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Title: Nitrogen mineralisation and leaching losses from farm-yard manure under simulated centre pivot irrigation
Author: Almadini, Addukrahman Mohammad
Awarding Body: Cranfield University
Current Institution: Cranfield University
Date of Award: 1997
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Nitrogen (N) leaching losses resulting from agricultural activity are a major concern to researchers and land managers in different parts of the world, due to the adverse effects of dissolved nitrogen on the water environment and on farmers’ returns. In this study the effects of intermittent irrigation, such as that occurring under centre pivot irrigation, on leaching losses of nitrogen mineralised by micro-organisms from different application rates of farm-yard manure (from 0 to 80 t FYM ha ̄1) and N fertiliser (300 kg N ha ̄1) mixed with sand have been examined using pots and leaching columns. Different N species (Ammonium, NH4ᵻ-N; nitrate, NO3 ̄-N; and total soluble nitrogen, TSN) have been investigated in the effluent samples collected from the bottoms of the pots and columns. Initially, in the pot experiments the results showed that there were significant differences (P = 5%) between the amounts of nitrogen mineralised from the different FYM application rates under different wetting treatments. The moisture conditions had greater effects on nitrogen mineralisation than FYM application rates. However, the opposite was observed when the C:N ratio of the applied FYM was narrowed by the addition of urea as a N fertiliser. Nitrification did not occur in a mixture of FYM- sand (i.e., un-modified sand), which was attributed to the lack of nitrifying bacteria in the mixture. However, inoculating the mixture with a sandy loam field soil caused NO3 ̄-N to be the major N species in the effluent samples. In the leaching columns,NO3 ̄-N was the dominant nitrogen form found in the effluent. NO3 ̄-N concentration was significantly affected by the irrigation practices. The highest concentration (95 mg NO3 ̄-N ɭ ̄1) has been found for the treatment in which the top sections containing the applied FYM have been maintained at the field capacity moisture condition. A relationship between the frequency of water application and NO3 ̄-N movement in the soil columns was found. The amount of NO3 ̄-N leached from the soil columns wetted every four days > eight days > twelve days. This suggests that frequent irrigation practices leach NO3 ̄-N further in the soil profile increasing the possibility of NO3 ̄-N leaching beyond the root zone. In addition to water application practices, the start of NO3 ̄-N breakthrough was related to the moisture conditions of the soil columns. For the soil columns maintained continuously at the field capacity, 812 ml cumulative effluent was needed before the NO3 ̄-N breakthrough, compared to 610, 464, and 381 ml which were needed for the soil columns intermittently wetted for 4, 8, and 12 days, respectively. This indicates that more water is needed before NO3 ̄-N breakthrough under wet conditions than under dry conditions. The amounts of N leached from the soil columns were correlated with the ratio of effluent to water applied, suggesting that irrigation and drainage practices have an impact on NO3 ̄-N leaching losses. This study has demonstrated that there are relationships between the frequency of irrigation and N mineralisation and leaching losses from the applied FYM, which lead to the conclusion that minimum NO3 ̄-N leaching losses are likely to be obtained under irrigated, fields when adequate adjustments for the nitrogen mineralised from the applied FYM are made and proper irrigation scheduling is practiced. The best management of nitrogen, which aims to maximise crop yields and minimise environmental impact, is proposed for centre pivot irrigation in the Kingdom of Saudi Arabia.
Supervisor: Leeds-Harrison, Peter B. Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available