Top Dry Matter Research Articles

Variation Analysis of Efficiency of Intercepted Radiation Conversion in the Accumulation of Dry Matter by Soybean.

Field experiments were conducted in 1989 on a converted paddy field at Shiga Agricultural Experiment Station (Azuchi, Shiga Prefec.), and in 1990 on an upland field at Shiga Prefectural Junior College (Kusatsu, Shiga Prefec.), in order to investigate stability of efficiency of intercepted photosynthetically active radiation conversion in the accumulation of dry matter (EPAR) by soybean and determine factors which might affect EPAR. In 1989, cultivar 'Enrei' was sown on 3 different dates in various planting patterns, and in 1990, cultivar 'Tamahomare' was grown at various plant population densities. The intercepted PAR and the top dry matter accumulation were in quite close relationship. But it was not always linear over the whole growth duration. EPAR increased in the early growth stage, then, approximately after the canopy closure, it was kept relatively stable or increased slightly until early grain filling period when EPAR began to decline. This time course of EPAR was considered to be resulted primarily from the change of crop photosynthetic activity. But in addition to that, the greater portion of light-saturated leaves at the early stage and the increasing maintenance respiration at the late growth stage also might cause lower EPAR at those stages respectively. Since almost all EPAR values calculated for the period through which those were observed to be stable, were within a small range, from 2.1 to 2.3gMJ-1 in 1989 and from 2.4 to 2.5gMJ-1 in 1990, respectively, due to sowing dates and planting patterns, it was concluded that the ability of dry matter production of soybean crop was not affected considerably by those conditions. Within the small variation of EPAR caused by different planting patterns in 1989, EPAR showed no correlation with N content per unit leaf area, while it showed relatively clear correlation (r=-0.651) with canopy light extinction coefficient KPAR.

Blueberry Species and Cultivar Response to Soil Types

Eight soil type and 4 blueberry cultivars were used in an outdoor pot study on the adaptability of blueberries to atypical soils. Two highbush (Vaccinium corymbosum L.) 'Spartan' and 'Collins' and 2 rabbiteye (V. ashei Reade), 'Woodard' and 'Bluegem,' cultivars were grown for two seasons under trickle irrigation but without organic amendments. Dry matter partitioning of the plants at the end of the experiment indicated greater root mass production by either highbush cultivar compared to either rabbiteye with no consistent differences on top dry matter production. This resulted in significantly lower shoot to root ratios for highbush blueberries. The absence of a significant soil type by cultivar interaction on shoot to root ratio indicates that highbush blueberries may be less efficient in nutrient acquisition than rabbiteye. Foliar elemental analysis showed significantly greater nitrogen, phosphorus and calcium in highbush versus rabbiteye while potassium and magnesium were variable among cultivars. Foli...

The Interaction Effects of Potassium and Drought in Field-Grown Barley. I. Yield, Water-Use Efficiency and Growth

Abstract In order to study the interaction of K application and drought a field experiment with spring barley (Hordewn distichum L. cv. Gunnar) was conducted in 1985, 1986 and 1987 on coarse-textured sandy soil low in natural K content and water-holding capacity. The drought occurred naturally or was imposed by shelters during the grain-filling period. K was applied as KCl at rates of 50, 125 and 200 kg K/ha top-dressed at emergence. High K applications (125 and 200 kg K/ha) significantly increased rate of growth of the vegetative parts of the crop. With high K application the leaf area increased up to 26% at anthesis, and top dry matter accumulation increased up to 15% between anthesis and milk-ripe stages of growth, resulting in about 10% higher straw yield at final harvest. Also, the number of ears increased with high K application. Final grain yield was unaffected by level of K application in fully irrigated plots. Drought during the grain-filling period decreased grain yield by decreasing grain weigh...

Dinitrogen fixation and soil n uptake by soybean as affected by phosphorus availability

Abstract The effects of phosphorus supply (0, 30, and 90 mg P kg‐1) on growth, N2 fixation, and soil N uptake by soybean (Glycine max (L.) Merr.) were studied in a pot experiment using the 15N isotope technique. Phosphorus supply increased the top dry matter production at flowering and the dry matter production of seeds, straw, pod shells, and roots at late pod filling of inoculated soybeans. Phosphorus supply reduced the N concentration of plant tops at flowering, but increased the amount of N accumulated at both flowering and late pod filling. In inoculated soybeans total N accumulation paralleled the dry matter production. The P concentration in above‐ground plant parts of nodulated soybeans was not affected by P application. At flowering only 18 to 34% of total N was derived from N2 fixation, whereas as much as 74% was derived from N2 fixation at late pod filling. Only the addition of 90 mg P kg‐1 soil significantly increased the amount of N2 fixed at the late pod filling stage. Phosphorus supply did not influence the uptake of fertilizer or soil N in soybeans, even if the root mass was increased up to 60% by the P supply.

Regulation of Photosynthate Partitioning into Starch in Soybean Leaves

Studies conducted in controlled environments indicate that daylength affects the proportion of photosynthate stored in leaves as starch or sucrose. To examine the response of partitioning to natural daylight, soybeans (Glycine max [L.] Merr. cv Williams) were grown at 12 different times between May and November in a constant temperature greenhouse without supplemental lighting. Plants were transferred from the greenhouse to a controlled environment chamber at the end of civil twilight at a set developmental stage (expanding seventh trifoliolate leaf, counting acropetally). Net photosynthesis and the accumulation of starch and sugar in fully expanded fourth trifoliolate leaves were determined the following day under standard conditions in the chamber (lights-on synchronized with sunrise). Photosynthesis on a leaf area basis decreased about 10% between midsummer and early autumn. Leaf soluble sugar accumulation was low at all harvests. However, a twofold increase in photosynthate partitioning into starch occurred over the same time period, resulting in an 80% increase in absolute starch accumulation rate. Starch was responsible for about 78% of the increase in leaf dry matter during the light at all harvests, indicating that starch accumulation as affected by prior daylight conditions will alter export of photosynthate during the light period. Photosynthate partitioning into starch was linearly correlated with daylength at harvest, prior average peak solar irradiance, and other parameters that correlated with daylength and solar radiation such as harvested top dry matter. The relation between growth and seasonal changes in daylight (including daylength, irradiance, and light integral) are discussed in relation to photosynthate partitioning under field conditions.

Effect of growth rate on internode elongation in rice.

The effect of growth rate (dry-matter increment per plant per day) at internode-elongation stage on the elongation of internodes was investigated, using a rice variety Gimbozu and 15 mutants of the variety, which differed in culm-length and/or heading time. The materials were grown in two cropping seasons in randomized block design with two replications. Every two weeks after transplanting, seven plants per plot were sampled and measured for top dry-matter weight per tiller. With 18 other standing plants, top dry-matter weight was estimated each by multiplying its tiller number by the top dry-matter weight per tiller. Then, Pearl-Reed's quadratic equation was fitted to thus estimated values, and the growth rate at any stage was evaluated through the equation. Heading date, culm length and internode length were also measured. The following results were obtained.

Corn responses to oxygen deficiency applied to nodal and/or seminal roots

Abstract A split root technique was used to study the effect of oxygen deficiency (D) and no deficiency (0) in soil on corn (Zea mays L.) growth. Treatments were 0–0, 0‐D, D‐0 and D‐D where the first letter corresponds to nodal roots and the second to seminal roots. Treatments were applied for 15 days to 13‐day‐old plants. Top dry matter production decreased 35.5% with D‐0, 51.1% with 0‐D and 61.5% with D‐D. However, root dry matter production increased 1.30% with D‐0, 12.4% with 0‐D, and 69.5% with D‐D. This behavior was due to higher nodal root dry matter production, which was 0.125 g in 0–0, 0.241 g in D‐0, 0.488 g in 0‐D, and 0.855 g in D‐D, while seminal root dry matter production was 0.546 g in 0–0, 0.439 g in D‐0, 0.265 g in 0‐D, and 0.273 g in D‐D. Root surface increased under D, due to a higher ramification of nodal roots that grew toward the soil or water surface. Leaf area decreased from 527.8 cm2 in 0–0 to 431.4 cm2 in D‐0, to 362.7 cm2 in 0‐D, and to 167.4 cm2 in D‐D.

Trigo: efeito de magnésio combinado com forças iônicas em solução nutritiva na tolerância ao alumínio

Os cultivares BH-1146, IAC-17 e Siete Cerros foram estudados em soluções nutritivas contendo 10 mg/litro de Al3+, combinados com três concentrações de sais (um décimo, um quinto e a metade da concentração de sais da solução nutritiva completa) e cinco níveis de Mg (0; 9,6; 48; 96 e 192 mg/litro). A tolerância foi medida pela capacidade de as raízes primárias continuarem a crescer em soluções sem alumínio após permanência de 24, 48 e 72 horas em soluções de tratamento contendo determinada força iônica combinada com determinada concentração de magnésio, na presença de 10 mg/litro de Al3+. Independentemente da força iônica, da concentração de magnésio, da atividade iônica do Al3+ e do período de crescimento nas soluções de tratamento, o 'BH-1146' apresentou tolerância e 'IAC-17', moderada tolerância a 10 mg/litro de Al3+. 'Siete Cerros' mostrou-se sensível nas soluções com baixos níveis de magnésio. A atividade fônica do Al diminuiu à medida que foram aumentadas as forças iônicas e os níveis de Mg das soluções de tratamento. As correlações simples entre a atividade iônica do alumínio e as concentrações de magnésio com o crescimento das raízes foram respectivamente negativas e positivas. Correlações negativas foram determinadas entre as concentrações de Mg nas soluções e os teores de Al na matéria seca da parte aérea dos cultivares estudados e entre os teores de Al na matéria seca da parte aérea e os comprimentos das raízes.

Responses of Sugarbeet to Deficit, High‐Frequency Sprinkler Irrigation. I. Sucrose Accumulation, and Top and Root Dry Matter Production1

AbstractInsufficient water frequently limits crop production worldwide. The present study was conducted to determine the effect of deficit daily sprinkler irrigation on sucrose accumulation and root and top dry matter production from sugarbeet (Beta vulgarisL.) grown on loam and sandy soils (Xerollic Camborthids and Xeric Torripsamments, respectively). Applied water ranged from 15 to 100% and 26 to 115% of the estimated evapotranspiration (Et) after near full canopy on the loam and sandy soil, respectively. On the loam soil, root sucrose concentration increased rapidly with time. The rate of increase was lower with adequate soil water than when it was limited. At the final harvest, maximum dry matter production occurred at irrigation rates equivalent to 40 to 50% of estimated Et. On the sandy soil, with limited water, root sucrose concentrations increased to a maximum about 8 weeks after irrigation treatments began and then decreased. With adequate water, root sucrose concentrations increased until harvest. Sucrose concentration was significantly higher with limited than with adequate water until near harvest. Dry matter production increased with increasing water applied up to about 85% estimated Et

Groundnut nitrogen fixation by three serologically and morphologically distinct rhizobia

Three cowpea miscellany rhizobia, a commercial strain (TAL 309) and two field isolates from Sudan (Wad Medani and Kadugli strains), were chosen for detailed studies because they could be separated by serological or morphological characteristics. The strains were screened in the greenhouse on three groundnut ( Arachis hypogaea L.) cultivars, “Ashford” and “MH383” (both Virginia types), and “Barberton” (a Spanish type). Whenever the TAL 309 strain was included in inoculum mixtures, it consistently occupied the majority of nodules with all three groundnut cultivars. Although significant differences were found in top dry-matter weights, color ratings, nitrogenase activities, and total nodule number among the three cultivars tested, there were no host-genotype-by-strain interactions either in growth measurements or in nodule occupancy. Correlation matrices indicated that several of the measures made could serve as reliable indicators of rhizobial efficiency. Both top dry-matter weight and plant color, and top dry-matter weight and C 2H 2 reduction were related at the 0.001 level of probability.

Potato growth in the subtropics of Florida

Dry weight of tops of LaRouge potatoes varied considerably among years. In turn this affected tuber growth and total plant dry matter accumulation. Maximum plant top dry matter accumulation occurred between 54 and 69 days after planting (DAP) with a maximum of 2.5 dry mt/ha. In all years tuber initiation was first observed 47–48 DAP. By 100 DAP, additional tuber growth was minimal. Among years, the highest tuber dry matter recorded was at 7.9 mt/ha. Of the variables that were evaluated for their effect on final yield and tuber growth rate (kg/ha/day), plant age in terms of DAP explained over 87% of yield variability. For most of the yield variables, the quadratic and cubic terms for DAP were significant in explaining variability. An additional 1 to 5% was explained by temperature variation. Between 95 and 99% of the variability in harvest index, the ratio of dry tuber to whole plant dry weight, was explained by DAP.

Dry Matter Production in Tops and Roots of Winter Wheat as Affected by Phosphorus Availability During Various Growth Stages1

AbstractThe timeliness of P availability to a plant is important for maximum plant growth. There is little information pinpointing the critical time(s) in the life cycle of winter wheat (Triticum aestivum L.) at which P uptake is the most important for maximum growth response. The objectives of this research were: i) to determine the effects of removing P from the growing medium during progressive stages of growth on dry matter production and P uptake of winter wheat; and ii) to compare the P demand pattern of winter wheat with that known for spring wheat. ‘Centurk’ winter wheat was grown using a modified Hoagland's nutrient solution in a greenhouse environment. Treatments consisted of evaluating the plant response to the time grown with and without available P in the nutrient solution. This was accomplished by replacing the complete nutrient solution with a nutrient solution devoid of P and allowing plants to continue growth to physiological maturity. Winter wheat had taken up sufficient P by the first node stage to ensure maximum dry matter production of the mature roots and tops. Phosphorus availability in later growth stages did not significantly increase mature root and top dry matter production. Maximum grain yield at maturity, however, was only realized when P was available through the mealy‐ripe stage (Feekes' Scale 11.2) of grain development. It appears that after noding stage only a small amount of P may be needed to allow carbohydrate translocation mechanisms to function. Spring wheat differs from winter wheat in that it only requires adequate P up to heading to produce maximum grain yields.

Variation among Inbred Lines of Crimson Clover for N2 Fixation (C2H2) Efficiency1

Inbred lines of crimson clover (Trifolium incarnatum L.) were assayed for N2 fixation using the acetylene reduction assay. The seedlings were inoculated with a single pure strain (162K13) of Rhizobium trifolii and cultured in a nil‐nitrogen nutrient solution contained in individual plastic growth pouches. The acetylene reduction assay was carried out on live plants using the plastic pouches to contain the gas mixture. In the first experiment, significant differences were noted among 14 crimson clover lines for acetylene reduction. Top dry matter, leaf number, and visual scores of nodulation, root growth and top growth were significantly correlated with the acetylene reduction assay. A relatively large coefficient of variation (27.1%) was noted for this experiment. In the second experiment refinement of culture and assay techniques resulted in a lower coefficient of variation (15.2%) and significant differences among six crimson clover lines for acetylene reduction were found.

Effect of defoliation on Virginia Bunch peanuts at Camden, N.S.W

It is not at all usual to defoliate peanuts; however, the low harvest index (less than 0.34) and high vegetative yield (> 5 t ha-1) at Camden, N.S.W., suggested there might be foliage which could be harvested as forage. Accordingly, the ability of peanuts to sustain kernel yield after defoliation to 10 cm was examined using the cultivar Virginia Bunch at Camden. Defoliation up to early pod formation (10 weeks from sowing) caused no reduction in kernel yield, in contrast to later treatments where yield reductions of up to 40% were observed. The top dry matter so removed provides an additional useful forage product from the crop, with an in vitro dry matter digestibility of 79% and average nitrogen concentration of 2.4 g nitrogen/100 g at age 10 weeks. The reasons for the increased sensitivity to defoliation of older plants (> 10 weeks) are explored.

Influence of Concentrations of K and Mg in Nutrient Solutions on Sorghum1

AbstractSeveral interactive effects of K and Mg are present both in plants and soils. Very limited information is available on the interaction of these two elements in sorghum [Sorghum bicolar (L.) Moench] plants. Thus a greenhouse experiment was conducted in sand culture to determine the main and interactive effects of K and Mg in the medium on growth and composition of sorghum plants.Nutrient treatments included seven concentrations each of K as KCI, and Mg as MgCI2. Seventeen of the possible 49 treatment combinations were used in a central composite factorial design with two replications. A sorghum hybrid (‘RS 671’), its male (‘Tx 415’), and female (‘Redlan’) lines were used. Aboveground parts of plants were harvested at 25, 50, and 75 days after emergence.The three sorghums showed similar effects for most treatments. Dry matter production was not affected by concentrations of K and Mg until 50 and 75 days after emergence, respectively. At final harvest, maximum top dry matter production was obtained at the optimum rates of 195 and 38 ppm of K and Mg, respectively. Effects of K were not affected by concentrations of Mg and vice versa.As long as the absolute amounts of K and Mg in the growth medium were adequate to meet the demands of the plants, the K/Mg ratio in the growth medium varied widely without causing any adverse effect on dry matter production of the plants.Plant nutrient concentrations were determined by rate of growth and consequent nutrient dilution. However, high levels of K in the growth medium reduced plant Mg concentrations. Also increased rates of applied Mg increased the concentrations of P in the plants.Increases of K/Mg ratio in the growth medium were associated with reductions in Mg, Ca, and P concentrations in the plant, but the sum (K + Mg + Ca) remained constant.These results show that K is probably more critical than Mg in the nutrition of sorghum, but low levels of both created growth problems particularly as the growth period of the plant exceeded 50 days. Two parent lines and a hybrid showed limited differences in K and Mg nutrition. The K/Mg ratio in the growth medium was not useful in predicting amount of growth.

Screening Sorghum for Aluminum Tolerance in Nutrient Solutions1

AbstractIdentification of Al tolerant sorghum [Sorghum bicolor (L.) Moench] is important if this crop is to be grown successfully on acid, Al‐toxic soils. A rapid method for screening genotypes for Al tolerance was developed by growing over 100 plants in the same container of relatively small volume (50 ml/plant). Mineral element conditions that gave good differential responses for Al tolerance were 148 µmol liter−1 Al, 64 µmol liter−1 P, 7.4 mmol liter−1 Ca, 1.6 mmol liter−1 Mg, 3.9 mmol liter−1 K, 24.7 mmol liter−1 N (8 NO3−:1 NH4+), light (17 hours)/dark (7 hours) temperatures of 28/23 C, and solution pH values below 4.0. Mineral element levels or temperatures higher or lower than these resulted in poorer differential responses of genotypes to Al, either because Al had essentially no effect or Al effects were too severe. Nitrate as a single N source could not be used to screen for Al tolerance because the solution pH increased as plants grew and Al in solution was inactivated. A mixture of NO3− or NH4+ gave better genotypic separation than NO3− or NH4+ alone. Visual Al toxicity symptoms on roots were noted within 10 days, and seminal root lengths could be used to assess Al tolerance of sorghum genotypes. Differences in root and top dry matter yields did not distinguish sorghum genotypes for Al tolerance.

Relationship between Root Dostribution of Upland Crops and their Yield : III. Influence of soil moisture levels on root distribution and root dry matter of upland-cultured paddy rice, crossbred rice of paddy rice and upland rice, and upland rice

This experiment was conducted to clarify the effects of different soil moisture levels on the root distribution and root dry matter of upland-cultured paddy rice (cv. Myojoo, Kochihibiki), crossbred rice of paddy rice and upland rice (cv. Ishioka glutinous No.10, Mizuhatamochi), and upland rice (cv. Norin No. 12, Norin No. 21). In the first experiment (1977), the root distribution and dry matter was investigated on the six cultivars which were cultivated under irrigation and nonirrigation. The irrigation treatments were begun at July 18. The soil moisture tension of the two irrigation plots were at pF 2.5 and pF 2.0 at l0 cm depth, respectively. During July 24 to August 8, the soil moisture tension of nonirrigation plot was over pF 2.9 and in the range of pF 2.5 to 2.9, at 10 cm and 30 cm depths, respectively. Therefore, the soil moisture of nonirrigation plots reached to first permanent wilting point at l0 A.M., August 4. Top dry matter, root dry matter and root distribution were investigated at maturity. The investigation of the root distribution was practiced by excavating soil masses, which were sectioned by 7 cm increments up to 35 cm depth. The second experiment (1978) was set up in cylindrical plastic pots of 30 cm height and 25 cm inner diameter using four cultivars (Myojoo, Mizuhatamochi, Norin No. 12, Norin No. 21). Soil moisture treatments composed by two levels of high and low were begun at July 10. That is, high soil moisture plot was irrigated by each pots every day. While, low soil moisture plot was irrigated when every time the soil moisture became to first permanent wilting point. The treatments were continued for 58 days. The results showed that root distribution of the rice plants was effectively influenced by different soil moisture levels. The roots of rice plants distributed in the shallow layer under irrigation, while the roots distributed in the deeper layer under nonirrigation. Root distribution of upland-cultured paddy rice and crossbred rice of paddy rice and upland rice distributed in the shallow layer than that of upland rice. Also, root dry matter was influenced by different soil moisture levels. The root dry matter was increased in drier soil condition, where rice plants proliferated numerous branches to gather a small amount of soil water. The root dry matter of upland rice cultivar 'Norin No. 12' was increased conspicuously in surface layer under nonirrigation. It is suggested that high growth rate of root weights in water stressed rice plants was correlated with drought resistance, because high growth rate of root weight was obtained by upland rice which has drought tore-lance. R-T ratio was increased in drier treatments, because root dry matter was increased and top dry matter was decreased by water stress.

Studies on competition between Setaria anceps and Eleusine indica

Summary:Experiments were conducted at Kairi. Queensland. Australia on the competitive effects or Eleusine indica (L.) Gaertn. on Setaria anceps Stapf. ev. Nandi. In one experiment S, anceps top dry weights and seed yields were reduced to a similar extent by 20, 40. 80 or 164 (unthinned) E. indica plants/m2. Similarly, the dry matter yields from populations of 20–164 plants/m2 of E. indica did not differ significantly. Varying the density of S. anceps from 6 to 9.3 plants/m2 had little effect on the yield of either species. The mean production of E. indica seed was 1968 kg/ha or approximately 5.3 109 seeds/ha.In two experiments where equal populations of both species were planted at varying times in relation to each other the above ground dry matter yield of S. anceps was not significantly affected when E. indica emerged 2 weeks or later than S. anceps. This was true whether the S. anceps was planted in rows or uniformly throughout the plot. Ina third, similar experiment S. anceps top dry matter was significantly reduced by 21% when the E. indica emerged 2 weeks after the crop.In a time of weeding experiment, removal of E. indica for the first 13 days after planting was sufficient to prevent a significant reduction in S. anceps top dry matter and seed yields. In this experiment the two species were shown to be mutually exclusive.

Studies on competition between Macroptilium atropurpureum and Crotalaria goreensis

Summary:Experiments were conducted at Walkamin, Queensland, Australia on the competitive effects of Crotalaria goreensis Guill. & Perr. on Macroptilium atropurpureum (DC.) Urb. cv. Siratro. In one experiment it was shown that varying C. goreensis densities of 10, 20, 40 and 200 plants/m2 produced successive reductions in M. atropurpureum yields and successive increases in C. goreensis yields. Varying the M. atropurpureum density from 2.3 to 6 plants/m2 did not significantly affect the yield of either species. Two hundred C. goreensis plants/m2 produced approximately 500 106 seeds/ha.In three time of emergence experiments it was shown that the competitive ability of one species relative to the other varied with environmental factors. In one of these experiments with equal numbers of each species C. goreensis lowered M. atropurpureum top dry matter yield only when the former species emerged 2 weeks prior to the M. atropurpureum. When there were many more plants of C. goreensis present, emergence of both species at the same time lowered M. atropurpureum top dry matter yield in one experiment and emergence of C. goreensis 2 weeks after the M. atropurpureum lowered the dry matter yield of the latter species in a third experiment.In a time of weeding experiment it was shown that under the particular environmental and plant density conditions prevailing removal of C. goreensis for 12 days after planting was sufficient to prevent a reduction in M. atropurpureum dry matter. In this experiment it was also shown that under these conditions the two species were not mutually exclusive. In mixtures the C. goreensis provided physical support to the M. atropurpureum, enabling the latter species to intercept more light energy than it could when growing in monoculture.

Yield effects of herbicides on competition between crop and weed communities

A literature review showed that the relationship between crop and weed top dry matter yields at harvest time is often linear. It is suggested that by including monocultures of both crop and weeds and a series of partial weeding treatments in any herbicide screening experiment, the true effect of a herbicide can be determined with the separation of any effect due to interspecific competition. To do this, confidence limits are constructed for a linear regression fitted to the crop by weed yield coordinates for the non-herbicide treatments. Points produced by yield coordinates from herbicide-treated plots which lie outside these confidence limits indicate either depression or stimulation of both yield components. From the relationships between these points and the regression line, weed competition and herbicide phytotoxicity esects can be estimated separately. Evidence supporting this theory was obtained in a field experiment with a crop of Desmodium intortum and a natural weed community.