J. Wooldridge

Effect of liming and parent material on the potassium quantity-intensity relationships of some upland soils of the western Cape.

Liming and parent material had major effects on the potassium (K) quantity/intensity (Q/l) relationships of a varied group of naturally base-depleted upland soils of the western Cape. Departures from the usual Q/l curve form were observed, the individual curve sections probably representing specific exchanger states. K buffering (PBCK) in the limed Bokkeveld shale (BS) soils was 4,0-fold that of the limed granite and 6,5-fold that of the limed Table Mountain sandstone (TMS) soils. The response in terms of PBCK to liming by the BS soils was 4,7 and 5,1-fold that of the granite and TMS soils respectively. The granite soils were characterized by high levels of K release (ΔKo), that from the unlimed granite soils being 15,9-fold that from the unlimed BS soils. Relative to the TMS and BS soils, liming had a very limited effect on Δo in the granite soils.

Effects of soil surface management practices on soil and tree parameters in a ‘Cripps Pink’/M7 apple orchard 1. Mineral nutrition

Effects on soil, leaf and fruit element concentrations of organic (compost, straw mulch and hand weeding) and integrated (inorganic fertilisers and herbicide usage; IP) soil surface management practices in the tree rows, in combination with weed covers, cover crops and straw mulch in the work rows, were investigated in a seven-year trial. The trial took place on a gravelly soil in a ‘Cripps Pink’/M7 apple orchard in the Elgin area, South Africa. The organic treatments promoted higher phosphorus (P) and potassium (K) concentrations in the soil, leaves and fruit than the IP treatments. Leaf and fruit nitrogen (N) levels were normal in both the organic and IP treatments. Compost application rates that supply adequate N therefore deliver excessive amounts of P and K. Use of such composts should be based on P and K contents, supplementing where necessary with N. In both the IP and organic treatments, element concentrations were higher in the tree rows than the work rows. Treatments applied to the work rows did not affect soil and tissue element concentrations consistently. Standardisation of compost composition is required, as is balanced delivery of N, P and K.

TISSUE ELEMENT CONCENTRATIONS AND MINERAL REMOVAL RATES IN HONEYBUSH TEA I: CYCLOPIA GENISTOIDES

Results from a five year survey of honeybush (Cyclopia genistoides) in the Cape Floral Kingdom, South Africa, showed that concentrations of nitrogen, phosphorus, potassium, calcium and magnesium in the top growth of mature plants grown from seedlings were 1.29, 0.05, 0.53, 0.22 and 0.09%, respectively. Removal rates at each harvest were 8.23, 0.32, 3.38, 1.40 and 0.57 g of the respective elements per plant. These quantities were equivalent to 48% to 61% of the total mass of each element in the plant. Concentrations in the top growth of sodium, manganese, iron, copper, zinc and boron were, respectively, 1423, 16, 172, 5, 12 and 23 mg kg−1. Seedlings of C. genistoides reached their peak mass around five years after planting, and attained higher dry masses in plantations than in the open veld. Mature, plantation-grown C. genistoides plants yielded around 638 g of top growth dry mass per plant at each harvest.

Effect of liming and mineral nutrition on growth of honeybush (Cyclopia spp.) plants

A short-duration pot trial was carried out to determine the effects of liming and of mineral nutrients on Cyclopia spp., a newly commercially significant member of the fynbos flora, which habitually grows in acid, low phosphorus (P) sandy soils. Total dry mass production after four months by C. subternata increased where the soil pH was limed from 4.4 to 5.2 (1M KCl), and also benefited from the addition of 10 mg P kg−1 to the native soil P concentration of 11 mg kg−1. No response was observed to the addition of potassium (K), where the soil contained 25 mg K kg−1. Manganese (Mn) addition did not give a positive response, even though the soil Mn concentration in the unamended soil was low (1.3 mg kg−1). Treatment of the seed with molybdenum, to stimulate Rhizobium, promoted dry mass production in C. subternata, but did not do so consistently in C. maculata. The effects of nitrogen and magnesium on dry mass production in C. subternata and C. maculata were inconsistent.

Effects of soil surface management practices on soil and tree parameters in a 'Cripps Pink'/M7 apple orchard - 2. Tree performance and root distribution

Effects of integrated production (IP) and organic-acceptable soil surface management practices were investigated in a ‘Cripps Pink’/M7 apple orchard in the Elgin area, South Africa. Work row treatments included cover crops, weeds and straw mulch. In the IP tree rows, weeds were controlled with herbicide and nitrogen (N) was supplied in inorganic form. Tree rows in the organic treatments received mineral nutrients in compost, and a straw mulch was used to control weeds. Tree and soil parameters were determined over a seven-year period. Compost usage in the organic treatments led to high soil phosphorus (P) and potassium (K) concentrations, but less acidity, than in the IP treatments. Stem circumferences, pruning weights and root numbers were generally greater in the organic than the IP treatments. Conversely, yields and yields per cm2 stem area were mostly lower in the organic, than in the IP, treatments. To improve yields in organic apple orchards the balance between vegetative growth and flowering and bearing structures must be improved, mainly through better control over orchard nutrition. Such control will be facilitated if composts are standardised with regard to mineral nutrient contents, ratios between N, P and K, and delivery rates.

TISSUE ELEMENT CONCENTRATIONS AND MINERAL REMOVAL RATES IN HONEYBUSH TEA II: CYCLOPIA SUBTERNATA

A survey of plantation-grown Cyclopia subternata showed that average concentrations of nitrogen, phosphorus, potassium, calcium and magnesium in the new top growth of mature seedlings and cuttings were 1.59, 0.09, 0.62, 0.32, and 0.17%, respectively. Respective removal rates of these elements at each harvest averaged 13.1, 0.7, 5.1, 2.6, and 1.4 g plant−1. These quantities were equivalent to. 28% to 45% of the total element in the plant. Concentrations in the top growth of sodium, manganese, iron, copper, zinc and boron averaged, respectively, 1459, 34, 143, 7, 9, and 30 mg kg−1. Old top growth dry mass and root dry mass increased with time. Peak new top growth yields from C. subternata plants derived from seedlings and cuttings differed by only 2.2%. At peak production, new growth constituted 15% of total seedling dry mass and 21% of total cutting dry mass.

Honeybush (Cyclopia spp.) response to phosphorus fertilisation and mulching

Honeybush (Cyclopia spp.) is endemic to the Western- and Eastern Cape where it grows naturally in sandy, acidic, low- phosphorus (P) soils. The effects of different rates of applied P, and of mulches, on the growth of four honeybush species were determined in a field trial. In soils containing around 6 mg P kg−1, the growth of plastic mulched Cyclopia subternata was significantly enhanced by the addition of sufficient P to increase the soil P concentration to 20 mg kg−1. At low (6 mg kg−1) soil P concentrations, mortality rates in honeybush species tended to be lower in sawdust mulched, relative to unmulched and plastic mulched treatments. Mortality was probably associated with a root nematode infestation.

Effect of foliar- and soil-applied boron in deciduous fruit orchards 2: apricot and peach

Between autumn 1996 and May 1998 a variety of boron (B) treatments were applied to mature apricot and peach trees in Western Cape orchards on soils containing 0.2 to 0.7 mg B kg−1. Leaf B levels in the B treatments averaged 11.1% higher than the controls in the apricot, and 22.8% higher in the peach orchard. Average apricot fruit B levels in the B-treatments were 47% higher than the controls in 1998. In the B-treated peach trees the average fruit B level was 63% higher than the controls in 1997, and 106% higher in 1998. Leaf and fruit B levels were not affected, relative to non-B treated controls, by single spring B spray applications at concentrations up to 26.0 g B 100 I1, or by treatments in which a single spring B spray at 19.5 g B 100 I−1 was supplemented by a single autumn B spray containing up to 97.5 g B 100 I−1. The application of four early-season sprays at 31.2 g B 100 I−1, followed by a single autumn spray at 41.6 g B 100 I−1, or by an autumn soil application of either calcium borate at 2.10 g B tree−1, or borax at 1.13 g B tree−1, resulted in excessively high fruit B levels in peach. In the absence of spring B sprays both apricot and peach showed increased leaf and fruit B levels where calcium borate was applied each autumn at 2.10 g B tree−1. The peach fruit B levels were excessively high where calcium borate was applied at 2.80 g B tree−1. Apricot and peach leaf and fruit B levels correlated with 0.02 M CaCI2- extractable soil B. Peach fruit calcium levels decreased with increasing soil, leaf and fruit B levels.

Effects of early season and autumn nitrogen applications on young ‘Keisie’ canning peach trees on a sandy, infertile soil

The effects of autumn (A) and early season (S) nitrogen (N) applications were investigated in a young ‘Keisie’ canning peach orchard on an infertile sandy soil in the Western Cape Province, South Africa. Over the first four consistent bearing seasons, AN was supplied at four levels, averaging 19.9, 39.8, 59.9 and 119.7 g N tree−1, respectively (treatments AN1, 2, 3, and 4). Early-season N was supplied at three levels, averaging 42.4 (SN1), 82.2 (SN2) and 157.0 (SN3) g N tree−1. Four-year average yields tended to increase as the AN application rate increased from AN2 to AN4 (39.8 to 119.7 g N tree−1), and also tended to increase with increasing SN application rate. At the lowest level of AN (19.9 g tree−1) the yield and growth responses to moderate (82.2 g tree−1) and high (157.0 g tree−1), but not to low (42.4 g tree−1) rates of SN, were large. Thus, whilst yields in AN2, AN3 and AN4 were greater by 4.6% on average in SN2 than in SN1, and by 6.8% in SN3 than SN2, the yields in AN1 were 44.6% greater in SN2 than SN1 and 1.2% greater in SN3 than in SN2. Only in SN1 were progressive yield responses observed with increasing AN. Annual increases in trunk circumference, averaged over the same period, showed the same pattern of response to AN, and to SN, as average yield. Fruit and leaf N concentrations increased with SN at all levels of AN, but fruit diameter and single fruit mass increased with SN only at the lowest level of AN. A high total N rate of 222 g tree−1 (247 kg ha−1), in three applications, was required for a 26.4 t ha−1 yield in the seventh season on this infertile, sandy soil.

Number and concentration of calcium nitrate plus Kelpak® sprays for control of bitter pit in 'Braeburn5 apple fruit

In a spray trial to test the effects of calcium nitrate and a kelp extract (Kelpak®), fruit calcium (Ca) concentrations in ‘Braeburn’ apples peaked between 7.6 and 9.5 mg 100 g−1 fresh mass (FM) on 19 December 2000, then declined to between 2.3 and 3.2 mg 100 g−1 FM at harvest (22 March 2001). Fruit Ca concentrations on 19 December were highest where 12 sprays, each containing 117 g Ca per 100 I water were applied, without Kelpak®, at weekly intervals from 42 days after full bloom to 30 January. At harvest, fruit Ca in this treatment was no greater than where 12 sprays containing either 117 or 58.5 g Ca per 100 I water were applied with Kelpak®. Incidences of bitter pit in these treatments were, respectively, 1.0%, 1.3% and 3.4%. Where six half-strength sprays were applied, with Kelpak®, over the same time period, bitter pit increased to 9.3%. At harvest, fruit Ca concentrations were 0.25 mg Ca per 100 g−1 FM lower in pitted, than in bitter pit-free fruit. Total soluble solids and starch conversion were lower where 12 full-strength sprays were applied without Kelpak® than where 12 half-strength sprays were applied with Kelpak®. Starch conversion was greatest where six half-strength sprays were applied with Kelpak®. The effects on fruit colour of calcium nitrate, alone or with Kelpak®, were inconclusive