Evaluation location: , United States
METHOD: Chemical Assay CONDITIONS: Field METHOD NARR: Seedlings were planted in rows and subjected to 2 Nitrogen treatments (0kg and 225kg N per ha). Nitrogen as ammonium nitrate was applied on three occaisions. Tubers, roots, shoots and fruits were collected seperately. After washing, the samples were oven-dried at 60C and the dry weight of the separate parts recorded. Total tissue N was determined conductimetrically, following a salicylic Kjeldahl nitrogen digestion procedure. Nitrogen uptake efficiency and percent N recovery were calculated. Wild accessions were ranked based on total dry matter accumulation and then categorized based on an efficiency index (E). RESULTS NARR: Total plant dry weight, N content and N concentration were significantly affected by N fertilizer and genotype. Nitrogen uptake efficiency was calculated as follows: NUE = (PN/SN) x (TDW/PN) = (TDW/SN) where (PN/SN) is (total plant N content/fertilizer N) and (TDW/PN) is (total dry weight of all plant parts/total plant N content). More simply, N use efficiency = (Uptake efficiency) x (Utilization efficiency) = (Yield efficiency). Efficiency index (E) = (TDWPN - TDWZN)/225 where TDWPN = total dry weight at 225kg N per ha and TDWZN = total dry weight at 0kg N per ha. If TDWZN greater than or equal to 300.00g, accession is Good Forager. If E greater than or equal to 10 g per g, accessions were Good Responders. AUTHOR EXPLANATION: Dry weight was found to be a good indicator of of N uptake. Poor tuber production by wild types was most likely due to the lack of short days. Authors suggest that higher N recovery by wild species could be due to deeper penetrating, denser and more branched root systems.