Crop Physiology Agronomy Princleples and Practice

this unit of study deals with crop physiology crop physiology is the study of functions and responses of crop plants to their environment the raw materials needed for plant growth and yield come from the environment including the soil and atmosphere the energy for growth comes from the Sun the yield of a plant or field of plants depends on the environment and on the management practices that utilize the environment by understanding how sunlight is converted into chemical energy used to form raw materials and two molecules of stored energy the agronomist is able to alter production practices to make this process more efficient crop physiology helps explain why plants react to different management practices such as changing row width and number of plants per acre cutting forage at a particular time of year or why the largest plants may not result in the largest yield in production fields knowing the factors that cause a plant to grow allow the farmer to adjust those factors to the levels that result in increased production efficiency the next topic for study is the section on yield you should now stop the VCR and study this section in your text then return to the VCR for further tutoring yield is a very general term it can be defined as the amount of dry matter produced per unit of land area the amount is usually expressed as bushels pounds kilograms or tonnes and the unit of land area is usually an acre or hectare yields are usually expressed as the weight of dry matter or the dried product because the water content in plants greatly varies throughout the growing season wet weight yields yields of the non dried product would not be an accurate measure of true organic matter production yield may refer to whole plant or to specific parts of the plant such as roots seeds or above-ground forage matter to further define yield the terms biological yield and economic or agricultural yield are used economic or agricultural yield refers to the amount of dry matter harvested that has marketable value therefore for a a farmer the vegetative portion of the plant is the economic yield and for a soybean farmer the amount of seed is the economic yield biological yield is the total dry matter produced by the plant including roots and top growth most of the biological yield of a crop such as sugar beets is really economic yield because sugar is processed from the roots and the tops may be used for forage harvest index is the ratio of economic yield to biological yield it is a measure of efficiency of the crop in converting its total dry matter accumulation into economic yield for example a grain crop variety may produce a lot of vegetative matter or biological yield but have low grain or economic yield this variety would have a low harvest index another variety however may be smaller in plant size but produce more grain this variety would have a high harvest and thus the crops or varieties that produce the greatest biological yield may not necessarily produce the greatest economic yield total seed or grain yields can be broken down into parts or components of yield that are developed sequentially knowing the progression and outcome of each component is very useful in explaining yield differences among environments genotypes and management practices the plants per unit area are determined first factors such as the germination percentage of the seed seedbed preparation soil temperature and planting procedures may affect the component called plants per area the number of heads per plant is determined after plants per unit area factors altering the number of heads per plant include light intensity soil fertility soil moisture and temperature the number of seeds per head as the next yield component formed seeds per head or panicle in oats are determined by the number of spikelets per panicle and then by the number of kernels formed per spikelet the number of seeds per head can be limited by environmental factors such as low soil fertility limited soil moisture or hot temperatures seed size or weight proceed as the last component developed seed size can be limited by deficiencies late in the life of the plant such as depletion of soil fertility or soil moisture hot temperatures or decreased photosynthesis due to leaf diseases the next section for study is rate of growth you should now stop the VCR and study this section in your text then return to the VCR for further tutoring the growth of a plant or plant part is described by a growth curve the curve is made up of three parts the logarithmic growth phase the linear growth phase and the maturation phase during the early part of the logarithmic growth phase the plants are actually preparing for fast growth however unless management and environment are fully adequate the plant will not grow as efficiently in subsequent phases the steeper part of the logarithmic growth phase may be impacted the most therefore overall production may be lowered during the latter part of the logarithmic phase the plants are establishing the slope of the line or the rate of growth for a large portion of the season during the latter part of the logarithmic growth phase and the early part of the linear growth phase a very large portion of the dry matter production of the plant is being produced the slope of the line which indicates the rate of dry matter production during these periods gives good indication of the production for the crop a more vertical slope would indicate a fast growth rate and possibly high yield a less vertical slope would indicate a slower growth rate and possibly less yield at some time usually near the time of maturity of an annual crop the maturation phase is reached during this final stage the plant is not growing it is not increasing in dry matter soon afterward the plant may decrease in total dry matter or total dry weight and death usually occurs plant growth regulators is a general term referring to substances that regulate plant growth in minut amounts these are called plant hormones or phyto hormones or they may be synthetically produced called synthetic hormones plant hormones can be produced in one part of the plant which can move to another part of the plant to inhibit or stimulate a particular response plant growth regulators are divided into five major groups auxins and gibberellins stimulates cell elongation cytokinins also called kinase stimulates cell differentiation growth inhibitors inhibit growth and development in seeds and plants ethylene is a gaseous hormone that hastens fruit ripening and inhibits other plant responses there are many other plant responses which are influenced by these hormones or by the interaction and balance of two or more hormones synthetic hormones have been widely used in the agricultural industry for many purposes one of the most common uses is for weed control many herbicides contain synthetic hormones which cause plant death when applied to weeds at rates above the normal concentration in plants rate of growth can be measured by taking length and weight measurements of plants or plant parts several times during the growth stage differences in rate of growth can be shown using growth regulators as demonstrated in your text and in the greenhouse where the experiment has been duplicated you should now stop the VCR and review this experiment and plot the results of the growth curves induced by the growth regulator treatments and calculate the dry weights then return to the VCR for further tutoring three growth curves are obtained when the growth of soybeans are plotted over time for gibberellin phosphine and the control treatments the growth curve of the first internode of plants treated with gibberellins has the steepest curve while plants treated with the growth inhibitor phosp on have a flatter or more horizontal growth curve stimulating crop growth with nitrogen fertilizer or irrigation may compare to the gibberellin growth curve while plants suffering from drought or poor soil fertility may closely approximate the slower growth curve of the phosphine treated plan the wet wait of a fast growing plant represented by the gibberellin treatment may be much greater than the wet wait of a slower growing plant represented by the phosphine treatment this is because the fast growing plant is usually more turgid that is has a higher water content the dry weight may not differ as much and therefore the percentage of dry weight may be higher in a slower growing plant in general treatments that stimulate plant growth in a field situation such as fertilizer and irrigation increase wet weight and total dry weight because plants are able to grow better thus the fast growing plant will usually excel in field production frequently crops are harvested or damaged by hail or insects and the ability of the plant to live and regrow becomes important stems and leaves form from meristematic buds on the plant cereal and legume plants differ in their manner of regrowth which is important in management decisions cereal crops produce new stem and leaf growth largely from the growing point or apical bud located at the stem apex cereal crops produce new stem and leaf growth however legumes can regrow from the apical bud and lateral buds located in the leaf axils thus regrowth potential depends on whether meristematic buds remain on the cut or damaged plant perennial legume and grass crops such as alfalfa and lawn grasses can be cut several times during the growing season because buds remain on the lower part of the plant after mowing in alfalfa the remaining lateral buds can produce new stem and leaf growth in lawn grasses the apical bud is frequently low enough on the plant to escape being mowed and there are basal buds in the crown or base of the plant in addition to possible rhizomatous or stolen if hrus buds that can produce new regrowth for annual row crops like maize and soybeans unexpected damage can occur such as hail damage farmers must decide whether to replant damaged crops or rely on regrowth if possible to produce adequate yields again the regrowth capacity of young corn and soybean plants depends on whether there are remaining meristematic buds on the damaged plant the regrowth potential of soybean and maize seedlings are described in your text you should now stop the VCR and review these demonstration experiments then return to the VCR for further tutoring soybeans with two cotyledons removed at emergence have less growth based on stem lengths than normal plants the cotyledons store food for energy before and shortly after emergence and then photosynthesize until other leaves form and begin to function when both cotyledons are removed the seedling is stunted but will continue to live regrowth occurs from lateral buds in the axles of the cotyledon airy leaves removing one cotyledon should not stunt stem regrowth under good growing conditions removal of the epicotyl allows axillary buds at the cotyledon airy node to develop stem structures the growing point of the main stem controls materials for growth to the main stem until it is removed then the axillary buds begin to function usually more than one stem begins to form from axillary buds if the main stem is deleted giving the plants a branched appearance soybean seedlings are killed when high picados are clipped below the cotyledons there are no meristematic buds below the cotyledon airy node so regrowth does not occur damage due to hail insects or other adversities would normally result in similar responses when maize seedlings are clipped at approximately 9 and 14 days regrowth occurred the growing point is not removed and enough energy remains in the plant for regrowth clipping 19 day old maize seedlings removes the growing point and the plants are killed in a greenhouse under warm ideal conditions the growing point is usually above the soil surface in 19 days but under cool field conditions the growing point may remain below the soil surface for 4 weeks or longer maize seedlings are thought to be more frost resistant than soybeans because the growing point is located just below the soil surface during the first few weeks of the maize Lance life thus Mays seedlings often live through a very cold freeze in early spring the next section for study is photosynthesis and respiration and crop plants you should now stop the VCR and study this section in your text then return to the VCR for further tutoring the green plant is a photosynthetic organism and at present the green plant is our major way of capturing the sun's energy and converting it to usable compounds a basic understanding of how the plant produces dry matter is essential for plant breeders and crop managers to select plants or practices that improve the efficiency of this conversion of solar energy into dry matter production photosynthesis is a process by which the energy of sunlight is used to convert carbon dioxide and water into organic compounds in the plant photosynthesis is essentially a two-step process first light energy is converted into chemical energy in the form of chemical bonds these bonds are located in ATP and nadph this chemical energy is then used to combine carbon dioxide taken from the air with water taken from the soil to form glucose sugar this photosynthetic process occurs in the chloroplast of plant cells respiration is the process by which complex molecules such as sugars are broken down producing chemical energy that is used to carry out energy requiring reactions respiration occurs in the mitochondria respiration in many ways is the reverse of photosynthesis in photosynthesis oxygen is released into the air from the chemical breakdown of water taken up from the soil co2 from the air moves into the leaf and is fixed into sugars conversely in respiration oxygen is used and combines with hydrogen to produce water sugars are respired producing co2 which goes back into the air respiration also produces ATP which is used as an energy source for many other plant functions therefore a certain amount of respiration is necessary for plant growth ATP energy from respiration is used in synthesis of other compounds synthesis is the conversion of sugars from photosynthesis to other compounds such as starches fats and oils and amino acids and proteins synthesis of different compounds occur in different parts of the cell for example carbohydrates are synthesized in the chloroplasts fats and oils in the cytoplasm DNA in the nucleus and proteins on the surface of ribosomes other terms and definitions important in relating photosynthesis to crop production Physiology are net photosynthesis also called net assimilation rate leaf area index and canopy net photosynthesis is defined as energy stored in photosynthesis - the energy released in the respiration process the energy stored in photosynthesis must be greater than the energy released in respiration for the net assimilation rate to be positive a positive net photosynthesis is necessary in order for crop plants to produce the desired products crop management practices such as planting rate plant spacing and soil fertility practices affect net photosynthesis although maximum net photosynthesis per leaf sounds desirable it is really the total amount of net photosynthesis of all leaves in a canopy that determines yield canopy refers to the space above the ground surface that is occupied by the aerial portion of plants canopy photosynthesis is the rate of photos of the canopy above a unit of ground area greater yields are obtained when many leaves and plants in the canopy are photosynthesizing at high but not necessarily maximum rates this results in more total canopy photosynthesis than when few leaves and plants are photosynthesizing at maximum rates thus plant population becomes an important management tool to obtain maximum net photosynthesis of the canopy plant population during the growing season should usually be at a level so that on a normally clear day the top leaves of a canopy should have a positive net photosynthesis however lower leaves due to a lower light intensity may be at zero or negative net photosynthesis leaf area index is the ratio of the total leaf area in the canopy to the soil surface area occupied by the plants measured farmers can alter the l AI to maximize leaf interception of sunlight by adjusting plant population rates the optimum L AI for a species depends upon many factors but is usually between three and eight the photosynthetic efficiency of a plant is affected by many factors such as crop species environment and management practices light quality refers to the wavelengths that are most effective in photosynthesis the visible spectrum of sunlight ranges from about 390 to 760 nanometers however the absorption by the leaf is most efficient between 400 and 500 nanometers and between 650 and 700 nanometers wavelengths in the green range are reflected by the leaf which is why leaves appear green to the human eye photosynthetic efficiency can also be increased by leaf interception of more sunlight to do this the leaf area index if too low can be increased by increasing plant population another method to increase light interception is to use a planting pattern that approaches an equidistant plant spacing for row crops such as maize and soybeans this would mean narrowing the row spacing to the point where the space between the rows is approximately the same distance as the space between plants within the rows for soybeans seeding with a grain drill in eighteen centimeter rows with seven and a half to ten centimeters between plants within the row would be a practical compromise it is easy to visualize that rows 18 to 36 centimeters apart would result in total light interception much earlier in the season then rows 76 to 102 centimeters apart once the proper management practices have been used to cause total light interception consideration should be given to using cultivars that allow efficient light interception the deep penetration of light into the canopy for example the wide leaves and plants of closed canopy soybean varieties in narrow rows are intercepting a major portion of the sunlight but only the outer layer of leaves are receiving direct sunlight the narrower leaves and plants of open canopy soybean varieties and narrower rows are also intercepting a major portion of the sunlight but direct sunlight is also penetrating much deeper into the canopy under highly productive situations leaf angle can affect photosynthetic efficiency varieties of several species do differ in leaf angle such as this upright leafed maize variety compared to the maize variety with more horizontally oriented leaves theoretically plants with leaves that are vertically oriented are more efficient in light utilization than plants with horizontally oriented leaves this is because leaves of crop species differ in their response to increased light intensity leaves of many crop species approach maximum photosynthesis when the light is less than the intensity of full sunlight a leaf at 60 degrees from the horizontal would receive 50% of the light intensity as compared to full sunlight the remaining 50% of the light could illuminate leaves at lower layers causing them to have net photosynthesis and thus add to the dry matter produced by plants photosynthetic efficiency is also influenced by the carbon dioxide concentration of the air and the plant's ability to utilize it in photosynthesis air is naturally low in carbon dioxide concentration which limits the photosynthetic rates of many crops c3 and c4 crop species differ in their capacity to photosynthetically fix carbon dioxide into sugars the terms c3 and c4 described two major photosynthetic pathways based on the first stable 3 carbon or 4 carbon product of the pathway c4 crop species such as maize are much more efficient in fixing carbon dioxide than c3 species such as soybeans under the normally low carbon dioxide concentrations of our air the next section for study is transport and uptake in crop plants you should now stop the VCR and study this section in your text then return to the VCR for further tutoring translocation is the movement of organic and inorganic solutes within the plant transport of various substances within the plant are necessary to supply raw materials for photosynthesis and metabolism the organic products then must be translocated to the proper plant structure to be further transformed into products or stored for future use xylem and phloem are the key structures in the plant where materials are translocated xylem consists of dead cell tissue and functions something like plumbing in a house water and minerals are absorbed by the roots and translocated upward in the xylem through the transpiration 'el stream flow him on the other hand consists of live cells sugars a form of carbohydrates and amino acids the components of protein are translocated from the leaves to other plant parts in the phloem movement in the phloem may be upward or downward depending on whether the material comes from the upper or lower leaves if the phloem tissue is killed there cannot be the proper translocation of sugars and amino acids to other plant parts weed control and herbicide technology have utilized this principle for example some herbicides must be translocated with sugars throughout the phloem to other plant parts in order to kill a weed if these types of herbicides are applied at abnormally high rates the phloem tissue may be killed before the toxic materials are translocated throughout the weedy plant some plant diseases may kill the phloem cells or clog the xylem vessels which transport water resulting in the plant having a wilted or blighted appearance transpiration is the evaporative loss of water from plant tissue most of the water losses from leaf surfaces through small openings called stomata in the leaf when the stomata are opened water can evaporate into the atmosphere carbon-dioxide necessary for photosynthesis also enters the leaf through these stomata thus open stomata are necessary for maximum photosynthetic rates of the leaf under warm dry conditions transpiration can occur so fast or for so long that soil moisture is depleted and the crop plant begins to wilt wilt encloses the stomata and as a result photosynthetic rates of the leaf are reduced or stopped excessive transpiration is generally a wasteful process however some transpiration is necessary for the plant to properly function because transpiration is an evaporative process it provides a cooling effect on crop leaves without the cooling effect of leaf transpiration leaf temperatures would rapidly exceed the optimum temperature for photosynthesis during a normal sunny day transpiration is also important for the uptake of water and minerals from the roots evapotranspiration refers to the total water loss in a canopy from crop transpiration and soil water evaporation evapotranspiration rates can be affected by environmental and plant factors sunny and windy days high temperatures and low humidity increased evapotranspiration as well as plant factors such as increased stoma total number and size leaf area wilting and rooting depth the water requirement or evapotranspiration ratio is the unit weight of water used to produce a unit weight of dry matter good fertility and weed control practices along with cooler climates generally lower the water requirement high soil fertility usually results in high production per acre and although the fertilized crop usually uses more water per acre the pounds of water evapotranspiration lower a low water requirement does not always indicate greater resistance to drought for example alfalfa is considered to be more drought resistant or drought tolerant than maize even though maize has a much lower water requirement than alfalfa alfalfa has a deep taproot system and can extract moisture from greater depths than maize root uptake of minerals and nutrients in the soil are essential for healthy crops and high yields in order for uptake to occur roots must come in contact with soil nutrients nutrients in the soil come in contact with roots by flowing to the roots in soil water and by simple diffusion from an area of high concentration in the soil to a low concentration near the root soil nutrients are also intercepted by growing and expanding roots after the root nutrient contact is made nutrients can be absorbed by passive or active uptake passive uptake occurs when nutrient ions move with the water into roots this water movement into the roots is driven by the transpiration applause from the leaf surfaces nutrient ions may also be actively absorbed by ion pumps this active uptake requires ATP energy to drive the ion pump nitrogen is a key element for many plant functions organic products legume crops unlike other crop species can utilize atmospheric nitrogen through a biological process of nitrogen fixation nitrogen fixation refers to the process of converting gaseous nitrogen into a nitrogen form that is usable by plants legumes have evolved a special symbiotic relationship with Rhizobium bacteria which convert gaseous nitrogen in the soil to a form that is usable by plants rhizobia infect the leg you mutes and stimulate the roots to produce small round structures called nodules in which the bacteria live the plant provides carbohydrates as an energy source for bacteria and the bacteria provide usable forms of nitrogen to the plan nodulation is the process of the bacteria entering the root hairs and forming colonies and swellings or nodules on the roots inoculation is the process of placing the appropriate species of Rhizobium in the vicinity of the legume seed so they may infect the roots of the plant the inoculant material containing rhizobia can be placed on the seed or in the soil where the seed is planted Rhizobium species are quite specific as to the plant species on which they will cause nodulation only certain species of plants can be Nadja lated with certain species of Rhizobium the group are plant species which can be nagy elated with the specific species of Rhizobium is known as a cross inoculation group some cross inoculation groups consist of several species of plants while others consist of only one or two species note the appearance of nodule ated roots and non nodule ated roots high nitrogen fertility in the soil seems to inhibit nodulation so these plants will take up mineral nitrogen in the soil like non leguminous crops this is probably one reason why soybeans fertilized with nitrogen produce no more seed than well-nigh baited soybeans with the increased cost of nitrogen fertilizer and with the pollution effects related to high fertilizer rates biological nitrogen fixation is becoming increasingly important the next section for study is crop plant responses to production environments you should now stop the VCR and study this section in your text then return to the VCR for further tutoring for crop seeds to germinate and produce adequate stands environmental requirements for seed germination must be met these include water suitable temperature oxygen and for some species light the ability of the soil to supply these necessary environmental factors are influenced by soil conditions weather and management practices for example seeds may germinate well at certain planting dates but germinate poorly at earlier or later planting dates this could be due to cloudy soil conditions cool soil temperatures or dry soils species differ in their germination response to temperature in general cool season species have lower minimum and optimum germination temperatures than due warm season species although species will begin the germination process at their minimum temperature the soil temperature should be several degrees higher for adequate field emergence of seedlings most crop species do not need light for proper germination however some species that do require light for germination such as many weed species would not germinate if they were planted too deeply another practical application of this principle is that deep tillage covers light sensitive seed and brings other light sensitive seed to the surface thus causing continuing problems with these weedy species crops respond to crowded conditions in production environments through eg elation elation is the elongated condition of plants grown in the dark or in low light intensity severely dilated plants often Lodge that is Bend or fall over under field conditions the equation was caused by high concentrations of indole acetic acid which builds up in shaded stems and is caused by crowded plant conditions under low plant population more light illuminates the stem reducing indole acetic acid buildup and consequently reducing stem height note the differences between the normal plants grown at a normal plant population and the etiolated lodged plants grown at a high plant population the lodging might lower yield and interfere with the harvesting operation tillering and branching are increased by high light intensity cool temperatures and adequate soil fertility and soil moisture lower plant populations result in more tillering or branching because of greater light intensity within the canopy early planting of a spring annual crop such as oats results in greater tillering because of cooler temperatures there for planting rates should be higher for late planting dates in order for an adequate number of tillers and thus panicles to be produced maize hybrids with horizontally drooping leaves generally have more plants without ears or barren plants then do maize plants with upright leaves the probable reason is that ear production is a form of branching and the upright leaves allow more light to penetrate thus allowing more ears or branches to be formed proper crop development in production environments is critical to maximum yields crop development refers to the progression of growth stages during the life cycle of the plant the transition from vegetative to reproductive growth differs among crop species and is frequently characterized into determinate and indeterminate growth types determinant species such as maize wheat and barley developed full vegetative growth before flowering indeterminate species such as alfalfa and other forage legumes continue to develop vegetative growth after flowering begins and the simultaneous production of vegetative growth and new flowers continue soybeans have both determinate and indeterminate growth types determinate soybeans are used primarily in the southern United States plants terminate growth in a heavily potted Racine indeterminate soybeans are primarily used in the northern United States plants may have a small terminal regime and fewer pods on the upper stem pods are located throughout the plant because indeterminate plants continue to develop vegetative growth after flowering begins indeterminate soybeans are usually taller and have a longer period of flowering than determinate soybeans of the same maturity soybeans also have a semi determinate type which is intermediate in characteristics to the other two types when grown in northern areas semi determinate soybeans are shorter and less susceptible to lodging than typical indeterminant types maize has determinant growth terminating in a tassel at flowering maize is more susceptible than in determinate soybeans to a period of hot dry weather during flowering because maize flowers only for a few days indeterminate soybeans typically flower for at least 3 weeks the time when crop plants begin reproductive growth is greatly influenced by temperature and in many cases photo period the photo period is the length of daylight in a 24 hour period reproductive growth begins when a crop reaches a particular growth stage moderately warmer temperatures stimulate development thus generally hastening the time to flowering the flowering response to temperature may also be modified by the crops response to photo period the effect of photo period on flowering and plant maturity is called photoperiodism days to flowering and days to maturity are the plant characteristics affected by photoperiodism and Richer the photo periodic response of plants are classified into three categories short day plants are stimulated to flower by day lengths shorter than a critical maximum length long day plants are stimulated to flower when day lengths exceed some critical minimum length day neutral plants are those whose flowering responses insensitive to day length flowering begins when plants reach a particular age or size photoperiodism in crops occurs through a special plant pigment called phytochrome which can exist in two interchangeable forms the ratio of these two phytochrome forms will influence the flowering response one form symbolized by pfr readily absorbs far red light and is formed during the day the other form symbolized by PR readily absorbs red light and is formed during the night therefore short days with long nights result in relatively less pfr and more PR which stimulates short day plants to flower long day plants remain vegetative in contrast long days with short nights result in relatively more pfr and less PR which stimulates long day plants to flower short day plants remain vegetative it is through this phytochrome response that photo periodically sensitive crops appear to sense the length of daylight and seasons of the year most summer annuals are short day plants winter annuals spring annuals and biennials are usually long day plants long day plants flower and produce seeds in late spring and early summer the shortening days and lengthening nights after June 21st cause short day summer annuals to flower and produce seeds in late summer and autumn since latitude effect day length and temperature latitude will affect the photo periodic response of day length sensitive crops soybeans a short day crop can be used to illustrate the latitude effect on photoperiodism if soybeans adapted to Ames Iowa latitude 42 degrees north are grown near Ames the variety will produce a normal-sized plant it will flower soon after June 21st and begin to mature about September 21st however if the same variety has grown under the longer and colder days at Duluth Minnesota latitude 47 degrees north it would flower much later and therefore produce more vegetative growth and would not mature early enough to be adapted to that area at Little Rock Arkansas latitude 35 degrees north under shorter and warmer days it would start flowering by June 21st would have reduced vegetative growth and would mature early thus it would not be adapted to the Little Rock area photoperiodism is a mechanism that allows the plant breeder to produce varieties of photo period sensitive species adapted to different latitudes an understanding of crop physiology is essential to the understanding of crop plant responses to the environment management practices such as soil tillage seedbed preparation planting date and population rate are a few examples of how management practices and change the environment in which crop plants live and produce understanding the physiological principles underlying crop growth will enable one to think more logically about the application of production and management practices to specific situations this is the end of the chapter on crop physiology you should now be ready to try the self-evaluation test at the end of the chapter in your text