Master of Science

In a large part of the soil fertility studies that have been attempted in the past, a great number of the results obtained were based almost entirely on crop yields. These yields were used as the final criterion upon which to draw conclusions as to whether a given system of soil management was a profitable one. At the Virginia Agricultural Experiment Station, Blacksburg, Virginia, a series of rotation and continuous cropping experiments have been undergoing a specified treatment for a period of 24 years. Conclusions as to the expediency of the practices followed have been approached from a purely crop yield basis. This method is serving its purpose in showing exactly how much the land is producing at the present time under a given soil management practice. It is believed, however, that a soil management program goes further than this. A practice based on crop production alone may prove, over a long period of time, to be a poor one. Perhaps just as important are the conditions arising within the soil relating to these practices. Whether or not the system evolved is one of soil building rather than one of soil depletion, is a question which necessarily must be considered before any recommendation as to the soil management practices to be followed, may be attempted. / Master of Science

An investigation of the amount of exchangeable potassium found in the surface and subsoils of a 33-year rotation experiment at Blacksburg, Virginia, was made. The rotation is located on Dunmore silt loam, Which is rated as a relatively fertile soil in Virginia. There are indications that sheet erosion has removed considerable amounts of the surface soil from the steeper slopes of the first nine treatments, and it is evident that an accumulation of this material has occurred on the four lower plots. It is believed by the writer, and others familiar with these plots, that.this erosion occurred prior to the beginning of the rotation in 1909. Composite soil samples were taken from each of the 8 treatments in each of the 4 series of this rotation and resulted in a total of thirty-two fertilized subplot samples, and a corresponding thirty-two unfertilized subplot samples were collected and analyzed for exchangeable potassium. Similar analyses were ma.de on the thirty-two subsoils of both the fertilized and the unfertilized treatments. The resulting data from the surface and subsoils were then statistically analyzed and the following conclusion drawn: 1. The applications of both muriate of potash and manure significantly increased the amount of exchangeable potassium found in both the surface and subsoils. 2. The surface soils are significantly higher in exchangeable potassium than the subsoils. 3. Exchangeable potassium may be leached from the surface horizon to the subsoil when applied in a complete fertilizer in excess of plant needs. 4. Manure applications which contained considerably less potassium than the potassium added to the soils in the muriate applications, resulted in larger amounts of exchangeable potassium in the surface soils, a 30 per cent increase in crop yields, and significantly less exchangeable potassium leached to the subsoils. 5. The difference in exchangeable potassium between the fertilized subplots receiving muriate of potash. and the unfertilized subplots. resulted in an increase in the amount of potassium found in the surface soils which was equivalent to 996 pounds of 50 per cent potash fertilizer, and this figure would represent an amount equivalent to 15 per cent of the total muriate added to the surface soils. 6. The difference in exchangeable potassium found in the subsoil between the fertilized and unfertilized plots represents an equivalent of approximately 9 per cent of the total potash added. 7. Significantly larger amounts of exchangeable potassium were leached to the subsoil from plots, receiving muriate of potash than soils which received manurial treatments. Greater utilization of the applied potassium is indicated by the manurial applications. 8. A chemical analysis should be made of the manure which is applied to this experiment in order to obtain a more comprehensive understanding of the yields, and physical and chemical properties of these soils. / M.S.

In 2003 eight peanut and cotton crop rotations were established in southeastern Virginia, 4 of which included 2 or 3 years of tall fescue or orchardgrass grown as high-value hay crops. Each crop rotation was evaluated for changes in soil quality indicators including soil carbon and nitrogen, water stable soil aggregates, plant available water content, bulk density, cone index values, and soil moisture. Cotton and peanut growth and yield were also observed to evaluate changes in crop growth associated with differences in soil quality. Soilborne plant pathogens including root-knot nematode, stubby root nematode, ring nematode, stunt nematode, and Cylindrocladium parasiticum microsclerotia were measured in the spring and fall of each year to determine differences associated with crop rotations. Water stable soil aggregates in 2007 were higher in rotations with 3 years of either perennial grass. Soil moisture tended to be the highest at depths 30 - 60 cm in the 3-year tall fescue rotation in August and September 2007. Cotton in 2006 and peanut in 2007 had higher growth and yield where the annual crop directly followed a perennial grass. Root-knot nematode tended to decrease in all rotations over time. Stubby root nematode populations tended to increase in rotations with either duration of orchardgrass. Including perennial grasses in cotton and peanut rotations has the potential to increase growth and yield as demonstrated in this research. / Master of Science

Thesis (Ph. D. Agriculture (Plant Production)) -- University of Limpopo, 2021 / Plant-parasitic nematodes inflict economic damages on vegetable and field crops due to a lack of suitable crop protection chemicals and integrated crop management practices. Toxic synthetic chemical nematicides were withdrawn from the agro-chemical markets in 2005 due to their damage to the environment and humans. As such, there is continuous need to develop integrated nematode management strategies that are economic, environment friendly yet capable of effectively controlling the pest to alleviate crop loss and food insecurity. Root-knot (Meloidogyne species) nematodes are a major yield- and quality-reducing pest in most potato (Solanum tuberosum L.) producing regions in South Africa. However, little is known about the different plant-parasitic nematode species that are associated with potato in some Provinces. The sustainable production of crops in the absence of nematode resistant genotypes depends on the availability of nematode resistant crops in crop rotation systems. However, the effectiveness of these nematode resistance crops in managing root-knot nematodes in potato-based cropping systems has not been investigated in South Africa. The aim of the study was the development of sustainable cropping sequences for management of population densities of Meloidogyne species in potato production using crops with different mechanisms of nematode resistance. Two main objectives were investigated, but the second objective was sub-divided into three. The objectives of the study were to investigate (1) whether the diversity and abundance of plant-parasitic nematodes associated with potato in Limpopo Province, would be different to those in other potato-producing regions of South Africa, (2) whether (a) monoculturing potato would have any effects on population densities of Meloidogyne species, plant growth and soil health, (b) sequencing potato with a post-infectional nematode resistant crop like Cucumis africanus would have any effects on population densities of Meloidogyne species, plant growth and soil health and (c) sequencing potato with a pre-infectional nematode resistant crop such as sweet stem sorghum would have any effects on population densities of Meloidogyne species, plant growth and soil health. Ten known nematode genera, namely, Scutellonema, Helicotylenchus, Telotylenchus, Rotylenchulus, Paratylenchus, Tylenchorhynchus, Criconema, Nanidorus, Meloidogyne and Pratylenchus species were present in potato production fields in Limpopo Province, South Africa. The study was conducted on 30 farms, located in Mopani, Sekhukhune, Capricorn, and Waterberg districts by randomly collecting 10 core soil samples per hectare in a zigzag-sampling pattern. A total of eight nematode genera except two (Meloidogyne and Pratylenchus species) were recorded for the first time in potato fields in Limpopo Province. Additionally, the sampled districts were predominated by different nematode species. The Meloidogyne species were the most prevalent nematodes associated with potato crops followed by Helicotylenchus and Scutellonema species. In contrast, the Tylenchorhynchus and Nanidorus species were the least prevalent parasitic nematodes in potato production fields in the Limpopo Province. To achieve Objective 2, two field experiments were conducted at the University of Limpopo (UL) and the Agricultural Research Council-Vegetable and Ornamental Plants (ARC-VOP). In Sequence 1, the treatments (sorghum cv. ʹNdendaneʹ, potato cv. ′Mondial G3′, Cucumis africanus and potato (cv. ′Mondial G3′)-(Velum) were laid out in a randomised complete block design. In Sequence 2, potato (cv. ′Mondial G3′) was cultivated on all plots as the successor main crop. In Sequence 3, the treatments were laid out as in Sequence 1, whereas in Sequence 4 sole potato crop was cultivated as in Sequence 2. Therefore, four cropping sequences namely, sorghum-potato, potato monoculture, C. africanus–potato and potato-(Velum)-potato (control) were investigated simultaneously.Generally, post-infectional resistant C. africanus-potato was more effective than pre-infectional nematode resistant sorghum-potato or potato monoculture cropping sequences in reducing the population densities of Meloidogyne species in the soil. This has led to reduced damage to subsequent potato crop providing higher tuber yield, increased shoot mass and nutrients elements accumulation in potato leaf tissues at both sites. The high soil organic carbon content, microbial diversity and enzyme activity observed in C. africanus-potato and sorghum-potato showed that these two cropping sequences enhanced soil health better than the monoculture production system of potato with or without Velum application. The different indices (maturity index, channel index, enrichment index and structure index) collectively demonstrated that the soil was highly disturbed with bacteria dominated decomposition pathways. The nematode faunal profile showed that sorghum-potato was the only cropping sequence that improved soil structure as exhibited by high structure index. Therefore, the inclusion of nematode resistant sweet stem sorghum in potato-based cropping system promoted soil health better than the other cropping sequences. In conclusion, C. africanus-potato sequence could be used to effectively manage root-knot nematode population densities, whereas sorghum-potato sequence could be considered where the aim is to improve soil health. / National Research Foundation(NRF) Green Biotechnologies Research Centre of Excellence(GBRCE) Agricultural Research Council-Vegetable and Ornamental Plants(ARC-VOP)

Master of Science / Department of Agricultural Economics / Jeffery R. Williams / This study examines the economic profitability of reduced-tillage and no-tillage systems for corn, soybeans, and grain sorghum production in annual rotation with winter wheat, and monoculture wheat and grain sorghum in south-central Kansas. Net returns to land and management per acre for each of 13 production systems are calculated several different ways. Net returns are calculated using the 10-year average yield for each crop, the average crop price from 2009, and 2009 input prices. A distribution of net returns is also calculated using the actual historical yields and crop prices from 1997 to 2006 and 2009 input prices. This process is repeated, except average crop prices from 2006, 2007, 2008 and 2009 are now used. Finally, net returns are calculated using simulated yield and price distributions based on actual historical yields, four historical monthly price series, and 2009 input costs. Overall, the reduced-tillage wheat-soybean systems (RTWS) have the greatest net returns for each of the net return distributions. No-tillage wheat-soybean (NTWS) generally has the second highest net returns. Stochastic Efficiency with Respect to a Function (SERF) is used to determine the preferred management strategies under various risk preferences. SERF analysis indicates that RTWS is the system most preferred by all producers, regardless of their level of risk aversion. NTWS is typically the second most preferred system to RTWS. Using historical annual prices for 1997 to 2006 and the simulated monthly prices series for 2006 to 2009 and 2007 to 2009 to calculate the net return distributions, managers with higher levels of risk aversion prefer reduced-tillage wheat-grain sorghum (RTWG) over no-tillage wheat-soybean (NTWS). Sensitivity analysis shows that as the price of glyphosate falls, no-till systems become relatively more profitable. SERF analysis using the historic yields, 2006 to 2009 simulated monthly prices, and 2009 input costs with reduced glyphosate prices indicate that NTWS would be the system most preferred by producers at all levels of risk aversion. RTWS closely follows NTWS as the next preferred system with those conditions also for all levels of risk aversion.

Fertility-building crops (FBCs) offer the opportunity to alleviate the costs of inorganic fertiliser by providing an alternative supply of available nitrogen (N) in soils. A survey of relevant literature reviewed the types of FBCs, their nitrogen accumulation potentials, residue characteristics, and subsequent release patterns. It also identified a paucity of data concerning the response of different species to UK climatic, soil, and management conditions. In order to investigate these relationships further pot and field trials were established in 2007 at the Royal Agricultural College, Cirencester (SP 00481 01382) and at Coates Manor Farm (SO 98473 00402) on Sherborne series (typical Cotswold) soils, to investigate the biology and morphology of FBCs potentially suitable for short term fertility-building, their accumulation of N under field conditions, and its subsequent recovery within test crops. Data so obtained was used as a verification and refinement tool for the FBC model (Cuttle et al, 2003), a simple, commercially applicable, rotation-based model which can be applied to both organic and conventional production systems. Nine leguminous and two non-leguminous FBC treatments were established in April 2007 by straight sowing, followed by mulching at the conclusion of the nitrogen accumulation phase and by undersowing in spring barley (Hordeum sativum). The recovery test crops (winter and spring wheat Triticum aestivum L.) were established in September 2007 and March 2008. All FBCs established successfully. Above-ground dry matter (DM) yield and residue quality (C:N ratio) of FBCs varied significantly (P<0.05) between crops and cropping regimes with a significant correlation (r2=0.418) between DM yields and C:N ratios. FBCs and cropping regimes had significant effects (P<0.001 and P<0.05 respectively) on potential mineralisable nitrogen (PMN) levels in the soil and on the grain yields of winter and spring wheat test crops. Straight sown Lupinus albus, Trifolium pratense, Trifolium repens and a legume mixture resulted in higher winter wheat grain yields. However, the opportunity cost associated with straight sowing (i.e. the gross margin foregone from a spring barley crop) meant that the rotation would probably not be viable economically. Undersown Medicago lupulina, Vicia villosa, T. pratense, T. repens and the legume mixture gave worthwhile yield increases in spring wheat without incurring a yield penalty in the spring barley cover crop. Following enhancement and using actual data from the trials, the FBC model (Cuttle et al, 2003) provided encouraging predictions (R>0.6) for soil mineral nitrogen (SMN) and key parameters were identified for future use. It was concluded that FBCs established for short term soil fertility building could provide a worthwhile enhancement of soil N levels and grain yields in a conventional arable rotation, particularly in spring wheat following FBCs undersown in spring barley. It was also concluded that the FBC model (Cuttle et al, 2003), following further enhancement, and using additional data from these and other similar trials, could provide reasonably accurate estimates of SMN to aid more precise applications of N fertiliser in the future.

Thesis (MAgricAdmin)--Stellenbosch University, 2001. / ENGLISH ABSTRACT: Crop rotation present a possible alternative to wheat mono culture production in the Middle Swartland region where farming circumstances became increasingly more difficult since 1996 due to decreasing profit margins. Crop rotation as such presents a number of advantages like higher yield for wheat within the system and reduced inputs costs mainly due to cuts in fertilizers, herbicides and pesticides. Crop rotation trials are currently undertaken at the Langgewens experimental farm in which canola and lupines are used in rotation with wheat while medics and medic/clover mixtures are used as pasture crops in rotation with wheat. The trials is scheduled to run over a period of 20 years, a study of the possible financial effect crop rotation might have on the typical farm can be of some importance to decision makers in the wheat industry. Due to a lack in reliable information the knowledge of a multi disciplinary panel of experts were use to obtain information concerning certain aspects of crop rotation. The expected profitability could thus be determined. To be able to determine the expected financial implications on farm level a typical farm model was developed with the help of the panel of experts. The typical farm of 630 ha was used for the model. The expected profitability and financial implications of the implementation of the eight different crop rotation systems on such a typical farm were estimated making use of long term budgets. The dispersion of rainfall over time was identified as the single most influential factor on the yields of the different crops in the region and was taken into account determining the profitability of the systems over time. The period used for the calculations were thus divided into good, average or poor rainfall years. The IRR (internal rate of return) was used as financial criteria in calculating the expected profitability of the different / AFRIKAANSE OPSOMMING: Wisselbou bied 'n moontlike alternatief vir koringmonokultuurverbouing in die Middel Swartland waar boerdery omstandighede sedert 1996 toenemend moeiliker word weens dalende winsmarges. Wisselbou as sulks bied verskeie voordele ten opsigte van verhoogde opbrengste vir veral koring wat in die wisselboustelsel voorkom, sowel as insetbesparings ten opsigte van hoofsaaklik bemesting en spuitprogramme. Wisselbouproewe word tans op Langgewens Proefplaas onderneem om wisselboustelsels waarin kanola en lupien as wisselbougraangewasse en medies en medics/klawer kombinasies as wisselbouweidingsgewasse saam met koring ondersoek word. Die proef is geskeduleer om oor 'n 20 jaar tydperk uitgevoer te word, maar 'n voortydige finansiële ontleding van die verwagte effek wat wisselbou vir die tipiese plaas kan inhou, kan waardevol wees vir besluitnemers in die betrokke bedryf Weens 'n tekort aan toepaslike betroubare inligting is van 'n multidissiplinêre span van kundiges gebruik gemaak om inligting ten opsigte van sekere aspekte van wisselbou te genereer. So kan die verwagte winsgewendheid van die geïdentifiseerde wisselboustelsels bepaal word. Ten einde die finansiële implikasies van gewaswisselbou relatief tot koringmonokultuurverbouing op plaasvlak te ondersoek, is van 'n tipiese plaasmodel gebruik gemaak wat met behulp van die paneel kundiges ontwikkel is. 'n Tipiese plaas van 630 ha is gebruik as ontledingsmodel. Die verwagte winsgewendheid en finansiële implikasies van die implementering van eik van agt verskillende wisselboustelsels is beraam deur middel van langtermyn begrotings. Reënval en reënvalverspreiding is geïdentifiseer as die faktore wat die grootste invloed op die opbrengs prestasie van gewasse in die betrokke omgewing uitoefen en is in ag geneem met die beraming van die finansiële prestasie van die stelsels oor die langtermyn. Die berekeningstermyn is gevolglik ingedeel in goeie, gemiddelde en swak reënvaljare ten einde die invloed van reënval op die opbrengste van die verskillende gewasse in ag te neem. Die lOK (interne opbrengskoers van kapitaal) is gebruik as finansiële maatstaf vir die meet van die winsgewendheid van eike wisselboustelsel, soos geïmplementeer op die tipiese plaas. Wisselboustelsels met kanola en lupien saam met koring toon goeie finansiële resultate, terwyl stelsels met weidingsgewasse en koring oor die algemeen meer winsgewend vertoon as koringmonokultuur.Na verwagting behoort die stelsel waar koring en medics/klawennengsel afgewissel word, die beste te vaar ten opsigte van winsgewendheid.

Research tasks. To accomplish the research objective, the following tasks were set: 1. To establish the effect of long-term reduced tillage on soil productivity (physical, chemical and biological properties); 2. To determine the conditions of agrocenosis components’ competition for solar radiation; 3. To identify the influence of tillage intensity on weed incidence in a crop stand; 4. To ascertain the impact of tillage of different intensity on the productivity of agrocenoses (yield, 1000 seed weight, etc.) and on biometric indicators (plant height, maize ear length). / Tyrimų uždaviniai. Tyrimų tikslui pasiekti numatyta nustatyti: 1. Ilgalaikio žemės dirbimo supaprastinimo įtaką dirvožemio derlingumui (fizikinėms, cheminėms ir biologinėms savybėms); 2. Agrocenozės komponentų konkurencijos dėl saulės spinduliuotės sąlygas; 3. Žemės dirbimo intensyvumo poveikį pasėlio piktžolėtumui; 4. Skirtingo intensyvumo žemės dirbimo poveikį agrocenozių produktyvumo (derlingumas, 1000 sėklų masė ir kt.) bei biometriniams rodikliams (kukurūzų augalų aukštis, burbuolių ilgis).

Soil phosphorus (P) is often unavailable in SK soils due to immobilization by microbial biomass and complexation with cations. The prohibition of synthetic fertilizer use in organic systems means farmers rely on crop rotation or approved inputs to supply P for crops. Legumes in crop rotation add P to soil through decomposition and deposition, and approved fertilizers such as bone meal (BM), rock phosphate (RP), and composted manure add P to soil through dissolution. Arbuscular mycorrhizal fungi (AMF) improve crop access to soil P. The fungi colonize roots of host crops, allowing roots to reach immobile pockets of soil P. Colonization by AMF is usually decreased or delayed following partial fallow periods, non-host plants, and the addition of soluble P fertilizers. This thesis consists of two studies. For the first, the effects of crop rotation were tested on AMF colonization and soil P dynamics. Colonization by AMF of mycorrhizal crops was examined following a non-mycorrhizal crop, a partial fallow period, and mycorrhizal crops. All crops were colonized evenly (63-70%) at flowering despite non-mycorrhizal and partial fallow periods, and the sequence most depleted in soil N (wheat-barley) had the lowest colonization in August (36%). The second study evaluated soil P and plant N and P after applications of BM, hydroxyapatite (HAP), and sheep manure compost. Compost application increased plant P uptake compared to the control (1.26 vs. 0.71 mg pot-1), while applications of BM and HAP alone did not. Compost application did not affect AMF colonization of wheat (Triticum aestivum L.). Overall this research highlights the importance of legumes and composted manure use in organic systems. Legume use in crop rotation simultaneously increased soil P deposition and may have preserved AMF communities despite fallow periods and non-host crops in rotation. Conditions normally affecting AMF colonization in conventional systems did not apply. The use of composted manure in the greenhouse study resulted in the greatest P uptake and concentrations in wheat. Thus the use of legumes and composted manure may increase P availability to crops directly and indirectly: directly through soil P deposition and perhaps indirectly through the preservation of AMF communities.