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

Fruit growers in Utah and other areas across the Intermountain West are faced with growing production challenges stemming from declining soil quality and water resources. Population growth presents challenges in terms of the cost and availability of land, but also presents opportunities in the form of new marketing options such as organic fruit. Few certified organic fruit orchards are operating in Utah currently, which is attributed to a lack of locally tested and adapted organic management practices. An organic peach orchard trial evaluated the effectiveness of different organic management approaches to enhance soil quality and conserve water without compromise to fruit tree growth and fertility. Two tree-row treatments: ‘straw mulch' (Triticum aestivum L.) and ‘living mulch’ (Lobularia maritima (L.) Desv.) were tested in combination with two alleyway groundcovers: ‘grass’ (Festuca rubra L. with Lolium perenne L.) and a legume, ‘Birdsfoot trefoil’ (Lotus corniculatus L.). The novel systems were compared with industry standards, tillage and weed fabric tree-rows with grass alleyways. Trefoil alleyway biomass deposited into tree-rows contributed an estimated 6.24 kg biomass and 0.21 kg total N/tree annually. Trefoil treatments had higher levels of organic carbon (C) and nitrogen (N), inorganic N, microbial biomass and enzyme activities, suggesting trefoil alleyways enhanced soil nutrient cycling, as well as C and N reserves in comparison to grass and tillage treatments. A functional gene array analysis was conducted to describe the mechanisms, microbial functional composition and diversity underlying the observed soil processes, however few differences were detected in soil community structure between soils under different orchard floor management. Significantly lower leaf δ15N in trees grown with trefoil compared to grass, and an association between root biomass, diameter and trunk cross-sectional area (TCSA) suggests nitrogen sources derived from the trefoil groundcover contributed to improved fruit tree vigor. Few differences resulted among orchard treatments for water use (mm/week). Trends indicated slightly higher water use in trefoil over grass, but not enough to offset observed soil quality and tree growth benefits. These findings suggest, trefoil alleyways may provide ecological benefits such as improved soil quality and efficient nutrient cycling, without substantial increases in water use.