The mineral particles found in soil range in size from microscopic clay particles to large boulders. The most abundant particles - sand, silt, and clay - are the focus of examination in studies of soil texture. Texture is the term used to describe the line composite sizes of particles in a soil sample, typically several representative handfuls . To measure soil texture, the sand, silt, and clay particles are sorted out by size and weight. The weights of each size are then expressed as a percentage of the sample weight.

   In the field, soil texture can be estimated by extracting a handful of sod and squeezing the damp soil into three basic shapes; (1) cast, a lump formed by squeezing a sample in a clenched fist; (2) thread, a pencil shape formed by rolling soil between the palms; and (3) ribbon, a flatfish shape formed by squeezing a small sample between the thumb and index finger. The behavioral characteristics of the soil when molded into each of these shapes, if they can be formed at all, provides the basis for a general textural classification. The behavior of the soil in the hand test is determined by the amount of clay in the sample. Clay particles are highly cohesive, and when dampened , behave as a plastic. Therefore the higher the clay content in a sample, the more refined and durable the shapes into which it can be molded.

   Another method of determining soil texture involves the use of devices called sediment sieves, screens built with a specified mesh size. When the soil is filtered through a group of sieves, each with a different mesh size, the particles become grouped in corresponding size categories. Each category can be weighed to make a textural determination. Although sieves work well for silt, sand, and larger particles, they are not appropriate for clay particles. Clay is far too small to sieve accurately; therefore, in soils with a high proportion of clay, the fine particles are measured on the basis of their settling velocity when suspended in water. Since clays settle so slowly, they are easily segregated from sand and silt. The water can be drawn off and evaporated, leaving a residue of clay, which can be weighed.

Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the questions

The author mentions "several representative handfuls" in the passage in order to show ______.

Câu hỏi liên quan

• According to the passage, which of the following statements is NOT true?

• What does the author imply in the last sentence of the passage?

• What is the main point the writer is trying to make in the last paragraph?

ZUNIA12

• The word “it” in paragraph 1 refers to ..............

• Which of the following could be considered a cause of the distress signals of trees?

• The expression get out of hand is closest in meaning to .........

• According to the passage, Melville’s early novels were ...............

• What kind of film is each program?

• The word “benign” in paragraph 3 is closest in meaning to ________.

• Which of the following is TRUE according to passage?

• According to the passage, which of the following is TRUE of webmasters?

• Based on its use in paragraph 2, it can be inferred that mitigate belongs to which of the following word groups?

• The author implies that the mammals of the "suburban forest" differ from most species of trees there in which of the following ways?

• It can be inferred from the passage that ___________.

• Which of the following is the best title for the passage?

• In the first paragraph, the word “emerged” is closest in meaning to____.

• According to the author, M.L. _______.

• What happened when the writer's father came?

• The phrase "All in all "in the passage  is closest in meaning to .............

• The author claims all of the following to be the benefits of rooftop gardens except .............