Effects of organic and inorganic phosphorus sources on agronomic performance, microbial communities and forage quality of silage corn cultivated under cool climatic conditions

Ali, Waqas (2018) Effects of organic and inorganic phosphorus sources on agronomic performance, microbial communities and forage quality of silage corn cultivated under cool climatic conditions. Masters thesis, Memorial University of Newfoundland.

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Abstract

Phosphorus (P) is a limiting nutrient for crop growth and yield on more than 30% of the world’s arable land, and by some assessments, global resources of mineral P might be depleted by 2050. Additionally, P fertilizer application to soil is predominantly bound to Al⁺³ and Fe⁺² in acidic soils or with Ca⁺² in alkaline soils, thereby reducing its availability to agricultural crop. Therefore, P availability in soil rhizosphere and efficient utilization by agricultural crops is vital for economic and environmental reasons. Dairy manure (DM) is an important source of macro and micro nutrients, and organic matter which can affect minerals solubility and plant nutrients availability by improving soil physiochemical properties, enzymes activities and soil microbial communities. To further enhance our understanding about the effects of organic and inorganic P fertilizer sources on growth, forage yield and quality of silage corn, soil biochemical attributes and microbial communities, a field experiment was carried out at Pynn’s Brook Research Station (PBRS) for two years (2016 and 2017). Experimental treatments were four P sources: [P₁: manure with high P conc.; P₂: manure with low P conc.; P₃: inorganic P and P₀ (control)] and five silage corn genotypes laid out in Randomized Complete Block Design (RCBD). Agronomic performance (leaf area, chlorophyll contents, photosynthesis, shoot dry weight, root shoot ratio and dry matter yield), rhizosphere soil biochemical attributes (pH, phosphatase activity and soil available P), and microbial community composition and forage quality parameters [(minerals, protein, sugar, fibers, non-fibrous carbohydrates (NFC), total digestible nutrients (TDN) and energy] were measured. Yukon R and DKC26-28RIB showed superior agronomic performance and produced higher dry matter yield compared to other genotypes. High P manure application increased the dry matter yield by 28% and 33%, acid phosphatase activity by 29% and 44%, soil available P by 60% and 39% compared to control in 2016 and 2017 respectively. High P manure application significantly increased active Gram negative (G-) bacteria, active fungi, total active bacterial phospholipids fatty acids (PLFAs), and active soil microbial biomass (total amount of PLFAs) compared to inorganic P and control treatments. Yukon R and DKC26-28RIB showed higher active fungal biomass, bacteria as well as total microbial activities in their root rhizospheres regardless of P sources compared to the other genotypes evaluated. Pearson correlation analysis demonstrated a positive and strong relationship between the active microbial community structure and the agronomic performance of the silage corn genotypes amended with P sources. The results indicate that DM application significantly enhanced agronomic performance, soil biochemical attributes and microbial communities compared to inorganic P fertilizer. Silage corn genotypes had significant effects on forage quality indices. Yukon-R and DKC26-28RIB showed superior agronomic performance and produced higher forage production of 16.43 and 15.47 Mg ha⁻¹ respectively. Contrarily, A4177G3RIB produced higher minerals, protein, total digestible nutrients (TDN), net energy for maintenance (NEM) and net energy for gain (NEG) compared to other genotypes, and proved high quality forage. However, it was statistically at par with DKC26-28RIB in producing minerals and ranked 2nd in protein synthesis. Yukon R was also statistically at par with A4177G3RIB genotype in few quality indices and produced similar TDN, NEM and NEG. Overall, Yukon‒R produced high forage and was either at par or ranked at 2nd position in most of the quality forage indicators. Phosphorus sources had significant effects on crude protein (CP), available protein (AP), sugars, and non-fibrous carbohydrates (NFC) contents of silage corn but not significantly higher with each other. Inorganic P fertilizer source enhanced CP, AP, simple sugars and NFC contents but statistically at par either with manure with high or low P. Phosphorus sources had non-significant effects on energy parameters, which are important indicator of high forage quality, however NEL, NEM and NEG values were slightly higher with DM application compared to inorganic P and control. Dairy manure application significantly improve the agronomic performance, silage corn quality, soil physiochemical properties and soil microbial communities. Future studies needed to investigate the effects of organic and inorganic P amendments on soil phenolics and root exudates on P availability and microbial community structure.

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