Split-plot Factorial Design Research Articles

Integration of Fertilizer Nitrogen, Farmyard Manure and Multi-strain Microorganisms for Sustainable Production of Rice-Wheat System

Use of high rates of commercial nitrogen (N) fertilizers over the years has resulted in adverse effects on soil and environment health. Integrated use of fertilizer N and organic N sources is expected to reduce the N losses and improve N use efficiency. The present field experiment was conducted for two years to evaluate the effects of commercially available multi-strain inoculant ‘Fertimine’ and farmyard manure (FYM) applied at variable rates of fertilizer N on the nutrition of rice-wheat system. Four treatment combinations of FYM (15 t ha-1, fresh weight) and fertimine were applied to main-plots and four N levels to sub-plots in factorial split-plot design. In the absence of fertimine and FYM, significant increase in rice yield was observed up to 120 kg N ha-1 during first season and 80 kg N ha-1 during second season. The application of FYM and fertimine significantly increased mean grain yield of rice by 12 and 5 per cent over no FYM and fertimine, respectively. Significant interaction effect of fertimine and fertilizer N observed on rice grain yield suggested that fertimine significantly increased the rice yield at low rates of fertilizer N. While fertilizer N and FYM caused significant increase in the total uptake of N, P and K in rice, fertimine showed significant increase in total P uptake only. The FYM applied to rice showed significant residual effect on the yield and total N, P and K uptake in the subsequent wheat. Application of FYM significantly improved the soil chemical and biological properties after two cycles of rice-wheat rotation.

Stable isotope technique in the evaluation of tillage and fertilizer effects on soil carbon and nitrogen sequestration and water use efficiency

Abstract Agricultural soil could be made to serve as a sink rather than a source of greenhouse gases by suitable soil management. This study was, therefore, conducted to assess the impact of tillage and fertilizer application on soil and plant carbon and nitrogen fractionation and intrinsic water use efficiency (iWUE). The experiment was a split–split-plot factorial design with three replications. The main plot consisted of two tillage treatments: zero tillage (ZT) and conventional tillage (CT). The sub-plot contained four NPK fertilizer treatments (0, 90, 120 and 150 kg N ha−1), while the sub–sub-plot comprised three poultry manure (PM) treatments (0, 10 and 20 Mg ha−1). Soil carbon and nitrogen sequestration were evaluated using stable isotope of carbon (δ13C) and nitrogen (δ15N). The δ13C in maize plant was used to obtain iWUE. It was observed that soil δ13C and δ15N were more depleted under ZT than CT and in plots treated with 20 Mg ha−1 PM (PM20) implying carbon and nitrogen sequestration under ZT and by PM20. Relative to the control, application of PM20 raised soil δ15N enrichment by 82% and 96% under CT and ZT, respectively. Higher iWUE of 25.7% was obtained under CT and was significantly higher than the iWUE values under ZT in the second year of the study while the iWUE was significantly lower with PM20 application than other fertilizer treatments. The significant δ13C depletion and hence lower iWUE with combination of NPK fertilizer and PM under CT than the control implied that soil disturbance under tilled plots was mediated by combined nutrient management thereby limiting soil C available for fractionation resulting in lower iWUE. This suggests that conservation tillage such as zero tillage and integrated application of organic and inorganic fertilizers are good strategies for reducing soil carbon and nitrogen emission.

Constructing General Orthogonal Fractional Factorial Split-Plot Designs

While the orthogonal design of split-plot fractional factorial experiments has received much attention already, there are still major voids in the literature. First, designs with one or more factors acting at more than two levels have not yet been considered. Second, published work on nonregular fractional factorial split-plot designs was either based only on Plackett–Burman designs, or on small nonregular designs with limited numbers of factors. In this article, we present a novel approach to designing general orthogonal fractional factorial split-plot designs. One key feature of our approach is that it can be used to construct two-level designs as well as designs involving one or more factors with more than two levels. Moreover, the approach can be used to create two-level designs that match or outperform alternative designs in the literature, and to create two-level designs that cannot be constructed using existing methodology. Our new approach involves the use of integer linear programming and mixed integer linear programming, and, for large design problems, it combines integer linear programming with variable neighborhood search. We demonstrate the usefulness of our approach by constructing two-level split-plot designs of 16–96 runs, an 81-run three-level split-plot design, and a 48-run mixed-level split-plot design. Supplementary materials for this article are available online.

Aggregate-based human pluripotent stem cell manufacturing with the ambr®15 platform

Human pluripotent stem cells (hPSCs) are a promising cell source for many biomedical applications including cell replacement therapy and drug screening. As such, robust and scalable hPSC manufacturing processes are needed to produce appropriate quantities of high quality hPSCs. Various processes have been proposed, but none are fully characterised and optimised. CCRM has undertaken the task of developing and characterising an efficient and robust aggregate-based hPSC manufacturing process in stirred-tank reactors (STRs). Here we present an hPSC aggregate culture process that has been translated from an orbital shaker system to the ambr®15 platform (Sartorius Stedim), a microscale and controlled STR system. With this process, aggregates can be consistently formed from a single cell suspension in the ambr®15 within 24 hours. These aggregates are 41% smaller than those formed on an orbital shaker, but can achieve 1.5 times greater cell expansion over a 4-day period. Over 75% of the hPSCs produced co-express the pluripotent markers Oct4, Nanog, Sox2 and SSEA4; however, on average, 6% more expression is observed in the hPSC product from the ambr®15. Strategies for routine passaging of the cells are being explored. The ambr®15 is capable of parallel processing and multi-parametric control of 24 bioreactors; thereby enabling the exploration of individual and interacting effects of multiple operating parameters on hPSC culture performance. We have begun to explore the effects of 5 operating parameters on aggregate size and size variability using one-factor-at-a-time and split-plot factorial design experiments. As aggregate size was observed to influence hPSC differentiation trajectory, an understanding of how to control and manipulate aggregation dynamics will allow us to tailor our process for specific end applications. Efficient small-scale studies enabled by the ambr®15 will ultimately be translated to larger scale STR systems for robust and routine production of hPSC.

Fractional Factorial Split-plot Designs with Two- and Four-level Factors Containing Clear Effects

Mixed-level split-plot designs are commonly used in experiments. This article studies the mixed-level split-plot designs with four-level factors in both whole-plot and sub-plot sections. We give the conditions under which the designs contain various clear effects and the construction methods of such designs.

Effect of Water Regime and Runoff Strip Width on Soil Water Balance for an Integrated In-Field Rainwater Harvesting

Integrating micro-flood irrigation with in-field rainwater harvesting (IRWH) was proposed and experiments were conducted in the 2007–2008 production season at Parady's Experimental Farm of the University of the Free State, South Africa. Three water regimes, dryland (DL), supplemental (SPI), and full irrigation (FI), were tested with 1, 2, and 3 m runoff strip width (RSW) to determine their effects on soil water balance components for the integrated IRWH. Four blocks with nine subplots were prepared for the 3 × 3 split plot factorial experimental design. Plots were 30 m long with a standard 1 m width. Site specific data were used to estimate rainfall-runoff and deep drainage functions. Soil water content (SWC) was measured with a Neutron water meter. Evapo-transpiration (ET) was partitioned into evaporation and transpiration using a β parameter. Deep drainage was the least significantly affected. Rainfalls not less than 24 mm had significantly higher gains on change in SWC for the 2 m and 3 m RSW. During dry spells these RSWs had significantly higher SWC deficit. For the vegetative and reproductive growth stages evaporation from the 3 m RSW constituted not less than 60% of ET compared to less than 40% from 1 m RSW. The 1 m RSW had significantly higher ET and T, irrespective of water regime with the highest values from irrigation treatments. The 1 m RSW can, therefore, be used with either FI or SPI to optimize soil water balance for the integrated IRWH water management.

Designed experiments to characterize PEMFC material properties and performance

We report on using Design of Experiments (DoE) methods to study the influence of the gas diffusion layer (GDL) material on Polymer Electrolyte Membrane Fuel Cell (PEMFC) performance. We applied DoE methods to discern and quantify the effect of a micro-porous layer (MPL) for the first time. Two full factorial split-plot designs were used based on six operating parameters, namely anode stoichiometry, cathode stoichiometry, temperature, anode inlet relative humidity and cathode inlet relative humidity and gas pressure and a categorical factor, the GDL type. The cell voltage and cathode pressure drop are the responses, measured and modeled under galvanostatic control at current densities of 1.0Acm−2, 1.4Acm−2 and 1.6Acm−2. The results of this work demonstrate the use of DoE to assess the differences and parameter dependencies of different materials in the GDL of PEMFC. Statistical tests to identify the performance-determining parameters and parameter dependencies were conducted. For all current densities the type of GDL material, temperature, and the interaction between these two factors had the most impact on the voltage. The cell with an MPL showed voltage changes of 0.1V when navigating the design space of temperatures from 40°C to 75°C and cathode stoichiometries from 1.5 to 3. The voltage of the cell without MPL had a strong dependence on temperature indicated by large voltage changes of 0.4V over the temperature range of 40–75°C.

Impact of Pima Defoliation Timings on Lint Yield and Quality

Chemical defoliation is a necessary pre-harvest practice in Pima cotton (Gossypium barbadense L.) production in the San Joaquin Valley of California. Cotton growers are advised to begin defoliation as early as possible with both Pima and Upland cotton, but not so early that it results in yield and quality loss Potentially harvestable bolls often fail to reach full maturity due to the recommended defoliation timing. Applying harvest aids before the recommended maturity can advance the start of harvest, avoiding late-season pests and adverse weather that can damage lint quality. The objective of this research was to compare different rates of Ginstar® (thidiazuron/diuron, Research Triangle Park, NC) or Ginstar plus Finish® (ethephon/cyclanilide, Research Triangle Park, NC) on defoliation, yield, and fiber quality of Pima cotton when applications began at an earlier timing, six to seven NACB (nodes above cracked boll), versus the common four to five NACB timing. ‘Delta Pine DP-340’ (Monsanto Company, St. Louis, MO) was treated with harvest aid materials in field trials and was analyzed as a factorial split-plot design with four replications. Starting the defoliation of Pima at six to seven NACB rather than four to five NACB brought about a potential seven to ten day earlier harvest and did not significantly affect yield or cotton fiber quality characteristics except for micronaire in one year of the study. These data indicate that earlier defoliation could be beneficial when later-maturing crops or worsening harvest-season weather necessitate the initiation of an earlier harvest.

Effect of nitrogen fertilizer levels and irrigation on quality characteristics in bread wheat (Triticum aestivum L.)

In order to evaluate irrigation regimes and nitrogen fertilization on quality characteristics of wheat cultivars, a field experiment was carried out using split-plot factorial design based on randomized complete block design with three replications in Quchan, Iran (2010–2012). Main plots were assigned with four irrigation regimes; I1, 90 mm; I2, 130 mm; I3, 170 mm based on evaporation from a class A pan; and I4, water deficit stress during post-anthesis stage; sub-plots were assigned with four levels of nitrogen (N1, 0; N2, 70; N3, 140; and N4, 210 kg ha−1); and three wheat cultivars (V1, Mihan; V2, C-87-6; and V3, C-87-11) were used as factorial. The results showed that nitrogen fertilization increased some quality characteristics. Under water deficit (I4), gluten index, grain protein content, grain yield, and sedimentation volume decreased. Significant interactions between irrigation regimes and both nitrogen levels and cultivars were observed.

Stocking Rate and Fuels Reduction Effects on Beef Cattle Diet Composition and Quality

An experiment was conducted to evaluate the influence of forest fuels reduction on diet quality, botanical composition, relative preference, and foraging efficiency of beef cattle grazing at different stocking rates. A split plot factorial design was used, with whole plots (3 ha) being fuel reduced or no treatment (control), and split plots (1 ha) within whole plots were grazed to three levels of forage utilization; (low) 3 heifers·ha−1, (moderate) 6 heifers·ha−1, (high) 9 heifers·ha−1, with a 48-h grazing duration. Grazing treatments were applied in August of 2005 and 2006. Cattle diet composition and masticate samples were collected during 20-min grazing bouts using six ruminally cannulated cows in each experimental unit. Relative preference indices indicated a strong preference for grass regardless of treatment and stocking rate. Grass consumption was lower in control pastures (P<0.05) and tended (P<0.095) to decrease with increased stocking rates. Shrub use was higher in control pastures displaying a quadratic effect (P<0.05) due to stocking, whereas shrub use increased with stocking rate across all treatments. Cattle grazing control pastures consumed diets higher in crude protein compared to cattle grazing treated pastures (P<0.05). In vitro dry matter digestibility values were lower (P<0.05) in control sites and tended (P=0.10) to decrease with increased stocking rates. In both control and treated pastures, bites per minute and grams consumed per minute declined (P=0.003) with increased stocking, indicating foraging efficiency of cattle decreases with increased stocking rates. Our data indicated cattle grazing late season grand fir habitat types have a strong preference for grasses regardless of treatment or stocking rate. However, as stocking rate increased in both control and treated pastures, grass consumption decreased, shrub consumption increased, and foraging efficiency decreased.

Efficient construction of split-plot design catalogs using graphs

Fractional-factorial split-plot designs are useful variants of the traditional fractional-factorial designs. They incorporate practical constraints on the randomization of experiment runs. Catalogs of split-plot designs are useful to practitioners as they provide a means of selecting the best design suitable for their task. However, the construction of these catalogs is computationally challenging as it requires comparing designs for isomorphism, usually in a large collection. This article presents an efficient approach for constructing these catalogs by transforming the design isomorphism problem to a graph isomorphism problem. A new graph representation of split-plot designs is presented to achieve this aim. Using examples it is shown how these graph representations can be extended to certain other classes of factorial designs for solving the (corresponding) design isomorphism problem. The efficacy of this approach is demonstrated by presenting catalogs of two-level regular fractional factorial split-plot designs of up to 4096 runs, which is much larger than available in existing literature.

Effect of Grafting Dates, Methods on Success and Growth of Mandarin (Citrus reticulata Blanco) Sapling

A field experiment was conducted at National Citrus Research Program (NCRP), Paripatle, Dhankuta to standardize the time and method of grafting and to assess the success and growth of mandarin saplings. Scions taken from ‘Khoku Local’ mandarin were grafted onto one-year-old trifoliate orange seedling rootstocks by shoot tip and veneer methods in eight different dates starting from 29th October, 2009 to 12th February, 2010 at 15 days interval. The grafts were planted inside closed tunnel of jute and plastic sheet at 10×10 cm spacing in 50×60 cm2 experimental plots in two factorial split-plot design with three replications per treatment, containing 30 grafts per plot. The grafting methods were allotted on main-plots and the dates on sub-plots randomly. The success and growth of sapling was significantly affected by the dates while the methods had no effect. Study results showed that the highest success (96.11 %) was found on 13th January, followed by 28th January (91.11%) and the least (51.67%) on 29th October grafting. The mortality of sprouted grafts was the lowest (0.17%) in 29th December grafting, while it was observed higher in earlier and late season grafting. Observation on growth taken at 180 days after grafting in successful grafts showed that 29th October had the highest number of primary branches (2.2); 14th November had the highest number of leaves (48.47) and secondary branches (2.505); 29th December gave the maximum sapling height (32.86 cm); 13th January produced the lowest number of leaves (21.93) per sapling and 28th January produced the lowest number of primary (1.533) and secondary branches (1.172) per sapling. From the study it was revealed that in Dhankuta, the most appropriate time of grafting was 2nd to 4th week of January. Nepal Journal of Science and Technology Vol. 14, No. 1 (2013) 23-30 DOI: http://dx.doi.org/10.3126/njst.v14i1.8873

Alternative optimal foldover plans for regular fractional factorial split-plot designs

McLeod and Brewster (Technometrics 46:135–146, 2008) considered the construction of optimal foldover plans for regular fractional factorial split plot designs. The construction process was based on the minimum aberration criterion for both the initial design and the combined design derived through the foldover. In this paper we give some additional foldover designs which have desirable properties that may provide viable alternative options to some of the plans provided in McLeod and Brewster (Technometrics 46:135–146, 2008).

The Impact of Cognitive Tools on the Development of the Inquiry Skills of High School Students in Physics

the purpose of the study was to compare the effectiveness of two teaching strategies that utilize two different cognitive tools on the development of students’ inquiry skills in mechanics. The strategies were used to help students formulate Newton’s 2nd law of motion. Two cognitive tools had been used: a computer simulation and manipulations of concrete objects in physics laboratory. A quasi-experimental method that employed the 2 Cognitive Tools ? 2 Time of learning split-plot factorial design was applied in the study. The sample consisted of 54 Grade 11 students from two physics classes of the university preparation section in a high school of the province of Ontario (Canada). One class was assigned to interactive computer simulations (treatment) and the other to concrete objects in physics laboratory (control). Both tools were embedded in the general framework of the guided-inquiry cycle approach. The results showed that the interaction effect of the Cognitive Tools ? Time of learning was not statistically significant. However, the results also showed a significant effect on the development of students’ inquiry skills regardless of the type of cognitive tool they had used. Although the findings suggested that these two strategies are effective in developing students’ inquiry skills in mechanics, students in the computer simulation group had shown larger gain in their inquiry skills test than their counterparts in the laboratory group.

Conditions of 2&amp;lt;sup&amp;gt;(&amp;lt;italic&amp;gt;n&amp;lt;/italic&amp;gt;&amp;lt;sub&amp;gt;1&amp;lt;/sub&amp;gt;+&amp;lt;italic&amp;gt;n&amp;lt;/italic&amp;gt;2)-(&amp;lt;italic&amp;gt;k&amp;lt;/italic&amp;gt;&amp;lt;sub&amp;gt;1&amp;lt;/sub&amp;gt;+&amp;lt;italic&amp;gt;k&amp;lt;/italic&amp;gt;&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;)&amp;lt;/sup&amp;gt;4&amp;lt;sup&amp;gt;2&amp;lt;/sup&amp;gt; mixed-level split-plot designs containing clear effects

Mixed-level fractional factorial split-plot designs are widely used in various experiments.Under the weak assumption that the interactions involving three or more factors can be ignored,the experimenter can obtain the unbiased estimations of the clear main effects or clear two-factor interaction components.The paper gives the conditions of a mixed-level split-plot design with two four-level factors and some two-level factors to have various clear main effects or clear two-factor interaction components.The methods of constructing the corresponding designs are also given.

Response of a new and a commonly grown forage sorghum cultivar to limited irrigation and planting density

Increasing scarcity of water for irrigation is one of the major challenges for forage producers in all arid and semi-arid regions. Selecting drought tolerant forage species such as sorghum (Sorghum spp. L.) over corn, as a common forage crop, could be a viable option to cope with the limited available water for irrigation and increasing the productivity in such climates. A two-year experiment was conducted during the 2009 and 2010 growing seasons to determine if limited irrigation regimes and different plant densities may produce high-yielding forage sorghum with acceptable forage quality. The experiment was arranged in a three-replicated split-plot factorial design with three irrigation regimes including optimum irrigation (when evaporation reached 70mm, using evaporation pan class “A”), moderate drought stress (100mm), and severe drought stress (130mm) as main plots. A common sorghum cultivar (Speedfeed) and a newly released cultivar (Pegah) were factorially combined with three plant densities (150,000, 200,000, and 250,000plantsha−1), as sub-plots. Results of this study indicated that forage dry matter and forage quality parameters were significantly influenced by irrigation regimes, plant densities, and cultivars. Increasing water stress from optimum irrigation (Ir70) to moderate (Ir100) and low irrigation (Ir130) resulted in 20 and 34% less forage dry matter yield. Protein yield was also lower when applying moderate and severe drought stress than with the optimum irrigation regime, whereas some forage quality parameters including crude protein, dry matter digestibility, water soluble carbohydrates, dry matter intake, relative feed value, and net energy for lactation improved when limited irrigation was imposed. Highest protein yield (1688kgha−1) was obtained from the combination of optimum irrigation regime and lowest plant density, whereas forage produced in moderate stress and low plant density was richer in relative feed value. Speedfeed outyielded Pegah cultivar and produced higher protein yield.

INTEGRATING MICRO‐FLOOD IRRIGATION WITH IN‐FIELD RAINWATER HARVESTING: MAIZE YIELD AND WATER USE EFFICIENCY

ABSTRACTThis study integrated micro‐flood irrigation (MFI) and in‐field rainwater harvesting (IRWH) for the purpose of improving soil water balance (SWB), crop yields and water use efficiency (WUE). The integrated system was tested in Parady's Experimental Farm of the University of the Free State, a semi‐arid region of the Free State Province (South Africa). Three water regimes (WR), dryland (DL), supplemental (SPI) and full irrigation (FI), were evaluated with 1, 2 and 3 m runoff strip width (RSW). The WR and RSW factors were studied using a 3 × 3 split plot factorial experiment design with four blocks. Plots were 30 m long with a width that constituted a standard 1 m basin strip and no tilled RSW. According to the BEWAB + irrigation scheduling software, the crop water requirement for FI amounted to 625 mm of which 50% was contributed by rainfall, while that of SPI was fixed at 60% of FI. Water from rainfall, FI and SPI amounted to 282, 330 and 210 mm, respectively. Soil water storage and transpiration were found to be affected by both the RSW and WR factors, while evapotranspiration (ET) and deep drainage were affected by RSW and WR, respectively. For the 1 m RSW, crop biomass and grain yield were respectively 19 and 32% above average. Correspondingly, seasonal ET and transpiration (T) were 10 and 44% above average. Full irrigation increased crop biomass and grain yield by 200%, while corresponding increases for SPI were 74 and 77% higher than DL. In conclusion, the 1 m RSW and FI produced optimum maize yields and WUE for the integrated MFI–IRWH system. Copyright © 2012 John Wiley &amp; Sons, Ltd.

Short-term responses of soil and wheat yield to tillage, corn residue management and nitrogen fertilization

Corn residues management is a major problem in the southern part of Iran where irrigated wheat–corn–wheat rotation is a common practice. A two-year (2008–2010) field experiment was conducted as a factorial split plot design with three replications at the Agricultural Research Centre, College of Agriculture, Shiraz University, Shiraz, Iran to determine the influences of different amounts of corn (Zea mays L.) residues (0, 25 and 50%) incorporation and nitrogen (N) rates (75 and 150kgha−1) on some soil properties, yield and yield components of winter wheat (Triticum aestivum L.) under two tillage systems. Tillage treatments were moldboard plow followed by two harrow diskings and chisel plow tillage followed by a single harrow disking. The soil with chisel treatment had about 8 and 15% more soil organic carbon (SOC) and total N than moldboard plow treatment, respectively. Incorporation of increased amounts of corn residues and a higher N rate reduced C:N ratios in the chisel treatment in both years. Soil electrical conductivity (EC) increased with chisel plow and increasing amounts of residues incorporation and N rates. The lowest pH found in plots with no residue incorporation was 8.1 compared to 8.2 in plots with 50% residue incorporation. For treatments receiving 150kgNha−1, soil pH was significantly higher compared to treatments receiving 75kgNha−1. The highest wheat grain yields (about 8.5tha−1) were obtained with chisel treatment, 25–50% corn residue incorporation and application of 150kgNha−1. Incorporation of 25–50% of corn residues (7500–15,000kgha−1) is recommended to increase SOC in a wheat–corn–wheat rotation in this region.

IPR 126 white oat forage potential under free growth, cutting and grazing at two management heights

The experiment was carried out to evaluate the structural characteristics, biomass accumulation, chemical composition and in vitro digestibility of dry matter and crude protein of white oat (Avena sativa L. IPR 126) under different management systems. Grazing, cut at two heights (15 and 20 cm) and free growth were all evaluated in three periods (July, August and September) with a 28-day average interval between evaluations. In the free growth system, samples at 15 and 20 cm were also taken at the intervals chosen for cutting and grazing. The experimental design was in randomized blocks with three replications, arranged in a 3 × 2 factorial split plot design over time; systems of management and heights were the factors of plots, and time was taken as subplot. There was higher straw production under free growth, but, with decreased chemical quality from the first to the second period and from the second to the third one, with 236.4, 172.5, and 91.4 g/kg crude protein values, respectively. Regarding cutting and grazing systems, they showed structural changes in tillering, which was favored by the cut, but with some reduction in the periods. Nutritional quality values were close to cutting and grazing with high crude protein content (216.6 g/kg), adequate neutral detergent fiber (535.4 g/kg) content and high in vitro digestibility of dry matter (826.3 g/kg). Management heights promoted few changes in the characteristics evaluated. After the third period, cutting and grazing systems showed no suitable residual straw for ground covering and set a summer crop under no-tillage system, with 738.39 kg/ha of residual dry matter on average.

On optimal two-level nonregular factorial split-plot designs

This article studies two-level nonregular factorial split-plot designs. The concepts of indicator function and aliasing are introduced to study such designs. The minimum G-aberration criterion proposed by Deng and Tang (1999) [4] for two-level nonregular factorial designs is extended to the split-plot case. A method to construct the whole-plot and sub-plot parts is proposed for nonregular designs. Furthermore, the optimal split-plot schemes for 12-, 16-, 20- and 24-run two-level nonregular factorial designs are searched, and many such schemes are tabulated for practical use.