Phosphorus (P) is essential to life on Earth and often the limiting nutrient in agricultural systems. P fertilizer is thus an essential resource to maintain food security. In the last half century, agricultural intensification has led to an increase in P fertilizer consumption from 4.6 to 17.5 Tg of P/year to meet rising global food demand. Mineral P (i.e., phosphate rock) is a non-renewable resource in the context of the Anthropocene, and its price is vulnerable to global market fluctuations. Increased efficiency of P use on farms is considered the most effective strategy to conserve P. The soybean industry demands 9.7% of global P use, of which Brazil’s soy industry consumes the most, accounting for 5.8% of the world’s P2O5 use in 2014. This global source of soy production is challenged by the unique tendency of weathered tropical soils, such as Oxisols, to retain (i.e., fix) P in forms that are unavailable to crops. The accumulation of soil P due to years of P fertilization in excess of harvested P is referred to as “residual” or “legacy” P. Historical hotspots for crop production in the US and Europe have relied on residual soil P stocks to maintain yields despite reduced P inputs. Whether Brazil will be able to utilize the same strategy depends on the accessibility of residual soil P stocks when applied fertilizer P is reduced. Field research on this topic remains relatively scarce for cultivated Oxisols in tropical climates. I conducted a field trial at Tanguro Ranch in Mato Grosso, Brazil on a field that has been fertilized at standard high rates for 10 years to test whether residual soil P can be accessed by soy crops. Soy yield response differed significantly (p < 0.05) based on the interaction between fertilization treatment (0%, 50%, or 100% of standard P fertilization) and soil texture. My results highlight opportunities to enhance P fertilizer use efficiency in intensive tropical agriculture.

Thesis (Msc. (Agriculture)) --University of Limpopo, 2011 / The impact of agricultural chemicals on the environment has come under close scrutiny in the country of South Africa, for that reason, we are investigating alternative and appropriate methods for nutrients management. The objective of the study was to assess infield spatial variability of soil nutrients in a uniformly managed corn field, and (ii) to recommend method that can potentially help corn (Zea mays L.) producers in Limpopo Province to enhance grain yield with optimal utilization of resources. The study was conducted at Syferkuil agricultural experimental farm (23o50’ S; 29 o40’ E) of the University of Limpopo, in the northern semi-arid region of South Africa. Prior to planting of corn on this uniformly managed 7 ha portion of a 1 705 ha farm, the field was mapped with Ag132 Trimble differentially corrected global positioning system (DGPS) equipped with Field Rover II® GIS mapping software. Land suitability assessment for corn was conducted before planting and the field was classified for suitability as S1 based on FAO guidelines for irrigated agriculture and South African Binomial System of Soil classification. Soils and corn leaf sample parameters, including N were collected and measured from geo-referenced locations on a 40 x 40 m grid. Nutrient distribution spatial maps were produced with Surfer software 8.0. There was a significant variability (P≤0.05) of soil nutrients and pH across the corn field. Corn grain yield ranged from 2.7 to 6.3 Mg ha-1. For a land suitability class of S1 under linear irrigation in a semi-arid environment, these grain yields were considered lower. This lower grain yields can be linked to variability of soil nutrients, and pH because the field was classified suitable according to FAO guidelines. This field, with its significant variability of nutrients and pH that resulted in lower grain yields, is potentially a good field for precision agriculture IX methods of nutrient management such site-specific management zones for environmental quality and economic efficiency. Keywords: Maize, Small-scale farming, Soil nutrient management, and Spatial variability

Thesis (MSc. Agriculture (Agronomy)) -- University of Limpopo, 2013 / Maize (Zea mays L.) is the third most important cereal crop after wheat and rice in the world. Maize/legume intercropping system has become one of the solutions for food security among small scale maize producers due to unaffordability of chemical nitrogenous fertilizers and limited access to arable land. A study was conducted to determine the effect of maize/dry bean and maize/lablab intercropping on maize grain yield and soil fertility status. A field experiment was conducted during 2010/2011 and 2011/2012 growing seasons at the University of Limpopo experimental farm. Treatments included sole maize (ZM 521, an improved open pollinated variety, ex- CIMMYT), sole lablab (Rongai, indeterminate cultivar), sole dry bean (DBS 360, indeterminate Type II cultivar), maize/dry bean and maize/lablab intercrops arranged in randomized complete block design with five replications. Phosphorus (P) was applied on sole and intercropped maize at the rate of 30 kg P/ha in the form of superphosphate (10.5%P) at planting and 40 kg N/ha of nitrogen (N) was applied in the form of Limestone Ammonium Nitrate (LAN) (28%N) on both sole and intercropped maize four weeks after plant emergence. For maize and dry bean, grain yield, yield components and biomass were determined. Only biomass yield was measured for lablab. Soil samples were collected for soil analysis at the beginning and the end of the experiment The results showed that maize/lablab intercropping yielded significantly (P<0.05) lowered maize grain (1259.3 kg/ha) than sole maize and maize/dry bean intercropping which yielded maize grain of 2093.7 kg/ha and 2156.3 kg/ha, respectively. Sole dry bean yielded significantly (P <0.05) higher dry bean grain (1778.5 kg/ha) than intercropped dry bean (691.8 kg/ha). Rongai was only flowering by the time maize and dry bean matured hence only maize yield is reported for the Maize/lablab intercrop. Maize/dry bean intercropping was advantageous to sole cropping with a Land Equivalent Ratio (LER) of 1.42. The partial Land Equivalent Ratio (PLER) for maize in maize/lablab intercropping was 0.60. Dry bean was outcompeted by maize as calculated aggressivity value was positive at +0.64.The highest monetary value was achieved in sole dry bean and the lowest monetary value was found in intercrop dry bean. Soil TN, P, K, Ca, Mg and Na were reduced by both sole cropping and intercropping systems. Intercropping with lablab is likely to significantly lower maize yield under dryland conditions. Key words: dry bean, grain yield, Intercropping, lablab, maize, smallholder, soil fertility.

Mit dem Anbau von Zwischenfrüchten kann die Nitratbelastung des Grundwassers reduziert oder niedrig gehalten werden. Zwischenfrüchte verbessern und erhalten die Bodenfruchtbarkeit, erhöhen die biologische Bodenaktivität und bieten Schutz vor Erosion. Auf Feldversuchsanlagen wurden Biomasseertrag, Stickstoffaufnahme und Stickstoffdynamik im Boden verschiedener Zwischenfruchtvarianten untersucht und ausgewertet. Eine Beschreibung der einzelnen Pflanzenarten und Hinweise zur Bestandesführung soll helfen, mit einer geeigneten Zwischenfruchtmischung gute Bestände zu etablieren.

Phosphorus (P) is an essential plant nutrient and is one of the most critical elements influencing crop production throughout the world. Phosphorus deficiency is widespread in most soils of northern Ghana, and ferruginous nodules contained in some soils in the region accentuate the deficiency problem because they act as P sinks. This research focuses on P fertility status of soils in landscapes common to northern Ghana. Three sites were selected for the study and were referred to as sites 1, 2 and 3. Soils in a catenary sequence from site 1 were sampled for detailed P distributions in profiles, and surface soils from the upper, mid and lower slope positions of the other landscapes (sites 2 and 3) were used. The nature of P in the soil fines and ferruginous nodules was investigated using a modified Hedley fractionation procedure. The objective was to quantify the labile and non-labile inorganic P (Pi) and organic P (Po) in relation to pedogenic weathering processes at different slope positions at site 1. A secondary objective was to assess the P distribution in the landscapes at sites 2 and 3. The largest P fraction in both soil fines and nodules at each site was resistant non-labile P forms. Primary P (Ca-P) decreased with depth in the profile at the upper slope position but it occurred in greater quantities in C horizons of the lower slope soils. Phosphorus sorption capacity of the soil fines and nodules was determined to predict the behaviour of P fertilizers in the soils. Phosphorus sorption by the soil fines increased to a maximum in the B horizon of each profile and a t-test showed that P sorption was similar in profiles at each slope position. The P sorption capacities of uncrushed ferruginous nodules varied according to their sizes. The small nodules were more reactive and sorbed more P than the larger sizes. Fractionation of P from the nonfertilized and fertilized soils at the end of cropping and anion exchange resin (AER) extraction, revealed that there had been redistribution of P into different fractions. A comparison of P fractions of the nonfertilized soils after the AER extraction with those of the native soil P showed decreases in some native labile and non-labile P fractions. This suggested that these P fractions could be available for plant uptake. Both 50% PAPR and SSP fertilizations increased the labile Pi and NaOH extractable Pi levels in the soils. (Abstract shortened by UMI.)

Univ., Diss.--Bonn, 2005.

Thesis (Ph. D.)--Ohio State University, 2009. / Title from first page of PDF file. Includes bibliographical references (p. 134-151).

This study compared the effect of two contrasting nutrient environments on the growth rates of 12 Carex species from the Mont St. Hilaire Biosphere Reserve, Quebec. All species demonstrated higher growth rates under conditions of high nutrient availability. There was no correlation found between maximum relative growth rate (RGRmax), leaf production, and biomass. High nutrient availability produced a reduction in root/shoot ratio, while leaf production was the trait that showed the greatest response to contrasts in nutrient availability The Carex species were found to be relatively slow growing plants, with growth potential ranging from stress tolerant to competitive. The species from lowlands are more competitive and have higher growth rates; the upland species are more stress tolerant and have lower growth rates. The abundance of a species at Mont St. Hilaire was found to be unrelated to its growth potential.

The potential shortage of phosphorus (P) fertilizer is a threat to food security and closing the nutrient loop through recycling human excreta, especially urine, has been considered, so as to mitigate this crisis. Struvite (magnesium, ammonium phosphate), a material derived from human urine, is a product which is gaining credence with regards to using urine as a P amendment since more than 90% of P in urine can be captured during struvite production. A study to evaluate the potential of struvite as a P amendment in three contrasting soils was conducted. The soils used were an A horizon of Inanda (Ia), A horizon Sepane (Se) and an E horizon of Cartref (Cf). Phosphate adsorption properties of the soils were studied and the Freundlich model used to derive sorption parameters. From these studies, Pmax was related to the Kf parameter of the Freundlich equation. Two sets of incubation studies were then conducted. The first ran for 122 days and the second for 22 days to examine in closer detail the early stages of dissolution of the struvite as the major P release occurred during this time period of the incubation. A pot experiment was conducted in a controlled environment so as to determine the effect of P released from struvite on maize growth. The Ia, with high content of iron and aluminum oxides, displayed high sorption and affinity for P, whereas soil texture was a principal factor in the sorption properties of the Se (clayey) and Cf (sandy). The Kf decreased in the order Ia > Se > Cf and external P requirements decreased in the order Se > Ia > Cf. In the incubation studies solution P content increased with an increase in application rate of struvite. Struvite dissolution and P release varied between the different soils and the dissolution was found to be related to the P adsorption maximum of each individual soil and soil pH. The magnesium content also increased with time. In the glasshouse study, drymatter yield after six weeks growth was improved by the addition of struvite. There were no benefits achieved by using more than the recommended application rates for each soil. Struvite was as effective as conventional single superphosphate in the Ia and Cf, while superphosphate outperformed struvite on the Se. The findings of this study suggest that struvite has the potential to release P in an available form although its effectiveness and capability to release P could depend on soil pH, exchangeable acidity and initial P levels. Further research needs to focus on the effect of pH on struvite dissolution, the effect of struvite on soil pH, as well as comparison of nutrient release patterns between struvite and rock phosphate. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2013.

Laboratory studies and field trials were carried out to investigate the effect of addition of some organic residues to acid soils on soil pH, exchangeable and soluble AI, nutrient status, microbiological and biochemical indices and maize response. The organic wastes used in the first laboratory study included plant materials (maize. sorghum, kikuyu grass, soybean, red clover residues and acacia prunings), animal manures (kraal, pasture-fed and feedlot cattle manure, layer and broiler poultry manure and pig manure), household compost, sewage sludge, and filter cake. The poultry manure, pig manure and leguminous plant residues had the highest content of basic cations while sewage sludge had the highest N content. Poultry manure had very high values for proton consumption capacity, CaC03 content and ash alkalinity. Proton consumption capacity, ash alkalinity, total basic cation content and CaC03 content were closely correlated with one· another. Soil pH was increased and exchangeable AI and total (AIT) and monomeric (AIMono) AI in solution were decreased by addition of all the organic wastes: the effect was greater at the higher rate of application. Strong correlations were recorded between the rise in soil pH and proton consumption capacity, ash alkalinity, CaC03content and basic cation content of the residues. The major mechanisms responsible for the elevations in pH were suggested to be the substantial CaC03content of poultry and pig manures, and filter cake, the proton consumption capacity of humic material present in household compost and manures and decarboxylation of organic acid anions during the decomposition of plant residues and manures. It was proposed that ash alkalinity is a suitable laboratory test for predicting the potential Iiming effect of organic residues since it is strongly correlated with the rise in pH that occurs, it is relatively simple to measure and the values reflect the initial content of organic acid anions, humic materials and CaC03in the residues. A preliminary field experiment was set up to investigate the effectiveness of kraal manure as a Iiming material in an acid soil (pHwater =4.1) at a site close to a Zulu village. The experiment consisted of two rates of lime (L1 = 2.5 and L2 = 5.0 t ha1) and two rates of kraal manure (K1 = 10 and K2 = 20 t ha-1 ) which were banded and incorporated in a 30 cm wide strip down the plant rows. Treatments were arranged in a randomized block design with three replicates. A commercial maize cultivar PAN 6710 and a traditional variety EMBO, used by the farmers in the locality, were grown. Soils in the plant row were sampled at tasselling and at harvest. The addition of kraal manure significantly raised soil pH and reduced concentrations of exchangeable AI and those of both total and monomeric AI in soil solution. Lime raised pH and the pH continued to increase between tasselling and harvest. Maize yields for control, kraal manure (K1 and K2) and lime (L1 and L2) for PAN 6710 were 2.5, 3.7, 5.1, 5.3 and 6.3 t ha-1 ; respectively and for EMBO they were 3.0, 5.4, 5.8, 5.9and 8.2 t ha-1 , respectively. These results demonstrate the high yield potential of the traditional maize variety under small scale farming conditions, and show that large yield increases can be obtained by applying kraal manure. The long-term effects (24 weeks) of incubation of organic wastes (soybean residues, poultry, pig and kraal manures and sewage sludge) with an acid soil were investigated in a laboratory study. After incubation for six weeks incubation, soil pH was raised and exchangeable AI and Air and AIMono in soil solution were decreased . by addition of the wastes. Soil pH generally declined and exchangeable and soluble AI increased over the remainder of the incubation period. The decline in pH was attributed mainly to nitrification of NH4+ originating from mineralization of wastes-derived organic N. Addition of organic materials generally resulted in a decrease in the proportion of solution Air present as AIMono. That is, the effects of addition of organic materials was two-fold; an increase in pH in the short term and complexation of AI by organic matter. Since these effects occur simultaneously, it would be desirable to separate them. For this reason, short-term equilibration experiments (3 days) were conducted to study the solubility of AI in aqueous solution or in an Oxisol when in equilibrium , with 3 manures (kraal, pig and poultry) at pH values of 4.0, 4.5, 5.0, 5.5, 6.0 and 6.5. Addition of manures tended to reduce the concentrations of total AI in solution (AIT) in the lower pH range (Le. pH 4.0 and 4.5) but increased AIT concentrations compared to the control, at higher pH values (Le. at pH 5.5 and above). This was explained in terms of the complexing ability of both the solid and solution phases. At lower pH, where AI is highly soluble, complexation by added solid phase manure-organic matter results in a reduction of AI solubility. However, at high pH, where AI solubility is limited, the most important mechanism is complexation of AI by soluble organic matter and this increased AI solubility. Additions of manure reduced the proportion of Air present in monomeric form (AIMono). This effect was more pronounced in aqueous solution but was also clearly evident above pH 5.0 in the Oxisol. This reflects the fact that a large concentration of soluble C in solution can maintain relatively high concentrations of complexed AI in solution but at the same time maintain low concentrations of AIMono. It was concluded that formation of AI-organic matter complexes caused by additions of organic manures can alter the solubility of AI and reduce the amount of phytotoxic AIMono present in soil solution. A second field trial was conducted to compare the effects of additions of kraal manure, grass residues, lime and fertilizer (N-P-K) under field conditions, on soil pH, AI solubility and maize response and, at the same time follow concomitant changes in the size and activity of the soil microbial biomass and enzyme activity. The greatest effects of kraal manure in increasing soil pH and decreasing AI toxicity were recorded six weeks after planting whereas those of lime and grass residues were recorded at harvest. Kraal manure and fertilizer increased significantly AMBIC extractable P and exchangeable K and Zn. In addition, Kraal manure, and to a lesser extent lime significantly increased exchangeable Ca and Mg.. Soils in the plant row in the grass residue treatments had the highest microbial biomass C and microbial quotient,followed by kraal manure, lime and controls. Basal respiration rates and arginine ammonification, protease, aryl sulphatase, and acid phosphatase activity rates were significantly increased by addition of all treatments and these increases tended to be accentuated by fertilizer. Low values for metabolic quotient in the grass residue treatments were associated with high values for microbial biomass C in these treatments. The addition of all treatments tended to increase maize yields and, in general, these yields were greater for the high rate of application of each amendment. Yields for unfertilized kraal manure were markedly greater than those for the unfertilized grass residue and lime treatments. This was attributed to the ability of kraal manure to both increase pH and add nutrients to the soil. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2004.