Krishi Chapter

[Saurabh Cloudas]

Weall know that Krishi Vigyan Chapter - 13 is a vast subject. Hence, referring to the Rajasthan Board Class 12th Syllabus helps students in making the study plan. The RBSE Board 12th Krishi Vigyan Chapter - 13 Textbook contains chapters. In each chapter, students will find a theory, solved examples, unsolved questions and Very Important points related to the topic. Also, at the end of each chapter students will find the answers to unsolved problems

We all know that Krishi Vigyan Chapter - 4 is a vast subject. Hence, referring to the Rajasthan Board Class 12th Syllabus helps students in making the study plan. The RBSE Board 12th Krishi Vigyan Chapter - 4 Textbook contains chapters. In each chapter, students will find a theory, solved examples, unsolved questions and Very Important points related to the topic. Also, at the end of each chapter students will find the answers to unsolved problems

Initially there were three major geographical chapters of HAA namely: East Coast, Midwest & West-Coast. Respective Vice Presidents organize each chapter activities.During 1997, twelve more sub-chapters with respective VPs were formed to facilitate better interactions among havyaka families located within a smaller regional level. Now we have 16 chapters across north America.These included New England (Boston Area, Rochester-Buffalo- NY area), Pittsburgh (East PA,West Virginia-Ohio, Carolinas), Florida, Atlanta (Including Tennessee/ GA area), Kansas (including Missouri-Iowa area), Huston/Texas area, Arkansas (including Arizona), Northwest (Seattle-Oregon area), Southern CA (Bay area, Los Angeles-San Diego area), and Canada -East. This concept was further expanded during 2003 by adding two more sub-chapters in Washington DC-Virginia area and Detroit/Michigan area. In 2014 Minnesota Chapter has started covering twin cities and nearby cities.

Havyaka Association of the Americas (HAA) was formed during 1982 with the aim of providing a common forum towards achieving these goals to the present and future generations. HAA is a Non-profit Organization registered in the state of New Jersy, USA.

Chapter 6 - ETc - Single crop coefficient (Kc)Length of growth stages

Crop coefficients

Construction of the Kc curve

Calculating ETc

Alfalfa-based crop coefficients

Transferability of previous Kc values

Annual cropsOnly three point values for Kc are required to describe and to construct the Kc curve. The curve such as that shown in Figure 34 is constructed using the following three steps:1. Divide the growing period into four general growth stages that describe crop phenology or development (initial, crop development, mid-season, and late season stage), determine the lengths of the growth stages, and identify the three Kc values that correspond to Kc ini, Kc mid and Kc end from Table 12.2. Adjust the Kc values to the frequency of wetting and/or climatic conditions of the growth stages as outlined in the previous section.3. Construct a curve by connecting straight line segments through each of the four growth stages. Horizontal lines are drawn through Kc ini in the initial stage and through Kc mid in the mid-season stage. Diagonal lines are drawn from Kc ini to Kc mid within the course of the crop development stage and from Kc mid to Kc end within the course of the late season stage.Kc curves for forage cropsMany crops grown for forage or hay are harvested several times during the growing season. Each harvest essentially terminates a 'sub' growing season and associated Kc curve and initiates a new 'sub' growing season and associated Kc curve. The resulting Kc curve for the entire growing season is the aggregation of a series of Kc curves associated with each sub-cycle. Figure 35 presents a Kc curve for the entire growing season constructed for alfalfa grown for hay in southern Idaho.FIGURE 35. Constructed curve for Kc for alfalfa hay in southern Idaho, the United States using values from Tables 11 and 12 and adjusted using Equations 62 and 65 (data from Wright, 1990)In the southern Idaho climate, greenup (leaf initiation) begins in the spring on about day 90 of the year. The crop is usually harvested (cut) for hay three or four times during the growing season. Therefore, Figure 35 shows four Kc sub-cycles or cutting cycles: sub-cycle 1 follows greenup in the spring and the three additional Kc sub-cycles follow cuttings. Cuttings create a ground surface with less than 10% vegetation cover. Cutting cycle 1 is longer in duration than cycles 2, 3 and 4 due to lower air and soil temperatures during this period that reduce crop growth rates. The lengths for cutting cycle 1 were taken from the first entry for alfalfa (" 1st cutting cycle") in Table 11 for Idaho, the United States (10/30/25/10). The lengths for cutting cycles 2, 3 and 4 were taken from the entry for alfalfa in Table 11 for "individual cutting periods" for Idaho, the United States (5/20/10/10). These lengths were based on observations. In the southern Idaho climate, frosts terminate the growing season sometime in the fall, usually around day 280-290 of the year (early to mid-October).The magnitudes of the Kc values during the mid-season periods of each cutting cycle shown in Figure 35 vary from cycle to cycle due to the effects of adjusting the values for Kc mid and Kc end for each cutting cycle period using Equations 62 and 65. In applying these two adjustment equations, the u2 and RHmin values were averages for the mid-season and late season stages within each cutting cycle. Basal Kcb curves similar to Figure 35 can be constructed for forage or hay crops, following procedures presented in Chapter 7.Kc mid when effects of individual cutting periods are averagedUnder some conditions, the user may wish to average the effects of cuttings for a forage crop over the course of the growing season. When cutting effects are averaged, then only a single value for Kc mid and a only single Kc curve need to be employed for the whole growing season. When this is the case, a "normal" Kc curve is constructed as in Figure 25, where only one midseason period is shown for the forage crop. The Kc mid for this total midseason period must average the effects of occasional cuttings or harvesting. The value that is used for Kc mid is therefore an average of the Kc curve for the time period starting at the first attainment of full cover and ending at the beginning of the final late season period near dormancy or frost. The value used for Kc mid under these averaged conditions may be only about 80% of the Kc value that represents full ground cover. These averaged, full-season Kc mid values are listed in Table 12. For example, for alfalfa hay, the averaged, full-season Kc mid is 1.05, whereas, the Kc mid for an individual cutting period is 1.20.Fruit treesValues for the crop coefficient during the mid-season and end of late season stages are given in Table 12. As mentioned before, the Kc values listed are typical values for standard climatic conditions and need to be adjusted by using Equations 62 and 65 where RHmin or u2 differ. As the mid and late season stages of deciduous trees are quite long, the specific adjustment of Kc to RHmin and u2 should take into account the varying climatic conditions throughout the season. Therefore, several adjustments of Kc are often required if the mid and late seasons cover several climatic seasons, e.g., spring, summer and autumn or wet and dry seasons. The Kc ini and Kc end for evergreen non dormant trees and shrubs are often not different, where climatic conditions do not vary much, as happens in tropical climates. Under these conditions, seasonal adjustments for climate may therefore not be required since variations in ETc depend mostly on variations in ETo.Calculating ETc Graphical determination of Kc

Numerical determination of Kc

From the crop coefficient curve the Kc value for any period during the growing period can be graphically or numerically determined. Once the Kc values have been derived, the crop evapotranspiration, ETc, can be calculated by multiplying the Kc values by the corresponding ETo values.Graphical determination of KcWeekly, ten-day or monthly values for Kc are necessary when ETc calculations are made on weekly, ten-day or monthly time steps. A general procedure is to construct the Kc curve, overlay the curve with the lengths of the weeks, decade or months, and to derive graphically from the curve the Kc value for the period under consideration (Figure 36). Assuming that all decades have a duration of 10 days facilitates the derivation of Kc and introduces little error into the calculation of ETc.The constructed Kc curve in Box 15 was used to construct the curve in Figure 36. This curve has been overlaid with the lengths of the decades. Kc values of 0.15, 1.19 and 0.35 and the actual lengths for growth stages equal to 25, 25, 30 and 20 days were used. The crop was planted at the beginning of the last decade of May and was harvested 100 days later at the end of August.For all decades the Kc values can be derived directly from the curve. The value at the middle of the decade is considered to be the average Kc of that 10 day period. Only the second decade of June, where the Kc value changes abruptly, requires some calculation.BOX 15. Case study of a dry bean crop at Kimberly, Idaho, the United States (single crop coefficient)An example application for using the Kc procedure under average soil wetness conditions is presented for a dry bean crop planted on 23 May 1974 at Kimberly, Idaho, the United States (latitude = 42.4N). The initial, development, mid-season and late season stage lengths are taken from Table 11 for a continental climate as 20, 30, 40 and 20 days (the stage lengths listed for southern Idaho were not used in this example in order to demonstrate the only approximate accuracy of values provided in Table 11 when values for the specific location are not available). Initial values for Kc ini, Kc mid and Kc end are selected from Table 12 as 0.4, 1.15, and 0.35.The mean RHmin and u2 during both the mid-season and late season growth stages were 30% and 2.2 m/s. The maximum height suggested in Table 12 for dry beans is 0.4 m. Therefore, Kc mid is adjusted using Eq. 62 as: As Kc end = 0.35 is less than 0.45, no adjustment is made to Kc end. The value for Kc mid is not significantly different from that in Table 12 as u2 2 m/s, RHmin is just 15% lower than the 45% represented in Table 12, and the height of the beans is relatively short. The initial Kc curve for dry beans in Idaho can be drawn, for initial, planning purposes, as shown in the graph (dotted line), where Kc ini, Kc mid and Kc end are 0.4, 1.19 and 0.35 and the four lengths of growth stages are 20, 30, 40 and 20 days. Note that the Kc ini = 0.4 taken from Table 12 serves only as an initial, approximate estimate for Kc ini. Constructed Kc curves using values from Tables 11 and 12 directly (dotted line) and modified using Kc ini from Fig. 29 and Lini = 25, Ldev = 25, Lmid = 30, and Llate = 20 days (heavy line) for dry beans at Kimberly, Idaho. Also shown are daily measured Kc (lysimeter data from Wright, 1990). Kc ini can be more accurately estimated using the approach described in this chapter. ETo during the initial period at Kimberly (late May - early June, 1974) averaged 5.3 mm/day, and the wetting interval during this period was approximately 14 days (2 rainfall events occurred averaging 5 mm per event). Therefore, as the wetting events were light (Comparison of constructed curves with measurementsBecause the ETc data for the dry bean crop at Kimberly, Idaho were measured using a precision lysimeter system during 1974 by Wright (1990), the actual Kc measurements can be compared with the constructed Kc curves, where actual Kc was calculated by dividing lysimeter measurements of ETc by daily ETo estimated using the FAO Penman-Monteith equation.As illustrated in the graph, the mid-season length as taken from Table 11 for the general, continental climate overestimated the true mid-season length for dry beans in southern Idaho, which averaged only about 30 days rather than 40 days as suggested by Table 11. This illustrates the importance of using the local observation of 30 days for mid-season period length rather than the general value from Table 11.The final, best estimate for the Kc curve for the dry bean crop in southern Idaho is plotted (lower curve in graph) using Kc values of 0.15, 1.19, and 0.35 and the actual observed lengths of growth stages equal to 25, 25, 30 and 20 days. Note the impact that the error in estimating mid-season length has on the area under the Kc curve. This supports the need to obtain local observations of growth stage dates and lengths.The value calculated for Kc mid (1.19) appears to have underestimated the measured value for Kc during portions of the mid-season period at Kimberly. Some of this effect was due to effects of increased soil water evaporation following four irrigations during the 1974 mid-season which increased the effective Kc. This is illustrated in Box 16, where the basal Kcb + Ke approach is introduced and demonstrated for this same example.The 0.15 value calculated for Kc ini using Fig. 29 agrees closely with measured Kc during the initial period. Measured Kc during the development period exceeded the final Kc curve during days on or following wetting events. The day to day variation in the lysimeter measured Kc is normal and is caused by day to day variations in weather, in wind direction, by errors in prediction of Rn and ETo, and by some random errors in the lysimeter measurements and weather measurements.FIGURE 36. Kc curve and ten-day values for Kc and ETc derived from the graph for the dry bean crop example (Box 15)first five days of that decade, Kc = 0.15, while during the second part of the decade Kc varies from 0.15 to 0.36 at the end of day 10. The Kc for that decade is consequently: 5/10 (0.15) + 5/10(0.15+0.36)/2 = 0.20.Numerical determination of KcThe Kc coefficient for any period of the growing season can be derived by considering that during the initial and mid-season stages Kc is constant and equal to the Kc value of the growth stage under consideration. During the crop development and late season stage, Kc varies linearly between the Kc at the end of the previous stage (Kc prev) and the Kc at the beginning of the next stage (Kc next), which is Kc end in the case of the late season stage: (66)wherei day number within the growing season [1.. length of the growing season],

Kc i crop coefficient on day i,

Lstage length of the stage under consideration [days],

S (Lprev) sum of the lengths of all previous stages [days].Equation 66 applies to all four stages.EXAMPLE 28. Numerical determination of KcDetermine Kc at day 20, 40, 70 and 95 for the dry bean crop (Figure 36).Crop growth stageLength (days)Kcinitial25Kc ini = 0.15crop development250.15... 1.19mid-season30Kc mid = 1.19late season201.19 .. Kc end = 0.35At i = 20:initial stage, Kc = Kc ini =0.15-At i = 40Crop development stage,

For:S (Lprev) = Lini =25daysand:Lstage = Ldev =25daysFrom Eq. 66:Kc = 0.15 + [(40 - 25)/25](1.19 - 0.15) =0.77-At i = 70:mid-season stage, Kc = Kc mid =1.19-At i = 95late season stage,

For:S (Lprev) = Lini + Ldev + Lmid = (25 + 25 + 30) =80daysand:Lstage = Llate =20daysFrom Eq. 66:Kc = 1.19 + [(95-80)/20](0.35-1.19) =0.56-The crop coefficients at day 20, 40, 70 and 95 for the dry bean crop are 0.15, 0.77, 1.19 and 0.56 respectively.Alfalfa-based crop coefficientsAs two reference crop definitions (grass and alfalfa) are in use in various parts of the world, two families of Kc curves for agricultural crops have been developed. These are the alfalfa-based Kc curves by Wright (1981; 1982) and grass-based curves by Pruitt (Doorenbos and Pruitt 1977; Jensen et al. 1990) and those reported in this paper. The user must exercise caution to avoid mixing grass-based Kc values with alfalfa reference ET and vice versa. Usually, a Kc based on the alfalfa reference can be 'converted' for use with a grass reference by multiplying by a factor ranging from about 1.0 to 1.3, depending on the climate (1.05 for humid, calm conditions, and 1.2 for semi-arid, moderately windy conditions, and 1.35 for arid, windy conditions):Kc (grass) = Kratio Kc (alfalfa) (67)whereKc (grass) grass-based Kc (this handbook),

Kc (alfalfa) alfalfa-based Kc,

Kratio conversion factor (1.0... 1.3).A reference conversion ratio can be established for any climate by using the Kc mid = 1.20 listed for alfalfa in Table 12 and then adjusting this Kc mid for the climate using Equation 62. For example, at Kimberly, Idaho, the United States, where RHmin = 30% and u2 = 2.2 m/s are average values during the summer months, a reference conversion ratio between alfalfa and grass references using Equation 62 is approximately: (68)whereh = 0.5 m is the standard height for the alfalfa reference.Transferability of previous Kc valuesThe values for Kc mid and Kc end listed in Table 12 are for a large part based on the original values presented in FAO Irrigation and Drainage Papers No. 24 and 33 (FAO-24 and FAO-33), with some adjustment and revisions to reflect recent findings. Similarly adjustments in Kc mid to compensate for differences in aerodynamic roughness and leaf area, as introduced in Equation 62 are derived from the Kc values given for different wind and RHmin conditions in the concerned Kc table in FAO-24, with some upward adjustment to better reflect increased ETcrop values under high wind and low RHmin when applied with the FAO Penman-Monteith equation.The Kc's from FAO-24 were based primarily on a living grass reference crop. The FAO Penman-Monteith equation presented in this publication similarly represents the same standardized grass reference. For that reason Kc values are in general not very different between these publications except under high wind and low RHmin.The No. 24 modified Penman was found frequently to overestimate ETo even up to 25 % under high wind and low evaporative conditions and required often substantial local calibration (see chapter 2). Kc values derived from crop water use studies which used the FAO-24 Penman equation to compute grass reference crop evapotranspiration, can therefore not be used and need to be adjusted using ETo values estimated from the FAO Penman-Monteith equation. Similarly crop water requirement estimates based on the FAO-24 Modified Penman equation will need to be reassessed in view of the found differences between the FAO-24 Penman and the FAO Penman-Monteith reference equations.

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