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AI physiologycourse--level and content

F.~ P. Gardner and R. B. Pearce

ABSTRACT amongcrops which tended to result in superficial treat- ment of basic concepts. (3) An introductory course Undergraduatecourses in crop science have crop science was offered at most institutions, but the traditionally beenpresented on a cropor crop-type content varied widely, ranging from essentially a begin- basis(grain, forage, oil, fiber, etc.) ratherthan on ning course to a general course in crop produc- conceptualbasis (crop physiology).Peer appraisal tion, often geographically oriented. Mitchell and of a coursein cropphysiology, proposed on a con- 3 ceptualbasis, wasobtained. Gardner suggested that key concepts in a body of In 1977, a questionnairewas sent to cropphysi. knowledge could be more effectively learned if subject ologists in the AmericanSociety of Agronomyfor matter was presented on a conceptual basis. Also, the their evaluation of the importanceof selected introductory course in crop science should contain the topics for a proposedcrop physiology course (1 broad, basic concepts. very important, to 5 = not important). Respond- Gardner (F. P. Gardner. 1971. A model for deriva- ents consideredthe proposedoutline logical. tion and organization of courses, p. 126. Agron. Abstr.) Sometopics were rankedas moreimportant than suggested that courses in crop science and science others for a crop physiologycourse. Major topics should embrace key concepts of these respective bodies suchas carbon(1.8), partitioning (1.8), of knowledge. The introductory course should consist stresses(1.9), (2o0), andlight (2.0) were viewedas moreimportant for the proposed of the families of concepts in the discipline as the basic coursethan respiration(2.1), growthand develop- units of instruction in the introductory course. An in- ment(2.1), harvestphysiology (2.1), mineralnutri- dividual family or group of related concepts, i.e., the tion (2.2), future challenges(2.3), andgrowth physical properties of , could be expanded in stances(2.5), Subtopicswithin a majorarea varied breadth and depth for a second-level or derivative (D) widelyin ranking,i.e., undercarbon; canopy char. course. Member(s)of a family of concepts could be ex- acteristics and CO, uptakewere consideredmore panded for a course at the third level of complexity importantthan ambientlevels, trends, and ferti. (D’) if additional expansion for specialization in the lization with CO2. subject is desired. Mostinstitutions surveyedoffer coursesin crop physiologywhich are taughtprimarily at the gradu- A plan for the organization and offering of courses in ate level. Mostrespondents felt that a dual level crop science, on a conceptual basis, was implementedat (senior-graduate)course in cropphysiology, with Iowa State University in 1964. One derivative course plant physiologycourse prerequisite, was most from the introductory course was in the area of physi- desirableas the first cropphysiology course. ology and management termed Crop Growth and If the undergraduatecurriculum in agronomyis Culture. Dr. Mitchell (1970) published the textbook, to be basedon conceptualcourses, we suggest Crop Growth and Culture, to support this new course. that a coursein crop physiologyshould be in- Because this was a major adjustment at the time, tradi- cluded. tional patterns seemed to mittigate against titling the course Crop Physiology as desired. Mitchell probably Additional index words: Conceptualcourses, Cropscience, Agronomycourses. titled his book with the same restraint. A course called Principles of Crop Physiology is currently taught at Iowa State University for majors in agronomy, with a offerings in agronomy or crop science at course prerequisite. COURSELand Grant universities have been examinedand re- This paper deals with developing appropriate content ported to the A-I Division of the American Society of for a course which would be titled Crop Physiology. Like Iowa State, Western Illinois University offers an Agronomy(ASA) 3. In their survey they found the fol- lowing. (1) Generally, content of undergraduate courses undergraduate-graduate level course in crop physiology in crop science was organized with emphasis on a crop (i.e., cotton or tobacco production) or a group ’Contribution fromDep. of Agric., WesternIllinois Univ., related (i.e., grain or cereal crops, forage crops, McComb,IL 61455and AgronomyDep., IowaState Univ., Ames,IA special crops, or "fiber and oil" crops). Except for 50011.Journal Paper No. 48, College of ,Iowa State Univ. 2 Visiting professorand professor of agronomy,Univ. of Florida , few courses were organized on a con- andIowa State Univ.,respectively. ceptual basis. (2) Crop oriented courses appeared 3R. L. Mitchelland F. P. Gardner.1963. A new subject matter ar- lead to redundance due to the commonalityof principles rangementfor field cropcourses, p. 126.Agron. Abstr. 59 JOURNALOF AGRONOMICEDUCATION, VOL. 10, 1981

titled Advanced Crop Science. Mitchell’s textbook, Table2. Detailedoutline andpeer rating of proposed Crop Growthand Culture, is required. coursetopics in CropPhysiology Wedesired peer appraisal of content and level of the 2.1 I. Introduction proposed course, outlined in Table 2. To accomplish 2.0 A. Crop Physiology--An emerging science this, a questionnaire was sent to crop physiologists in 1.5 B. Dynamicrelationships of growth and yield the ASAin August 1977. Responses to a series of ques- 2.9 C. Distinction between crop physiology and plant physiology tions and the ranking of topics in the course outline as 2.1 n. Growth and development 1.6 A. Definitions to relative importancewere requested. 2.1 B. Cells, tissues, organs, and 2.6 C. Kineticsofgrowth 2.7 D. Allometry RESULTS AND DISCUSSION 1.7 E. and related crop development(tillering, branching, rooting) The percentage return on the questionnaire was about 2.4 F. Ontogeny and morphogenesis 2.2 G. Internal and external factors affecting growth 60°70 (28/50). Rankingof majortopics or the broadsub- 2.1 H. Differentiation divisions of the proposed Crop Physiology course is 2.1 I. Factors affecting differentiation given in Table 1. 1.9 J. Growth-differentiationcorrelations Carbon,partitioning, plant stresses, photosynthesis, 2.5 In. Growthsubstances 2.1 A. Classification and terminology andlight received the highest rating of all majortopics 3.1 B. Classical work and historical (between 1.8 and 2.0). Growthsubstances received the 2.5 C. Auxins and crop responses lowest rating (2.5). Mineral nutrition was ranked2.2 2.4 D. Gibberellins and crop responses 2.7 E. l(inins and crop responses "important" with some comments suggesting that 2.8 F. Inhibitors/retardants and crop responses mineral nutrition could or should be taught in soil sci- 2.9 G. Ethylene and other crop substances ence. Likewise, there were commentssuggesting that 2.8 H. Defoliants and dessicants 2.5 I. Agriculturalapplications growth regulation is more applicable to 2.1 1. Rooting and/or weed science and could be omitted from Crop 2.3 2. Thinning 2.5 3. Growth modification Physiology. No respondents suggested that photo- 2.4 4. Fruiting modification synthesis and related areas (light, carbon, respiration, 2.2 IV. Mineral nutrition and partitioning of assimilates) be omitted in the pro- 2.1 A. Requirement byplants posed course. However, there were numerous comments 2.1 B. Transport 2.6 1. Outer and freespace as to the nature or kind of coverage these topics should 2.5 2. Active and passive movement receive. Most respondents felt that photosynthesis and 1.8 3. Movementof organic and inorganic substances in plant tissues related topics should be treated at the plant community 2.3C. Metabolism of minerals 2.6 1. Uses in plant processes level rather than at the cellular level. Several suggested 2.4 2. Biological fixation that a plant physiology course should be required as a 2.0 D. Nutrition, , and quality 2.0 E. growth and development prerequisite to the proposed crop physiology course. 1.6 G. Root system architecture as related to growthand yield Respondentsapparently felt that students should have a 2.0 V. Light backgroundin the biochemical and cellular aspects of 1.5 A. Energy budget plant physiology before enrolling in a course in crop 1.9 B. Propertiesoflight physiology, represented by the proposed outline. Crop 2.3 C. Pigments: Action and absorption spectra 2.3 D. Control mechanisms--Seedgermination, flowering, other scientists could then concern themselves with photosyn- 1.8 Vl. Carbon thesis and other physiological phenomenaat the canopy 2.3 A. Ambient levels and CO2trends or communitylevel. 1.5 B. Carbon sources and availability Table 2 presents respondent rankings of the sub- 1.5 C. Canopy features and CO2uptake 1.7 D. Canopy ventilation--Natural and manipulated tropical componentsof each major topic. Definitions, 2.2 E. CO=fertilization meristems, and growth-differentiation subtopics were 1.9 VII. Photosynthesis 2.3 A. Light and dark phases: Electron transport Table1. Topicaloutline. Peerratings of topicsin a 2.4 B. Energy sinks and emerson enhancement proposedcourse in CropPhysiology 2.3 C. Alternative carboxylation pathways 1.6 D. Crop canopy--Characteristics and CER Ratings~" Topics 1.6 I. LAI 1.6 2. Plantgeometry--Leafangleandorientation 2.1 I. Introduction 1.8 3. Opticalqualities, extinction 2.1 II. Growth and development 1.6 E. Cropresponse to irradiance levels 2.5 ill. Growthsubstances 2.2 IV. Mineral nutrition 2.1 VIII. Respiration V. Light 1.8 A. Mitochondrial 2.0 1.8 B. Photorespiration 1.8 VI. Carbon 1.6 C. C~/C, characteristics: Anatomical, biochemical, physiological 1.9 VII. Photosynthesis 2.6 1. Theoriesoforigin 2.1 Vlll. Respiration 2.3 2. Variation between and amongtaxa 1.8 IX. Partitioning 2.3 3. Alternatives for photorespiration tenuation 1.9 X. Stresses 2.1 XI. Harvest physiology 2.3 XII. Future challenges

1 = very important, 2 = important, 3 = good to know, 4 = of some value, (continued) and 5 = not important. CROP PHYSIOLOGY COURSE 61

Table 2. Continued stood at the cellular level to understand how they in- fluence crop development and yield. Subtopics under 1.8 IX. Partitioning partitioning of assimilates were ranked high except for 1.6 A. Translocation and partitioning life cycle and related growth habits. Partitioning of 1.7 B. Harvest fraction and biomass 2.1 C. Yield components mineral elements should also be included. 1.6 D. Source-sink relationships Plant stresses were considered important; however, 1.7 E. Senescence there was less interest in stresses from pollutants. 2.3 F. Cyclic behavior--Annuals, biennials, perennials 1.9 G. reserves and storage organs Harvest physiology was rated important except for size and size effects on seedling growth. Seed size and 1.9 X. Stress and crop responses 1.8 A. seedling growth mayhave received a higher rating if it 1.7 B. Temperature had been listed in a better context, probably under 2.3 C. Atmospheric pollutants growth and development. The extensive and excellent 2.1 XI. Harvest physiology work on seed physiology and relationships to crop 2.0 A. Physiologic maturity and harvest maturity 2.3 B. Black layer and indicators growth makes it worthy of inclusion in crop physiology. 1.9 C. Harvest schedules, maintenance of food reserves, production and Respondents reflected little enthusiasm for the future stand survival 2.1 D. Relationship of regrowth of perennials forages to food reserves challenges topic. and basal LAI Twenty respondents replied that their university 2.1 E. Fall managementof perennials forages offered a course(s) in crop physiology (Table 3). The 2.4 F. Seed size and quality dication was that most or practically all offerings were 2.3 XII. Future challenges to the student in CropPhysiology at the graduate level. However, 56%(17/30) replied that the proposed outline should be a senior-graduate or dual-level course (Table 4). This response some perceived as being more important than kinetics, al- confusion. (1) Is the proposed course less sophisticated lometry, and ontogeny. Based on responses received, than the course(s) now offered (most at the graduate the latter topics could be omitted, especially if fitting the level)? (2) Dorespondents feel there is a need for a dual- course into a semester term is a problem. However, level course in the subject matter despite present offer- from our point of view, the relationship of size of plant ings? (3) Do the respondents feel that undergraduate parts (allometry) and pattern of development over time students in agronomy should take a crop physiology (ontogeny) are important in a course on crop physi- course taught at the undergraduate level? The outline of ology. the proposed course (Tables 1 and 2) was developed Growth substances was considered least important of with questions (2) and (3) in mind. the major topics in the course outline. These ratings re- Apparently, somerespondents classified all plant bio- flect an attitude that growth substances should probably and plant physiology course offerings at their be covered in horticulture or weed science courses. institution as crop physiology. Some stated three or However, such a decision seems quite arbitrary to the more courses in crop physiology are offered, all at the authors since the use of growth substances on field graduate level. Wefeel that crop physiology is a body of crops, except as a weedcontrol agent, would probably knowledge in its own right and disagree with a not be covered in other disciplines. classification of plant physiology and plant biochemis- Subtopics under mineral nutrition received variable ratings (Table 2). Transport was considered important. Table3. Responsesto selectedquestions pertaining to a proposedcourse in CropPhysiology Energetics and mechanisms of uptake and movement were viewed as less important than transport. Respond- Question No. and responses ents mayhave assumedthat these topics were covered in Doesyour institution offer a course in 20 Yes* Plant Physiology or courses. Root system Crop Physiology? 2 No architecture was viewed as important (1.6), the special At what level should course (Table 2) be offered? 3 Junior-Senior arrangement of and effective surface might have 4 Senior 17 Senior-Graduate been viewed as analagous to canopy architecture in im- 5 Graduate portance to crop growth. 1 None Subtopics of light-pigments--action and absorption ls organization of course outline logical and wouldit 20 Logical spectra, and control mechanisms--in light responses build on student progress in his discipline? I Not logical were viewed as less important. Respondents may have viewed these as duplications of topics in plant physi- Table 4. Additional comments ology. Changesin the ambient level or the upward trend of CO2in recent years were not perceived as important Needs more emphasis on physical environment and community behavior. Whyseparate light and carbon from photosynthesis? as course topics nor was CO2fertilization (Table 2). All topics important--can’t rank them. Respondents considered respiration important, but Outline too broad for single course. slightly less so than photosynthesis. Assimilate require- Not enough emphasis on crop physiology as compared to plant physiology. Not enoughemphasis on nitrogen, especially biological nitrogen. ments for growth and maintenance and losses due to Not enough emphasis on of crop production. photorespiration and dark respiration were of interest. Should have plant physiology as prerequisite. Photorespiration and dark respiration need to be under- Partitioning would more logically fit under growth and development. 62 JOURNAL OF AGRONOMIC EDUCATION, VOL. 10, 1981

try as crop physiology. A majority of respondents be- cipally at the graduate level) and that the outline we pro- lieve that the outline (Table 2) is logical and that it posed should be a dual, senior-graduate level course. builds on progress of the student. Many respondents would require plant physiology as a The proposed course would be the first crop physi- prerequisite although this was not a specific question in ology course the student would take with plant physi- the survey. Write-in comments indicated that the course ology as a prerequisite. We agree with many comments should emphasize physiology of the crop community offered by respondents (Table 4) to the extent that the rather than cellular metabolism (the emphasis in plant proposed outline could be changed in several ways. The physiology). The respondents suggested that the greatest topics light and carbon could just as well be subtopics emphasis should be on photosynthesis in the crop com- under photosynthesis. Partitioning is an integral part of munity and associated phenomena. Respondents were vegetative and growth and development, and could less impressed with growth regulation as a topic. Many be a subtopic of growth and development, especially felt that the coverage (as outlined in Table 2) for a single since partitioning involves both minerals and carbon as- course is too broad. The authors hold that a survey similates. course in crop physiology is needed just as survey courses are needed in other bodies of knowledge, i.e., SUMMARY AND CONCLUSIONS soil science or plant breeding. A survey course is intrin- sically broad. Crop Physiology is no exception. A questionnaire was sent to crop physiologists in ASA to obtain their evaluation of appropriateness of content, context, and level for a course in crop physi- ology. Responses indicated that most Land Grant uni- versities offer a course or courses in crop physiology (prin-