On the Variability of Harvest Indices

The harvest index Z is defined, for example for cereals, as the ratio between grain yield X and biological yield Y: Z = X/Y. For many purposes the variance of Z is of major interest. In this paper several approximations for this variance are derived and their accuracy was investigated. These explicit formulae depend on some characteristics (means, variances or coefficients of variation, covariances or correlations) of the component variables grain yield X and biological yield Y. It is shown that for most practical applications the approximation v²z = v²x + v²y - 2rv_xv_y provides a sufficient accuracy for numerical calculations (v_x v_y and v_z are the coefficients of variation for grain yield X, biological yield Y and harvest index Z and r denotes the correlation coefficient between X and Y). Some conclusions on the relations between v_x, v_y and v_z are derived.
Finally, all the theoretical investigations and results are demonstrated and applied to a numerical example of winter-rapeseed data.     

Character Associations Among Grain Yield, Biological Yield and Harvest Index

The harvest index Z is defined, for example for cereals, as the ratio between grain yield X and biological yield Y: Z = X/Y. In this paper the character associations among biological yield, grain yield and harvest index have been investigated theoretically by calculating the covariances and correlation coefficients between harvest index and grain yield and, additionally, between harvest index and biological yield. Explicit formulae are derived for these covariances and correlation coefficients and conclusions are derived and discussed. Many facts and relations among these characters which are well-known and frequently established by many experimental studies with quite different crops can be obtained and characterized by these theoretical investigations as necessary implications of the underlying statistical relationships.
Finally, all the theoretical studies and results are demonstrated and applied to a numerical example of winter-rapeseed data.     

Water Relations, Abscisic Acid and Yield of Wheat Plants in Relation to the Interactive Effect of Seawater and Growth Bioregulators

Irrigation of wheat plants with seawater (10 and 25 %) led to significant increases in free and bound abscisic acid (ABA) in leaves, especially at 25 %. The relative water content (RWC) and water use efficiency (calculated from grain yield, WUE_G, or from biomass yield, WUE_B) of the seawater-irrigated plants were lower than those of the control. Grain pre-soaking in gibberellic acid (GA₃), indole-3-acetic acid (IAA) or ABA reduced the levels of accumulated ABA (free and bound) produced by seawater irrigation. The stress imposed by seawater generally reduced yield and yield components of wheat plants and the effect was more pronounced at the higher level of seawater irrigation (25 %). Furthermore, seawater treatments decreased the carbohydrate content and increased the protein content of the developing grains. The effect of seawater treatments on ion concentrations in the developing grains was not consistent. The application of growth bioregulators appeared to mitigate the effect of seawater salinity stress on wheat productivity. GA₃ was the most effective hormone in this regard. The economic yield (grain yield) had a strong positive correlation with RWC, WUE_G, WUE_B, plant height, shoot fresh and dry weight, grain number/main spike, kernel weight and harvest index.     

Irrigation Water Management for Efficient Water Use in Mulched Onion

Caused by the necessarily imperfect seed placement accuracy of sowing machines and, additionally, caused by many other biotic and abiotic factors, the resulting plant stands exhibit nonregular spatial distributions of its plants. Based on several simplifying assumptions, a stochastic approach is developed which allows an estimation of the effects of nonregular spatial patterns on yield per area. In this approach, two random variables are attached to each plant: single plant yield E and individual space A . The latter is estimated by the area of Thiessen polygons. Yield per area, calculated by the expectation of the ratio E/A , can be approximately expressed dependent on the means ( Ē and Ā ) and coefficients of variation ( v _E and v _A ) of E and A and their correlation ( r _EA ). In relation to the commonly used estimate Ē/Ā for yield per area, one obtains yield decreases if v _A / v _E  <  r _EA . This inequality, however, will be usually valid in the field of applications. The theoretical approaches and results were applied to three experimental data sets for drilled seeds of winter oilseed rape ( Brassica napus L.) (plant density: 60 plants m⁻², row distance: 10 cm). These data sets are characterized by different accuracies of longitudinal distributions within rows (58 %, 101 %, 150 %): yield depression increases with an increasing variability of plant distances within rows.     

On Harvest Indices of Winter Oilseed Rape (Brassica napus L.)

Ten quite different European winter rapeseed cultivars were grown in a 3-year field trial at one location. The traits grain yield and biomass were measured based on single plant measurements (first year) or on plot basis (second and third year). Individual harvest indices were calculated.
Besides a general discussion of the experimental results for this collection of winter rapeseed cultivars the main aim of the present investigations was an examination whether these experimental results are in agreement with the theoretical conclusions on harvest indices which have been published in this journal in three preceding publications.
Hence the investigations of this paper are divided into the three chapters: 1) Calculation of mean harvest indices, 2) Variability of harvest indices and 3) Correlations among harvest index, grain yield and biomass. In all three chapters the agreement between the empirically obtained and the theoretically expected values is quite good.     

The Nutritive Value and Yield of Alfalfa in Relation to Nitrogen Fertilization on Sulphur Industry Reclaimed Lands

The aim of this study was to determine the direction and magnitude of change in morphological and agronomical characters of spring barley ( Hordeum vulgare L.) in Germany over a period of 80 years and to assess the value of various strategies for further crop improvement. Old and new two-rowed cultivars, eight in each case, were tested together with their F₂ intra-group diallel crosses in a field trial at Braunschweig-Völkenrode in 1994. New parents and their crosses showed a higher dry matter grain and total biomass yield, a lower plant height, and a higher harvest index as compared to the respective old germplasm. The annual genetic gain in grain yield was estimated at 0.15%. The superior grain yield of the new germplasm was attributable to the higher number of ears per plant and the larger kernel weight. The F₂ mid-parent heterosis in grain yield was 7.6 and 7.2 % for the old and new crosses, respectively. The differences between the two types of crosses were nonsignificant except for the higher heterosis for plant height in the new crosses. General combining ability effects were significant for all characters in both types of crosses, whereas specific combining ability effects were significant in a few cases only. In the new crosses, a significant positive correlation was found between grain yield and straw yield (r = 0.52), whereas no such association was observed between grain yield and harvest index. For further gain in grain yield, improvement of the straw yield is more promising than increasing harvest index.     

Response of Mustard (Brassica juncea L.) to Applied Nitrogen with or without Ethrel Spray under Non-irrigated Conditions

Field studies were conducted during the winter seasons of 1995–96 and 1996–97 at the Agricultural Farm of Aligarh Muslim University, Aligarh, India on mustard ( Brassica juncea L. Czern & Coss., var. Alankar) under non-irrigated conditions, to evaluate the effect of foliar spray of 200 p.p.m. ethrel (2-chloroethyl phosphonic acid) at flowering growth stage along with basal 0, 40, 80 or 120 kg N ha⁻¹ on net photosynthetic rate (P_N), stomatal conductance (C_S), stomatal resistance (R_S), leaf K content, relative water content (RWC), leaf area index (LAI) and total dry matter (TDM) production monitored at 20 days after spray application, and plant N content, seed N content, nitrogen harvest index (NHI), nitrogen yield merit (NYM), pods plant⁻¹, 1000 seed weight, seed yield, biological yield, harvest index (HI), seed yield merit (SYM) and merit of genotype (MOG) at harvest. Results indicated that, at 0 or 40 kg N ha⁻¹, ethrel did not produce any significance effect, but at basal 80 kg N ha⁻¹, ethrel affected the parameters favourably with the exception of 1000 seed weight, HI, seed N and NHI. Ethrel-sprayed plants utilized N from the soil more effectively and showed increased NYM. Yield attributes, seed yield and merit of genotype (in terms of NYM and SYM) were also enhanced. Ethrel spray enhanced seed yield under water stress conditions mainly by increasing K uptake and retaining higher RWC, thereby decreasing R_S and increasing LAI, P_N and TDM production.     

The Effect of Seeding Rate and Nitrogen Fertilization on Barley Yield and Yield Components in a Cool Maritime Climate

Soil and climatic conditions in Newfoundland are on the margins of agricultural capability, and almost all feed grain is imported. The overall objective of this work was to develop guidelines for the production of barley in Newfoundland, with the goal of establishing modern cropping recommendations. We conducted a 4-year study near St. John's to examine the effect of seeding rate and topdress ammonium nitrate (N) fertilization rate on Chapais six-row barley ( Hordeum vulgare L.) yield components and grain yield. Increasing seeding rate from 200 to 380 seeds m^–2 did not alter grain yield in any year. Increasing topdress fertilization from 0 to 60 kg N ha^–1 increased spike density m^–2 at harvest, resulting in linear increases in grain yield in all years. Highest N rates had greatest lodging in two years. Based on our results, agronomic recommendations for eastern Newfoundland now include barley seeding rates of 250 ± 50 seeds m^–2, with topdress applications up to at least 30 kg N ha^–1.     

The Performance of Pea (Pisum sativum L.) and its Role in Determining Yield Advantages in Mixed Stands of Pea and Oat (Avena sativa L.)

On a brown warp soil (Fluventic Eutrochrept) near Goettingen, Germany, conventional leafed pea ( Pisum sativum L. cvs Messire and Bohatyr) and semileafless types (cvs Profi, Juno and Azur) were grown in mixed stands together with oat ( Avena sativa cvs Alf and Lutz) in substitutively designed experiments from 1995 to 1997. Oat was the dominant component. Crowding coefficients for oat averaged 7.4. No relationship could be detected between the crowding coefficient of oat and any yield advantage from the mixture. Crowding coefficients for pea varied substantially, between 0.1002 (Juno and Alf in 1996) and 0.2979 (Bohatyr and Alf in 1996). Crowding coefficients for semileafless pea cultivars were smaller than for conventional leafed types. The yield advantage of the mixture increased as the crowding coefficient of pea increased. The maximum yield increase for the mixture was achieved when the relative yield total (RYT)=1.17 or + 11 dt grain DM ha^–1 for mixtures of the long-strawed conventional leafed cultivars Bohatyr and Alf (in 1996). The crowding coefficients of pea were positively correlated with the level of symbiotically fixed N₂ in the mixed stands. When N₂ fixation with mixed cropping was about 30 kg N ha^–1, RYT was unity. Increasing symbiotic N₂ in the mixtures resulted in increasing yield advantages in the mixture. Short-strawed pea cultivars seem unsuitable for mixing with oat. Plant height of pea appeared to be more important than plant leaf type. Accordingly, mixtures containing the long-strawed semileafless pea cultivars Profi and Alf were more successful. It is concluded that increased competitiveness of the pea component in the mixture with oat entails increasing the level of symbiotic N₂ fixation including resource complementarity and thus yield advantage in the mixed stands.     

Interactive Effect of Seawater and Growth Bioregulators on Water Relations, Abscisic Acid Concentration and Yield of Wheat Plants

Irrigation of wheat plants with seawater (10 and 25 %) led to a significant increase in free and bound ABA in leaves, especially at 25 %. The relative water content (RWC), particularly at 25 %, and water use efficiency of the seawater-irrigated plants were lower than those of the control. Grain pre-soaking in GA₃, IAA or ABA reduced the levels of accumulated ABA (free and bound) resulting from seawater irrigation. The stress imposed by seawater generally reduced yield and yield components of wheat plants, and the effect was more pronounced at the higher level of seawater (25 %). Furthermore, seawater treatments decreased the carbohydrate content and increased the protein content of the developing grains. The effect of seawater treatments on ion concentration in the developing grains was not consistent. The application of growth bioregulators appeared to mitigate the effect of seawater salinity stress on wheat productivity. Gibberellic acid gave the best effect. The economic yield (grain yield) had a strong positive correlation with RWC, water use efficiency for grain yield, water use efficiency for biomass, plant height, shoot fresh and dry weights, grain number/main spike, kernel weight and harvest index.     

Stickstoffaufnahme und Stickstoffrückstände von Hauptfrucht-und Ausfallrapsbeständen

Nitrogen Uptake and Nitrogen Residuals of Winter Oil-Seed Rape and Fallout Rape
The objective of the investigation was a study of the relationship between seed dry-matter production and vegetative dry-matter production in oil-seed rape crops and their dependence on the production conditions. In addition to the relationship between the N-uptake during the vegetation period and the N-residue after harvest was of major interest. Furthermore the potential for N-uptake in fallout rape was measured. Over two vegetation periods factorial field experiments with winter oil-seed rape, cv. Lirabon, different drilling techniques and different nitrogen fertilization levels were tested. Measured traits were: the dry-matter accumulation including root mass and fall-off leaf-material mass, the N-uptake of both the oil-seed crops and the fallout rape stands, and, simultaneously, the soil NO₃-N content. Finally the harvest indices and the N-harvest indices were calculated.
Combined with a N-uptake of up to 330 kg N/ha, oil-seed rape crops produced up to 200 dt dry matter/ ha. At seed yield levels of 33dt/ha (d.m.), harvest indices varied from 0.14—0.23 and N-harvest indices varied from 0.30–0.50. As a result of the residue of vegetative plant material at harvest, leaf losses before harvest and the soil NO₃-N-contents at harvest up to 275 kg N/ha remained in the field. After the harvest of oil-seed rape, the soil NO₃-N-contents were quickly reduced by emerging and growing fallout rape stands. However, following soil-preparation measures in the autumn, a continuous rise in the soil NO₃-N-content was observed.     

Intercropping of Corn with Soybean, Lupin and Forages: Silage Yield and Quality

Intercropping of corn with legumes is an alternative to corn monocropping and has a number of advantages, for example, lower levels of inputs, lower cost of production and better silage quality than monocrop systems. An experiment was carried out at two sites in 1993 and 1994 to investigate the effects of seeding soybean or lupin alone or in combination with one of three forages (annual ryegrass, Lolium multiflorum Lam.; perennial ryegrass, Lolium perenne L.; red clover, Trifolium pratense L.) on silage yield and quality. The intercrop plots received 90 kg ha⁻¹ less nitrogen fertilizer than monocrop plots, which received 180 kg ha⁻¹. Corn biomass yield had a variable response to the treatments, but showed no change at most site-years. Soybean and lupin biomass yields were decreased by intercropping (80–98 % for soybean, and 94–100 % for lupin). However, when corn growth was limited due to poor establishment at one site in 1994, soybean was able to grow well and produce yields similar to those of monocropped soybean. The three underseeded forages did not grow well during the period examined (up to silage harvest) and had no effect on the yield of any crop. Total silage yields were similar to corn monocrop biomass yields even during 1994 at the site with low corn population densities because soybean was able to compensate for reduced corn growth.     

How does the harvest index affect water‐use efficiency and nutrient‐utilization efficiency of sunflowers (Helianthus annuus L.)?

Besides oilseed rape and soybean, sunflower is one of the most important annual oilcrops. Apart from seed yield, which is the most important trait in many crops, oil yield is of utmost interest for sunflower breeders and farmers. Compared to the seed yield of sunflowers, their total biomass is often very high, and it is of great agronomic interest to increase the ratio of both parameters, which is defined as harvest index. With an increase in harvest index, improvements of resource‐use efficiencies can be expected. To generate an adequate seed yield, water and nutrients are key factors and their efficient use becomes increasingly important under conditions of aridity and higher production goals. A pot experiment was conducted in summer 2017 to determine differences in harvest index of various sunflower genotypes which could have an influence on the use efficiencies of water and nutrients (N, P, K). In total, 25 genotypes of different origin and with various morphological traits were investigated under optimal growth conditions. The harvest index varied from 29% to 47% and showed significant differences among some genotypes. The harvest index was less affected by the total biomass of the plants but more by the seed yield. The seed yield itself was mainly determined by the single seed weight rather than by the number of seeds. The experiment also confirmed significant positive correlations between harvest indices and all use efficiencies. Genotypes with high harvest indices were characterized by high oil concentrations in the seeds and particularly by high oil yields. In conclusion, cultivation of sunflower genotypes with high harvest indices most likely results in high water‐use efficiency and high nutrient‐utilization efficiencies as well as in high oil yields.     

Effect of Gibberellic Acid Spray and Basal Nitrogen and Phosphorus on Productivity and Fatty Acid Composition of Rapeseed-Mustard

Two field experiments were conducted during] 994-95 to study the effect of spray of 10⁻⁵ M GA3 at 40 days after sowing on mustard ( Brassica juncea (L.) Czern & Coss.) cv. Varuna grown with basally applied 0, 40, 80 and 120 kg N ha⁻¹ (Expt. 1) and 0,15, 30 and 45 kg P ha⁻¹ (Expt. 2) on pod number per plant, seeds per pod, 1000 seed weight, seed yield, biological yield, harvest index and fatty acid composition of oil. No significant difference between water and GA3 spray was found when basally applied nitrogen was 0 or 40 kg N ha⁻¹. N₈₀ proved to be the best for yield characteristics. In another experiment on phosphorus, GA₃ and 30 kg P ha⁻¹ individually enhanced the yield, but interaction of GA₃ and P remained non-significant. The fatty acid composition of oil in both experiments was significantly affected only by nitrogen and phosphorus treatments for oleic acid and erucic acid. It was found that return in the form of yield was more for every kg applied fertilizer under GA, spray treatment. The response was more for N fertilizer in comparison to P. GA₃ at a low level of fertilization significantly increased the return from fertilization.     

Optimal regimes of selection for grain yield and harvest index in spring wheat

Summary Alternative strategies of multi-site testing of advanced lines in the northern wheat belt of New South Wales have been evaluated, using genetic parameters for large plot grain yield and hill plot harvest index estimated from dryland and irrigated trials at regional sites during 1975–1981. The average pairwise genetic correlation of large plot grain yields recorded at different sites within years was 0.45±.03, with a mean repeatability within trials of 0.56±.05. Harvest index measured in 20-grain hill plots in 1978 showe genetic correlations of 0.98±.08 with plot yield at the same site, and 0.39±0.06 with plot yield assessed at other sites in the same year.The genetic correlation between harvest index in hill plots and total biological yield in large plots at the same site was 0.84±.13, the relationship showing no evidence of curvilinearity. Selection for harvest index in hill plots is therefore expected to lead to an increase in biological yield as well as grain yield in the breeding populations studied. Quantitative genetic theory suggests that the response to selection for grain yield can be increased by approximately 40% with an initial screening using hill plot harvest index at three sites instead of one, and reallocation of resources in the first stage of large plot yield assessment to include 6–8 sites, rather than dryland and irrigated trials at a single location.     

Interactive Effect of Nitrogen and Sulphur on Growth and Yield of Rape-seed-Mustard (Brassica juncea L. Czern. and Coss. and Brassica campestris L.) Genotypes

A simple randomized field experiment was conducted to assess the growth and yield of rape-seed-mustard in relation to sulphur and nitrogen interaction. Three levels of sulphur (0, 40 and 60 kg ha⁻¹) in combination with three levels of nitrogen (60, 100 and 150 kg ha⁻¹) were tested as treatments, T₁, T₂, T₃, T₄, and T₅. Results indicated significant favourable effects of sulphur and nitrogen, when applied together, on yield components, seed and oil yield. Maximum response was observed with treatment T₃ (having S and N of 40 and 100 kg ha¹, respectively). Percentage oil content of seed was maximal at T₄ (having S and N of 60 and 100 kg ha¹) in both cultivars. The increase in N dose from 100 to 150 kg ha⁻¹ without any change in applied S, i.e. 60 kg ha¹ (T₅), decreased the percentage oil content. The seed and oil yield, however, were similar to T₃. Favourable responses of S and N interaction on leaf area index, rate of photosynthesis and biomass production were also observed.     

Yield and water-use efficiency of water- and nitrogen-stressed wheat crops increase with degree of co-limitation

Availability of water and nitrogen are key constraints to primary productivity in arid and semiarid ecosystems. Theoretically, plant growth is maximised when all resources are equally limiting. This paper tested the hypothesis that for a given amount of available water, the gap between actual and attainable yield of dryland crops in semiarid southern Australia is inversely proportional to the degree of nitrogen and water co-limitation.

Field and simulation experiments were combined in an analysis involving three steps. Step 1 assessed the capacity of a crop simulation model to estimate yield and its responses to water and nitrogen inputs in the semiarid Mallee region. Step 2 derived a boundary function relating grain yield and water availability using simulations with long-term weather records. Step 3 explored the link between degree of co-limitation and deviations between actual yield and the boundary function. Degree of co-limitation (C_WN) was calculated as a function of model-derived nitrogen (NSI) and water stress indices (WSI), i.e. C_WN = 1 − |NSI − WSI|. Stress indices range from zero (no stress) to 1 (maximum stress), and C_WN tends to 1 when both resources impose constraints of similar magnitude to crop growth.

The field experiment combining locations, seasons and management practices generated a range of grain yield from 0.6 to 3.8 t ha⁻¹. Water availability, i.e. seasonal rainfall plus change in soil water content from sowing to harvest, ranged from 127 to 370 mm. Nitrogen fertiliser varied from nil to 36 kg N ha⁻¹ and inorganic nitrogen in the soil profile at sowing ranged from 29 to 497 kg ha⁻¹. For these ranges of conditions, the relationship between simulated and measured yield was statistically undistinguishable from the y = x function.

A factorial modelling experiment combining sites, seasons, initial soil water content and dose of nitrogen fertiliser was used to derive a boundary function which provided an objective and independent upper limit for the field data. Actual yield was below the boundary function in most cases. The difference between actual and attainable yield was inversely proportional to C_WN. This study thus supported the hypothesis that yield and water-use efficiency of water- and nitrogen-stressed crops increase with increasing degree of co-limitation.     

Physiological Investigation of the Impact of Nitrogen and Sulphur Application on Seed and Oil Yield of Rapeseed (Brassica campestris L.) and Mustard (Brassica juncea L. Czern. and Coss.) Genotypes

Field experiments were conducted to determine the physiological basis of the effects of N and S interactions on seed and oil yield of Brassica species. Five combinations of N and S (in kg ha⁻¹) 0S+100N (T₁), 40S+60N (T₂), 40S+100N (T₃), 60S+100N (T₄) and 60S+150N (T₅), were used for this purpose. Nitrate reductase (NR) activity and ATP-sulphurylase activity in the leaves were measured at various growth stages, as the two enzymes catalyse rate-limiting steps of the assimilatory pathways of nitrate and sulphate, respectively. The activities of these enzymes were strongly correlated with seed and oil yield. The highest nitrate reductase activity, ATP-sulphurylase activity and yield were achieved with the combination T₃ in both species. Any variation from this combination decreased the activity of these enzymes, resulting in a reduction of the seed and oil yield of Brassica species. The higher seed and oil yield achieved in these species at T₃ could be due to optimization of leaf soluble protein and photosynthetic rate, as these parameters are influenced by N and S assimilation.     

Stability Analysis of Winter-rape (Brassica napus L.) by Using Plant Density and Mean Yield per Plant

The yield F per area can be expressed multiplicatively by using yield components. For the most simple case of including only two yield components one obtains: F = X₁− X₂ with X₁= number of plants per area (= plant density) and X₂= mean yield per plant.
For normal variables X₁ and X₂ the phenotypic yield stability of F, which has been measured quantitatively by the variance V(F) of F, can be explicitly expressed dependent on 1) the component means, 2) the component variances and 3) the correlation between the two components. V(F), therefore, depends on 5 parameters.
For many applications the use of the coefficient of variation v of F instead of the variance itself may be advantageous, v can be explicitly expressed dependent on 1) the coefficients of variation of the yield components and 2) the correlation between the components, v, therefore, depends on 3 parameters.
The different conditions leading to the same phenotypic yield stability can be investigated by using these explicit expressions for V(F) and v.
The main purpose of the present paper is the application of these theoretical models and results to the data of an extensive field trial with winter-rape, which has been performed for 5 years with 4 plant densities and 3 row distances.
For the lowest plant density (40 plants/m²) there results a very good agreement between the theoretically expected and the experimentally obtained values for the phenotypic stability of yield per area. But, for the higher plant densities this result don't hold true. Possible causes and explanations are discussed in detail.     

冬小麦生物量及氮积累量的植被指数动态模型研究

利用遥感技术实时监测小麦生长状况,依据监测结果适时促控,可提高产量。本研究以高产小麦品种周麦27为试验材料,在不同试验地点设置了水氮耦合的大田试验,筛选出了适宜监测冬小麦地上部氮积累量和生物量的植被指数,并构建了不同产量水平下优选植被指数的动态模型。结果表明,(1)不同的水氮耦合模式显著影响小麦冠层光谱变化,在350~700nm和750~900nm表现相反的反应特征;(2)对2个农学生长指标反应敏感且兼容性好的植被指数主要有修正型红边比率(mRER)、土壤调整植被指数[SAVI(825,735)]、红边叶绿素指数(CIred-edge)和归一化差异光谱指数(NDSI),其与产量间相关性较好的时期为拔节至灌浆中期;(3)双Logistic模型可以很好地拟合植被指数的动态变化,高产和超高产水平下拟合精度较高(R^2>0.82),而低产水平下相对较低(R2=0.608~0.736)。比较而言,CIred-edge和SAVI(825,735)用于评价小麦长势较为适宜。研究结果对作物因地定产、以苗管理、分类促控具有重要意义。