Mineral nutrition of slash pine in subtropical australia. I. stand growth response to fertilization

Fertilization at plantation establishment and later age is often required to maximize stand growth of slash pine (Pinus elliottii) in subtropical Australia. A field experiment was conducted to examine stand growth response of slash pine in the first 11.5 years of plantation following (1) initial fertilization at plantation establishment with phosphorus (P) at 11, 22, 45 and 90 kg P ha^–1 which were either banded or broadcast in the presence or absence of basal fertilizers containing 50 kg nitrogen (N) ha^–1, 50 kg potassium (K) ha^–1 and 5 kg copper (Cu) ha^–1 and (2) additional application of 40 kg P ha^–1 at age 10 years.The initial P fertilization significantly increased the stand growth in the first 9.6 years. The P banded application was more effective in improving the stand growth than the P broadcast application. Application of the N, K and Cu basal fertilizers did not affect the stand growth. Overall, 53–73% of the variation in basal area and volume growth in the first 9.6 years was explained by the initial P fertilization, indicating that P deficiency was the major factor limiting the stand growth under the experimental conditions. Optimum plantation age, at which the maximum periodical annual increment (PAI) of basal area was obtained, increased from age 10.9 to 12 years when the initial P rate increased from 11 to 90 kg P ha^–1. Application of additional 40 kg P ha^–1 at age 10 years resulted in a further improvement in the stand growth at age 11.5 years. With 66% of the variation in basal area PAI between ages 9.6 and 11.5 years, 50% was explained by the initial P fertilization and 16% by the additional P applied at age 10 years. Similarly, 51% and 12% of the variation in volume PAI were attributed to the initial P fertilization and the additional P application, respectively. This highlights the need of refertilization with P on some established stands of slash pine at later ages.     

Mineral nutrition of slash pine in subtropical Australia. II. foliar nutrient response to fertilization

In the previous paper, we reported the stand growth of slash pine (Pinus elliottii) during the first 11.5 years of plantation in response to (1) initial fertilization at plantation establishment with P rates of 11, 22, 45 and 90 kg P ha^–1 which were either banded or broadcast in the presence or absence of basal fertilizers containing 50 kg N ha^–1, 50 kg K ha^–1 and 5 kg Cu ha^–1 and (2) application of additional 40 kg P ha^–1 at age 10 years. Here we present the responses in foliar nutrient concentrations of slash pine in the first 11.5 years to the initial fertilization and the additional P applied at age 10 years.Foliar N and K concentrations in the first 9.6 years of plantation decreased with the initial P rate. Application of the basal fertilizers improved foliar Cu concentration. Foliar Ca and Mg concentrations increased linearly with the initial P rate. The initial fertilization did not affect foliar Mn concentration in the first 9.6 years. Foliar P concentration increased quadratically with the initial P rate, which accounted for 77–86% of the variation in foliar P concentration. Most of the explained variation in foliar nutrient concentrations was attributable to the plantation age except for foliar P concentration. In the case of foliar P concentration, 53% was explained by the initial P rate, 31% by the plantation age and 2% by the positive interaction between the initial P rate and the plantation age. Foliar P concentration of slash pine at age 11.5 years increased quadratically with the initial P rate and linearly with the additional 40 kg P ha^–1 applied at age 10 years, accounting for 81% of the variation in the foliar P concentration. Foliar nutrient analysis indicated that P was the major limiting nutrient affecting the stand growth of slash pine in the first 11.5 years.     

Post-establishment phosphatic fertilizer treatments in a New South WalesPinus radiata plantation

A five-year-oldPinus radiata plantation treated with a spot application of phosphatic fertilizer (13.5 g P per tree)(23 kg P ha^–1) at planting was given various additional booster treatments: two levels of superphosphate (48 and 72 kg P ha^–1) and one level each of basic superphosphate (61 kg P ha^–1) and monoammonium phosphate (70 kg P ha^–1, 35 kg P ha^–1) all broadcast applied. All fertilizer treatments resulted in significant increases in timber volume production which were not significantly different from each other. The stands which had received no additional treatment produced 108 m³ ha^–1 merchantable timber at age 17 years while the treated plots produced between 188 and 201 m³ ha^–1. The best financial gains were from the higher rate of superphosphate. The experiment is discussed in relation to foliar analysis and routine management practice.     

Effect of long-term fertilization on the biomass production and nutrient status of Scots pine stands

The effect of repeated fertilization on soil properties, nutrient status of the stand and the biomass production of the above-ground components of the trees are examined in the study on the basis of material from three fertilization experiments. Two of the experiments were established in sapling stands, and the third in a pole-stage stand. The stands had received repeated doses of fertilizer totalling N 597–776 kg ha^–1 and P 69–80 kg ha^–1 over a 26 to 30-year study period in accordance with a factorial experimental design.Nitrogen fertilization increased the amount of organic matter in the humus layer of two of the experiments by 25–35%, and the amount of total nitrogen by about 50%. The C/N ratio of the humus layer in all three experiments decreased as a result of nitrogen fertilization by 11–18%. No decrease in soil pH was detected.At the end of the experimental period, i.e. 5–6 years after the most recent fertilization, the nitrogen concentration of the current needles on the nitrogen-fertilized plots was clearly lower than that of the older needle age classes. Fertilization did not have any marked effect on the concentrations of other macronutrients in the needles.Of the above-ground components, stemwood production was affected the most by nitrogen fertilization. The range of the relative growth response was 22–36%. The effect on branch biomass was 25% on the least fertile site, but there was no effect on the most fertile site. The effect of nitrogen fertilization on the needle biomass component was least, from –8 to 18%, owing to the 5 to 6-year time lag between the preceding fertilization and biomass sampling. A negative response was found on the least fertile site, where six years had elapsed since the most recent fertilization. However, on this site the proportion of over one-year-old needles was greater on the nitrogen-fertilized plots (24%) than on the others (19%). Phosphorus fertilization had only a slight effect on stemwood production.In general, nitrogen fertilization decreased the crown biomass per unit volume of stemwood.     

Nitrogen requirements in young Douglas-fir of the Pacific North-west

A series of fourteen Pacific North-west Douglas-fir installations, ranging in age from 6 to 26 years were analysed with respect to site factors, foliage nutrients, and growth response to applied fertilizer. Unfertilized basal area increment ranged from 1.2 to 3.1 m² ha^–1 yr^–1 with no apparent relationship with soil, stand age or site index. Basal area increment was correlated with foliage N and a critical level for N was calculated as 1.7%. Applications of 220 kg N ha^–1 as urea increased growth between 0 and 95% of the unfertilized basal area growth, with an average of 24.9%. Response could be predicted from foliage N and unfertilized basal area increment. When the same relationships were applied to previously older stand data, results were more variable as elements such as B and S showed evidence of being limiting.     

Biomass and nutrient uptake ofAilanthus excelsa as affected by N and P fertilization on an aridisol

A field experiment was conducted on a coarse sand soil having pH 8.8 and organic matter 0.06% in Indian arid region, to study the influence of N and P fertilizers on growth, biomass and nutrient content ofAilanthus excelsa, which is an important fodder species of arid and semi arid regions. Three levels of nitrogen (0, 9 and 18 g N tree^–1 as Urea) and of phosphorus (0, 3 and 6 g P₂O₅ tree^–1 as Single Superphosphate) in factorial combinations were taken in triplicate and the experiment was laid in Randomised Block Design. Application of 9 g N plant^–1 improved tree height by 15 to 25%, collar circumference by 30 to 37% and crown diameter by 18 to 26% in the initial 3 years. Total biomass increase due to 9 g N plant^–1 was 76% and 59%, respectively, after 1 and 2 years of planting. Application of 3 g P₂O₅ tree^–1 increased tree height by 8 to 18% and collar circumference by 17 to 24% during initial three years, and total biomass by 70% at 1 year and 30% at 2 years of age. Combined application of 18 g N and 3 g P₂O₅ tree^–1 (N₁₈P₃) was the best treatment which increased tree height by 49%, 85% and 35% and collar circumference by 56%, 10% and 11% at 1, 2, and 3 years of age, respectively. N₁₈P₃ treatment increased the total biomass by 181% at 1 year and 185% at 2 years of age. N and P applications improved considerably the branching of roots and root length and enhanced root biomass by 2 to 3 folds. N₁₈P₃ treatment increased the nitrogen uptake by 304% (4.02 g tree^–1) at 1 year and 211% (42.56 g tree^–1) at 2 years of age. The P uptake was maximum (290.4 mg tree^–1) due to N₁₈P₃ treatment in 1 year old and 11.37 g tree^–1 due to N₉P₆ treatment in 2 year old plantation.     

Response to fertilization and nutrient deficiency diagnostics in peach palm in Central Amazonia

Peach palm (Bactris gasipaes Kunth) is increasingly grown in the tropics for its heart-of-palm and fruit. Determining fertilization response and diagnosing nutrient status in peach palm may require methods that consider the particularities in nutrient acquisition and recycling of perennial crops. Responses to nutrient additions, and the diagnostic value of soil and foliar analyses were examined in three field experiments with three-year old peach palm stands on Oxisols in Central Amazonia. To diagnose P-deficiency levels in soils, samples from 0–5 cm and 5–20 cm depth were analyzed for available P by different methods (Mehlich-1, Mehlich-3 and Modified Olsen). The second and fifth leaves were analyzed to assess N, P and K deficiencies. Field experiments involved several combinations of N (from 0 to 225 kg ha^–1 yr^–1), K (from 0 to 225 kg ha^–1 yr^–1) and P (from 0 to 59 kg ha^–1 yr^–1). Palms on control plots (unfertilized) and those receiving 225 kg ha^–1 yr^–1 N and 2 Mg ha^–1 of lime yielded between 4 and 19% of the maximum growth which was obtained with N, P and K applications. In one of the experiments, yield of heart-of-palm was positively related to N additions at the lowest levels of P (8.6 kg ha^–1 yr^–1) and K (60 kg ha^–1 yr^–1) additions. In one experiment, critical leaf N level was 2.5% for the second leaf and 2.2% for the fifth leaf. Some growth responses to P additions at constant N and K levels were observed (e.g., 797 kg ha^–1 yr^–1 of heart-of-palm with 39.3 kg ha^–1 yr^–1 of applied P, and 632 kg ha^–1 yr^–1 of heart-of-palm with 10.9 kg ha^–1 yr^–1 of applied P in one experiment, and 2334 kg ha^–1 yr^–1 of heart-of-palm with 39.3 kg ha^–1 yr^–1 of P and 1257 kg ha^–1 yr^–1 of heart-of-palm with 19.7 kg ha^–1 yr^–1 of P in another trial). In the experiment for fruit production from peach palm, total plant height did not respond to P additions between 19.7 and 59 kg ha^–1 yr^–1 and K additions between 75 and 225 kg ha^–1 yr^–1. Leaf P levels were found to be above the proposed critical levels of 0.23% for the third leaf and 0.16% for the fifth leaf. Plants in this experiment, however, showed evident symptoms of Mg deficiency, which was associated with a steep gradient of increasing Mg concentration from the fifth leaf to the second leaf. Standard leaf diagnostic methods in most cases proved less useful to show plant N and P status and growth responses to N and P additions. Soil P determined by common extractions was in general too variable for prediction of growth.     

Investigation into manganese deficiency in mature oil palms(E. guineensis) in Malaysia

Manganese deficiency was confirmed on prominently chlorotic palms with small canopies grown on very sandy colluvium. An experiment to assess the effects of the Mn deficiency on palm growth and yield was carried out. The effectiveness of the application of MnSO₄ at various rates to correct the deficiency was tested. Manganese concentration < 25µg Mn g^–1 in Frond 17 was found to be indicative of deficiency. Soil application of MnSO₄ at 150 g palm^–1 plus 60 g palm^–1 as foliar spray was most effective for short term correction. Higher rates (300 g MnSO₄ palm^–1) were required for soil application only. Cumulative yield over 42 months after treatment showed significantly higher number of harvested fresh fruit bunches. Full recovery of canopy size, colour and vigour took up to two years.     

Alfalfa response to lime,phosphorus, potassium,magnesium, and molybdenum on acid ultisols

Alfalfa (Medicago sativa L.) is a high protein forage, cultivated widely in young, fertile soils. There is considerable potential for alfalfa production in areas with acidic, highly weathered soils, but few field studies on fertility requirements under these conditions have been published.Two field trials were conducted on ultisols to study the effects of lime, P, K, Mg and Mo on alfalfa growth and tissue composition. A trial with three rates of calcitic lime (0, 2400, and 3800 kg ha^–1) and P (0, 25, and 50 kg ha^–1) and two rates each of K (20 and 200 kg ha^–1 the first year, 250 and 500 kg ha^–1 in subsequent years), Mg (36 and 106 kg ha^–1) and Mo (0 and 0.25 kg ha^–1) was conducted on an Appling coarse sandy loam (Typic Hapludult). Another factorial experiment with three levels each of lime (0, 2000, and 4,000 kg ha^–1), P (0, 100, and 200 kg ha^–1), and K (0, 150, 300 kg ha^–1) was conducted on a Davidson sandy clay loam (Rhodic Paleudult).Application of lime or P resulted in increased dry matter (DM) production at both locations. Liming also raised plant tissue N concentration. Addition of Mo had no effect on DM production or on foliar composition. Addition of K depressed soil Mg, plant tissue Mg, and plant Mg uptake at both locations. On the Davidson soil DM increased when K was applied, but on the Appling soil K increased DM production only where Mg was also added. Addition of Mg decreased K uptake and depressed DM production unless K was also added.The observed antagonism between K and Mg is of importance for alfalfa production in highly weathered soils. Successful alfalfa production in these soils is unlikely unless attention is paid to the balance between these two nutrients. Raising soil pH increased foliar N concentration affecting forage quality as well as DM production.Contribution from the Dept. of Agronomy, Univ. of Georgia, Athens, GA 30602.     

Fertilization response and nutrient diagnosis in peach palm (Bactris gasipaes): a review

Peach palm (Bactris gasipaes Kunth) is a relatively new food crop with great potential for the humid tropics. Native to tropical America, it is commercially grown to produce hearts-of-palm and, to a lesser extent, an edible fruit. Peach palm is well adapted to nutrient poor, acid soils, and is cultivated in Brazil and Costa Rica on highly weathered soils with low pH, high aluminum saturation and, often, low organic matter content. Fertilization trials on peach palm have shown significant responses to applied nitrogen while the response to other nutrients such as phosphorus has been less frequent. Additional research, however, is necessary to determine soil and foliar nutrient critical levels and to address questions concerning peach palm growth responses to nutrient additions varying in time and space. Recycled nutrients likely contribute significantly to peach palm nutrition because plant residues are produced in considerable amounts and can decompose rapidly in commercial peach palm plantation in humid environments where cut leaves and stems are left in the field following harvest. On the other hand, nutrient exports from the system are relatively small (e.g., 4.8–6.4 kg P ha^-1yr^-1, 28–32.3 kg N ha^-1 yr^-1, 31–45.2 kg K ha^-1 yr^-1). As for most perennial tree crops, diagnosis of nutrient deficiencies in peach palm is less clear than in annual crops because of factors such as nutrient cycling, internal retranslocation, stand age, foliage age and position within the crown, and seasonal and climatic variations. Some studies on peach palm have examined variation in nutrient content within leaves and plants, and among plants as well, but the sensitivity of different plant tissues to reflect changes in nutrient uptake and response to nutrient additions should be investigated in controlled field experiments.     

Distribution of acid extractable P and exchangeable K in a grassland soil as affected by long-term surface application of N, P and K fertilizers

Information on the fate and distribution of surface-applied fertilizer P and K in soil is needed in order to assess their availability to plants and potential for water contamination. Distribution of extractable P (in 0.03 M NH₄F + 0.03 M H₂SO₄ solution) and exchangeable K (in neutral 1.0 M ammonium acetate solution) in the soil as a result of selected combinations of 30 years (1968–1997) of N fertilization (84–336 kg N ha^–1), 10 years of P fertilization (0–132 kg P ha^–1), and 14 years of K fertilization (0 and 46 kg K ha^–1) was studied in a field experiment on a thin Black Chernozem loam under smooth bromegrass (Bromus inermis Leyss.) at Crossfield, Alberta, Canada. Soil samples were taken at regular intervals in October 1997 from 0–5, 5–10, 10–15, 15–30, 30–60, 60–90 and 90–120 cm layers. Soil pH decreased with N rate and this declined with soil depth. Increase in extractable P concentration in the soil reflected 10 years of P fertilization relative to no P fertilization, even though it had been terminated 20 years prior to soil sampling. The magnitude and depth of increase in extractable P paralleled N and P rates. The extractable P concentration in the 0–5 cm soil layer increased by 2.2, 20.7, 30.4 and 34.5 mg P kg^–1 soil at 84, 168, 280 and 336 kg N ha^–1, respectively. The increase in extractable P concentration in the 0–15 cm soil depth was 1.5 and 12.8 mg P kg^–1 soil with application of 16 and 33 kg P ha^–1 (N rate of 84 N ha^–1 for both treatments), respectively; and it was 81.6 and 155.2 mg P kg^–1 soil with application of 66 and 132 kg P ha^–1 (N rate of 336 N ha^–1 for both treatments), respectively. The increase in extractable P at high N rates was attributed to N-induced soil acidification. Most of the increase in extractable P occurred in the top 10-cm soil layer and almost none was noticed below 30 cm depth. Surface-applied K was able to prevent depletion of exchangeable K from the 0–90 cm soil, which occurred with increased bromegrass production from N fertilization in the absence of K application. As only a small increase of exchangeable K was observed in the 10–30 cm soil, 46 kg K ha^–1 year^–1 was considered necessary to achieve a balance between fertilization and bromegrass uptake for K. The potential for P contamination of surface water may be increased with the high N and P rates, as most of the increase in extractable P occurred near the soil surface.     

The fate of urea nitrogen applied in a foliar spray to wheat at heading

Nitrogen losses from irrigated wheat (cv. Matong) grown on a heavy clay in the Goulburn-Murray Irrigation Region following foliar applications of urea at heading were investigated. Ammonia (NH₃) volatilization was determined by a micrometeorological method and total nitrogen (N) loss was determined by a¹⁵N balance technique. The effects of the foliar application on grain N concentration and grain yield were determined also.Little nitrogen was lost by NH₃ volatilization following the foliar application. The rate of NH₃ loss increased briefly from <11 g N ha^–1 hr^–1 to >19 g N ha^–1 hr^–1 following rainfalls of 3 and 2 mm which washed 34% of the applied N from the plant onto the soil and increased the pH of the surface soil. The pH effect was short lived and total NH₃ loss amounted to only 2.13 kg N ha^–1 or 4.3% of the applied N.The¹⁵N balance study also showed that little N was lost from the plant-soil system until rain had washed the fertilizer from the plant onto the soil. In the period 152 to 206 DAS, the soil component of the applied N decreased from 34% to 9%. This fraction then increased slightly to 12% of the applied N at harvest. At that time, 69% of the applied N was recovered in the plants indicating that 19% of the applied N had been lost from the plant-soil system. As there was no evidence for leaching of N, the difference between total N loss as measured by¹⁵N balance (19%) and NH₃ loss (4%) is considered to be loss by denitrification (15%).The fertilizer N assimilated by the plant was efficiently remobilised from the leaves and stems to the head; 78% of the fertilizer N assimilated by the plant tops had been translocated to the head by the time of harvest. Grain N concentration responded to the foliar N application. The fitted response function had significant linear (P = 0.004) and quadratic (P = 0.10) trends to N rate, whereas there was no significant effect on grain yield.     

Mineral nutrition and fertilizer response of grain sorghum in India — A review over the last 25 years

Researches on the mineral nutrition and fertilizer response of grain sorghum (Sorghum bicolor (L) Moench) carried out during the last 25 years in India are reviewed here. In general, N,P,K, Fe and Mn concentrations in vegetative plant parts decreased with crop age, while the concentrations of Ca, Mg and Cu increased. The concentration of N and P increased in panicle or grains of sorghum with advance in crop age. The seasonal change for other nutrients has not, however, been studied.Accumulation and uptake of N,P, and K by grain sorghum were characterized. Usually N and P accumulated slowly compared with the rapid accumulation of K in early crop growth stage and vice-versa in later stages of growth. As against the sizable mass of N and P into panicle, K was partitioned into stalk.Fertilizer responses to N and P were observed throughout India. Improved varieties and hybrids of sorghum responded to N rates ranging from 60 to 150 kg N ha^–1, whereas a response to P application was observed up to 40 kg P ha^–1. Although responses to K application had been inconsistent, an increase in grain yield of sorghum was observed due to 33 kg K ha^–1. A balanced fertilizer schedule consisting of 120 kg N ha^–1, 26 kg P ha^–1, 33 kg K ha^–1 and 15–25 kg Zn50₄ ha^–1 is recommended for improved productivity of grain sorghum.It is concluded that systematic research efforts should be directed so as to identify problem soils showing deficiencies and toxicities of different nutrients. Characterization of the seasonal changes in the concentration and uptake of different nutrients and determination of critical concentration and hidden hunger of different nutrients in plant tissues would lead to the recommendation of balanced fertilization for different sorghum-growing regions in India.A part of the paper presented in the Silver Jubliee Conference of Indian Society of Agronomy held at H.A.U., Hissar (India) in March, 1981     

Growth response to fertilisation and recovery of 15N-labelled fertiliser by young hoop pine plantations of subtropical Australia

The stand growth responses to fertilisation were investigated in 1-year-old and 5-year- old second rotation (2R) hoop pine (Araucaria cunninghamii) plantations in subtropical Australia. At the 1-year-old plantation, 4 rates of nitrogen (N) fertiliser (0, 20, 60 and 120 kg N ha-1) were banded either with or without basal fertilisers (BF) containing 60 kg P ha-1 and 50 kg K ha-1. In the 5-year-old plantation, 4 rates of N fertiliser (0, 100, 300, 600 kg N ha-1) were banded with or without the BF. At both sites N fertiliser was applied as ammonium sulphate in 4 equal split dressings over 2 growing seasons. 15N-labelled ammonium sulphate was also used at the 5-year-old plantation in conjunction with the 100 kg N ha-1 treatment. The 15N-labelled fertiliser was applied to 3 trees during the first split application in spring, and to 3 more trees during the second split application in midsummer. The 15N-labelled trees were harvested and the surrounding soil excavated 6 months after the second 15N application. In the 1-year-old plantation, no stand growth response to fertilisation was noted, indicating that fertilisation at plantation establishment was unlikely to increase plantation productivity. In contrast, a significant stand response to N fertilisation was demonstrated at the 5-year-old site. There were no significant differences between the plus N treatments and the increase in basal area and volume due to N fertilisation 2.3 years after commencement of the trial was 45.1 and 43.5%, respectively. No response to basal fertiliser was observed. The mean 15N recovery from the soil–plant system was 79%, with no significant difference noted between the two split applications. The mean 15N recovery in the tree biomass was 56%, with the majority being partitioned into the foliage. On average 21% of the applied 15N could not be accounted for, and was assumed to be lost from the soil–plant ecosystem.     

Fate of phosphorus applied in slurry and mineral fertilizer: accumulation in soil and release into surface runoff water

Phosphorus (P) accumulation on the soil surface and its effect on the concentration of dissolved orthophosphate P (PO₄-P) in surface runoff water were studied after three years of surface application of slurry and mineral fertilizer to grass ley on a sandy soil, poor in P. The total amount of P applied was 107–143 kg ha^–1>, of which 72–119 kg ha^–1> was applied on the soil surface during two or three years without incorporation or mixing. The addition of slurry and mineral fertilizer resulted in an increase in inorganic P in the 0–5 cm but not the 5–25 cm soil layer, but organic P was not affected. The measured changes in inorganic P deviated only by 4–6 kg ha^–1> from the values derived from inputs and outputs of P (crop uptake + losses in surface runoff and drainage water). The increase in inorganic-P was accompanied by increases in the degree of P saturation (DPS) and in P extracted with acid am monium acetate (P_Ac ), sodium bicarbonate (P_Olsen) and anion-exchange resin (P_Resin). In surface runoff, 10–18 months after the last surface application of P, the mean flow-weighted concentration of PO₄-P was linearly increased with the values of DPS, P_Ac, P_Olson and P_Resin in the 0–5 cm soil layer. PO₄-P was lowest (0.033 mg l^–1> ) in the control plots and highest (0.62 mg l^–1>) in the plot where 143 kg ha^–1> P had been applied in slurry and fertilizer. On that plot, the corresponding values of DPS, P_Ac, P_Olson and P_Resin were 16%, 13 mg kg^–1>, 85 mg kg^–1> and 71 mg kg^–1 , even within a few years, and multiply the P loading to surface runoff from the site. A very shallow soil sampling (< 5 cm) is needed to assess P loading potential in a soil where P has been surface-applied.     

Effect of phosphate fertiliser type on the accumulation and plant availability of cadmium in grassland soils

Cadmium (Cd), a potentially toxic heavy metal for humans and animals, accumulates in the liver and kidneys of older animals grazing New Zealand and Australian pastoral soils. Phosphorus (P) fertiliser is the major input of Cd into these farming systems. A study was conducted to evaluate the effects, over 10 years, of annual application (30 kg P ha^–1 yr^–1) of four forms of P fertilisers having different solubilities and Cd contents [41, 32, 10 and 5 g Cd g^–1 for North Carolina phosphate rock (NCPR), single superphosphate (SSP), diammonium phosphate (DAP) made from low Cd phosphate rocks and Jordan phosphate rock (JPR) respectively] on soil and herbage Cd concentrations. Ten years of fertiliser application caused a marked increase in surface soil Cd concentrations. Total soil Cd was significantly higher in SSP and NCPR treatments compared to control (no P fertiliser), JPR and DAP treatments in the 0–30 and 30–75 mm soil depths. Plant-available Cd (0.01 M CaCl₂ extractable Cd) was higher in SSP treatments than in control and other fertiliser treatments. Chemical analysis of herbage samples showed that there was no significant difference in Cd concentration in pasture grasses between treatments in the second year of the trial but in the eighth and tenth year, plots fertilised with SSP and NCPR had significantly higher Cd in pasture grasses in most of the seasonal cuts compared to control, JPR and DAP. Cadmium recovery by both grasses and clover was less than 5% of Cd applied in fertiliser. Clover Cd concentration and yield were much lower than those for grass and therefore its contribution to pasture Cd uptake was very low (< 7%). A strong seasonal effect on grass Cd concentration, which is inversely related to pasture growth rate, was observed in all three sampling years — Cd concentration was highest during autumn and lowest in spring. Total Cd contents of the fertilisers and their rate of dissolution rather than soil pH [pH (H₂O) at 30–75 mm depth of 5.39, 5.20, 5.11 and 5.36 for NCPR, SSP, DAP and JPR treatments respectively]influenced soil and herbage Cd. These results showed that the use of P fertilisers with low Cd contents will reduce herbage Cd levels and has the potential of reducing Cd levels in grazing animals and their products.     

An evaluation of water extraction as a soil-testing procedure for phosphorus II. Factors affecting the amounts of water-extractable phosphorus in field soils

The effects of seasonal variation, sampling depth, and fertilizer P addition on water-extractable P values were investigated in two field experiments, involving soils of contrasting P retention capacity (Ramiha and Tokomaru) under permanent pasture over 12 months. The effects of the same parameters on Olsen-extractable P were also evaluated. The amounts of water-extractable P in soil were always lower than those of Olsen-extractable P. Over the 12-month period, the average value of water-extractable P in the unfertilized Ramiha soil (0–7.5 cm depth) was 1.8µg g^–1 soil compared to an Olsen-extractable P value of 12.6µg g^–1. The variability associated with water-extractable P at each sampling time was comparable with that for Olsen-extractable P. However, the relative seasonal variation over 12 months was larger for water-extractable P than for Olsen-extractable P. The results obtained with both extractants showed a seasonal fluctuation which was closely related to the pattern of pasture P uptake. The amounts of water- and Olsen-extractable P were higher in samples taken from the 0–4.0 cm than the 0–7.5 cm sampling depth. Fertilizer P addition resulted in larger increases in water-extractable P in the 0–4.0 cm sampling depth than in the 0–7.5 cm depth. The relative increase in water-extractable P following fertilizer P addition was larger than that of Olsen-extractable P. Seasonal changes in the soil microbial biomass P were not related to changes in either water-extractable P or plant uptake of P. Microbial biomass P may be a less sensitive index of soil P availability than is commonly thought.     

Synthesis and Properties of Novel Fluorinated Poly(amide-imide)s from the 4,4′-Bis(4-trimellitimido-2-trifluoromethylphenoxy)biphenyl and Aromatic Diamines

A novel fluorinated diimide dicarboxylic acid, 4,4′-bis(4-trimellitimido-2-trifluoromethylphenoxy)biphenyl (III), was synthesized from the condensation of 4,4′-bis(4-amino-2-trifluoromethylphenoxy)biphenyl (I) and trimellititc anhydride. A series of soluble poly(amide-imide)s (PAI) V_a–h having inherent viscosities of 0.56–0.97 dL/g were prepared from reacting III with an equivalent amount of diamines by direct polycondensation using triphenyl phosphite and pyridine as condensing agents. The polymer V series afforded tough, transparent, and flexible films. They had tensile strengths ranging from 88 to 112 MPa, elongations at break from 8 to 31%, and initial moduli from 1.9 to 2.7 GPa. The glass-transition temperature (T_g) of the polymers was recorded at 235–300^○C. They had 10% weight loss at a temperature above 502^○C and left more than 54% residue even at 800^○C in nitrogen. In comparison with the nonfluorinated PAI VI series, the fluorinated V exhibited better solubility.     

Potassium and magnesium fertilizers on banana in Uganda: yields, weevil damage, foliar nutrient status and DRIS analysis

Low soil fertility and pest pressure are two causes of the decline in banana (Musa AAA) production in central Uganda. Foliar analysis by the Diagnosis and Recommendation Integrated System (DRIS) pinpoints K and Mg as the most limiting nutrients. This study tested the effects of K and Mg additions on plant performance and weevil damage for 2.75 yr, at Buligwe in central Uganda and Muyogo in southwest Uganda. All treatments received 25 kg P ha^–1 and 100 kg N ha^–1 annually, while K and Mg were applied (kg ha^–1) at 0 K–0 Mg, 100 K–0 Mg, 100 K–25 Mg and 100 K–50 Mg. Fresh fruit yields (Mg ha^–1 yr^–1) ranged from 3.2 to 5.0 at Buligwe and 14.4 to 18.9 at Muyogo, with similar treatment trends at both sites. The 100 K–0 Mg treatment produced higher yields than no-K control (p = 0.022 for the combined dataset). Yields with K+Mg tended to be lower than with K only, though not significantly different. Foliar nutrient concentrations were little affected by treatments, but varied substantially among sample dates. With increasing cumulative rainfall between foliar samplings, foliar P declined (p = 0.077), K declined (ns), and Ca and Mg increased (p = 0.02 to 0.03). Weevil damage was higher at Buligwe, but was little affected by K and Mg treatments at either site.     

Effect of green manuring with Sesbania aculeata and nitrogen fertilization on the performance of direct-seeded flood-prone lowland rice

Green manuring of rice with dhaincha (Sesbania aculeata) is widely practised under irrigated puddle-transplanted conditions. In flood-prone lowlands, the rice is established through direct seeding early in the season and flooding occurs after 1–2 months of crop growth following regular rains. The low yields are due to poor crop stands and difficulty in nitrogen management under higher depths of water. The effect of green manuring with dhaincha intercropped with direct-seeded rice vis-à-vis the conventional practice of incorporating pure dhaincha before transplanting was investigated under flood-prone lowland conditions (up to 50–80 cm water depth) at Cuttack, India. Treatment variables studied in different years (1992, 1994 and 1995) were: rice varieties of different plant heights, crop establishment through direct seeding and transplanting, varying length of periods before dhaincha incorporation, and urea N fertilizer levels. Dhaincha accumulated 80–86 kg N ha^-1 in pure stand and 58–79 kg N ha^-1 when intercropped with direct-seeded rice in alternate rows at 50 days of growth. The growth of rice improved after dhaincha was uprooted manually and buried in situ between the rice rows when water depth was 10–20 cm in the field. The panicle number was lower but the panicle weight was higher with dhaincha green manuring than with recommended level of 40 kg N ha^-1 applied as urea. The grain yield was significantly higher with direct seeding than with transplanting due to high water levels (>60 cm) immediately after transplanting. Dhaincha manuring was at par with 40 kg N ha^-1 as urea in increasing the yield of direct-seeded and transplanted crops. The highest yield of direct-seeded crop was obtained when 20 kg N ha^-1 was applied at sowing and dhaincha was incorporated at 50 days of growth. The results indicate that green manuring of direct-seeded rice with intercropped dhaincha is beneficial for substituting urea fertilizer up to 40 kg N ha^-1 and augmenting crop productivity under flood-prone lowland conditions.