Variation In Dry Matter Yield Research Articles

Identification and evaluation of agro-ecological variation in dry matter yield and nutritional values of local grasses used as livestock feed in Adola Reedde, Guji Zone, Ethiopia

ABSTRACT A study was conducted in Adola Reedde to identify major grass species and evaluate their chemical composition, in vitro digestibility, and dry matter yield. Sixty key informants taken from the sampled kebele of three agro-climates were interviewed to identify common grasses in their vernacular name. Relative feed value and dry matter digestibility were computed using neutral detergent fibre and acid detergent fibre contents. Spearman's rank correlation was used to examine relationships between laboratory results and farmers' perception of grass quality. Fifteen grass species were identified and ranked by farmers according to the species' preferences for cattle. Crude protein values ranged from 56.5 g/kg DM for lowland to 113 g/kg DM for highland agro-climate. overall mean of neutral detergent fibre was 662 g/kg DM, and in vitro dry matter digestibility and relative feed value were 446.5 g/kg DM and 60.97%, respectively. Total dry matter yield and dry matter of individual grass species were significantly (P < 0.001) higher in highland than in low land agro-climate. Dry matter yield across agro-climate ranged from 92.47 ± 0.04 g m−2-119.41 ± 0.07 g m−2 for highland and lowland agro-climate, respectively. Generally, study highlights the potential of herbaceous species to support livestock production if the grassland is properly rehabilitated and managed.

Grass Growth and N2O Emissions From Soil After Application of Jellyfish in Coastal Areas

The supply of nutrients for agricultural production faces enormous challenges as food security and sustainability goals have to be ensured. Processing of marine biomass has high potential to provide nutrients for agricultural purposes in coastal areas. One underexplored resource are jellyfish, which occur as blooms and by-catch of the fishing industry. In this context, a pot experiment investigated the effects of jellyfish as a fertilizer on biomass accumulation of annual ryegrass (Lolium multiflorum), and its effect on the important greenhouse gas N2O as a sustainability indicator of novel fertilizers. Dried and ground jellyfish was applied [3 species: Aurelia aurita (AA), Cyanea capillata (CC), Periphylla periphylla (PP)] and compared with an unfertilized and a mineral fertilized (calcium-ammonium-nitrate, CAN) treatment. Dried jellyfish and CAN were applied at equal N rates of 5 g N per m2. The N2O-fluxes from soil were measured over 56 days after fertilizer application. Grass dry matter yields, when using CC and PP treatments, were not significantly different to the CAN treatment (p &amp;gt; 0.05). After reducing its salinity, AA also showed no differences to CAN on plant growth and the lowest coefficient of variation for dry matter yield as an indicator for yield stability. Accumulated N2O-emissions were lowest in the control and were 3-times higher in AA and CC compared to CAN (p &amp;lt; 0.05). If salinity levels are moderate, jellyfish application to soil can compete with artificial mineral fertilizers in terms of N-supply for above- and belowground yield response, regardless of jellyfish species used. However, elevated N2O-emissions are likely to affect its suitability for large-scale application. Nevertheless, if energy-efficient methods of drying and desalination of jellyfish can be developed, in coastal areas dried jellyfish is a valuable fertilizer in coastal areas, particularly in situations where nutrient supplies for agriculture are limited.

Modelling inter-annual variation in dry matter yield and precipitation use efficiency of perennial pastures and annual forage crops sequences

In livestock systems of the Argentinean Pampas, its forage production stability relies on the integration of two landcovers, annual forage crop sequences and perennial pastures. Despite the key role that these forage cropping systems have on current milk and beef production, it is unclear how year-by-year variability of precipitation affect forage dry matter (DM) yield and precipitation use efficiency (PUE, i.e. the quotient between forage DM yield and precipitation). The aims of this study were to analyze the impact (i) of year-by-year precipitation variability on DM yield and PUE of oats-maize (Avena sativa L. - Zea mays L.) double-crop and alfalfa (Medicago sativa L.) and (ii) of cumulative precipitation during the critical period of maize on DM yield and PUE of oats-maize double-crop. We used a modelling approach to estimate DM yield and PUE of oats-maize (sequence) and alfalfa in five locations of the Argentinean Pampas, which differed in annual precipitation (AP) and variability of it. Coefficient of variation (CV) was used as the main statistical variable to compare the variability of AP (CVAP), DM yield (CVDM), and PUE (CVPUE). Mean DM yield of both landcovers was higher in locations with high AP (>800 mm) than with low AP (<800 mm). Although alfalfa had lower mean DM yield than sequence in all locations, it showed a lower CVDM than sequence. In contrast, sequence showed lower and higher CVDM than CVAP, depending on location. Moreover, changes in DM yield due to variations of AP were higher in sequence than in alfalfa. On the other hand, mean PUE was higher for sequence (2.2 g DM m−2 mm−1) than that of alfalfa (1.6 g DM m−2 mm−1). The CVPUE between locations, i.e. an index that reflects the spatial variability, ranged from 20 for the sequence to 68% for alfalfa, whereas CVPUE between years, i.e. an index that reflects the temporal variability, ranged from 16 to 31 % for both landcovers. Precipitation use efficiency tended to be similar across locations in years with low AP (<800 mm) compared to years with high AP (>800 mm). Our results provided valuable knowledge for decision making in livestock systems of this region through the development of spatial and temporal models between DM yield and AP. In a broader sense, they also showed that shifts from perennial to seasonal forage covers increased yields but also its inter-annual variability, posing a risk for farmers.

Constructing Italian ryegrass yield prediction model based on climatic data by locations in South Korea

AbstractA yield prediction model for Italian ryegrass (IRG) was constructed based on climatic data by locations in South Korea using a general linear model. The sample size of the final dataset was 312 during 25 years. The forage crop and climatic data were collected from the reports of two national research projects on forage crops and Korean meteorological administration, respectively. Five optimal climatic variables were selected through the stepwise multiple regression analysis with dry matter yield (DMY) as the response variable. Subsequently, three climatic variables were selected after considering the interpretability of the five variables. The three selected climatic variables were spring accumulated temperature, mean temperature in January and spring rainfall days. Then, the yield prediction model was constructed based on these three climatic variables using general linear model with the cultivated locations as dummy variables. The model constructed in this research could explain 73.6% of variation in DMY of IRG. The goodness‐of‐fit of the model was tested through residual diagnostics and 10‐fold cross‐validation. For climatic variables, the high partial eta squared value of spring accumulated temperature and spring rainfall may reflect the growth characteristics that spring is the main growing period for IRG and IRG has strong waterlogging tolerance and weak drought tolerance. The results may also support the possibility to sow IRG in the subsequent spring if autumnal seeding was missed in South Korea.

Genetic Parameters and Prediction of Breeding Values in Switchgrass Bred for Bioenergy

Estimating genetic parameters is an essential step in breeding by recurrent selection to maximize genetic gains over time. This study evaluated the effects of selection on genetic variation across two successive cycles (C1 and C2) of a ‘Summer'x‘Kanlow’ switchgrass (Panicum virgatum L.) population. Two progeny tests were planted in 2007 and 2011 near Mead, NE and respectively analyzed for 2 and 4 yr. Each test was a randomized complete block design, with four replicates of 34 halfsib families in single‐row plots of 10 seedlings in C1 and with three replicates of 111 halfsib families in single‐row plots of five seedlings in C2. The C2 test included C0, C1, and parental populations for comparison. Multivariate mixed linear models revealed ample additive genetic variation for dry matter yield (DMY), Klason lignin (KL), and predicted ethanol yield (ETOH) in both cycles, with heritability ranging from 0.40±0.18 to 0.5±0.14 at the family level, from 0.22±0.17 to 0.36±0.22 at the individual level, and from 0.25 to 0.31 within family in C1. Matching values in C2 were: from 0.42±0.09 to 0.63±0.07, from 0.10±0.07 to 0.34±0.13, and from 0.12 to 0.48. More opportunity exists to improve DMY, with a coefficient of additive genetic variation of 11 to 32%, than KL (3–5%) or ETOH (3–6%). The traits were properly aligned for joint improvement for high DMY and reduced KL in C1, owing to favorable genetic correlations (rA=−0.33±0.11) and each having respective rA of 0.60±0.05 and −0.62±0.07 with ETOH. In C2, the rA between DMY and KL (−0.19±0.10) or ETOH (0.04±0.04) decreased towards zero, and that between KL and ETOH was moderately less negative (−0.35±0.15). These results suggest a strong genetic basis for improvement of the traits and monitoring of their patterns every cycle to find the proper weights that maximize the breeding goal of designing the ideal bioenergy switchgrass.

Adaptation and forage yield of Vetches (Vicia spp.) in the southern highlands of Ethiopia

Aim. To study the adaptation of vetch species and the level of their forage yield in the highlands of the region. Methods. Field and laboratory methods, statistical analysis. Results. The study was conducted in Bulle and Chencha districts of Southern region of Ethiopia with the objective to identify adaptable and high forage yield- ing vetch species for the high lands of the region. Five vetch species (Vicia sativa L., V. dasycarpa Ten., V. atropurpurea Desf., V. villosa Roth. and V. benghalensis L.) were tested at both locations for two years. The result showed that there was signifi cant variation in dry matter yield of the tested species in the two locations. Vetches planted at Bulle performed well when compared with Chencha area with mean DM yield of 5.3 and 1.2 t/ha, respectively. Among the vetch species, Vicia sativa, Vicia villosa, Vicia dasycarpa, and Vicia bengalensis adapted well at Bulle and produced on average 4 to 7 t/ha forage DM. In Chencha area, V. dasycarpa and V. villosa were the best performing species with forage DM yield of 1.6-1.8 t/ha. Conclusions. The vetch species tested in the current study could be used for conventional pasture and forage production, in livestock exclu- sion areas, in forage strips, as an under-sowing with food crops, or as a backyard forage crop in the southern highlands of Ethiopia.

Forecasting phenology of mustard crop in North-western Himalayas

Field experiments were conducted during rabiseason of 2007-08 and 2008-09 to study the phenology, thermal indices and its subsequent effect on dry matter accumulation of mustard (Brassica juncea L.) varieties viz., RCC-4, Kranti and Varuna grown under varying environmental conditions of Himachal Pradesh. The early sown (10th October) crop varieties took maximum average growing degree days for flower initiation (492±1), 50% flower-ing (682±1), pod initiation (742±1), 90% pod formation (811±4) and maturity (1394±8) which decreased with subse-quent delay in sowing time and recorded lowest under late sown (9th November) crop. The accumulated helio-thermal units and photo-thermal units decreased from 9824 to 7467 oC day hour and 19074 to 15579 oC day hour, respectively. High heat-use efficiency was obtained under late sown condition on 30th October. The heat-use efficiency (HUE) was high at 90% pod formation stage as compared to other stages in all the varieties and sowing dates (except 9th November sowing). The early sown (10th October) crop had maximum calendar days and cumula-tive pan evaporation (158 days and 448.2 mm) followed by normal (20th and 30th October) (153 days and 434 mm) and late (9th November) (138 days and 403.1 mm) sown crop indicating higher water requirement under early sow-ing. The predictive regression models explained 83-85% variation in dry matter yield in three varieties of mustard. The agro climatic indices are important determinants for temperature, radiations and photoperiods behaviors of crop. The accurate predictions of crop phenology are useful inputs for crop simulation modeling and crop management, and used for climate change assessment and simulated adaptations in present scenarios.

Genetic Variation for Dry Matter Yield, Forage Quality, and Seed Traits Among the Half‐Sib Progeny of Nine Orchardgrass Germplasm Populations

ABSTRACTA potential strategy to address the lack of success of North American orchardgrass (Dactylis glomerata L.) breeding programs to increase forage yield and other agronomic traits is the incorporation of novel sources of germplasm. In an attempt to identify novel orchardgrass germplasm sources with agronomic potential, the study described herein characterized 162 half‐sib families (HSFs) from six orchardgrass germplasm populations and three orchardgrass cultivars. Study conditions were Millville, UT, and Rexburg, ID, field sites with data collection from 2008 to 2010. The genotype × location interaction variance differed from zero for dry matter yield, crude protein, in vitro true digestibility (IVTD), neutral detergent fiber, and seed weight. Within location broad‐sense heritability differed for all traits at both locations (0.36 ±0.10 to 0.77 ±0.03) except IVTD at Rexburg. For each trait there were HSFs that possessed values similar to or better than the included check cultivars (CCs). Additionally, in several instances the mean phenotype of the HSFs from a specific family was better than the phenotype of the corresponding parental population and/or the mean phenotype of the CCs. Overall, for each trait there existed sufficient genetic variation to develop an elite orchardgrass breeding program for irrigated conditions.

Variation Within Accessions of Switchgrass Germplasm for Dry Matter Yield and Forage Quality in a Semiarid Environment

ABSTRACTSwitchgrass (Panicum virgatum L.) is valued for conservation, forage, and biofuel in many areas of North America and worldwide. The extent of switchgrass productivity has not been characterized under semiarid conditions. A study was designed to characterize the variation within a set of 114 switchgrass germplasm accessions and six switchgrass cultivars for dry matter yield, crude protein, in vitro true digestibility, and neutral detergent fiber under limited irrigation conditions at a Millville, UT, field site from 2008 to 2010. Variation among the accessions for each of these traits was greater than zero within individual harvests and across the four harvests. Accession × harvest variation was also greater than zero for each trait. A set of 11 switchgrass accessions, including the cultivar ‘Cave‐in‐Rock’, were identified that had consistently high phenotypic values for each of the traits at the several harvests. The highest dry matter yield values at any harvest (∼4 Mg ha−1) were low compared to other regions of the United States. However, the identified genetic variation for dry matter yield and forage quality was sufficient to improve germplasm for these traits either for use in semiarid regions or to increase the drought tolerance of germplasm used in wetter regions.

Agronomic and molecular analysis of heterosis in alfalfa

Double ‘free-hybrids’ (DH) in alfalfa were obtained by crossing in a diallelic scheme, six multiplied simple hybrids (SH) derived from four partly inbred (S2) lines. Analysis of the specific combining ability demonstrated that the main source of variation was for dry matter yield (DMY) in DHs and supported heterosis values of DHs versus the best parent of an average +45% (ranging from +5 to +76%). Investigation at the molecular level was carried out by analysis of simple sequence repeat markers on the six parental SHs and 15 DH progenies and by comparison of gene expression profiles using microarrays of a single DH line to its parental lines. The variation of heterozygosity estimates of the DHs explained a small part (about 20%) of their variation in DMY, while the number of alleles was significantly related to DM performance (r = 0.61; P &lt; 0.05). The microarray analysis identified genes with both significant additive and non-additive levels of expression in the hybrid compared with the parents. The majority of the variation in gene expression was additive (87%), but among the genes with a non-additive pattern of expression, the greater proportion of probe sets (86%) fell outside the parental range. Gene ontology analysis of these genes revealed the presence of a number of terms related to metabolism and genetic information processing.

Effect of Plant Density on Morphological Characteristics, Yield and Chemical Composition of Napier Grass (&lt;i&gt;Pennisetum purpureum&lt;/i&gt; (L.) Schumach)

An experiment to assess the effect of plant density on morphological characteristics, dry matter production and chemical composition of Napier grass (Pennisetum purpureum (L.) Schumach) was conducted in 2004 and 2005 at Haramaya University, eastern Ethiopia. There were a total of nine treatments with 1.5, 1 and 0.5m spacing between rows and 0.75, 0.5 and 0.25m spacing between plants, which consisted of 8,888.9, 13,333.3, 26,667.7, 13,333.3, 20,000, 40,000, 26,667.7, 40,000, and 80,000 plants per ha, arranged in a randomized complete block design with three replications. The plot size was 3m width x 6m length and the spacings between replications and plots were 1.5m and 1m respectively. There was no significant (P > 0.05) effect in morphological characteristics of Napier grass due to plant density during the establishment year. However, the number of tillers, total leaves, internode number, internode length, basal circumference and leaf length per plant were significantly (P < 0.05) affected by plant density in the second year. There was a significant (P < 0.05) difference in dry matter (DM) yield due to plant density. A considerable variation in DM yield between the two years and number of harvests in each year was observed during the study and the DM yield in 2005 was much greater than the 2004 crop season. Higher DM yields were obtained from 80,000 (7.80 t/ha) and 40, 000 (39.9 t/ha) plant density in 2004 and 2005 respectively. There was no significant (P > 0.05) effect on the chemical composition of Napier grass due to plant density. However, the crude protein (CP) content of all the treatments was above 15%, which is the optimum required for animal growth or production. The fibre fractions were also below the threshold level (600 g/kg DM) at which DM intake of cattle is affected. Based on DM yield production and CP content, the production of Napier grass using 40, 000 plants per hectare is recommended to livestock producers in eastern Ethiopia agro-ecologies of the country. Keywords: Chemical Composition; Dry Matter Yield; Morphological Characteristics; Napier Grass; Plant Density East African Journal of Sciences Vol. 2 (1) 2008: pp. 55-61

Adaptation of sulla cultivars to contrasting Mediterranean environments

Sulla coronaria (L.) Choi &amp; Ohashi (syn. Hedysarum coronarium L.) may become a major forage species in various Mediterranean-climate areas. This study aimed to assess the extent of genotype × environment (GE) interaction in the western Mediterranean region and its implications for breeding programmes. The milestone Italian varieties Grimaldi and Sparacia, one recent Italian variety, and the Tunisian cv. D’Italie (evolved under moderately favourable conditions from Italian germplasm introduced about 40 years ago) were evaluated in three environments of Tunisia (of which two were irrigated), two of Algeria, and one of Sardinia (Italy). Water available over the crop cycle (rainfall + possible irrigation from October 2004 to June 2006), ranging from 881 to 1906 mm, accounted for 85% of the variation among environments and 72% of the GE interaction variation for dry matter yield. The latter was adequately described by one-covariate factorial regression, which was preferable to joint regression and additive main effects and multiplicative interaction modelling. D’Italie was specifically adapted to environments with available water exceeding 1200 mm, Grimaldi was top-ranking between 950 and 1200 mm, and Sparacia below 950 mm. The crossover GE interaction between top-yielding material (P &lt; 0.05) has implications for adaptation targets, genetic resources, selection environments, and opportunities for international co-operation between breeding programmes. It suggests breeding either for rainfed cropping in semi-arid or near semi-arid environments, or for definitely subhumid or irrigated environments.

Influence of Dry Matter and Length of Roots on Growth of Five Field Crops at Varying Soil Zinc and Copper Levels

Information on influence of root dry weight and root length on shoot dry matter accumulation in annual crops grown in the Cerrado region of Brazil is limited. Ten greenhouse experiments were conducted on Oxisols with the objective to assess the influence of the root dry weight and root length on shoot yield of rice (Oryza sativa L.), common bean (Phaseolus vulgaris L.), corn (Zea mays L.), soybean (Glycine max L. Merr.), and wheat (Triticum aestivum L.). Significant and positive relations were observed between root length and root weight and shoot yield of five crops. Overall, variation in dry matter yield of crops was higher by root dry weight compared with root length. This shows that dry weight of roots is relatively a better indicator to predict shoot dry matter accumulation in annual crops. Shoot dry matter production efficiency (shoot dry weight/root dry weight) was in the order of common bean > soybean > wheat > upland rice > corn. Hence, legume crops roots have higher dry matter production efficiencies compared to cereal crops.

Genetic variation and correlation of agronomic traits in meadow bromegrass (Bromus riparius Rehm) clones

Meadow bromegrass (Bromus riparius Rehm.) is a recently introduced pasture grass in western Canada. Its leafy production and rapid regrowth have made it a major grass species for pasturing beef animals in this region. As relatively little breeding work has been done on this species, there is little information on its breeding behaviour. The main objective of this study was to estimate total genetic variability, broad-sense heritability, phenotypic and genetic correlations. Forty-four meadow bromegrass clones were evaluated for agronomic characters. Genetic variation for dry matter yield, seed yield, fertility index, harvest index, plant height, plant spread, crude protein, neutral detergent fiber and acid detergent fiber, was significant. Broad-sense heritability estimates exceeded 50% for all characters. Heritability estimates were at least 3.5 times greater than their standard errors. Phenotypic and genetic correlation between all possible characters were measured. There was general agreement in both sign and magnitude between genetic and phenotypic correlations. Correlations between the different characters demonstrated that it is possible to simultaneously improve seed and forage yield. Based on the results, it appears that the development of higher yielding cultivars with higher crude protein, and lower acid and neutral detergent fibers concentration should be possible.

Impact of residue characteristics on phosphorus availability in West African moist savanna soils

The role of residue characteristics in enhancing the availability of P was investigated in a greenhouse study using two soils from the northern Guinea savanna (NGS) and four from the derived savanna (DS) zones of the West African moist savanna. Eight organic residues of varying C-to-P ratio were used and maize ( Zea mays) was grown for 7 weeks. The effect of the organic residues on P availability (measured as resin P and maize P accumulation) differed among the soils. On average, the increase in resin P, calculated as {[(soil+residue)−control]/(control)×100}, was between 8% (Davie, DS) and 355% (Danayamaka, NGS). Maize P accumulation was increased by ca. 11% in Davie and Niaouli (DS) soils and 600% in Danayamaka soil. The increase in maize total dry matter yield (DMY) ranged from 2% to 649%. Residues with C-to-P ratio >200 produced lower DMY than those with lower ratios. Residue organic P (Po) extractable with 0.2 N H2SO4 (acid-Po) accounted for 92% ( P =0.0001) of the variation in DMY in a step-wise regression with residue parameters as independent variables and mean DMY as the dependent variable. The residue Po extractable with 0.5 M NaHCO3 (HCO3-Po) correlated significantly with DMY in Danayamaka and Davie soils, and with P accumulation in Danayamaka soil. The relationships between the residue Po and DMY might imply that Po fractions in decomposing residues contribute to P availability. However, the suitability of using the Po content of organic residues to predict their agronomic value with respect to P nutrition needs further evaluation.

The use of radiation interception and transpiration to predict the yield of healthy, droughted and virus-infected sugar beet

This paper reports an analysis of the yield of sugar beet crops grown under experimental conditions between 1993 and 1995 in the UK. Crops were either healthy (unstressed) or subjected to drought, infection with Beet yellows virus (BYV) or a combination of both. The study investigated whether the large differences in yield between the crops grown in different seasons and subjected to different stresses could be accounted for by simple relationships between total biomass and radiation interception (εs), transpiration (εw) or εs and εw adjusted for mean saturation deficit (Ωs and Ωw respectively). Mean values of εs, εw, Ωs and Ωw in healthy crops were 1·42 g/MJ, 0·89 g/kg, 6·76 g/kPa/MJ and 4·29 g/kPa/kg respectively. Variations in the dry matter yield between seasons were best accounted for by Ωw and less well by εw or εs. Ωs accounted for least variation in yield between seasons. None of these relationships remained constant in stressed plants; both drought and BYV-infection decreased εs (and Ωs) but Ωw was increased by drought and decreased by BYV-infection. However, in common with healthy crops, seasonal variation in yields was best accounted for by Ωw. Mean values of εs, Ωs, εw and Ωw for all healthy, infected and droughted crops accounted for 61, 50, 88 and 97% of the variation in dry matter yield between experiments respectively. Accurate prediction of the yield of stressed plants requires a knowledge of their infection and drought status. If this information is unavailable then the mean value of Ωw for healthy, infected and droughted crops will provide a reasonable prediction of the yield of such crops.

Soil factors affecting the availability of potassium to plants for Western Australian soils: a glasshouse study

A glasshouse experiment was conducted with 41 surface and 8 subsurface soils to measure their potassium (K) supply capacities and K depletion of soils by ryegrass growth for 260 days and harvesting at ~40-day intervals. Dry matter yield ranged from 0.22 g to 25.4 g/kg soil, cumulative K uptake ranged from 0.006 to 1.49 cmol/kg soil, and values of K concentration (%) in the first cut herbage ranged from 0.40% to 5.97%. Some of the light-textured soils were so impoverished in K that symptoms of K deficiency appeared during the first growth period. Water-soluble K + exchangeable K accounted for 43–100% of cumulative K uptake by the ryegrass. Multiple regression analysis indicated that 68% of the variation in dry matter yield and 90% of the variation in K uptake may be predicted by the exchangeable K content of these soils. The 6 harvests of ryegrass extracted only 0.21–12.07% of total K from these soils, which was not sufficient to cause discernible mineralogical changes in most soils. For some soils vermiculite was formed at the expense of illite/mica by K release to plants. For soils containing vermiculite but no other K-bearing clay minerals, vermiculite peaks broadened on K depletion by plants. Major proportions of total K in these soils are present in silicate minerals, yet only minor amounts are released to plants by very slow weathering processes. For soils that do not contain any K bearing clay minerals, very minor amounts of feldspar may have dissolved to release K.

Variation for Yield, Water‐Use Efficiency, and Canopy Morphology among Nine Alfalfa Germplasm

Alfalfa (Medicago sativa L.) production under irrigated and rainfed conditions may benefit from improvements in water‐use efficiency (WUE), the amount of forage and root biomass produced per unit of water transpired. If benefits from improved WUE are to be realized, correlations between important agronomic traits and key physiological traits associated with WUE must be determined. This study characterized variation for dry matter yield, forage maturity, leaf‐to‐stem ratio (LSR), carbon isotope discrimination (Δ), canopy temperature, ash content, and specific leaf mass (SLM) in alfalfa. Associations between traits were also determined. Nine alfalfa germplasms representing eight of the nine historical genetic diversity groups, and a very fall‐dormant (YFD) population, were established in seeded, irrigated plots for 2 yr near Las Cruces, NM. Significant variation (P ≤ 0.10) was detected for all traits and was greatest for Δ and maturity, intermediate for yield, canopy temperature, ash content, and LSR, and least for SLM. The African, Peruvian, and Indian germplasms exhibited a higher Δ than either the Turkistan, YFD, M. varia Martyn., or Ladak germplasms. Carbon isotope discrimination was positively correlated with forage yield (r = 0.64; P ≤ 0.10; n = 9) and forage maturity (r = 0.66; P ≤ 0.05; n = 9). No association was detected between Δ and either canopy temperature, ash content, SLM, or LSR. The results indicate that differences in stomatal conductance or photosynthetic capacity exist among the nine populations, and that germplasms with low Δ tended to have slower growth and development rates under irrigated conditions. Neither canopy temperature, ash content, nor SLM provided suitable alternate measurements of A among the nine alfalfa germplasms.

Variation for dry matter yield, seed yield and other agronomic traits in Ladino white clover landraces and natural populations

A set of Ladino white clover ecotypes including the last available landraces and some natural populations collected from old permanent meadows, together with some white clover varieties of various origins, were evaluated as monocultures for dry matter (DM) and seed yield assessed in separate field experiments. Other agronomic traits were also recorded. The best performing variety, ‘Espanso’, was significantly outyielded by some ecotypes for DM and seed production. Compared to landraces, natural populations yielded on average far less seed but as much DM and tended towards higher persistence indicating that domestication of the native Ladino at the farm level only improved seed yield of the crop. Natural populations showed, besides lower values of most seed yield components, a distinct canopy architecture characterized by smaller leaves, longer internodes and denser stolons. Seed weight proved the best character discriminating between the two ecotype groups. Significant variation for most traits was found both among landraces, in which it was mostly relatable to differences among provenances, and among natural populations. The relations between the main multivariate patterns of phenotypic variation and a set of environment collecting variables suggested that evolutive adaptation to different agronomic practices was a major determinant of the overall variation found in landraces. Evidence is provided that a relevant part of the variation observed among ecotypes for some important traits could be genetic.

Relations between soil factors and herbage yields of natural grassland on sandy soils in the south‐eastern Transvaal

Forty systematically‐placed observation points were established in a 1.5‐ha area of floristically unifoim veld in which productivity varied spatially. At each point grass yields were determined by harvesting quadrats at eight‐week intervals during the growing season, and the volumetric water content of the soil was measured weekly. In addition, root mass and root‐N content, and soil variables involving C and N contents, extractable P, K, Ca and Mg, cation exchange capacity and base saturation, pH, clay content and soil depth, were determined. The data were examined using linear correlations between variables, principal components analysis and multiple regression. The major factors associated with variations in yield were, in order of importance, soil water content, the N supply (as expressed by root‐N content or root‐N mass) and the cation supply (as expressed by the topsoil variables, extractable Ca or cation exchange capacity or percentage base saturation). There was a relatively weak positive association between yields and the H+ concentration in the subsoil, and a weak negative association between yields and the clay content of the topsoil. A multiple regression function involving all five factors accounted for 77.3% of the variation in dry matter yield.