A THESIS SUBMITTED FOR THE DEGREE OF MASTER OF SCIENCE IN AGRICULTURE AT THE UNIVERSITY OF NEW ENGLAND

JULY, 2012

Abstract

Sulfur (S) is an important macronutrient needed for the normal crop performance. As S in an essential constituent of protein, S deficiency results in a limitation in protein synthesis. Sulfur deficiencies are becoming more common because of the cultivation of high yielding crop cultivars, intensive cultivation, application of fertilisers with little S or no S, cleaner atmospheres as well as reduction in retention of crop residues. Many fertiliser materials contain S either as sulfates-S and/or elemental-S source with sulfate-S the most common form.  S is mostly a component of what are generally considered N or P fertilisers such as ammonium sulfate, single superphosphate, potassium sulfate or as a component of multi-nutrient fertilisers. Gypsum is often un-economical as it does not contain macronutrients other than calcium. Elemental sulfur (S⁰ or ES) containing sources provide the most concentrated S fertilisers. Modern technologies have enhanced the capacity for direct application of S⁰or as additives to NPK sources. There is S⁰are a diversity of S⁰ containing fertilisers including granulated sulfur bentonite, S⁰ modified N/P fertilisers, sulfur coatings and liquid sulfur fertilisers.

The objectives of these glasshouse studies werefirstly to determine any residual effect of different S sources on maize that had been applied three crops earlier in a previous project and secondly to evaluate the initial response to S from a rage of sources in flooded rice and maize. In the first part of the current project (chapter 3) was to grow a crop of maize in the same pots that had grown three previous crops and which had been stored for two years. The experiment was a randomized block pot experiment with four replicates with six fertilisers S sources namely, gypsum, ES<53µm, ES<106µm, ES<75µm, TSPS, MAP12,withTSP and un-fertilised controls. Total S application of 20kg S/ha was applied in the S treatments in the first crop and none for crops 2 and 3. An application of 5 kg S/ha as ammonium sulfate was applied to all treatments when the fourth crop was planted. Four germinated maize seeds were sown into the pots on 25 January 2012, thinned to two plants per pot after 5 days and harvested on 24 February 2012 (28 DAT) in glasshouse of University of New England. The temperature of the glasshouse was maintained at 20-30⁰C throughout the experiment. The pots were watered daily to field capacity by weighing until harvested. The tops of plant were cut approximately 1.5 cm above the soil surface, dried at 60⁰C until a constant weight and prepared for analysis for and total S, as well as other macronutrients and micronutrients by Inductively Coupled Plasma Optical Emission Spectrometer (ICP-OES).

The results showed that all S fertilisers increased the maize tops yield over the control. The high initial response to gypsum and crushed ES<75µm was maintained throughout the trial such that these treatments had the highest apparent fertiliser S recovery at the end of the experiment. The low apparent fertiliser S recovery in the two granular fertilisers, TSPS and MAP12, may have been the result of lower uniformity of S distribution throughout the soil, differences in elemental S particle size within the granule and/or lower accessibility of the S within the granules.

In the second part of the study (chapter 4) two experiments were conducted. The first was with maize where eight S fertiliser sources were included namely; Super M12, TSPS, DAP-SEF, MAP-Modified, PastureKing, Pastille, S-bentonite, gypsum and one unfertilized S control. The experimental design was a randomised block with three replicates. Two plants per pot were grown for 33 days with the soil moisture maintained near field capacity and the temperature of the glasshouse maintained at 20-30⁰C. The maize was harvested by cutting plants 1.5cm above the soil surface, dried and ground and chemical analysis of the tops performed as in the residual maize experiment.

The results of this study revealed that the application of S fertiliser increased the tops dry matter yield. The effectiveness of gypsum was equal to that of fertilisers containing a mixture of elemental S and sulfate-S. S bentonite and S-pastille elemental S containing fertilisers were found to be ineffective S fertilisers in this short-term study.

In the second experiment reported in Chapter 4 a pot experiment with flooded rice was carried out in the same glasshouse as the maize experiment and it consisted of a -S control, MAP modified, Super M12, DAP-SEF and PastureKing treatments and was a randomized block design with three replicates. Three germinated seeds of rice were sown each pot and the pots maintained in a flooded condition until near maturity. Plant tops were cut approximately 3 cm above the soil surface and separated into filled grain, unfilled grain and straw+panicle and the samples dried and ground before being analysed in the same way as the residual maize experiment.

The rice data showed that there was a sulfur response with all four S fertilisers. A mixture sulfate and elemental sulfate sources coated on the outside of MAP granules (MAP modified) was found to be better than elemental sulfur or sulfate containing sulfur sources where the S is incorporated into the granule. Because roots were not analysed it is not possible to calculate the total recovery of fertiliser S so no calculation can be done to estimate the amount of elemental S oxidized but the generally low apparent S recoveries recorded in the elemental S containing fertilisers suggests little S oxidation occurred in this rice experiment.

The results of these experiments, carried out in the glasshouse, indicate considerable differences in the ability of S fertiliser sources to provide adequate S to maize in the short and long term and in a single rice crop. Field studies are needed to verify these results.