Broadbent, Francis

Christensen, L. Peter : L. Peter Christensen is Farm Advisor, Fresno County.

Peacock, William L

inorganic N in the soil was followed by Late - fall nitrogen application samplingthe profile to a depth of 4 feet in in - 0to 0.5 , O.Sto 1 , l to 2,2to 3 , and 3 crements in vineyards is inefficient to 4 feet . Soil cores were taken from four locations in each plot , and the cores compo - sited for laboratory analysis . Soil samples William L . Peacock 0 Francis E . Broadbent 0 L . Peter Christensen were taken from the Delhi location on De - cember 4 , 1979 , and on April ll and May 23 , Sampling dates at the Greenfield site 1980 . were December 6 , 1979 , and April 13 and May 23 , 1980 . Soil sampleswere immediately frozen and stored in a freezerbefore analysis . In the laboratory , inorganic N , consisting of ammonic and nitrate forms , was extracted and the isotopic composition determined to identify the portion derived from the added fertilizer . N concentrations in soils As expected , with no fertilizerapplication , inorganic N concentrations in the Delhi sand profile remained low at all sampling times vary greatly with depth ( fig . 1 ) . and did not During the 25 days between the November 4 fertilizer application and the December sampling , 0.70 inch of rain fell . The Decem - ber samplingreflects the November fertilizer application : no appreciable leaching had occurred . By April 11 , 1980 , however , when 10.7 inches of rain had fallen since the No - vember fertilizer application and the grower Grapevines are fertilized with nitrogen available for use by the plant when it breaks 3 to 4 inches of had applied an additional ( N ) in amounts intended to promote proper dormancy the following spring . This assump - water for frost protection , all evidence of the shoot , leaf , and berry development and to tion is based on the relativelylow winter rain - November fertilizer application had disap - provide for maturation of the crop . The need fall of the southern San Joaquin Valley , but peared . In the case of the March - applied fer - N is greatest during rapid shoot growth in for experimentaldata to support it are lacking . tilizer , which had received 0.34 inch of rain the spring through the berry development A study to evaluate the relative leaching 3 to 4 inches of irrigation water , the April and stage , then diminishes after mid - summer and denitrification losses of late - fall and 11 sampling revealed a surface inorganic N when ripening begins . Application should be spring applications of N to vineyards was concentration somewhatlower than the max - timed to ensure an adequate N supplyduring conducted in 1979 - 80at two locations , one in imum observed with the November applica - spring development , but available N in late Fresno County on Delhisand and the other in tion to this soil . By May 23 , even the spring summer should not be high enough to en - Tulare County on Greenfield sandy loam . application had disappeared . Presumably all courage late - season shoot growth , delay a Delhi sand is a wind - deposited soil with the fertilizer N appliedin March had been ab - maturity , and promote immature canes . Fer - deep , uniform , well - drained profile . Green - or leached below 4 feet . sorbed by plants tilizer N should also be used to maximize field sandy loam absorbs water readily , but The Greenfield - sandy - loam location re - uptake efficiency and minimize losses by drainage is impeded by a hardpan at 4 feet . ceived approximately the same amount of volatilization and leaching . Immediateincor - Both vineyards are in mature Thompson as the Delhi site . Vines were irrigated rainfall of all ammonic fertilizers can greatly poration Seedless grapes produced for raisins . for frost protection in the last week of of reduce volatilization . Appropriate timing A randomized complete block design was March , and two additional irrigations total - nitrogen application and avoiding over - used with five blocks and three treatments . 8to 12 incheswere appliedbefore the May ing application of water can decrease leaching 12 by 24 Plots , with four vines each , were 23 sampling.Inorganic N after the November and denitrification . feet . Treatments consisted of the unfertilized fertilizer application was high near the sur - Fall application of nitrogen fertilizer in the control , 100 pounds N per acre applied No - 13 concen - face on December 6 , but by April San Joaquin Valley is convenient for the vember 9 , 1979 , and 100 pounds N per acre trations were not much different from those grower and has increased in popularity in re - applied March 12 , 1980 . The fertilizer was of the control soil . By May 23 , concentra - cent years . It allows better use of time and " N - depleted ammonium sulfate , isotopically tions had increaseda littlein the surface2 feet labor , and the grower can take advantage of labeled to permit distinction between fertil - because of mineralizationof soil N astemper - lower fertilizer prices when working condi - soil nitrogen . It was applied in a izer and atures increased . In the case of the March tions in the vineyard are good . It has been a 6 - foot strip on each side of the row by 13 sampling reflected application , the April N applied in the late fall re - assumed that hand - held boom on a backpack sprayer and of fertilizerto the soil . By the recent addition mains in the root zone over the winter and is then incorporated by disking . Distribution of May 23 some downward displacement of this 22 CALIFORNIA AGRICULTURE , JANUARY - FEBRUARY1982 fertilizer had clearly occurred , but most of the N remained within the surface 4 feet of soil . Fertilizer - derivedN Figures 1 and 2 reflect the combined fertilizer and soil N present in the profile . Figure 3 shows concentrations of fertilizer - derived N , calculated on the basis of isotopic data . In Greenfield sandy loam , high concentrations of November - applied fertilizer were present in the December sampling , whereas by April of this N had disappeared . and May most Fertilizer applied to this soil in March was displaced downward between the April and May samplings . In the Delhi soil the concentration of fer - tilizer N in the surface 6 inches of soil receiv - ing a November application decreased from 22 parts per million ( ppm ) on December 4 to less than 1 ppm by the following April . Where Delhi sand received fertilizer in March , someleachinghad occurred by April , 23 fertilizer N throughout the and by May profile had dropped to a very low value . Discussion Thesedata indicatethat ammonic nitrogen applied in the late fall was subject to severe leaching losses by normal rainfall and irriga - tion between November and May . Soil tem - perature was not low enough during the winter to retard nitrification significantly . This study suggests that N should be applied ir - in the spring just before frost - protection rigation on loam or sandier soils . Subsequent imgation will leach the N into the root zone for uptake during the most critical period of need . On very sandy soils , such as the Delhi sand , it would be useful to split the fertilizer application , with half applied in March and the remainder in May . of the Still unanswered is the question value of early - fall application ( September to mid - October ) , when the vines may be active of N enough to take up a significantamount and store it in canes , trunk , and roots . There as to whether this uptake can be is concern accomplished without stimulating undesir - able late shoot development . Further study is in progress to develop information on sum - mer and early - fall fertilizer application to grapes , but present evidence suggests that late - fall fertilization is highly inefficient . WilliamL . Peacock is Farm Advisor , Coopera - tive Extension , Tulare County , Visalia ; Francis E . Broadbent is Professor of Soil Microbiology , Department ofLand , Air , and WaterResources , University of California , Davis ; and L . Peter Christensen is Farm Advisor , Fresno County . CALIFORNIA AGRICULTURE , JANUARY - FEBRUARY1982 23