Plant Relative Yield Research Articles

Plant responses to nitrate and ammonium availability in Australian soils as measured by diffusive gradients in thin-films (DGT) and KCl extraction

Determining soil nitrogen (N) availability is essential in agriculture to minimise over-application, maximise growers’ returns and reduce potential environmental consequences. The present study assesses soil mineral N (nitrate-N and ammonium-N) using the diffusive gradients in thin-films (DGT) technique against the conventional potassium chloride (KCl) extraction. The DGT technique has demonstrated reliable predictability for plant-available P, Cu and Zn. However, the use of DGT to quantify soil N bioavailability is underreported and N measurements made with DGT have not been compared to plant growth responses or N uptake. A pot trial using wheat was performed to determine the suitability of the DGT technique to predict N plant uptake and plant biomass. Four contrasting soil types from South Australia were used, and four rates of N were applied to the soil. DGT devices and KCl extraction were used at sowing to measure soil mineral N. These data were then compared with plant relative yield (YR) and N uptake after harvesting the plants. Soil mineral N, as measured by both the DGT and KCl extraction techniques, demonstrated a significant positive correlation with YR, with an R2 value of 0.6; however, DGT-N extracted comparatively more nitrate (NO3–, >87 % of CN) than KCl-N (65 % of EN). Mineral N and NO3– extracted by both DGT and KCl significantly correlated with plant N uptake albeit this correlation was stronger for KCl (R2 = 0.8) than DGT (R2 = 0.6). The same parameters also positively and significantly correlated with YR, however in this case, both correlations were similar and only modest (R2 < 0.6 in all cases). These results are explained in terms of the differences between the pools of N accessed by these techniques and limitations related to soil N dynamics. In conclusion, KCl showed similar or better predictive ability for N uptake and yield response (YR) in wheat compared to DGT across four Australian soils. Given its low cost and ease of application, KCl presents a competitive advantage in this study.

Mutual Effects of Rottboellia cochinchinensis and Maize Grown Together at Different Densities

A greenhouse experiment was performed to test whether competition, and possibly allelopathy, were involved in Rottboellia cochinchinensis–maize interactions in two soil conditions: fertilized and unfertilized. Changes in morphological and physiological growth parameters for each species were determined by classical plant growth analysis. The dry weight and total leaf area of maize grown with Rottboellia decreased significantly as the density of the weed or maize plants increased, particularly under unfertilized conditions. At high densities of Rottboellia, regardless of fertilization, its root biomass allocation was 38% greater than the stem and leaf biomass allocation. In contrast, in unfertilized conditions, Rottboellia biomass allocation was higher in leaves than in roots and stems at high densities of maize or Rottboellia. Relative crowding coefficient values indicated that maize had a competitive advantage over Rottboellia. Mutual allelopathic effects of maize–Rottboellia interactions were not fully demonstrated because plant relative yield values were not significant among treatments. When the density of Rottboellia increased, its total leaf area and total dry weight significantly decreased, greater than when the density of maize increased. These results indicate that intra‐specific competition between Rottboellia plants was greater than inter‐specific competition with maize. High densities of maize significantly reduced the total leaf area of maize and Rottboellia. Reductions in the total leaf area of maize were greater under unfertilized conditions. The results showed that maize was more affected by fertilization than by the density of plants.

Competitive Interactions between Cultivated and Red Rice as a Function of Recent and Projected Increases in Atmospheric Carbon Dioxide

Because wild lines of the same species often represent a weedy constraint to cultivated crops in the field, any differential response to atmospheric carbon dioxide concentration, [CO2], may alter weed–crop competition and seed yield. We evaluated the growth and reproduction of cultivated rice (Oryza sativa L.; Clearfield, CL161) and red or weedy rice (Stuttgart, StgS) in monoculture, and at two competitive densities (8 and 16 plants m−2) using [CO2] that corresponded to the 1940s, current levels, and that projected for the middle for the current century (300, 400, and 500 μmol mol−1, respectively). Competition was determined using plant relative yield (PRY) for biomass and seed yield as a function of [CO2]. At maturity, PRY significantly increased for wild rice, but decreased for the cultivated line as a function of competitive density. Increases in [CO2] resulted in significant decreases in the PRY of seed yield at both competitive densities for CL161; while significant increases in seed yield and aboveground biomass were noted for StgS, but only at the higher competitive density. In addition, the relative increase in seed yield for CL161–StgS, determined at the same competitive density, increased as a function of [CO2] suggesting a greater amount of seed rain from the weedy rice. Overall, these are the first data to indicate that for rice, weedy lines may have been favored as a function of rising carbon dioxide, with greater relative impact on the seed yield and biomass of cultivated rice lines.

Changes in competitive ability between a C4crop and a C3weed with elevated carbon dioxide

Abstract Using climate-controlled glasshouses, the growth of grain sorghum was evaluated with and without the presence of common cocklebur at current and projected future atmospheric concentrations of carbon dioxide [CO2]. Single-leaf photosynthetic rates declined for both species in competition; however, elevated CO2 reduced the percentage decline in common cocklebur and increased it in sorghum by 35 d after sowing (DAS) relative to ambient CO2. In monoculture, elevated CO2 significantly stimulated leaf photosynthetic rate, leaf area, and aboveground dry weight of common cocklebur more than that of sorghum. However, the stimulation of aboveground biomass or leaf area for monocultures of sorghum and common cocklebur at elevated CO2 did not adequately predict the CO2 response of aboveground biomass or leaf area for sorghum and common cocklebur grown in competitive mixtures. Overall, by 41 DAS, plant relative yield (PRY), in terms of aboveground biomass and leaf area, increased significantly for common cock...

The Influence of Increasing Carbon Dioxide and Temperature on Competitive Interactions Between a C3 Crop, Rice (Oryza sativa) and a C4 Weed (Echinochloa glabrescens)

Many of the most troublesome weeds in agricultural systems are C4 plants. As atmospheric CO2 increases it is conceivable that competitive ability of these weeds could be reduced relative to C3 crops such as rice. At the International Rice Research Institute (IRRI) in the Philippines, rice (IR72) and one of its associated C4 weeds, Echinochloa glabrescens, were grown from seeding to maturity using replacement series mixtures (100:0, 75:25, 50:50, 25:75, and 0:100, % rice:%weed) at two different CO2 concentrations (393 and 594 μL L-1) in naturally sunlit glasshouses. Since increasing CO2 may also result in elevated growth temperatures, the response of rice to each CO2 concentration was also examined at daylnight temperatures of 27/21 and 37/29�C. At 27/21�C, increasing the CO2 concentration resulted in a significant increase in above ground biomass (+47%) and seed yield (+55%) of rice when averaged over all mixtures. For E. glabrescens, the C4 species, no significant effect of CO2 concentration on biomass or yield was observed. When grown in mixture, the proportion of rice biomass increased significantly relative to that of the C4 weed at all mixtures at elevated CO2. Evaluation of changes in competitiveness (by calculation of plant relative yield (PRY) and replacement series diagrams) of the two species demonstrated that, at elevated CO2, the competitiveness of rice was increased relative to that of E. glabrescens. However, at the higher growth temperature (37/29�C), growth and reproductive stimulation of rice by elevated CO2 was reduced compared to the lower growth temperature. This resulted in a reduction in the proportion of rice:weed biomass present in all mixtures relative to 27/21�C and a greater reduction in PRY in rice relative to E. glabrescens. Data from this experiment suggest that competitiveness could be enhanced in a C3 crop (rice) relative to a C4 weed (E. glabrescens) with elevated CO2 alone, but that simultaneous increases in CO2 and temperature could still favour a C4 species.

Seed-predators reduce broadleaf weed growth and competitive ability

Based on field observations that fewer broadleaf weeds were found in low-input no-tillage systems (LINTS), a series of greenhouse experiments was conducted to investigate the effect of weed seed-predators on the competitive ability of broadleaf weeds grown with grass weeds. Two major broadleaf weeds, which were found in LINTS, red root pigweed Amaranthus retroflexus and lambsquarters Chenopodium album, and two major grass weeds, large crabgrass Digatara sanguinales and fall panicum Panicum dichotoflorum were tested singularly and in pairs (always one broadleaf with one grass) in the study. These seed pairings were exposed to (1) seed-predators (carabids and field crickets found in LINTS) which were at different densities, (2) wheat straw residue, (3) seed-predators and residue, and (4) a control (no seed-predators or residue). Seed-predators reduced the plant relative yield (PRY) of broadleaf weeds to the same extent as the wheat residue. Seed-predators preferred to feed on the broadleaf seeds which reduced the broadleaf weeds competitive ability when grown with grasses. Decreasing seed-predators by 50% resulted in almost no change in broadleaf plant relative yields compared with the control (no seed-predators). The decrease in seedling PRY caused by seed-predators was still evident as the plants matured. There was a significant interaction between seed-predators and residue in reducing broadleaf PRY probably because of differing effects of each on plant growth.

A model of the competitive relationships between R. cochinchinensis and Z. mays

SUMMARYAn understanding of the competitive relationship between weed and crop can be used in assessing what physiological aspects of the association can be exploited in the control of the weed. Field and greenhouse studies were conducted with Z. mays L. and Rottboellia cochinchinensis (Lour.) W D Clayton using a modified replacement series model in which the overall weed crop density in each treatment was maintained as a constant, but the proportion of the two species varied. The results indicated that the crop had greater competitive ability (Kmr) than the weed even at increasing weed densities. Under field conditions, the values of the Plant Relative Yield (PRY) indicated that severe specific competition was occurring and suggested that some environmental factor was limiting, while the Relative Yield Total (RYT) suggest that either the crop and the weed were exploiting the resources in mutual antagonism or that allelopathy was occurring. The limiting environmental factor that both species exploited in mutual antagonism in the field was light under conditions of adequate soil moisture and nutrients.

Eastern Black Nightshade (Solanum ptycanthum) Interference in Processing Tomato (Lycopersicon esculentum)

In replacement experiments in the greenhouse, plant relative yield (PRY) of both eastern black nightshade and tomato increased as the proportion of nightshade plants increased in the pots, indicating that nightshade is less competitive than tomato. In field studies tomato yield was reduced by two-thirds if three nightshade plants m–1of row were allowed to grow with tomato more than 6 weeks following tomato establishment The percent marketable fruit decreased linearly from 73% with no nightshade to 49% when nightshade were present for 12 weeks. When nightshade and tomato were transplanted together, tomato yield was 9000 kg ha–1and 49% of the fruit was marketable, while tomato yields were 30 000 kg ha–1and 70% of the fruit was marketable when nightshade was established 9 weeks after tomato planting.

Effects of CO2Enrichment on Competition Between a C4Weed and a C3Crop

The C4weed johnsongrass [Sorghum halepense(L.) Pers. ♯3SORHA] and the C3crop soybean [Glycine max(L.) Merr. ‘Ransom’] were grown separately and in inter- and intraspecific competition at 350 and 675 ppm CO2in controlled environment chambers with 29/23 C day/night temperatures and 950 μE·m-2· s-1PPFD (photosynthetic photon flux density). In the absence of competition, the higher CO2concentration stimulated dry matter accumulation, leaf area expansion, net assimilation rate, and leaf area duration of soybean more than that of johnsongrass. The plant relative yield (PRY) of soybean in competition with johnsongrass increased, and the PRY of johnsongrass in competition with soybean decreased, as the CO2concentration was increased from 350 to 675 ppm. Thus, the competitiveness of the C3crop with the C4weed increased with increasing CO2concentration. Relative yield totals were not significantly different from 1.0, indicating that the two species were competing for the same resources. With the increases in global atmospheric CO2concentration predicted for the next 50 to 100 yr, the competitiveness of C3crops with C4weeds could be increased.

Phosphate availability and phosphate needs of soils under Siratro pastures as assessed by soil chemical tests

In field trials covering a range of soils and environmental conditions, the variation in soil equilibrium phosphate potentialSP accounted for 86 per cent of the variation in the percentage yield response of Siratro (Phaseolus atropurpureus) to phosphorus, compared to 72 per cent accounted for by the Olsen extraction, 51 per cent by Truog's and 38 per cent by Morgan's. The Truog and Morgan extractants gave improved correlations with phosphate uptake, but all four methods were poorly correlated with phosphate concentration in the plant. For the prediction of the soil's phosphate requirement for 90 or 95 per cent of the maximum yield, the Morgan method was superior to the equilibrium potentialSP, Olsen and Truog methods, and comparable to the quantity measurement P sorbed, derived from the soil's quantity-intensity (Q/I) relation at the minimum, non-limiting solution activity of 2.2 �M P : each accounted for 67 per cent of the variation in P required for 90 per cent of the maximum yield. The precision of the extractions in estimating P required decreased as the extractant/soil ratio and the extraction period increased. Of the conventional extractants, a method could be chosen that was well correlated with either P required (Morgan's) or plant relative yield (Olsen's), but none that was well correlated with both criteria. On the other hand, the measurement: of the one Q/I relation provided intensity (equilibrium potentialSP) and quantity (P sorbed) terms for the prediction, respectively, of a soil's phosphate availability and its phosphate needs for optimum plant growth.