SummaryFour peanut cultivars of Spanish or Virginia botanical type and varying time to maturity were grown at a range of plant densities (44 000 to 352 000 plants ha-1) and spatial arrangements under irrigated conditions in sub-tropical southern Queensland, Australia. Total and pod dry matter production of the very early maturing Spanish cultivar Chico showed strong positive responses to increased plant density up to the highest density tested. Responses were less pronounced for the later maturing Spanish cultivar McCubbin and were minimal for the Virginia cultivars Early Bunch and Mani Pintar. All cultivars were insensitive to spatial arrangements. Accumulation of total dry matter, adjusted for the higher synthesis costs of oil and protein during seed filling, was well correlated to intercepted photosynthetically active radiation (PAR). Much of the variation in dry matter production among cultivars and plant populations could be accounted for by the effects of differing leaf area duration on cumulative intercepted PAR. Radiation use efficiency was negatively associated with the canopy extinction coefficient (k) within most sowing dates, and also negatively associated with minimum temperature across sowing dates for all cultivars except Mani Pintar.Crecimiento y eficacia del use de radiación en el maní

The physical fertility of krasnozems and euchrozems (Red Ferrosols) in Australia has declined substantially as a result of continuous cropping. Much of this decline is associated with reduced levels of soil organic carbon and soil compaction due to vehicle trac when soils are too wet. We examined the impact of kikuyu (Pennisetum clandestinum) and Rhodes grass (Chloris gayana) pasture leys with various management inputs on the regeneration of physical fertility of continuously cropped krasnozems from 2 locations in the South Burnett region of southern Queensland. Pasture leys significantly improved the physical fertility of continuously cropped soils within 2–4 years. The most significant effects were on the creation of improved surface and subsurface macroporosity, and in a reduction in surface crust formation under high energy rain due to improved aggregate stability. Final steady state infiltration rates under well-managed leys increased 4-fold compared with those in continuously cropped soil. Pastures were unable to ameliorate compacted layers below approx. 15 cm, although significant improvements in hydraulic conductivity through these layers (and to depths of at least 70 cm) were made, presumably by creating of continuous biopores. Introduced earthworms improved pasture effectiveness in ameliorating this layer, but only to depths of 20 cm, while deep ripping during the ley phase was the most effective treatment. Kikuyu was the more effective pasture species in overcoming soil physical infertility, particularly in terms of improving aggregate stability under rain. In addition, the ability of kikuyu to resist the compacting influence of cattle trampling during wet weather meant that rainfall infiltration eciency was maintained during the ley phase and management options on returning to cropping were more flexible (e.g. direct drill strategies can be used). However, if pastures were ungrazed, the advantages of kikuyu in soil physical restoration were evident in only 2 years.

Negative potassium (K) balances in all broadacre grain cropping systems in northern Australia are resulting in a decline in the plant-available reserves of K and necessitating a closer examination of strategies to detect and respond to developing K deficiency in clay soils. Grain growers on the Red Ferrosol soils have increasingly encountered K deficiency over the last 10 years due to lower available K reserves in these soils in their native condition. However, the problem is now increasingly evident on the medium-heavy clay soils (Black and Grey Vertosols) and is made more complicated by the widespread adoption of direct drill cropping systems and the resulting strong stratification of available K reserves in the top 0.05-0.

Effects of plant density and spatial arrangement on growth and yield responses of 4 peanut cultivars were examined under fully irrigated conditions at Kingaroy, south-eastern Queensland (26�33'S., 151�50'E.). Cultivars represented either the Spanish or Virginia botanical type. Spanish cultivars had either very early (Chico) or early (McCubbin) maturity, while Virginia cultivars had either medium (Early Bunch) or very late (Mani Pintar) maturity. The interaction of plant density (44 000-376 000 plants/ha) with sowing date was assessed in 3 sowings in 1984-85 (S1, 1 November; S2, 5 December; S3, 15 January), with a further sowing in 1985-86 (S4, 21 November). The interaction of plant density and spatial arrangement was assessed in 1985-86. Total dry matter (TDM) and pod yields showed highly significant (P<0.01) linear and quadratic responses to increasing plant density. Cultivars differed in their response to density. McCubbin, Early Bunch and Mani Pintar showed no responses to increased density above 88 000 plants/ha, while maximum TDM and pod yields of Chico were recorded at 352 000 plants/ha. Sowing date had no significant effect on the response of any cultivar to plant density. However, all cultivars except Chico produced significantly less TDM and pod yield in S3, due to cool temperatures and/or frosts terminating growth. A 1 : 1 (square) planting arrangement produced significantly greater pod yields and more TDM than the conventional commercial practice of rows 90 cm apart. Planting in a double-row arrangement (20 cm between 2 rows) based on 90 cm centres produced intermediate pod and TDM yields. A simple model was used to describe the effects of plant density and sowing date on yield, and proved useful for highlighting differences among cultivars and sowing dates. A limitation of the model was a tendency to overestimate pod yield at low plant density in Spanish cultivars, where the harvest index declined at very low plant densities.

The partitioning of dry matter between vegetative and reproductive yield components was analysed for four diverse peanut cultivars at a range of sowing dates and plant populations in sub-tropical Queensland, Australia. Rates of accumulation of pods (pod addition) varied significantly with both cultivar and sowing date. Within cultivars, much of this variation could be attributed to variation in crop growth rate during the critical pod addition period. The proportion of current assimilate distributed to pods depended on inherent cultivar characteristics and also correlated well with the current crop growth rate relative to the crop growth rate during pod addition (that is, with relative source activity). Neither plant density nor spatial arrangement had any significant effects on patterns of assimilate distribution. All cultivars appeared capable of remobilizing stored assimilate to maintain constant rates of pod yield increase despite fluctuations in crop growth rate which might be expected to produce short term source limitations to pod yield accumulation. The harvest index (HI) increased linearly during the entire pod fill period in all cultivars except the very early maturing Spanish cultivar Chico. Neither density nor spatial arrangement affected rate of increase in HI except in Chico, where increased density produced increased rates of increase in HI. Variation in the rate of HI increase among sowing dates was small. Distribution de la materia seca en el mani RESUMENEn cuatro diferentes variedades de cultivo de mani se analizo la distribution de la materia seca entre los componentes de rendimiento vegetativo y reproductivo, con una diversidad de fechas de siembra y poblaciones de cultivo, en la zona subtropical de Queensland, Australia. El indice de acumulacion de vainas presento variaciones significativas con las distintas variedades y fechas de cultivo. Dentro de las variedades, gran parte de estas variaciones podrfa atribuirse a la variation del indice de crecimiento del cultivo durante el perfodo cn'tico de la acumulacion de vainas. La proporcion de material asimilado corriente distribuido a las vainas dependio de las caractensticas inherentes de cada variedad de cultivo, y presento una buena correlacion con el indice de crecimiento de cultivo corriente con relation al indice de crecimiento de cultivo durante el periodo de acumulacion de vainas (o sea, con relativa actividad de fuentes). Ni la densidad de cultivo, ni su distribucion tuvo un efecto significativo en los patrones de distribucion de material asimilado. Todas las variedades parecieron capaces de volver a movilizar material asimilado almacenado, para mantener indices constantes de incremento en la production de vainas a pesar de las fluctuaciones en el indice de crecimiento de cultivo, lo cual puede llegar a producir limitaciones a corto plazo en las fuentes que alimentan la acumulacion de rendimiento de vainas. El indice de cosecha (IC) se incremento en forma lineal durante todo el periodo de llenado de vaina en todas las variedades de cultiv...