Growth and yield of six short varieties of spring wheat derived from Norin 10 and of two European varieties

Five short varieties of spring wheat derived from Norin 10: Lerma Rojo 64A (R), Penjamo 62 (P), Sonora 64 (S), Mexico 120 (M), and an unnamed selection obtained from Mexico (X), had grain yields equal to, or only slightly less than those of the taller European spring varieties Kloka (K) and Jufy I (J). Yields ranged from 500 to 580 g/m² of dry matter. The short variety NBJ115 (N) was severely infected with yellow rust and yielded only 290 g/m². Total dry weight (excluding roots) of the short varieties was less than of J and K; hence grain accounted for 49 % of the total for the short varieties and 42 % for J and K. Most of the short varieties had fewer ears than the tall ones because sowing difficulties and poor germination produced fewer plants. The relative yields of X, P, R and S seemed to be correlated with their plant and ear densities. Leaf area duration after flowering (D), based either on total green area or on green area above the flag-leaf node only, was less for the short varieties than for J and K. The apparent mean efficiency of this area in grain production (grain yield divided by D) was 50% greater for the short than for the tall varieties. The height of the short varieties ranged from 43 cm (M) to 79 cm (N). K was 92 cm and J 97 cm tall. Differences in height depended on the lengths of the top four internodes and not on number of internodes. Main shoots of all varieties produced seven or eight leaves. All varieties initiated spikelets 45–48 days after sowing. The short varieties flowered 103 days and matured 155 days after sowing; J and K flowered and matured about 1 week earlier.     

Effect of Radiation and Temperature on Efficiency of Cereal Leaves during Grain Growth

Grain: leaf ratio, G (the ratio of grain yield to leaf areaduration between ear emergence and maturity), in 15 experimentson wheat and barley in different seasons (Group A experiments)was highly correlated with mean daily radiation, R, mean dailytemperature, T_µ, and mean daily maximum temperature, T_max,during the grain growth period. The regression of G on R accountedfor 81 per cent of the variance of G, and introducing T_µto the regression significantly increased this to 88 per cent.The regression of G on T_max alone accounted for 87 per cent,perhaps because T_max effectively integrates radiation and temperature. When R was varied artificially by shades in two experimentson wheat in different years (Group B experiments) the relationshipbetween G and R was approximately linear in both, but the slopeof the line was less in one year, when R and temperature wereless, than in the other. For this second year, when R and temperatureswere about the middle of the ranges found in Group A experiments,the calculated relationship agrees with the Group A resultsafter correcting values of G for differences of Tu from itsvalue in the shading experiment. A formula relating G and Rderived from the results of both Group B experiments and theobserved correlation of R and temperature in the field, assumingthat the regression of G on R depends on temperature, agreeswith the relationship between G and R in the Group A experiments. It is concluded that differences in radiation and temperatureare about equally responsible for the differences in G foundbetween seasons. The positive effect of temperature on G suggeststhat factors other than leaf photosynthesis, e.g. translocationrate or capacity of the grain to accumulate carbohydrate, areimportant in determining G.     

A Study of the Nitrogen and Water Factors in Competition with Agropyron repens (L.) Beauv.

From a consideration of the possible relationships between thelevel of a nutrient in the soil, the depletion due to a competitor,and the response of a test plant, it is argued that a validcriterion for the implication of a nutrient factor in root competitionis that some growth response of the test plant to competitionshould be less at higher levels of supply of that nutrient thanat lower levels. Young test plants of Impatiens parviflora were transplantedinto pans of soil in which stands of Agropyron repens were growing.Two levels of nitgrogen and gtwo rates of watering were appliedin a multifactorial design, and from half of the test plantsroot competition was excluded, so that their responses to rootcompetition could be measured under the various nitrogen andwatering treatments. A preliminary experiment hadf shown, and the competition experimentconfirmed, that the optimum nitrogen level for root growth andNet Assimilation Rate was less than the higher level employed,whereas this level was not sufficient for maximum leaf-growth.In agreement with this, the depressions of relative root growth-rateand Net Assimilation Rate caused by competition at the lowernitrogen level were significantly reduced at the higher level,but for relative leaf-growth this reduction did not reach significance.The effects of competition were reduced by the higher rate ofwstering, and for relative leaf growth-rate this interactionwas highly significant. It is deduced that competition from A. repensfinvolves bothnitrogen and water, and that water is probably the more importantfactor under normal conditions. There is no need to postulkateany toxic root product to account for the experimentalo results.Compared with competition above ground, it appeared that rootcompetition could have an effect on the relative growth-rateof I. parviflora about as great as a reduction of light intensityfrom full to 5–10 per cent. of summer daylight.     

Root and shoot growth of semi-dwarf and taller winter wheats

Investigations are reported of root and shoot growth in semi-dwarf and taller winter wheat varieties grown in contrasting soils over three years. Comparisons were made of the distribution with depth of roots, estimated by injecting rubidium-86 into stem bases and counting the content in soil cores. The relative ability to absorb phosphate from different zones was measured from the recovery in aerial parts of ³²P injected into the soil at different depths. The distribution of dry matter in roots and aerial parts, and total root length, was measured using soil cores and samples of aerial parts taken during the growth of the crop. Relative growth rates of the aerial parts followed a sigmoid curve, but those of the roots showed little change between germination and anthesis. There was little evidence of varietal differences in root growth, though there was some indication that at depth the roots of the semi-dwarf varieties were more extensive and absorbed more phosphate than those of the taller varieties.     

The Effects of Competition with Agropyron repens and of Nitrogen-and Water Supply on the Nitrogen Content of Impatiens parviflora

The nitrogen contents of plants of Impatiens parviflora grownin pots with and without root competition from Agropyron repens,and with two levels of nitrogenand water-supply, were determined. The nitrogen percentage and the nitrogen content were depressedby competition and increased by nitrogen application. Wateringincreased nitrogen content and percentage in plants growingwith competition; the increased growth associated with suchwatering was approximately equivalent to the nitrogen increase.These effects were chieftly due to responses in the nitrogenabsorption rate per unit root dry-weight. Root dry-weight/totaldry-weight ratio changes were generally in the opposite direction,but were relatively small. When Net Assimilation Rate was calculated on a leaf nitrogenbasis, the effect of competition was relatively less than whenit was calculated on a leaf area basis, but the depression causedby high nitrogen status was much larger. When Net AssimilationRate calculated on a leaf area basis was compared with nitrogenper unit leaf area there was evidence of a single relationshipfor all treatments. It appeared that most of the variation inNet assimilation Rate between treatments was caused by differencesin nitrogen status.     

Dependence of Yields of Wheat Varieties on their Leaf Area Durations

In a field experiment three wheat varieties: autumn-sown CappelleDesprez, Prestige, both autumn-sown and spring-sown, and spring-sownJufy I, each supplied with 0.5 or 1.0 cwt nitrogen/acre (6₃or 126 kg/ha), had grain yields nearly proportional to theirLeaf Area Durations (D) during grain development. Squarehead'sMaster had a smaller grain yield relative to its total D, butwith 0.5 cwt N/acre the ratio of its grain yield to D of partsabove the flag leaf node (D_F) was similar to the other varieties.The difference in this ratio between varieties was less whenD_Fwas calculated from anthesis than from ear emergence to ripening.Squarehead’s Master with 1.0 cwt N/acre had a smallerratio of grain yield to D_F than other treatments, implying lessgrain per ear relative to D_Y per shoot, perhaps because of lodging,or because factors limiting size of ears restricted their abilityto accept all the assimilate the shoots could produce with thisamount of N.     

Competition for Nitrogen and Potassium in Agropyron repens

Stands of Agropyron repens (couch grass) and single young sugar-beetplants were grown in pots, separately and in competition, withnitrogen and potassium each supplied at three rates in a factorialdesign. Both nitrogen and potassium increased relative growth-ratesof sugar-beet leaves and crowns and fresh-weight/dry-weightratios of all plant parts; the responses were usually curved,the high nutrient levels having little more effect than theintermediate levels. Competition decreased relative growth-ratesand freshweight/dry-weight ratios of all plant parts and alsoleaf-area ratio (F) and net assimilation rate (E). High ratesof nitrogen diminished the effects of competition on relativeleaf growth-rate, F, and on fresh-weight/dry-weight ratios,indicating competition for nitrogen, but high rates of potassiumdiminished only its effect on relative growth-rate of the crown,suggesting that competition for potassium had only a small effect. Competition depressed leaf nitrogen and potassium percentagesand total nitrogen and potassium uptake by the whole plant,but the depressions were small at high rates of nutrient supply,suggesting that the amounts of nitrogen and potassium availablewere nearly adequate for both sugar-beet and A. repens. When total dry weights and leaf areas of sugar-beet were comparedwith corresponding nutrient contents, variation in nitrogencontent alone could account for most of the effects of competitionon growth, but potassium depletion probably also contributeda little. E was correlated with potassium, but not nitrogen,per unit leaf area, but potassium differences could not adequatelyaccount for the effects of competition on E. Competition for potassium produced small effects compared withcompetition for nitrogen, in spite of large responses to addedpotassium, perhaps because potassium moves less readily in thesoil.