrogen (N) decreases at numerous Great Plains locations. Crops at some locations now respond to applied ? fertilizers. Objective of this study was to compare soil nitrate‐N (NO3‐N) contents after a 12‐year field study for which different management practices [cropping systems (rotations or continual cropping), tillage methods (SMT or no‐tillage), land leveling (level or nonlevel), and ? fertilizer (applied or not applied)] were used for dryland grain sorghum [Sorghum bicolor (L.) Moench] and winter wheat (Triticum aestivum L.) production. Pullman clay loam (fine, mixed, superactive, thermic Torrertic Paleustoll) was sampled by increments to a 20‐cm depth. Relatively few differences in NO3‐N contents due cropping system, land leveling, or tillage treatments were significant for individual depths or means across all depths. Cropping systems had no effect, but contents were greater in wheat than in sorghum or fallow plots. Land leveling and tillage methods resulted in no consistent differences, but contents usually were greater with than without applied fertilizer. Although ? fertilizer treatments were imposed early in the field study because plant ? deficiencies symptoms were noted, crops did not respond to applied fertilizer. This suggests the NO3‐N content differences found will have little effect on dryland crop yields under present management conditions.

Differential response of wheat to tillage management systems in a semiarid area of Morocco

Low, unreliable rainfall and high evaporation potential in semiarid parts of Morocco, but also inappropriate management of soil resources, produce erratic crop yields and uncertain economic returns. The need to maximize soil water conservation and optimize wheat grain production in Moroccan dryland areas have contributed to the emergence of direct seeding technology in this region. A field experiment was conducted to investigate the effects of no-till, minimum till, traditional and deep tillage systems on wheat yield as well as on water use efficiency. The experiment was conducted from 1995 to 1999, under rainfall regimes that varied from as low as 195 mm to 440 mm. Grain yields under no-tillage (2.47 Mg ha −1) were equal to those obtained using a chisel plow or deep tillage and superior to yields obtained by rotovating, conventional off-set disking, stubble mulching or subsurface traditional tillage. Water use efficiency (6.6–7.1 kg mm −1 ha −1) was similar following no-till, deep disking and chisel plowing, while other tillage systems had lower but similar values (varying from 5.4 to 5.9 kg mm −1 ha −1). Tillage systems did not differ significantly in terms of total dry matter or straw production and water use. Improvements in no-till drill design, which focus on proper seed and fertilizer placement and which prevent seed and straw being placed in close contact, are needed and may contribute to enhanced wheat yield and biomass under no-tillage.

The effects of crop rotation and fertilization on wheat productivity in the Pampean semiarid region of Argentina: 2. Nutrient balance, yield and grain quality

Wheat ( Triticum aestivum L.) in the semiarid region of Argentina has often been grown as a low-input crop. Rainfall scarcity and distribution are the main characteristics of the region. Consequently, a knowledge of the effect of different management practices is the key to sustainable crop production. The objective of this work was to study the effect of 15 years of different wheat management practices on plant nutrition, dry matter production and grain yield and quality. The treatments were: continuous wheat (WW), wheat-grazing natural grasses (WG) and wheat–legume: [vetch ( Vicia sativa L.) plus oat ( Avena sativa L.) or Triticale ( Triticum aestivum L. × Secale cereale L.)] (WL), with and without fertilizer (N + P) application. The WW and WL treatments involved annual tillage and a long fallow period (4–6 months) under stubble mulch, and WG involved annual alternate tillage and a short fallow (1 month). The experiment was started in 1975 and the data presented were obtained in 1989. Wheat yields were higher with the WW than with the WG rotation, but in both rotations fertilization was required to obtain better grain quality (protein content higher than 11 per cent). The wheat–legume rotation resulted in the highest yield, protein content, and better yield components. Fertilizer application did not increase dry matter production but improved nutrient uptake and grain quality. Yield component differences could be attributed to water availability due to different fallow length. The wheat–legume rotation seemed to be the best practice in the semiarid Pampean region.

Carbon and Nitrogen Conservation in Dryland Tillage and Cropping Systems

Soil C and N greatly influence long‐term sustainability of agricultural systems. We hypothesized that cropping and tillage differentially influence dryland soil C and N characteristics in the Southern High Plains. A Pullman clay loam (fine, mixed, thermic Torrertic Paleustol) cropped to wheat (Triticum aestivum L.)–sorghum [Sorghum bicolor (L.) Moench]–fallow (WSF), continuous wheat (CW) and continuous sorghum (CS) under no‐tillage (NT), and stubble mulch (SM) was sampled at three depths to determine soil C and N characteristics. For CW, CS, and WSF phases (FWSF, SWSF, WWSF), soil organic C (SOC) averaged 10.6 to 13.1 kg m−3 and was greatest for CW. Carbon mineralization (CMIN) at 0 to 20 mm was 30 to 40% greater for CW and FWSF than for CS, SWSF, or WWSF Cropping system by depth influenced soil organic N (SON) with greatest SON at 0 to 20 mm in CW (1.5 kg m−3). At 0 to 20 mm for SM and NT, SOC was 9.9 and 12.5 kg m−3, soil microbial biomass C (SMBC) was 0.80 and 1.1 kg m−3, and soil microbial biomass N (SMBN) was 0.14 and 0.11 kg m−3 Also at 0 to 20 mm, NT had 60% greater CMIN, 11% more SMBC as a portion SOC, and 25% more SON compared to SM. Summed for 0 to 80 mm, NT had more SOC (0.98 vs 0.85 kg m−2) and SON (0.10 vs 0.9 kg m−2) than SM, and CW had greater or equal C and N activity as other systems. Negative correlations between yield and SOC, SMBC, CMIN, SON, and SMBN indicate N removal in grain negatively affects active and labile C and N pools. Under dryland conditions, C and N conservation is greater with NT and with winter wheat because of less soil disturbance and shorter fallow.

Weed seeds in long‐term dryland tillage and cropping system plots

Successful crop production depends on effective weed control. Weed seedbanks were determined after 12 years of dryland cropping with winter wheat and grain sorghum under different tillage methods (no‐ and stubble mulch) and cropping sequences. Seeds of 12 species were detected. Amaranthus retroflexus was most abundant, but seed numbers were similar under all conditions. Portulaca oleracea, Panicum capillare, Setaria viridis and Sorghum halepense seed numbers differed because of some factors, with those for P. oleracea being greatest. For others, seed numbers were low (≤0.11 kg−1 soil), except for Digitaria sanguinalis with 7.8 kg−1 soil and Bromus japonicus with 1.3 kg−1 soil. Most seeds were near the surface with both tillage methods, with enough present under most conditions to cause a problem if proper control measures were not used, especially with continuous cropping. When a weed problem occurs under conditions as in this study, the results indicate that it could be reduced by growing winter and summer crops in rotation, which permits controlling weeds with tillage and/or herbicides when a crop is not growing. Other possibilities for controlling weeds under conditions as in this study are to alternate between dicotyledonous and monocotyledonous crops, which would permit use of a wider range of herbicides, and to use selective in‐crop herbicides.

Reduced Tillage Increases Population Density of Soil Macrofauna in a Semiarid Environment in Central Queensland

The effects of modified tillage practices on population densities of beneficial and harmful soil macrofauna were investigated. Soil-inhabiting macrofauna were sampled during 5 yr in a field experiment on a black Dermasol and Vertisol in semiarid central Queensland. The experimental treatments were 4 tillage practices applied during the fallow periods between grain crops. Reduced frequency and intensity of tillage increased the level of crop residues providing surface cover. Zero tillage had the highest population of macrofauna (74/m2), followed by reduced tillage (50/m2), stubble mulch tillage (44/m2), and traditional tillage (31/m2). Detritivore populations also were highest in zero tillage (44/m2) followed by reduced tillage (29/m2), stubble mulch tillage (26/m2), and traditional tillage (15/m2). Earthworm populations were highest in zero tillage (17/m2) and lowest in traditional tillage (5/m2). The incidence of termite colonies was higher in zero tillage (7.0/m2) than in reduced tillage (0.9/m2), stubble mulch tillage (0.3/m2), or traditional tillage (0.2/m2). Zero tillage usually had the greatest diversity of macrofauna species. Population density of herbivores, which are generally agricultural pests, was similar in all tillage treatments. These results indicate that long-term reduced or zero tillage will not lead to increased problems with soil insect pests.

Aggregation of Soil Cropped to Dryland Wheat and Grain Sorghum

AbstractSuccessful and sustainable semiarid dryland cropping depends on effective soil water storage and erosion control, which are influenced by surface soil aggregate size and stability. We hypothesized long‐term tillage and cropping system treatments affect water‐stable aggregate size distribution, aggregate water stability, and dry soil aggregation. A study on a Torrertic Paleustoll from 1982 to 1994 at Bushland, TX, involved tillage methods (no‐tillage, NT; stubble mulch tillage, SMT) and cropping systems for dryland winter wheat (Triticum aestivum L.) and grain sorghum [Sorghum bicolor (L.) Moench] production. In 1994, mean percentages of &gt;4‐mm water‐stable aggregates at 0 to 2 cm were 3.5 with NT and 1.0 with SMT in wheat, sorghum, fallow, rotation phase, or crop comparison plots. Mean percentages of &lt;0.25‐mm aggregates were 49.0 with NT and 37.8 with SMT. More small aggregates with NT help explain why infiltration was 90% greater with SMT than with NT during fallow after sorghum and 26% greater with SMT during fallow after wheat in a similar study on the same soil when surface coverage by residues was limited (25% with SMT, 57% with NT for sorghum; 73% with SMT, 86% with NT for wheat). Aggregate sizes differed due to cropping system, rotation phase, and crop, but aggregate water stability and dry aggregation differences generally were nonsignificant. Both NT and SMT are deemed suitable for dryland crops under conditions as in this study because neither resulted in unfavorable soil conditions or major yield differences.