Tải bản đầy đủ - 0 (trang)
VII. Contribution to Plant Nutrition

VII. Contribution to Plant Nutrition

Tải bản đầy đủ - 0trang

THE SOIL ORQANIO FRBOTION



177



1. Nitrogen



Nitrogen occupies a unique position among the nutrient elements in

that it occurs almost entirely in the organic form in soils. Since the

supply of available nitrogen is very closely related to crop yields, the

factors governing the conversion of the organic reserve to the available

form are of grea,t importance. The soil organic fraction furnishes the

raw material for many of the important processes in the nitrogen cycle

and provides the fuel for most of the microbial transformations involved. This close relationship between the carbon and nitrogen cycles

makes it possible to relate certain nitrogen transformations to the carbon :

nitrogen ratio. Thus, when the ratio is large, an unbalance exists in the

proportion of energy material available to the soil population to the

quantity of nitrogen which can be used for synthesis of new cells. Under these conditions no net increase in inorganic nitrogen can occur ; in

fact any available nitrogen present is rapidly assimilated by microorganisms. The well-known nitrate depression which follows plowing under

large quantities of wheat straw or stubble is a typical example of the

situation just described. Nitrogen mineralization does not occur until

the unbalance has swung over to an excess of nitrogen, corresponding to

a low carbon: nitrogen ratio. This is accomplished by the conversion of

excess energy material to carbon dioxide and water. The ordinary circumstance in the soil organic fraction is that the carbon : nitrogen ratio

is low, but the supply of readily available energy material is limited and

ammonification is rather slow. This arrangement is advantageous in

several respects. The main reserve of soil nitrogen is held in an insoluble

form which cannot be leached away and is slowly converted to forms

which can be utilized by plants. In many cases, however, mineralization

is too slow to supply the current needs of a growing crop. I n this apparently anomalous situation two or three thousand pounds of nitrogen

may be present in an acre of soil, and yet a crop requiring perhaps 70

pounds in a season may suffer from nitrogen deficiency. The mineralization process can be speeded u p by increasing the activity of the soil

population; this may be accomplished through the addition of decomposable organic material, provided the nitrogen requirements of the

microbial population are also met. Thus, plowing under a green manure

crop stimulates microbial activity, supplies nitrogen for synthesis of

microbial cells, and accelerates mineralization of soil nitrogen.

When inorganic nitrogen fertilizers are applied to a soil, some of the

soluble nitrogen is assimilated by soil organisms and becomes part of the

organic nitrogen fraction, although it may be subsequently mineralized.

A large portion of the nitrogen is therefore derived from the soil organic



178



P. E. BROADBENT



fraction, even though the soil on which it is grown may have been fertilized with green manures, farmyard manure, or inorganic nitrogen

compounds.

As Ensminger and Pearson (1950) have pointed out, our knowledge

of the nitrogen cycle is seriously lacking in certain respects. Most of

the processes are understood in a general way and can be explained in

terms of over-all changes taking place, as has just been done in the case

of ammonification. More detailed information concerning spec,ific reactions and factors controlling them is urgently needed. Provided environmental conditions are suitable for microbial activity, the controlling

factor is usually the available energy supply. However, expression of

the energy status in terms of carbon : nitrogen ratios is an oversimplification not justified by the great diversity of substrates and of microbial

populations which occur in soils. A long step forward will have been

taken when the availability of a given type of organic matter can be

accurately predicted and a good estimate of cell synthesis obtained. The

availability of the nitrogen in organic materials has been assessed in

greenhouse pot tests, such as those conducted by Parbery and Swaby

(1942) and by Rubins and Bear (1942). A procedure which places

emphasis on the rate of liberation of nitrogen from the organic form in

humus has been developed by Harmsen and Lindenbergh (1949). Their

technique involves depletion of inorganic nitrogen reserves to a very low

level by cropping the soil to be tested with a fast-growing crop, which is

allowed to grow until nitrogen deficiency symptoms are manifest. The

crop plants in their entirety are carefully removed, root fragments are

sieved out, and the soil sample is then incubated under controlled temperature and moisture conditions. Determination of water-soluble nitrogen in the soil samples a t intervals permits calculation of the rate of

mineralization. Estimates of the capability of soils to supply mineral

nitrogen based on incubation procedures have also been obtained by

Pritchett e t aZ. (1947) and Cornfield (1952). The latter author concluded that ammonia as well as nitrate accumulation should be considered in assessing mineralizable nitrogen. He found that total nitrogen

may be used as a rough indicator of nitrogen availability, provided no

recent additions of fertilizers or organic material have been made,

whereas in the soils he studied carbon: nitrogen ratios were of no value

in predicting nitrogen availability.

The chief disadvantages of tests such as have been used to estimate

mineralizable nitrogen lie in their time-consuming nature and in the

fact that the information obtained is usually applicable only to conditions similar to those under which the test was conducted. The situation

is further complicated by differences i n behavior of the soil population



THE SOIL ORGANIC FRACTION



179



between cropped and fallow soils. Clark (1949) has pointed out that

nitrogen mineralization is usually less in cropped soils. Goring and

Clark (1948) attributed this decrease to immobilization in the soil, owing

probably to the increase in numbers of microorganisms that occurs with

plant growth.

2. Phosphorus



The contribution of phosphorus in the soil organic fraction to plant

nutrition has been the subject of intensive research in recent years. Considerable evidence has been accumulated which indicates that under

some conditions a substantial part of the phosphorus taken up by a

growing crop may be derived from organic forms. I n many soils organic phosphorus compounds may account for more than half the total

reserve (Bower, 1949). The mineralization process is not well understood but appears to be analogous to nitrogen mineralization in many

respects. Thompson and Black (1949) and Kaila (1949) have obtained

evidence of a relationship between carbon : phosphorus or nitrogen : phosphorus ratios and the occurrence of immobilization or phosphorus release. Kaila (1950) estimated the critical phosphorus content of natural

materials a t 0.2 per cent. I n materials having a higher content, phosphorus in excess of microbial requirements is present, and mineralization

would be expected to occur. It is sometimes pointed out in objection

to the view that soil organic phosphorus supplies part of the crop needs

for this element that peat soils having almost all their phosphorus in

organic form frequently are deficient in available phosphorus. This objection can be met satisfactorily by Kaila’s (1950) explanation that the

phosphorus content of peat soils is often below the critical value and

the mineralization which would follow a decrease in the carbon : phosphorus ratio is limited by a lack of available energy material. This is

essentially the same situation as with nitrogen, except that the critical

carbon : phosphorus ratios appear to be somewhat more variable than the

corresponding carbon : nitrogen ratios.

3. Other Elements



As a direct source of plant nutrients other than nitrogen and phosphorus the soil organic fraction is of relatively minor importance, although evidence of organometallic complexes has been obtained by

Bremner et al. (1946), and other nutrients are, of course, retained in

exchangeable form by the organic colloids. On the other hand the availability of some nutrient elements, notably iron, manganese, and sulfur,

may be profoundly influenced by organic matter and the activities of

the soil population. I n this connection the soil reaction and oxidation-



180



F. E. BBOADBENT



reduction status are of particular importance. Robinson (1930) haa

called attention to the changes which accompany submergence of soils.

Owing to the rapid depletion of oxygen through absorption by microorganisms, reducing conditions develop quickly ; combined oxygen in

various chemical compounds may then be utilized with resultant alteration in chemical composition of the soil solution. Sulfates may be reduced to sulfides, and insoluble ferric and manganic compounds reduced

to the relatively more soluble ferrous and manganous forms. Microbially produced carbon dioxide helps to keep in solution ions which

might otherwise be precipitated as carbonates or as the more soluble

bicarbonates. Toxic quantities of suMdes, iron, manganese, and aluminum may soon accumulate under the conditions described. Mann and

Quastel (1946) have shown that the addition of an available substrate

such as glucose to soil will cause an increase in soluble manganese under

aerobic conditions; a decrease in manganous ion follows the disappearance of glucose.

Under oxidative conditions, particularly in soils of neutral or alkaline reaction, iron and manganese are oxidized to insoluble forms, and

deficiency of these elements may result. Leeper and Swaby (1940) reported that microbial oxidation of manganese occurred over the pH

range 4.8-8.9, with the most rapid oxidation occurring between 6.0 and

7.5. Gerretson (1937) pointed out that manganese deficiency usually

occurs between the p H limits 6.5-7.8, the range in which he found the

manganese oxidizers to be effective.

The activities of chemosynthetic autotrophes capable of oxidizing

ferrous iron to the ferric form are well known; soil autotrophes also can

convert sulfur or sulfides to sulfates. Little is known concerning the importance of such groups of organisms under field conditions, but certainly

they exert some influence on nutrient availability,

The indirect effects of the organic fraction, particularly the living

portion, on soil fertility have received relatively little attention and deserve much greater emphasis in future research.



VII.



CONOLUSION



Ten years ago Norman (1942), in discussing the chemistry of soil

organic matter, expressed the belief that the time was ripe for a new

assault on the problems related to the fundamental nature of this important soil constituent, one which would bring our knowledge of it to

a level comparable to our present knowledge of clays. Progress in the

intervening decade has been hampered by a world war, but some real



THE SOIL ORGANIC FRACTION



181



advances have been made, although the number of workers in this particular field is still quite small.

The goal of a fairly complete characterization of the soil organic

fraction is still f a r from realization, but it may confidently be expected

that intensive application of new techniques already a t hand, such as

chromatographic and electrophoretic separation, use of isotopic tracers,

and ultraviolet and infrared spectrophotometry, will greatly accelerate

progress in that direction.



REFERENCES

Alexander, L. T., and Byers, H. G. 1932. 77.5. Dept. Agr. Tech. Bull. 317.

Allison, F. E., Sherman, M. S., and Pinck, L. A. 1949. Soil Soi. 68, 463-478.

Barshad, I., and Rojas-Cruz, L. A. 1950. Soil Sci. 70, 221-236.

Bartholomew, W. V., and Goring, C.A.I. 1948. Soil Sci. ,900. Amer. Proc. 15, 238241.

Bartlett, J. B. 1939. Iowa State CoZZ. J . Sci. 14, 11-13.

Bartlett, J. B., Ruble, R. W., and Thomas, R. P. 1937. Soil Sci. 44, 123-138.

Beijerinck, M. W. 1898. Centr. Bakteriol. Parasitenb. 11, A b t . 4, 209-216.

Bennett, E. 1949. Soil Soi. 68, 399-400.

Bingeman, C. W.,Varner, J. E., and Martin, W. P. 1953. Soil Sci. SOC.Ame-r.

Proc. 17, 34-38.

Bower, C. A. 1949. Iowa Agr. E z p t . Sta. Research Bull. 362.

Bremner, J. M. 1949a. J . Agr. Sci. 39, 183-193.

Bremner, J. M. 1949b. J . Agr. Sci. 39, 280-282.

Bremner, J. M. 1950a. J . Soil Sci. 1, 198-204.

Bremner, J. M. 1950b. Nature 165, 367.

Bremner, J. M. 1951. J. Soil Sci. 2, 67-82.

Bremner, J. M.,Heintze, S. G., Mann, P. J. G., and Lees, H. 1946; Nature 168,

790-791.

Bremner, J. M., and Lees, H. 1949. J. Agr. Sci. 39, 274-279.

Broadbent, F. E., and Bartholomew, W. V. 1948. Soil Sci. SOC.Amer. Proo. 13,

271-274.

Broadbent, 3’. E., and Bradford, G. R. 1952. Soil Sci. 74, 447-457.

Broadbent, F. E.,and Norman, A. a. 1946. Soil Sci. Soo. Anter. Proc. 11, 264-267.

Brown, A. J. 1886. J. Chent. SOC.London 49, 172-187.

Brown, I. C., and Byers, H. G. 1935. U.S. Dept. Agr. Tech. Bull. 602.

B r o w , I. C., and Thorp, J. 1942. U.S. Dept. Agr. Tech. Bull. 834.

Byers, H. G., Alexander, L. T., and Holmes, R. 5. 1935. U.S. Dept. Agr. Tech.

Bull. 484.

Chandler, R. I?. 1939. J . Agr. Besearch 69, 491-505.

Clark, F. E. 1949. Advances in Agron. 1, 241-288.

Cornfield, A. H. 1952. J. Sci. Food Agr. 3, 343-349.

DeBary, A. 1887. Comparative Morphology and Biology of the Fungi Mycetozoa

and Bacteria. Oxford. pp. 8, 13. Oxford Univ. Press.

Ensminger, L. E., and Gieseking, J. E. 1939. Soil Sci. 48, 467-471.

Ensminger, L. E., and Gieseking, J. E. 1942. Soil Sci. 63, 205-209.

Enminger, L. E., and Pearson, R. W, 1950. Advawe8 in Agron. 2, 81-111.



182



F. E. BROADBENT



Evans, T. H., and Hibbert, H. 1946. Advances in Carbohydrate Chem. 2, 204-233.

Feustel, I. C., and Byers, H. G. 1936. Soil Sci. 42, 11-21.

Flaig, W. 1950. 2. Pfianzenernahr. Diing. Bodenk. 51, 193-212.

Forsyth, W. G. C. 1947. J. Agr. Sci. 37, 132-138.

Forsyth, W. G. C. 1948. Chemistry & Industry, pp. 515-519.

Forsyth, W. G. C. 1950. Biochem. J . (London) 46, 151-146.

Forsyth, W.G. C., and Webley, D. M. 1949. J. Gen. Microbial. 3, 395-399.

Fuller, W. H. 1946. Soil Sci. SOC.Amer. Proc. 11, 280-283.

Fuller, W. H. 1947. Soil Sci. 64, 183-197.

Geoghegan, M. J. 1947. Proc. SOC.Appl. Bacteriol. 2, 77-82.

Geoghegan, M. J. 1950. Trans. Intern. Congr. Soil Sci. 4 t h Congr. Amsterdam 1,

198-201.

Gerretson, I?. C. 1937. Ann. Botany (London) 1, 207-230.

Gieseking, J. E. 1949. Advances in Agron. 1, 159-204.

Gillam, W.S. 1940. Soil Sci. 49, 433-453.

Goring, C. A. I., and Bartholomew, W. V. 1949. Soil Sci. SOC.Amer. Proc. 14,

152-156.

Goring, C. A. I., a n d Bartholomew, W. V. 1950. Soil Sci. SOC.Amer. Proc. 15,

189-194.

Goring, C. A. I., and Clark, F. E. 1948. Soil Sci. SOC.Amer. Proc. 13, 261-266.

Gottlieb, S., and Hendricks, S. B. 1945. Soil Sci. SOC.Amer. Proc. 10, 117-125.

Gray, P. H. H., and McMaster, N. B. 1933. Canadian J. Research 8, 375-389.

Gray, P. H. H., and Taylor, C. B. 1935. Canadian J. Research 013, 251-255.

Hallam, M. J., and Bartholomew, W. V. 1953. Soil Sci. SOC.Amer. Proc. 17,

Harmsen, G. W.,and Lindenbergh, D. J. 1949. Plant and Soil 2, 1-29.

Hebert, A. 1892. Ann. Agron. 18, 536-550.

Henin, S., and Turc, L. 1950. Trans. Intern. Congr. Soil Sci. 4th Congr. Amsterdam 1, 152-154.

Hopper, T. H., Nesbitt, L. L., and Pinckney, A. J. 1931. North Dakota Agr. Expt.

Sta. Tech. Bull. 246.

Jenny, H. 1930. Vissouri Agr. Expt. Sta. Research Bull. 152.

Jenny, H. 1941. Factors of Soil Formation. MoGraw-Hill Book Co., New York.

Jenny, H. 1950. Soil Sci. 69, 63-69.

Jenny, H., Gessel, 8. P., and Bingham, F. T. 1949. Soil Sci. 68, 419-432.

Kaila, A. 1949. Soil Sci. 68, 279-289.

Kaila, A. 1950. Trans. Intern. Congr. Soil Sci. 4th Congr. Amsterdam 1, 191-192.

Kelley, C. W., and Thomas, R. P. 1942. Soil Sci. SOC.Amer. Proc. 7, 201-206.

Kojima, R. T. 19478. Soil Sci. 64, 157-165.

Kojima, R. T. 1947b. Soil Sci. 64, 245-252.

Leeper, G. W., and Swaby, R. J. 1940. Soil Soi. 49, 163-169.

Mangin, L. 1899. J . Botany Brit. and Foreign 13, 209-216, 276-287, 307-316, 339347.

Mann, P. J. G., and Quastel, J. H. 1946. Nature 168, 154.

Martin, J. P. 1945. Soil Sci. 69, 163-174.

Martin, J. P. 1946. Soil Sci. 61, 157-166.

Mattsou, S., and Koutler-Andersson, E. 1943. Lantbruks-Hogskol. Ann. 11, 107134.

MeGeorge, W. T. 1930. Ariaona Agr. Expt. Sta. Tech. Bull. 30.

McHenry, J. R., and Russell, M. B. 1944. Soil Sci. 67, 351-357.

McLean, E. 0. 1952. Soil Sci. SOC.Amer. Proo. 16, 134-137.



THE SOIL ORaANIC FRACTION



183



McLean, W. 1931. J. Agr. Soi. 21, 595-611.

Milbr, H. C., Smith, F. B., and Brown, P. E. 1936. J . Am. SOC.Agron. 28, 753766.

Mortland, M. M., and Gieseking, J. E. 1952. Soil Sci. ,900. Amer. Proc. 16, 10-13.

Myers, 11. E. 1937. Soil Sci. 44, 331-359.

Newman, A. S., and Norman, A. G. 1941. Soil Sci. SOC.Amer. Proc. 6, 187-194.

Norman, A. G. 1931. Ann. Appl. Biol. 18, 244-259.

Norman, A. G. 1933. Science Pfog. 27, 470-485.

Norman, A. G. 1942. Soil Sci. Soe. Amer. Proc. 7, 7-15.

Norman, A. G., and Bartholomew, W. V. 1940. Soil Sci. SOC.Amer. Proc. 5, 242247.

Norman, A. G., and Bartholomew, W. V. 1943. Soil Sci. 56, 143-150.

Norman, A. G., and Peterson, W. H. 1932. Biochem. J. (London) 26, 1946-1953.

Olson, F. R., Peterson, W. H., and Sherrard, E. C. 1937. Ind. Eng. Chem. 29,

1026-1029.

Olson, L. C., and Bray, R. H. 1938. Soil Sci. 45, 483-496.

Parbery, N. H., and Swaby, R. J. 1942. Agr. Gaz. N . S. Wales 53, 357-361.

Peele, T. C. 1940. J . Am. Soo. Agron. 32, 204-212.

Pinck, L. A., and Allison, F. E. 1944. Soil Sci. 57, 155-161.

Pinck, L. A., and Allison, F. E. 1951. Soil Sci. 71, 67-76.

Plice, M. J., and Lunin, J. 1941. J. Am. SOC.Agron. 33, 851-855.

Pritchett, W. L., Black, C. A., and Nelson, L. B. 1947. Soil Sci. SOC.Amer. Proc.

12, 327-331.

Rather, J. B. 1917. Arkansas Agr. Ezpt. Sta. Bull. 140.

Read, J. W., and Ridgell, R. H. 1922. Soil Sci. 13, 1-6.

Robinson, W. 0. 1930. Soil Sci. 30, 197-217.

Rubins, E. J., and Bear, F. E. 1942. Soil Sci. 64, 411-423.

Russell, E. J. 1950. Soil Conditions and Plant Growth. 8th edition, E. W. Russell,

Editor. Longmans Green & Co., London, p. 192.

Scheffer, F., and Welte, E. 1950. 2. Pjlunzenerniihr. Dung Bodenk. 48, 250-263.

Schmidt, M. 1936. Arch. Y i k r o b i o l . 7, 241-260.

Siegel, 0. 1941. ForschDienst. Sonderh. 17, 32-35.

Smith, H.M., Samuels, G., and Gernuda, C. F. 1951. Soil Sci. 72, 409-427.

Sowden, F. J., and Atkinson, H. J. 1949. Soil Sci. 68, 433-440.

Springer, U. 1943. Bodenkunde u. PJlanzenerniihr. 32, 129-146.

Stevenson, F. J., Marks, J. D., Varner, J. E., and Martin, W. P. 1952. Soil Poi.

Soc. Amer. Proc. 16, 69-73.

Swaby, R. J. 1950. J . Soil Sci. 1, 182-194.

Thom, C., and Phillips, H. 1932. J. Wash. Acad. Sci. 22, 230-239.

Thomas, R. C. 1928. Am. J . Botany 15, 537-547.

Thompson, L. M., and Black, C. A. 1949. Soil Sci. SOC.Amer. Proc. 14.

Vandecaveye, S. C., and Eatznelson, H. 1938. Soil Sci. 46, 139-167.

Vandecaveye, S. C., and Eatznelson, H. 1940. Soil Sci. 50, 295-311.

Van Slyke, D. D., and Folch, J. 1940. J. B i d . Chem. 136, 509-511.

Waksman, S. A., and Iyer, E. R. N. 1932. Soil Sci. 34, 43-69.

Waksman, 8. A., and Reuszer, H. W. 1932. Soil Sci. 33, 135-151.

Waksman, S, A., and Smith, H. W. 1934. J . Am. Chem. SOC.56, 1225.

Waksman, 8. A,, and Stevens, K. R. 1930. Soil Sci. 30, 97-116.



This Page Intentionally Left Blank



Progress in Agricultural Engineering

L . W. HURLBUT

Nebraska Agricultural Experiment Station Lincoln. Nebraska

Page



.

. . . . . . . . . . . . . . . . . . . . . . 185

. . . . . . . . . . . . . 186

I11. General Characteristics of Modern Farming . . . . . . . . . . . 187

I Introduction

I1. Concept of Agricultural Engineering



.

.

.

.



. . . . . . . . . . . . . . 187

. . . . . 188

. . . . . 189

. . . . . . . . . 190

. . . . . . . . . . . . . . . . . . . . .

190

. . . . . . . . . . . . . . . . . . . .

190

. . . . . . . . . . . . . . . . . . 190

. . . . . . . . . . . . . . . . . . 192

. . . . . . . . . . . . . . . . . . 192

. . . . . . . . . . . . . . 193

. . . . . . . . . . . . . . 193

. . . . . . . . . . . . 194

. . . . . . . . . . . . . . . . . . . 195

. . . . . . . . . . . . . . 196

. . . . . . . . . 196

. . . . . . 198

. . . . . 200

. . . . . . . . . . 206

. . . . . . . . . . . . . . . 206

.

. . . . . . . . . . . . 207

.

. . . . . . . . . . . 207

. . . . . . . . . . . . . . 207

. . . . . . . . . . . . . . . . 207

. . . . . . . . . . . . . . . . . . 209

. . . . . . . . . . . . 209

. . . . . . . . . . . . 209



1 Increased Power per Worker

2 Comparisons of Crop Yields and Per Capita Production

3 Impact of a 20 Per Cent Increase in Total Farm Output

4 A Few Important Developments, 1900-1950

I V Future Trends

1 Farm Power

a Tractor Power

b Electric Power

c The Airplane

2 Soil and Water Management

a Surface-Mulch Farming

b . Runoff-Water-Control Systems

c Irrigation

3 Harvesting and Storing Grain

a Some Harvesting and Storage Losses

b. Moisture Limits for Some Harvesting Machines

c Conditioning Wheat and Shelled Corn for Storage

4 Harvesting and Storing Hay and Forage

a Main Sources of Loss

b Sun-Cured vs Dehydrated Hay

c Silage vs Dehydrated Green Corn

d Need t o Define Quality

e New Developments

5 Cotton Production

a Weed Control and Defoliation

b New Harvester Developments

c New Ginning Developments

6. Equipment for Applying Fertilizers

7 Mechanization of Special Crops

V Concluding Statements

References



.



.

.



.



.



.



.

.

.



.

.

.



.



.

.

.

.

.

.

.



.



.



.



. .

.

. .

. . . . . . .

.............



.

.

.

.

.



.

.

.

.

.



.

.

.

.

.



. . . . . . . . 210

. . . . . . . . 210

. . . . . . . . 211

. . . . . . . . 216

.......

216



I. INTRODUCTION

Agricultural engineers and agronomists find many areas of mutual

interest throughout the agricultural industry . Both groups have helped

to establish the fact that the production per agricultural worker is di186



186



L. W. EUBLBUT



rectly related to the investment in farm machinery and farm power,

which in turn depends upon the development of certain characteristics

in crops. The widespread use of farm power and machinery in agricultural production has been one of the most significant features in the

development of both American agriculture and American industry.

All developments stem from basic interests of the general public.

Viewed from a national standpoint, the public’s interest in the agricultural industry includes four fundamental features : first, adequate quantity of production ; second, satisfactory quality of products ; third,

production a t low cost ; and fourth, the well-being of the people engaged

in the industry.

11. CONCEPTOF AGRICULTURAL

ENGINEERING)



It seems appropriate to review briefly the various phases of agricultural engineering. Among these are :

1. Development and application of farm power and machinery.

2. Farm buiIdings and rural housing.

3. Farm electrification, involving the application of electric energy

as heat, light, radiation, and power.

4. Mechanical processing of farm products.

5. Engineering phases of soil and water usage, including erosion control, drainage, and irrigation.

6 . Methods engineering.

Engineering may be defined, generally, as “the art and science of

utilizing the forces and materials of nature for the benefit of man and

the direction of man’s activities toward this end.” This definition implies two activities, namely, art and science. The science of engineering

is based upon the pure sciences, physics, chemistry, and mathematics.

This is the phase of the field which is exact and rational. The a rt of

engineering refers to the ability to judge, estimate, and manipulate the

uncertainties of engineering to a satisfactory solution of a problem. It

refers to a procedure which has been found by a series of trial-and-error

events, carried out in as logical a sequence as possible, to produce a desired result without a knowledge of all of the basic principles involved.

It is well known that a t the present time the field of agricultural engineering encompasses more uncertainties than do the more common engineering fields.

The use of basic science in research in agriculture is already very

great, but there are good indications that it will continue to expand.

The work of Bu rr (1942, 1943, 1945, 1947), Burr and Sinnott (1944),

and Nelson and B u rr (1946) indicates the possibility of a search for in-



Tài liệu bạn tìm kiếm đã sẵn sàng tải về

VII. Contribution to Plant Nutrition

Tải bản đầy đủ ngay(0 tr)

×