Planting Depth Research Articles

Research on the Performance and Control Strategy of Electro-Hydraulic Servo System for Selective Hole Digging Tree Planter

Compared to agricultural environments, afforestation sites are more complex, often presenting issues such as undulating and uneven terrain. These conditions lead to instability in hole digging depth and plant spacing during continuous movement, and the hole shape may not meet expectations. Additionally, the hydraulic system exhibits slow response speed and long steady-state time, affecting the quality of sapling planting. To address these issues, this paper designs an intelligent planting control system for intermittent hole digging under continuous dynamic movement, based on a large tree planter. The focus is on studying the dynamic accuracy of the hole digging cylinder to resolve the instability of plant spacing and planting depth in actual planting processes. Firstly, a motion trajectory model of the intermittent hole digging mechanism is established to obtain the relationship between the displacement trajectory of the rotating cutter and the displacements of the floating cylinder and the hole digging cylinder. Secondly, a mathematical model of the electro-hydraulic servo system is established to control the dynamic accuracy of the hole digging operation. Finally, a Simulink simulation model of the system is established to analyze the performance indicators of the hydraulic system during operation using step and sinusoidal excitation signals. The test results show that the displacement of the hydraulic piston rod can ensure a linear extension trend within the range of 0 to 0.4 m, and the extension distance of the hole digging cylinder in the planting system is 0 to 0.35 m, ensuring linear change within this stroke. When the system’s extension command is 1 V, the actual output is 0.6 m, with a relative error of less than 10% compared to the simulation value, indicating that the control strategy can effectively improve the dynamic performance of the system. When the hydraulic system is in a steady-state extension state at 50 to 58.6 s, the relative error with the simulation value is 7.3%, meeting the “double ten indicators” requirement. The research results clearly verify the superior performance of the proposed intelligent control system, and the proposed control strategy has great potential in practical applications, promising to improve afforestation quality by stabilizing planting spacing and planting depth.

Design and Experiment of Compound Transplanter for Sweet Potato Seedling Belt

To address the issues of high labor intensity, excessive manpower requirements, low planting spacing qualification rates, low planting depth qualification rates, and low operational efficiency associated with sweet potato transplanting, a sweet potato seedling belt transplanter has been designed. This machine can perform multiple processes: precision tillage and ridge shaping, orderly seedling feeding from rolls, the efficient separation of seedlings from the belt, flexible gripping and shaping, precise soil covering and the mechanism of exposing seedling tips. A three-factor, three-level orthogonal test was carried out using the forward speed of the machine, the pitch of the screw belt and the rotational speed of the screw as the influencing factors of the performance test, and the qualified rate of planting spacing and the qualified rate of planting depth as the evaluation indexes. The test results indicated that the significance order of the factors affecting the qualification rate for planting spacing with the optimal combination of factors was as follows: a forward speed of 0.3 m·s−1, a ribbon spacing of 60 mm, and a screw speed of 160 rpm. Field trials confirmed that under optimal conditions, the average qualification rate for planting spacing was 90.37%, meeting relevant technical standards and agronomic requirements.

Effect of Land Configuration and Planting Depth on Corm and Cormel Production of Gladiolus (Gladiolus spp.)

The present experiment was carried out at department of Floriculture and Landscape Architecture, College of Horticulture, Junagadh Agricultural University, Junagadh (Gujarat) during the years 2021-22 and 2022-23 with randomized block design (Factorial) having three replications. The treatment combinations consisting three land configuration methods (L1- Flat bed, L2- Raised bed with 2 rows and L3- Ridge and furrow) and two planting depth (D1- 3.5 cm and D2- 5.5 cm). The results indicated that maximum number of corms (1.58), number of cormels (26.98), diameter of corms (63.77 mm), diameter of cormels (3.16 mm), weight of corms (64.13 g) and weight of cormels (22.11 g) were recorded with raised bed with 2 rows (L2). The variation due to planting depth was also found significant for all the parameters and maximum number of corms (1.46), number of cormels (25.52), diameter of corms (56.43 mm), diameter of cormels (3.09 mm), weight of corms (56.02 g) and weight of cormels (21.78 g) were obtained with planting at 3.5 cm depth (D1). Raised bed planting had favourable effects on growth and flowering of gladiolus as compared to ridge and furrow and flat bed planting.

Design and field experiment of Codonopsis pilosula film covering transplanter

To address the low efficiency and high labor demands of manual Codonopsis pilosula cultivation, as well as the limitations of existing flat-type transplanting machines that create trenches of inconsistent depth hindering root growth and seedling emergence, a C. pilosula film-covered outcrop tilted transplanting machine was developed. Based on theoretical analysis of the prototype's key components and agronomic requirements for oblique C. pilosula transplanting, the structure and working parameters of the rotary tiller soil throwing device, soil lifting device, track-type soil conveying device, seedling throwing device, and film covering device were determined. The core components' working principles were analyzed, and the soil throwing process of the rotary tiller device was simulated using the discrete element method (DEM). A calculation domain was established, and the results showed that the average mass of the rotary tiller device was 49.44 kg, while the required soil lifting amount for the scraper-type soil lifting device was 21.84 kg, meeting the soil throwing requirements. Field experiments in 10 test areas demonstrated an average qualified rate of 89.50% for planting depth, 84.00% for planting posture, 90% for exposed plant spacing, 4.51 cm for plant spacing, and 8.67% coefficient of variation for planting spacing. These results meet industry standards for planting depth and planting spacing, confirming the machine's effectiveness in achieving high-quality tilted transplanting of C. pilosula seedlings.

EFFECT OF PLOUGHING AND PLANTING DEPTHS ON DRAFT OF DUAL-PURPOSE MOULDBOARD PLOUGH CUM PLANTER

This study presents an experimental inquiry into the effects of two independent variables on the draft force of a mouldboard plough/planter: planting depth (0 – 5 and 6 – 10 cm) and plowing depth (6 – 10 and 11 – 15 cm). A dual-purpose mouldboard plough/planter was developed to expedite the cultivation of maize by speeding up the ploughing and planting processes. Based on planting and ploughing depths, the draft force of the implement was evaluated. Field experimental procedures were used to conduct the trials, and parametric testing was used to analyze the data. The final formula for calculating the draft force depends on a number of soils engineering characteristics, including soil bulk density and type, tool specifications, such as cutting width and implement weight, and operational factors, such as ploughing depth and moisture content. The study's findings show that ploughing depth has a greater impact on a mouldboard plough/planter's draft force; the maximum draft force of 1.5 kN was recorded at planting depths of 6 to 10 cm and ploughing depths of 11 to 15 cm. The data indicates that the draft force of the cum planter is significantly (p~0.05) affected by the depth of ploughing. The ploughing depth and planting depth on draft force were shown to have a strong association in the linear regression model, with a coefficient of determination (R 2 = 0.75) for draft force indicating high correlations among the components. Ploughing depths are always responsible for explaining the difference in draft force. The results suggest that any change in the plowing depths provides a considerable forecast of the implement's draft force, since the plowing depth was the largest predictor of the draft force. The best results from the mouldboard plough/planter are achieved when planting and ploughing are done at depths of 0–5 cm and 5–10 cm, respectively.

Impact of burial depth and root segment length on vegetative propagation of common milkweed (Asclepias syriaca)

Abstract Common milkweed (Asclepias syriaca L.) is widely planted as part of monarch butterfly (Danaus plexippus) conservation efforts. Vegetative propagation is an alternative to planting A. syriaca from seed, which offers advantages such as high emergence rates. The aim of this study was to determine the ideal planting depth and initial root segment length to vegetatively propagate A. syriaca. In a greenhouse trial with two runs, A. syriaca was grown from seed and then 3, 8 and 15-cm segments were harvested. These segments were then planted at depths of either 3, 8, or 15 cm. Planting depth did not impact A. syriaca growth, but an initial root segment length of 15 cm was associated with greater above- and belowground biomass and height in both runs of the experiment. Emergence rates were not impacted by either factor. Overall, A. syriaca was likely to establish regardless of the initial root segment length or planting depth, but plants grown from root segments of 15 cm were more vigorous than plants grown from shorter segments.

Impact of lithovit and planting depth on growth, productivity and quality of potato crops'

Impact of lithovit and planting depth on growth, productivity and quality of potato crops'

An Assessment of Some Mechanical Properties of Harvested Potato Tubers cv. Spunta

Mechanical properties of vegetables or crop materials play a noteworthy part in designing new related implements. These properties can be extracted from force–deformation curves. Several factors, such as soil preparation, irrigation, and pre- and post-harvest treatments influence them. The core objective of this investigation work was to analyze force–deformation curves obtained from compression, penetration, and shear tests of potatoes (Spunta cv.) produced with three tillage implements. The potatoes cv. Spunta were cultivated in loamy sand soil under the center-pivot irrigation system. The tillage implements used were a disc harrow plow, chisel plow, and moldboard plow. The trials were performed at a constant planting depth (15 cm) below the soil and a single plowing speed of 5.4 km/h. All data were expressed as an average of five replicates ± standard deviation. The force–deformation curves analysis showed that the modulus of elasticity for potatoes cv. Spunta ranged from 4.32 to 5.8 N/mm, the bioyield force ranged from 84.25 to 114.12 N, and rupture forces ranged from 100.90 to 139.78 N. Furthermore, the results showed that the average values of the elastic and plastic ranges were 3.0 and 2.1 mm, respectively. The mean value of hardness was 1671.53 N·mm. No significant differences were observed with respect to the two planting seasons, but tillage implements had a significant impact on the characteristics extracted from the compression tests. The mean of the maximum forces required to penetrate the potato during the penetration stage were 41.24 N, 44.86 N, and 47.16 N for potatoes produced with the disc harrow plow, chisel plow, and moldboard plow, respectively. Similarly, the means of the maximum forces required to cut the potato in the shear stage were 724.38 N, 761 N, and 773.43 N for the disc harrow plow, chisel plow, and moldboard plow, respectively. The force–deformation curves showed that additional information might be required to obtain a complete description of the potato quality necessary to harvest potatoes cv. Spunta using harvesting and handling equipment with reduced economic loss. An extensive study of the soil characteristics and the above-mentioned properties is also recommended. The results obtained about the mechanical characteristics of potatoes cv. Spunta can be useful in providing information that aids in designing potato harvesting machines and in potato products factories.

Revealing the dynamics of saffron growth: Optimizing corm size and planting depth for increased yield synergies.

Saffron, the "golden spice" derived from Crocus sativus L., is renowned for its richness in secondary metabolites such as crocin and safranal, contributing to its unique properties. Facing challenges like decreasing global production, optimizing cultivation techniques becomes imperative for enhanced yields. Although the impact of factors like planting density, planting depth, spacing, and corm size on saffron growth has been studied, the interaction between corm size and planting depth remains underexplored. This study systematically investigates the interactive effects of corm size and planting depth on saffron growth and yield, providing evidence-based guidelines for optimizing cultivation. A factorial experiment, employing a completely randomized design, was conducted to assess the influence of corm size (05-10g, 10.1-15g, 15.1-20g) and planting depth (10cm, 15cm, 20cm) on saffron yield. Uniform-sized corms were obtained, and a suitable soil mixture was prepared for cultivation. Morphological and agronomic parameters were measured, and statistical analyses were performed using ANOVA and Tukey's HSD test. The study revealed that planting depth significantly affected saffron emergence. The corms sown under 15cm depth showed 100% emergence regardless of corm size (either 05-10g, 10.1-15g, 15.1-20g) followed by 10cm depth corms. Corm dry weight exhibited a complex interaction, where larger corms benefited from deeper planting, while intermediate-sized corms thrived at shallower depths. Similar patterns were observed in shoot fresh weight and dry weight. Specifically, the largest corm size (t3, 15.1-20g) produced the greatest fresh-weight biomass at the deepest planting depth of 20cm (T3), while intermediate-sized corms (t2, 10.1-15g) were superior at the shallowest 10cm depth (T1). The total plant biomass demonstrated that larger corms excelled in deeper planting, while intermediate-sized corms were optimal at moderate depths. This research highlights the intricate interplay between corm size and planting depth in influencing saffron growth. Larger corms generally promote higher biomass, but the interaction with planting depth is crucial. Understanding these dynamics can aid farmers in tailoring cultivation practices for optimal saffron yields. The study emphasizes the need for a coordinated approach to corm selection and depth placement, providing valuable insights for sustainable saffron production and economic growth.

Sunflower root growth and distribution under varied water regimes in two edaphoclimatic conditions

Sunflower growth is adversely impacted by both excess and insufficient water. Research on root growth in this crop under water stress conditions remains limited and does not fully elucidate the plant's response to varying soil and climatic conditions. This study aimed to determine root growth, depth, and distribution of sunflower plants under different water stress conditions, such as deficit or excess, in two soil classes and sown during two distinct periods. Experiments were conducted after sowing at the beginning of September (first crop season) and at the beginning of January (second crop season) in an Ultisol (Santa Maria, Rio Grande do Sul State, Brazil) and an Oxisol (Panambi, Rio Grande do Sul State, Brazil). Water condition treatments applied from stage V6 included control, water deficit, and water excess. Roots were collected using an auger drill during the first crop season. The variables analyzed comprised root length density and accumulated root within the soil profile. During the second crop season, sunflower roots were visually assessed in the soil profile after trench excavation. Root system depth and root dry mass were evaluated during both sowing periods. Results indicated that sunflower root penetration is deeper in Ultisol than in Oxisol. Water deficit promotes root depth, while water excess promotes root growth near the surface. Sowing during the first crop season results in deeper root penetration and higher root dry mass production compared to the second crop season.

高速作业种肥播深可控的花生播种机的设计与试验研究

Aiming at the traditional peanut planter seed and fertilizer sowing depth inconsistency caused by seed burning and injury, fertilizer waste and low seed emergence rate, the design of a peanut planter with high-speed operation and controllable seed and fertilizer sowing depth was performed. The laser sensor is added to detect the height of the ridge and the furrow opener position feedback, and the speed sensor detects the operating speed of the peanut planter. The mechanical analysis of the four-link rod clarifies the control principle, improves the PID algorithm of the integral term, designs the control strategy based on the operating speed of the planter, controls the electro-hydraulic system, and realizes the sowing and fertilizing depth adjustment of the furrow opener. Through the design of three-factor three-level orthogonal simulation test, it is concluded that the vehicle speed and height deviation value are significant factors affecting the sowing and application depth, and under the verification of the field test, it is obtained that when the sowing depth is 50 mm under the speed of 3 km/h, the dynamic sowing depth qualification rate is 96.26%, and the maximum coefficient of variation of the sowing depth is 2.58%, which improves the effect of the existing control of the sowing depth of the peanut by 6.05%, and reduces the variation of the sowing depth by 2.85%. The research has demonstrated superior performance compared to traditional mechanical adjustment in regulating the planting depth of peanuts, thereby achieving the intended design objective.

Working speed optimisation of the fully automated vegetable seedling transplanter

The purpose of this study was to determine the optimal operating speeds for a modified linkage cum hopper type planting unit that was used in low-speed automated vegetable transplanters. The transplanter utilizes a biodegradable seedling plug-tray feeding mechanism. The movement of the planter unit was simulated at different operating conditions using kinematic simulation software, and the resulting trajectories were compared based on factors such as plant spacing, soil intrusion area, soil intrusion perimeter, and horizontal displacement of the hopper in soil and found optimal result at 200, 250 and 300 mm/s and 40, 50 and 60 rpm combinations. The optimal operating speeds were then tested in a soil bin facility and found to perform well when transplanting pepper seedlings, with measured plant spacing that was close to the theoretical spacing. The planting depth in each case was not significantly different and the planting angle in different speed combinations was found to be significantly different, but within permissible limits. The mulch film damage was low for the selected optimised speed combinations. This study resulted in the determination of the optimal speeds for the transplanter, which can be used as a basis for optimising the other mechanisms within the transplanter.

Development and field testing of biodegradable seedling plug-tray cutting mechanism for automated vegetable transplanter

Removing seedlings from plug-trays to transplant in the field poses transplanting shocks to the seedlings and may reduce the survival rate. Therefore, this study designed biodegradable plug-tray cutting mechanism (SPCM) that separates seedlings with plug-cells from plug-trays and eliminates a complex clamping mechanism. SPCM consists of three sub-mechanisms that align the plug-cell at the seedling discharge point to cut and separate the plug-cell from the plug-tray, allowing the seedling to fall into the transplanting hopper. The SPCM separated around 82% of the plug-cell and delivered it to the planting unit. Furthermore, the SPCM-equipped transplanter achieved a transplanting performance of 74% with pepper and cabbage seedlings, with an average field efficiency of 68%, field capacity of 0.032-0.035 ha h-1 and required 73% less labour than manual seedling transplanting. The transplanting performance was satisfactory, with most pepper seedlings (85%) transplanted with a planting angle less than 10°, and 7% of cabbage seedlings were inclined and had sufficient planting depth of 48 mm for cabbage and 53 mm for pepper. In conclusion, the SPCM is a step towards sustainable and efficient vegetable seedling transplanting. Increasing efficiency, planting accuracy, and sustainability present exciting opportunities for further research and development in the field.

Cultivation of seeds and commercial crops from in vitro grown minitubers

In the conditions of the Zarafshan valley, the growth, development and productivity of potato cultivars were studied at different weights and planting depths for seed and commodity crop production. Correct determination of the planting depth of in-vitro-grown minitubers of different weights serves to increase the reproduction coefficient of rapidly multiplying minitubers. The red scarlet variety has 5-6 cm minitubers, 5-10 gram minitubers 6-7 cm, 10 grams and more minitubers 7-8 cm, and the Arnova variety has minitubers weighing up to 5 grams. Planting 6 cm, 5-10 grams and larger ones at a depth of 7-8 cm is 25-30 pieces per square meter, 456.5-485.5 thousand pieces per hectare and 6.7-6.8 hectares next year providing the field with seed.

Feasibility Study of Sustainable Coastal Protection through the Integration of Bamboo Breakwater and Green Mussel Cultivation

One pressing issue posing a significant threat to the coastal ecosystem is abrasion. Therefore, it is imperative to implement an effective and stable coastal protection structure using readily available and cost-effective materials combined with green mussel cultivation to bolster economic benefits for the community. The methodology employed in this study encompasses the integration and analysis of secondary data and the collection of archival information. The findings indicate that the ecological conditions of the waters in Bedono Village, Sayung District at Demak Regency meet the necessary criteria for green mussel cultivation. Bamboo with a minimum length of 7.5 meters and a planting depth of 2 meters is utilized. Financially, this approach proves to be quite advantageous, yielding a Net Present Value (NPV) of Rp1,202,383 for the stake method of green mussel cultivation. The Net Benefit-Cost Ratio (Net B/C) for the stake method of green mussel cultivation is 1.20. Based on the NPV and Net B/C feasibility criteria, the stake method of green mussel cultivation is considered viable. This structural concept is evaluated as adhering to ecological principles across all its components.

LEADER (Leaf Element Accumulation from DEep Roots): A nondestructive phenotyping platform to estimate rooting depth in the field

AbstractDeeper rooted crops are an avenue to increase plant water and nitrogen uptake under limiting conditions and increase long‐term soil carbon storage. Measuring rooting depth, however, is challenging due to the destructive, laborious, or imprecise methods that are currently available. Here, we present LEADER (Leaf Element Accumulation from DEep Roots) as a method to estimate in‐field root depth of maize plants. We use both X‐ray fluorescence (XRF) spectroscopy and ICP‐OES (inductively coupled plasma optical emission spectroscopy) to measure leaf elemental content and relate this to metrics of root depth. Principal components of leaf elemental content correlate with measures of root length in four genotypes (R2 = 0.8 for total root length), and we use linear discriminant analysis to classify plants as having different metrics related to root depth across four field sites in the United States. We can correctly classify the plots with the longest root length at depth (deeper than 30 or 40 cm) with high accuracy (accuracy >0.6) at two of our field sites (Hancock, WI and Rock Spring, PA). We also use strontium (Sr) as a tracer element in both greenhouse and field studies, showing that elemental accumulation of Sr in leaf tissue can be measured with XRF and can estimate root depth. We propose the adoption of LEADER as a tool for measuring root depth in different plant species and soils. LEADER is faster and easier than any other methods that currently exist and could allow for extensive study and understanding of deep rooting.

Impact of eco-physiological factors on the weed seed germination and emergence: A review on its role in weed management

Dormancy is a typical feature of many weed seed populations, which makes forecasting the time and magnitude of weed emergence difficult. The mean minimum temperatures required for undergoing germination of different weed seeds varies considerably depending on the place of their origin as well as the season on which the plants grow. For instance, the temperature requirement for the germination of summer weeds was observed to be 40% higher than for the winter weeds. Decreasing the water potential from 0 Mpa (mega pascal) to -1.0 Mpa tends to reduce the germination capacity of many weed seeds with some seeds totally failing to germinate at -1.0 Mpa (Chloris truncate, Retama raetam). The effects of planting depth on seed germination and seedling growth of Aframomum citratum on varied soil types indicated that sowing depth greatly influenced the plant's cumulative germination percentage and early growth. The seeds of Sysimbrium officinale (L.), a summer annual species, displayed greater sensitivity to nitrates and lost dormancy throughout the winter. The germination of Thlaspi arvense was also discovered to be stimulated by nitrate only in the presence of light. Tilling the surface of soil has a positive impact in the weed seed germination, however if the tillage depth increases more than 9cm, it tends to lower down the germination of several weed species. However, weed seeds of Bernard grass are among the exceptions in which they germinate better at a shallow depth (2cm). The nature and the thickness of the mulching component influence the germination of weed seeds. Thicker mulches and mulching materials like pearl millet resulted in a greater suppression of the weed seed germination due to an increased allelopathic effects.

Injection System Cultiving Machine for Plant Soybean in Panduman Village, Jelbuk District, Jember District

This low soybean production is caused by various factors, including farming technology that is still not good, the readiness and skills of soybean farmers are still lacking, The current conventional/traditional system used by farmers to grow soybeans is to make holes with a small hole or wood. After that put 2-3 soybean seeds in each hole and then cover it with soil, this kind of activity takes a long time, causing discomfort for farmers or farm workers. The target of this activity is farmers by encouraging them planting soybeans in Panduman Village which is still possible from a geographical point of view and directing profit-oriented farming in an effective planting time process. In the planting activity, the design prototype planted soybeans in 2 planting rows with a working capacity of ≤ 18 hours/ha with a seed output of 2-3 seeds/planting hole and a planting depth of 3-5 cm and regular spacing of 40 cm and the seeds were covered with soil cover. The design of the development of this planting machine is considered quite good in planting soybeans.

Determination of the Efficiency of Moringa Leaf Extract Treatments on Seedling Vigor in Marigold

The effect of different planting depths on emergence characteristics was investigated in this study carried out using seeds of Marigold (Tagetes patula) collected from nature. In addition, the most effective dose that can be used in priming treatments was tried to be determined by examining the effects of moringa leaf extract treatments applied at different doses in terms of emergence rate, emergence time, survival seedling rate, true leaf emergence time, emergence speed index, coefficient of velocity of emergence and vigor index values. After the T test, it was determined that different planting depth treatments created statistically significant differences especially in the survival seedling rate. It has been observed that the fact that the planting is exposed causes an increase in the survival seedlings rate. In addition, following hydropriming and moringa treatments, the highest seedling emergence rate at both planting depths was achieved with hydropriming and moringa leaf extract (4 g L-1) treatment. Moreover, moringa leaf extract (8 g L-1) treatments exhibited the earliest emergence compared to other treatments. All treatment groups were statistically different compared to the control group in terms of emergence speed index, coefficient of velocity of emergence and vigor index values in both planting depths, and HP and M3 treatments were the treatment groups that gave the best results. As a result of the study, it has been determined that surface sowing can be recommended in marigold cultivation and moringa treatments improve the emergence characteristics.

Experimental study of automated soil density control system of garlic planting machine

An automated system for adaptive regulation of soil density has been developed, which makes it possible to improve the quality of garlic incorporation when planting within the range of soil density regulation in the range of 1.2 -1.4 g/cm?. A methodology has been developed for conducting experimental studies of a machine for planting garlic with an installed automatic monitoring and control system for regulating soil density during planting. The results of experimental studies of the uniformity of soil compaction using a compaction roller with an automatic density control system and a closing device represented by a skid-type harrow indicate that after passing through a skid-type harrow, the value of the studied parameter increased by 18% relative to the initial state of the soil. The results of experimental studies of the quality indicators of the planting machine without an automatic monitoring and control system indicate a deterioration in the quality of the process of planting garlic bulbs with increasing forward speed in the range from 0.8 to 1.2 m/s at values of the coefficients of variation of the depth of planting of garlic bulbs ?_Hl from 32% to 42%. The results of experimental studies of the influence of a digital system for automatic control and management of garlic planting indicate the prospects of conducting research in this direction, which is confirmed by an increase in the quality indicators of the planting machine by 15% in comparison with the closing organ in the form of a skid-shaped harrow.