Precautions for Regional Comparative Trials of Cotton Varieties (Lines)
Regional comparative trials of cotton varieties (lines) compare newly introduced varieties (lines) with locally dominant varieties to assess their earliness (growth period), quality, yield potential, and resistance to pests and diseases, as well as their economic traits and fiber quality. The main purpose is to evaluate the performance of the test varieties (lines) across cotton regions and provide a scientific basis for selecting superior varieties in each region.
1. Selection of trial site
The selected trial site must be representative and uniform. It should have level land, medium-to-high and uniform fertility, a uniform previous crop, convenient irrigation and drainage, properly positioned plots, adequate light, and freedom from the influence of microclimatic factors.
2. Plot design requirements
Before sowing in the trial site, prepare a field planting map of the comparative trial plots and a schematic diagram of the arrangement of the test varieties in the plots. Use plastic film mulching, arrange the test varieties randomly, and use 4 replications. The net area of each plot is 20 sq m; there are no walkways between plots within the same replication, a guard row is set along the edge of each replication, and a 50-100 cm wide walkway is set between replications. Use wide-narrow row planting, and determine plant and row spacing according to the local field cultivation model and trial requirements. Sow 2-3 cotton seeds per hill by hand.
3. Trial methods and requirements
Field observations in the trial must be assigned to a dedicated person responsible for them and kept stable; records must be timely and accurate to ensure comprehensive and reliable data are obtained. Record books should be made in duplicate, with the original used in the field and the copy kept indoors. Recorded data must be organized promptly. Investigation items must be recorded according to uniformly prescribed methods and standards and entered in uniform forms.
After thinning to a stand, select 10 consecutive healthy, disease-free plants in the middle section of the two middle rows of each plot and mark them as dedicated plants for observing growth and traits in each plot.
Growth-period trait investigations mainly include: the five major growth stages; at the seedling stage, the number of surviving seedlings per plot, seedling survival rate, headless plant rate, dead seedling rate, growth vigor, uniformity, cold tolerance, and pest and disease conditions; at the flowering and boll-setting stage, observe growth vigor, uniformity, agronomic traits before topping, leaf color, and plant type; at the boll-opening stage, observe growth vigor, uniformity, node position of the first fruiting branch and height of the first fruiting node, number of fruiting branches per plant, number of effective bolls, number of fruiting nodes, boll-setting rate, number of bolls opening before frost, and so on.
4. Requirements for recording farm operations
Record the date, quantity, method, and other details of each farm operation, which helps correctly analyze the trial results.
Trial site management must be timely to ensure sufficient soil moisture and level land. After the seeder lays the film, divide the plots promptly afterward to avoid delays caused by hand sowing. Hand sowing must be completed on the same day, at an appropriate depth (3-4 cm), with 2-3 seeds per hill; the soil cover should not be too thick, and fine, moist, crumbly soil should be used, followed by manual pressing to ensure good soil moisture contact and uniform, consistent emergence.
Record soil traits and previous crop stubble, plowing and land preparation, dates of thinning and final thinning, intertillage and weeding, fertilization (including foliar fertilizer), irrigation, chemical regulation, topping and pruning, pest and disease control, and a series of other farm operation activities in the trial, as well as the varieties' responses to adverse environments.
5. Main climatic observations and records
Any change in environmental conditions will cause corresponding changes in crops, which are ultimately reflected in yield. Without climatic records, it is often impossible to clarify the reasons for the high or low yield of certain varieties. Comparative variety trials require recording the average temperature for each ten-day period from March to October of that year, the maximum and minimum temperatures for each month, the active accumulated temperature at >=10 degrees C, the dates of the first and last frosts, the number of frost-free days, the total precipitation from March to October, and the main weather change processes.
6. Requirements for cotton harvest and indoor seed testing
In order for observations, records, and measurements to truly help draw more comprehensive and correct conclusions about the trial, technical personnel must work meticulously and accurately. First, the observed samples must be representative. Second, the recorded and measured items must follow unified standards and methods, and the same person must complete the judgment and recording of each observation item in the trial to ensure the trial's precision. In the two middle rows of each plot, randomly collect 30 normal, fully opened, intact cotton bolls from the first fruiting node of the 3rd-5th fruiting branches as seed-testing bolls. Indoor seed-testing items include single boll weight, lint length, lint length uniformity, lint percentage, lint index, seed index, and abortive seeds.
7. Yield analysis
Harvesting must be timely, meticulous, and accurate. The picking time should be determined flexibly according to the opening time and amount of bolls in each plot. Picking in each plot should be completed on the same day. All four plots are included in yield calculation; pre-frost cotton and post-frost cotton are calculated separately, and ginned bolls are not included in yield calculation.
Calculate separately the pre-frost seed cotton and lint cotton yield, the post-frost seed cotton and lint cotton yield, and the total seed cotton and total lint cotton yield for each plot, then convert them into yield per 667 sq m. For pre-frost cotton, use 2 days after frost as the boundary and pick once uniformly. Plot lint cotton yield = plot seed cotton yield x lint percentage of the plot's seed-testing bolls. After harvest, investigate the number of harvested plants per plot, then convert it into the number of harvested plants per 667 sq m, and finally calculate the missing plant rate based on the theoretical number of plants per 667 sq m.
For plot yield analysis, first conduct analysis of variance on pre-frost lint cotton yield, then use the new multiple range test to determine the significance of differences among varieties.