Acid Soil

This paper presents the effect of hydric stress on Select sunflower hybrid grown under near-neutral and acid soil conditions. The experiment was conducted in green - house with sunflower plants grown in PVC tubs filled with: near- neutral soil (pH = 6.2 ) (I), acid soil (pH = 5.27) (II) and ferti-lized acid soil ((phosphorus (100 kg/ha), potassium (100 kg/ha)

In tropical acid soils, acidity is an important constraint for availability and uptake of nutrients by annual crops, and this leads to lower crop yields. Factors that contribute to low nutrient uptake efficiencies in these soils are low natural levels of most essential plant nutrients and unfavorable soil and plant environments. High P fixation capacity, Al, Mn and H toxicity,

Biochar, because of its porous nature, calcium carbonate (CaCO 3) equivalent, surface functional groups, and other properties, could serve as an acid soil amendment. To investigate the liming potential of bio-chars, laboratory characterization and greenhouse and field experiments were conducted in Hawaii and West Java, Indonesia, respectively. Six wood-derived biochars were characterized and amended to a Hawaiian acid soil (pH 4.6, exchangeable aluminum [Al] 1.8 cmolc kg −1) at 2% and 4% alone or in combination with 2 cmolc kg −1 of lime and then planted with Desmodium intortum (a forage legume sensitive to Al) twice in a greenhouse trial. To the Indonesian acid soils (pH 3.9-4.0, exchangeable Al 8-14 cmolc kg −1), a rice husk and a lac tree biochars at 4% and 8% alone or in combination with lime at 4 and 8 cmolc kg −1 and compost at 0.1 and 0.2% were applied and then planted with soybean (Glycine max) cv. Anjasmoro twice in field trials. Biochar effects on soil properties and plant growth were measured. The results indicated that the six biochars varied in pH, ash content, CaCO 3 equivalent, total basic cations, cation exchange capacity , and other properties (pore size, surface functional groups). Soil pH was increased, soil exchangeable Al was reduced, and plant nutrients were enriched to different degrees upon additions of biochars. Total dry weights of Desmodium were increased 2-to 4-fold over the control or lime treatment upon applications of biochar. Similar effects on soils and soybean were obtained for the Indonesian field trials. It was concluded that CaCO 3 equivalent and total basic cations were among the most important properties of bio-char responsible for improving acid soil productivity and plant growth.

Soil fertility and crop production are affected by biological processes and these processes, including enzyme activites, are influenced by pH. We investigated the potential of using alkaline phosphatase (AlkP) and acid phosphatase (AcdP) activities, for determining the optimum soil pH for crop production and the amount of lime required to achieve this optimum. Five acid soils, which varied widely in selected properties, were treated with CaCO3 at rates of 0, 0.2, 0.5, 1.0 and 2.0× the soil's lime requirement needs. To remove soil variations in absolute enzyme activity values, an AlkP/AcdP activity ratio was used to test soil response. The ratios of AlkP/AcdP responded immediately to the changes in pH caused by CaCO3 additions and an AlkP/AcdP ratio of approximately 0.5 divided soils into those with appropriate pH adjustment and those still needing additional lime treatment. However, incubation of the lime-treated soils for 67 days followed by treating the soils with organic amendments (which included finely ground chicken manure and alfalfa residues) increased the AlkP/AcdP ratios to approximately 3.0. For cropping systems that rely heavily on natural biological processes to maintain productivity, measuring the AlkP/AcdP ratio may be preferable to chemical approaches for evaluating effective soil pH and liming needs.

Percentage aluminium saturation as a criterion for liming acid soils in Nigeria was examined. Surface soil (0-15 cm) samples with extreme
acidity (3.8-4.9), formed on coastal plain sands (Obio-Akpor and Egor) and sandstone (Nsukka), as part of the soils occurring over the sedimentary
rocks in the humid region of southern Nigeria were collected to grow a hybrid maize (DMR White) in pots in green house for six weeks. Four
rates ranging from 0 to 3 tons/ha of calcium oxide (CaO) were used as the lime, ranging from 0 to 3 tons/ha for six weeks in greenhouse. The
treatments were arranged in a completely randomized design (CRD) with three replications. Soil chemical properties tested were significantly
(P<0.05) influenced by increased rates of lime application. Soil pH increased from 4.6 in the unlimed soils to 6.7 in soils treated with 3 t/ha CaO.
The exchangeable calcium increased from an average of 0.44 cmolkg-1 at a pH 4.6 and 3.96 cmolkg-1 at a pH 6.7. Liming depressed the uptake of
manganese and zinc in all the soils but increased the uptake of calcium and phosphorus. The exchangeable aluminium and percentage aluminium
saturation decreased with increasing rates of lime application. Available Phosphorus was low even with a reduction of soluble aluminium in
the soil solution, indicating that for proper management of these soils, liming should be supplemented with adequate phosphorus fertilization.
Increase in calcium uptake at 3 t/ha was not reflected in the dry matter yield of maize compared to 1 t/ha of lime thus, the 3 t/ha of lime can be
regarded as fertilizer rather than as soil amendment. The percentage aluminium saturation was reduced from the mean value of (68.7 to ≤ 33.3)%
at 1 t/ha of lime established to be the most suitable criteria for liming acid soils of Nigeria; hence, it is recommended for maize cultivation.

Plants acquire phosphorus from soil solution as phosphate anion. It is the least mobile element in plant and soil contrary to other macronutrients. It precipitates in soil as orthophosphate or is absorbed by Fe and Al oxides through legend exchange. Phosphorus solubilizing bacteria play role in phosphorus nutrition by enhancing its availability to plants through release from inorganic and organic soil P pools by solubilization and mineralization. Principal mechanism in soil for mineral phosphate solubilization is lowering of soil pH by microbial production of organic acids and mineralization of organic P by acid phosphatase. Use of phosphorus solubilizing bacteria as inoculants increases P uptake. These bacteria also increase prospects of using phosphatic rocks in crop production. Greater efficiency of P solubilizing bacteria has been shown through co-inoculation with other beneficial bacteria and mycorrhiza. This article incorporates the recent developments on microbial P solubiliz...

Soybean is an important crop with nutrition, economic and soil fertility improvement benefits to farmers. However, its production in western Kenya is partly constrained by low soil pH and soil fertility levels. A greenhouse pot study was conducted to evaluate the effects of inorganic fertilizers, farmyard manure and lime application on soil pH, nutrient uptake, growth and nodulation of soybean grown in acidic soils from western Kenya. The experiment was set up in a randomized complete block design with eight treatments: control; NPK; manure; lime; manure+lime; NPK+manure; NPK+lime and manure+lime+NPK. Significant effects of inorganic fertilizers, manure and lime applications were observed on all the variables. Manure, lime and manure+lime treatments increased soil pH by 1.33, 2.19 and 2.28, respectively, above the control treatment. The shoot N was lower under control (1.71-1.81%), NPK (1.85-1.98%) and manure (2.00-2.11%) than under all other treatments. Treatments NPK+lime and manure+lime+NPK recorded higher uptake of P and K nutrients than all other treatments. The control and NPK treatments recorded shorter plants and low leaf area and above-ground biomass compared to other treatments. The NPK+lime and manure+lime+NPK treatments recorded higher plant height and aboveground biomass than other treatments. Lime+manure treatment recorded highest nodule numbers and dry weights per plant. Positive relationships were observed between pH and N, P and K nutrient uptake (R 2 ranged between 0.30 and 0.77) and between biomass and N, P and K nutrient uptake (R 2 ranged between 0.68 and 0.99). From this study, use of manure and lime could result in improved soil pH for better uptake of nutrients, nodule formation and productivity of soybean in Western Kenya.

The increasing sulphur (S) deficiency in soils of several parts of world has led to the use of fertilizer S, an important factor in enhancing the production and quality of crops. Very limited information is available on the use of elemental sulphur (S0) as a fertilizer, its oxidation into SO42- and transformation into organic S in semiarid subtropical soils. We studied the impact of three temperature regimes on the mineralization of soil organic S, and the oxidation and immobilization of S0 in acidic (pH 4.9), neutral (pH 7.1) and alkaline (pH 10.2) subtropical soils of north-western India. Repacked soil cores were incubated under aerobic conditions (60% water-filled pore space) for 0, 14, 28 and 42 d with and without incorporated S0 (500 μg g-1 soil). Temperature had profound effects on all three soils processes, the rates of mineralization of native soil organic S, oxidation of applied S0 and transformation of S0 into soil organic S being greatest at 36 °C, irrespective of soil pH. Mineralization of native soil organic S (without added S0) resulted in the accumulation of 39, 66 and 47 μg SO42-–S g-1 soil in acidic, neutral and alkaline soil in 42 d period at 36 °C. Of the total mineralization, the majority (62 – 74%) occurred during the first 14 d period. Oxidation rate of added S0 during initial 14 d period at 36 °C was highest in alkaline soil (292 μg S cm-2 d-1), followed by neutral soil ((180 μg S cm-2 d-1) and lowest in acidic soil (125 μg S cm-2 d-1). Of the applied 500 μg S0 g-1 soil, 3.2 – 10.0%, 6.8 – 15.4% and 10.0 – 23.0% oxidized to SO42-, and 13.4 – 28.6%, 16.0 – 29.0% and 14.6 – 29.0% were transformed into organic S in 42 d period in acidic, neutral and alkaline soil, respectively. The results of our study suggest that in order to synchronize the availability of S with plant need, elemental S may be applied well before the seeding of crops, especially in acidic soil and in regions where temperature remains low. Substantial mineralization of native soil organic S in the absence of applied S0 and immobilization of applied S0 into organic S suggest that the role of soil biomass as source and sink could be exploited in long term S management.

Theee trials to evaluat the potential of alley cropping in maize production on the low fertility, acidic soils in Northern Zambia are described. Leucaena leucocephala, Gliricidia sepium, Sesbania sesban, Albizia falcataria, Fleminga congesta, and Cassia spectabilis, were grown in alley crops with hybrid maize and soybean. All trials received recommended rates of P and K fertiliser; N fertiliser was applied at three rates as a subplot treatment. One trial received lime before establishment. Only in the limed trial was there a significant improvement in maize yields through alley cropping; when no N fertiliser was applied, incorporation of Leucaena leucocephala prunings resulted in an increase of up to 95% in yields, with a smaller improvement being produced by Flemingia congesta. There was a significant correlation between the quantity of prunings biomass applied and the proportional increase in maize yields over the control treatment. It is suggested that the lack of effect of most of the tree species on crop yields was due to low biomass production. An economic analysis showed that alley cropping with limed Leucaena was only profitable when fertiliser costs were high in relation to maize prices. However, lime is both expensive and difficult to obtain and transport for most small scale farmers in the region, and is therefore not a practical recommendation. It is suggested that future alley cropping research should focus on screening a wider range of tree species, including other species of Leucaena, for acid tolerance and higher biomass production.

Low soil pH is a major constraint to maize (Zea mays L.) production on tropical soils due to toxic levels of aluminium (Al) and the concomitant phosphorus (P) deficiency that hinders plant root growth. A preliminary laboratory screening was conducted to test 75 Kenyan landrace maize accessions and 12 commercial varieties for response to low soil pH and Al toxicity

Phosphorus (P) is needed in large areas of developing countries toimprove soil fertility for crop production. The use of phosphate rock (PR) isan alternative to costly soluble P fertilizers, but it is ineffective usuallyin non-acid soils unless it is modified i.e. partially acidulated (PAPR). Alaboratory incubation study using the isotopic exchange kinetic method of32P and field experiments were undertaken on a neutral Ferralsol ofCuba to evaluate the effectiveness of PAPRs as fertilizers for common bean(Phaseolus vulgaris, L.). Sulfuric-acid based PAPR using40%, 50% and 60% of the acid required to produce singlesuperphosphate were studied. In the laboratory experiment Trinidad de GuedesPAPR was effective in providing P to the soil, through increases inisotopicallyexchangeable P and the percentage of P derived from fertilizer (%Pdff). In the three field experiments carried out to compare the P sources,yields of common bean were increased by PAPR, though the response was less thanwith triple superphosphate (TSP). The relative agronomic effectiveness (RAE) ofPAPR was greater than that of unacidulated PR. Taking into account the RAEvalues and the current cost of the P sources, the choice of Trinidad de GuedesPAPR instead of TSP could be economic, although the RAE value for PAPR waslowerthan that of TSP. This result indicates that PAPR could be used in thesoil understudy to obtain the best economic return. DM yield, P uptake and grain yield ofcommon bean were significantly increased by applying P as 50% PAPR. Lowcost improvement of the agronomic value of PR can be achieved by partialacidulation, so this modification of the phosphate rock show promise forutilization of PR reserves indigenous to developing countries.

The development of temperate deciduous and conifers forests stands usually results in accumulation of forest floor organic matter and a shift from mull to moder humus forms. It has been suggested that an increase in nutrient uptake by trees during their rapid growth phase leads to topsoil acidification, decrease in earthworm density and thereby a decrease in litter turnover. The focus of this paper was to examine if the mull-moder shift with forest ageing results from higher leaf litter production and/or lower litter decay rates. The objectives of this research were to determine (1) changes in macro-morphological properties of humus forms, leaf litter production, litter decay rates, soil nutrients content and pH along a 130-year pure beech (Fagus sylvatica L.) chronosequence in Normandy (Northwest France), (2) if humus form varied from mull to moder with increasing stand age, and (3) if a shift from mull to moder resulted from increased litter production, decreased litter decay rate...