Materials used as mulches may be either transported to the farm then laid on the soil surface or grown in situ. To assess biodegradable alternatives to non-degradable polyethylene film, the response of capsicum (Capsicum annuum L. cv. Target) grown in soil beds covered with hessian (burlap), hardwood sawdust, sugarcane (Saccharum spp.) trash, paper film, black biodegradable polymer film, white polyethylene film, or left uncovered was investigated in a field trial during the autumn–winter growing season in subtropical Australia. Use of a split-plot design (mulch whole plots with weeded or unweeded subplots) permitted both weed growth and the effect of weed competition on fruit yield to be measured. The presence of substances within the materials that were possibly detrimental to plant growth was assessed in a separate experiment. The weight of marketable fruit was highest for capsicum plants grown in the weeded subplots of biodegradable polymer and polyethylene, although the yields from these subplots were not different from those for plants grown in the weeded subplots of the paper and sawdust or the unweeded subplots of the biodegradable polymer and paper. The reduction in weight of marketable capsicum fruit from weed competition was ranked for the various mulch treatments as follows: paper < biodegradable polymer < cane trash < polyethylene < hessian < sawdust < bare soil. More hours at optimum soil temperature for root growth (18.9–30˚C) before canopy closure probably accounted for the variation in marketable yield of the capsicum crop. Results from the mulch toxicity experiment indicated that the mulch materials were unlikely to contain phytotoxic substances. Provided the practical difficulties of laying paper film can be overcome and the high cost of biodegradable polymer is reduced, these materials appear to be the best of the biodegradable alternatives tested to polyethylene film.

This study was conducted to assess the usefulness of petiole sap nitrate and total nitrogen (N) in dried leaf for determining N status and yield response in capsicum (Capsicum annuum L.) grown with plastic mulch and trickle irrigation in subtropical Australia. Five rates of N (0, 70, 140,210, 280 kg/ha) were applied in factorial combination with 2 rates of potassium (K: 0, 200 kg/ha) in randomised block experiments to capsicum cv. Bell Tower grown at Bundaberg Research Station in spring 1990 and autumn 1991. Critical nutrient ranges for nitrate concentration in petiole sap and for total N concentration in dried youngest mature leaf blades plus petioles (YMB + P) were derived at different stages of crop development (bud development, BD; first anthesis, FA; 80% flowering, F; fruit set, FS). Sap nitrate was about 5 times more sensitive to changes in N application than total N. Petiole sap nitrate accounted for a greater amount of the variation in marketable fruit yield (quadratic square root relationships, 0.45 < R2 < 0.83) than total N concentration in dried YMB + P (linear relationships, 0.29 < R2 < 0.74). Simple linear regressions indicated a stronger relationship between applied N and petiole sap nitrate concentration than total N concentration in dried YMB + P (range in R2 values among 8 sampling events: 0.71-0.91 for petiole sap nitrate, 0.35-0.78 for YMB + P total N). For the fertiliser application strategy, 60% of N was applied pre-fruitset and 40% after. Sap nitrate concentrations associated with 95 and 100% of maximum marketable fruit yield increased from BD (5010-6000 mg/L spring, 4980-5280 mg/L autumn) to FA (6220-7065 mg/L spring, 555M000 mg/L autumn). After FA, the range progressively decreased to 1640-2800 and 520-1220 mg/L at FS, for spring and autumn, respectively. It was concluded that petiole sap nitrate was a better indicator of plant N status and yield response than total N concentration in dried YMB + P for capsicum in subtropical Australia. A critical petiole sap K concentration (corresponding with maximum yield and at which no yield response to K addition was measured) of >4800 mg/L was proposed by correlating sap K with yield responses.

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I..imlted information on phenology of sweet com (Zea mays L.) grown in .subtropical regions is available to processors wishing to manage han•est scheduling. This study was conducted to investigate developmental characteristics of both standard sugary (su) and mutant endosperm sugary enhancer (se), and shrunken-2 (sh~) sweet com in subtropical Australia. Field experiments were conducted at three lo· cations with numerous times of planting so that a broad range of environments were encountered. Models of daily rate of development for the period sowing to kernel maturity (720 g kg-1 moisture) were derived by an iterative optimization procedure. Development rate was related to mean daily temperature and photoperoid. Temperature was the most important factor affecting rate of development. The temper· ature response was best described by a broken linear function. Various photoperiod functions fitted as multipliers to the temperature response did not improve goodness-of-fit. Cultivars were classified J.

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