Soil Phosphate Levels Research Articles

Effects of soil phosphate level and shade on plant growth and mycorrhizas

Abstract Seedling growth of 11 forest species was compared in steamed soils containing 11, 14, 25, and 60 ppm Truog available phosphorus. Species with coarse root systems required progressively higher soil-P levels for growth without mycorrhizas. In the soil with 60 ppm Truog P, coarse-rooted plants were still mycorrhizal but fine-rooted plants were not. Fuchsia excorticata with fine roots benefitted from mycorrhizas only at 11 ppm P; at 25 ppm P mycorrhizas decreased its growth. Mycorrhizal seedlings of shade-tolerant species had less infection when grown in heavy shade than in full sun and did not accumulate P, whereas light-demanding species retained high infection levels and accumulated P in heavy shade. Rhizophagus tennis appeared to be a more effective mycorrhizal inoculum than Acaulospora laevis.

Some factors affecting the establishment and early production of oversown grasses

The effects of rate of sowing, herbicide, and superphosphate on seedling establishment of two oversown improved grass species, their sward performance, and the resultant soil phosphate levels were studied in two experiments at Glen Innes, New South Wales in 1973. The experimental area had received 1250 kg ha-1 superphosphate prior to sowing and was carrying native grasses and white clover (Trifolium repens). In the first experiment, treatments applied were combinations of: four sowing rates (5.5, 11, 22, 44 kg ha-1) ; three herbicide rates (0 + 0, 8.3 + 0.55, 49.5 + 3.3 kg a.i. ha-1 2,2-DPA 4- amitrole) and two superphosphate rates (0, 250 kg ha-1). In the second experiment, three rates each of herbicide (0 + 0, 8.3 + 0.55, 16.6 + 1.1 kg a.i. ha-1 2,2-DPA + amitrole) and superphosphate (0, 125, 250 kg ha-1) were applied in a factorial design. Both experiments were sown with Phalaris aquatica and Festuca arundinacea. For both species, seedling numbers increased as herbicide and sowing rates increased but declined with superphosphate application. These main effects were more pronounced during the earlier samplings. Seedling numbers of both species, particularly phalaris declined with time. As herbicide rates increased, total dry matter production was progressively reduced, but production of fescue increased from 19 to 232 and phalaris from 0.5 to 60 kg dry matter ha-1. The addition of superphosphate eliminated the adverse effect of herbicide on the legume component. Superphosphate increased fescue dry matter production but decreased that of phalaris. Prior application of herbicide at the heaviest rate and superphosphate applied at 125 kg ha-1, both increased soil phosphate by approximately the same amount (7.5 and 8.2 p.p.m. respectively).

Prediction of plant response to fertilisers by means of soil tests

Abstract Data from 82 rates-of-fertiliser trials on wheat, in which double superphosphate was the source of phosphate, were used to evaluate the predictability of grain yield responses from soil-test measurements. Yield data were reduced to single values for correlations with soil phosphorus tests by calculating (a) relative yields % and (b) the first principal components of the yield responses. Regression of these parameters on values from eight different soil tests, using a quadratic model in the square root scale, showed that the Olsen soil test modified to 16-h extraction and a soil: solution ratio of 2.2 ml : 100 ml accounted for more variation than other soil tests examined. The correlations with soil tests were closer for the relative yields than for the first principal components. Predictions of yield responses and their confidence limits were calculated for the rates of phosphatic fertiliser used in the trials from regressions of the absolute yield responses on this modified Olsen soil test, and the profitability of applying phosphatic fertiliser was assessed. Predicted relative yields were calculated by a similar regression. The profitability of phosphate applications for selected soil phosphate levels was determined.

Soil Phosphate and Its Role in Molding Segments of the Australian Flora and Vegetation, with Special Reference to Xeromorphy and Sclerophylly

It is postulated that the Australian angiosperm flora ins derived from a sample of a one—time world flora of about 180 families that entered Australia by a land bridge from Asia. Many of the genera that entered still persist. New genera evolved in all habitats, many from lineages which were adapted to soils of low fertility determined primarily by phosphate level. Soil parent materials with the highest phosphate content are derived mainly from the Tertiary basalts in the east and support rainforests (except in cold regions). Soil phosphate levels decrease from east to west across the continent. The number of rainforest genera in any community is usually correlated with soil P. The converse holds for xeromorphic genera. Some rainforest genera therefore are more readily adapted to aridity than to low fertility conditions. Expansion and contraction of the rainforest is determined partly by climate and partly by soil fertility levels. A sudden expansion of the rainforest in the Oligocene occurred when the basalt flows covered part of eastern Australia. Since that time the rainforests have contracted, partly as a result of the removal of basaltic material and partly because of the development of colder climates in the ranges. The absence of rainforest and the paucity of rainforest genera in southwest Western Australia are accounted for by low fertility levels rather than by a decimation of rainforest genera by a past dry climate. Xermorphy, a result of high lignification, heavy cutinization, silicification, or a combination of these may occur in rainforest species. Adaptation to low fertility accentuates xeromorphic characters through a reduction in leaf size. The low fertility xeromorphs are not xerophytes. Anatomical features have little significance in their survival, which is determined by the ability of the plants to withstand long periods of mineral starvation. Experimental work indicates that the degree of xeromorphy can be reduced in many taxa by the addition of phosphorus and nitrate; four different types of leaf response have been identified.

Some effects of potassium and lime on the relation between phosphorus in soil and plant, with particular reference to glasshouse tomatoes, carnations and winter lettuce

AbstractThe phosphorus content of the leaves of glasshouse tomatoes, carnations and winter lettuce was decreased by additions of potassium sulphate and lime to the soil, except at low levels of soil phosphate. Liming also increased the amounts of phosphorus extracted by 0.5N‐acetic acid and by Morgan's solution. The relation between phosphorus in the plants and in the acidic soil extracts was thus markedly affected by liming the soil. The effect of pH on the content of acid‐soluble phosphorus in the soil is discussed.

Principles of Nutrient Uptake From Fertilizer Bands 1. Effect of Placement of Nitrogen Fertilizer on the Uptake of Band‐Placed Phosphorus at Different Soil Phosphorus Levels1

SynopsisPlacement of nitrogen fertilizer caused a relative increase in the feeding power of the root system on the band‐placed phosphorus. Nitrogen had a greater influence when mixed with the phosphorus than when placed in a band 3 to 4 inches from the phosphorus band. The influence was nearly independent of the soil phosphate level when the nitrogen was mixed with the band phosphorus, but was not independent of the soil phosphate level when the nitrogen was separated from the phosphorus band.