Radiation balance components of maize hybrids grown at various plant densities.

Components of the energy and heat balances were examined in two maize hybrids grown at three different plant densities (40, 70 and 100 thousand plants per hectare). One of the hybrids was drought tolerant, while the other was bred for cultivation under irrigated conditions. An increase in plant density influenced not only the size of the leaf area, but also the distribution of the leaves at various plant heights. The extinction coefficient, which provides a quantification of radiation penetration, was higher in the irrigated treatments. By contrast to the other two treatments, the plant canopy in the thinly sown stands remained open throughout the vegetation period, and thus behaved quite differently to the closed stands, making it impossible to compare them. Smaller albedo values were recorded for the hybrid bred for irrigation and in thinly sown stands. The low plant density allowed more energy to reach the soil, from which it was reflected, making a considerable contribution to the final temperature in the stand. The latent heat, in keeping with the quantity of water transpired, was the greatest in the densely sown stands. There was little difference between the latent heat values of the normal and dense stands in either hybrid, indicating that they both had a similar sensitivity to increased stand density. If sufficient water is available it would appear that the stand density could be increased even for the drought-tolerant hybrid

A low environmental impact system for fertirrigation of maize with cattle slurry

The applicability of an alternative system for managing and distributing cattle slurry during irrigation on maize was evaluated. An experiment was carried out by equipping a traveller boom with drop tubes and fed from a hose-reel machine. The new system was used for the distribution of the liquid separated fraction of slurry mixed with irrigation water (fertigation) on the soil surface between the rows of the crop. This system was compared with the conventional management system, utilizing a tank wagon equipped with splash plate for slurry application and a fixed irrigation system for irrigation. Analysis on leaching water samples indicate that the quality of percolation water is better due to a reduction in nitrate nitrogen losses. Besides, this alternative technique reduces the emissions of ammonia in the air and consequently the diffusion of ammonia in the atmosphere

Rapid phenotyping of different maize varieties under drought stress by using thermal images

The development of maize genotypes with high yields under drought is of pivotal relevance for the International Maize and Wheat Improvement Centre (CIMMYT). Thermal images of the canopy of different 92 maize genotypes were acquired in the time interval between anthesis and blister stage with each picture containing five plots of different genotypes. Mean temperature differences of more than 2°C between different genotypes under water stress were then detected using thermal images. Genotypes better adapted to drought exhibiting lower temperatures. A canopy thermal image is a potential promising method to accelerate the screening process and thereby enhance phenotyping for drought adaptation in maize

A New Soil Conservation Methodology and Application to Cropping Systems in Tropical Steeplands: A comparative synthesis of results obtained in ACIAR Project PN 9201

Land Economics/Use,

Abundance of Coccinellids and Their Potential Prey in Field-Crop and Grass Habitats in Eastern South Dakota

A rich fauna of coccinellids occurs in eastern South Dakota, but the abundance of some species has declined in association with the establishment of an exotic lady beetle, Coccinella septempunctata (L.) (Coleoptera: Coccinellidae), in the mid-1980s. In this study, coccinellids were sampled within field-crop and grass habitats in eastern South Dakota from 1990 to 1995 to survey for various coccinellid species and to determine any effects of habitat management on abundance. Field crops (maize, wheat-alfalfa intercrop, and alfalfa) were subjected to high, intermediate, or low crop-management intensity (CMI), and grass habitats were managed for stands of warm season, cool season, or mixed species. A total of 1,306 adult and 155 larval coccinellids were collected. Four native species (Coleomegilla maculate (DeGeer), Hippodamia convergens Guerin Meneville, Hippodamia parenthesis (Say), andHippodamia tredecimpunctata tibialis (Say)) and C. septempunctata comprised over 96 percent of all coccinellids collected. Of declining species, four Coccinella transversoguttata richardsoni Brown were collected from alfalfa, but Coccinella novemnotata Herbst and Adalia bipunctata (L.) were not found during the study. Coccinellid abundance was seldom affected by CMI. Coccinellids were more abundant in wheat-alfalfa in 1995 under high than low CMI. Coccinellid abundance in maize and alfalfa did not differ with CMI. A prey species, Empoasca fabae (Harris) (Heteroptera: Auchenorryncha: Cicadellidae), was more abundant in alfalfa in 1995 under high and intermediate than under low CMI. Coccinellid abundance was not correlated with that of E. fabae in 1995, and showed inconsistent association with E. fabae during the study. In grass, adult coccinellids (total across species), adult H. tredecimpunctata tibialis, and aphids were more abundant in warm- season grasses than in cool-season or mixed grass stands in one of three years. Our results provide further evidence that C. septempunctata has become relatively abundant in eastern South Dakota, whereas C. transversoguttata richardsoni, C. novemnotata, and A. bipunctata have become rare or absent

Integrated disease management

Integrated disease management in organic farming combines the use of various measures. The usefulness of certain measures depends on the specific crop-pathogen combination. In many crops, preventative measures can control diseases without the need of plant protection products. However, for certain disease problems, preventative measures are not sufficient. For example, organic apple production strongly depends on the multiple use plant protection products

The growth and yield of maize (Zea mays L.) and soyabeans (Glycine max. (L) Merrill) grown as intercrops : a thesis presented in partial fulfilment of the requirement for the degree of Master of Agricultural Science in Plant Science at Massey University

The effect of plant population maize (Zea mays L.) cultivar (Pioneer 3901) and AMT and Matara cultivars of soyabeans (Glucine max (L) Merill) grown together in an intercropping system was studied. In the experiment three rows of maize were sown at populations of 6, 8, 10 plants/m2 and three rows of soyabeans were planted between the rows of maize at either 50 or 75 plants/m2 replacing one of the three rows of maize. Plants were sampled for vegetative analysis during the growth of the crops and at final harvest. Total dry matter, grain yield and the components of yield and leaf area index were determined. Grain yield of maize increased from 794 to 1522 g/m 2 as the population of maize increased. However the yield of the maize was not affected by either the cultivar or the populations of the soyabeans grown among it. Grain yield and the component of yield of the intercropped soyabeans were not affected when population of maize in the mixture was increased. Matara produced higher yields than AMT when grown with maize and this was associated with production of more grain per plant and larger seeds. As the plant population of the soyabeans was increased the grain yield of Matara increased and up to 336.9 g/m2 was obtained, however the yield of AMT was not affected by a similar increase in plant population, possibily Matara had greater temporal difference and was more competative than AMT when grown in the mixture. Three methods were used to evaluate the yield of intercropped plots. These were the seed yield summed for both crops, Land Equivalent Ratio (LER) and a yield ratio based on maize. Although the results obtained depended on the method used all the three methods indicated intercropping could be more advantageous than growing maize and soya­ beans as pure stands. All the three methods indicated that the highest yield was obtained when the highest population of maize was combined with the highest population of soyabeans. Higher yields were obtained when Matara rather than AMT was grown in the intercropped plots

Improving competitive ability of chickpea with sowthistle

An experiment was conducted to examine the extent of root and canopy interference of chickpea (Cicer arietinum L.) with sowthistle (Sonchus oleraceus L.). Sowthistle was surrounded with either two or eight chickpea plants. There were different types of competition: no competition, shoot competition, root competition and full competition (root and shoot). The performance of sowthistle grown in full competition with two chickpea plants was the same as that grown with root competition only. Also, there were no significant differences between sowthistle grown with chickpea canopy shade and the control, where there was no competition. On the other hand sowthistle grown with eight neighbours was significantly suppressed in full, canopy or root competition

Plant analysis as a tool to determine crop nitrogen status

An effective plant nutrient management strategy optimises nitrogen (N) use efficiency for minimised environmental impact, while ensuring an optimum N status of the crop for good product quality and maximum growth. Soil or plant analysis can be used to evaluate the strategy; however the use of plant analysis for this purpose has been limited. One reason is lack of reliable reference values for the critical concentration needed for optimal growth. This study builds on theories that relate ontogenetic changes in the critical N concentration to changes in the relation between mass and surface area of the entire plant and of individual leaves. Through the establishment of critical N concentrations on the basis of these theories, some of the drawbacks hitherto experienced with plant analysis, such as difficulties in defining growth stage or plant part to sample, can be avoided. The aim of this thesis was to establish critical N concentrations for white cabbage (Brassica oleracea L. var. capitata L. f. alba D.C.) on the basis of these theories. Multi-N-rate and multi-harvest experiments were conducted in the field and in a climate chamber. The results showed that the critical N concentration declined at the same rate (-0.33) as the plant's leaf area ratio (leaf area divided by plant mass), which is in agreement with the 2/3-Power rule or "skin-core" hypothesis. The critical N concentration (% of DM) on a whole plant basis was estimated to 4.5 (W1.5 t ha-1), where W is weight per unit area of plant dry matter exclusive of roots. Moreover, it was concluded that the unshaded horizontally orientated leaves of cabbage can be used for leaf area based plant analysis of individual leaves. The critical N concentration of these leaves expressed on an area basis was found to be 3.7 g N m-2, while that for the whole plant N on a leaf area basis was 4.7 g N m-2. The ratio of these two critical concentrations, 0.8, was similar to the leaf N ratio (leaf N/whole plant N) of young plants before self shading occurs