Acidification of < 1% of the effective root zone of a mature pecan tree (Carya illinoensis (Wanghenh.) C. Koch) significantly increased uptake of Zn into the tree and maintained elevated Zn in leaves for 9 years. Sulfuric acid and ZnSO4, applied in a shallow trench, lowered soil pH to a depth of 60 cm and increased volubility of Zn in the acid band. Large concentrations of CaSO4 were formed. Laboratory tests confirmed the movement and volubility of Zn in soils under conditions similar to those in the field. Tree roots did not grow into the acidified band, presumably due to high salinity, but proliferated extensively at the interface of the acidified band and calcareous soil.

Abstract. Volatile losses of NH 3 from surface-applied urea are known to decrease in the presence of soluble Ca-salts or with a decrease in easily decomposable organic matter content (EDOM), both of which influence urease activity. How these factors interact to affect NH 3 losses is not fully understood. Studies were conducted to determine the effect CaC12 in sand with varying rates of EDOM on NH 3 losses from surface applied urea. The same effects were examined on agricultural soils containing partially decomposed native organic matter (NOM). Determinations were made in the laboratory on field soils, sand free of organic matter and sand with known amounts of grass clippings (GC, EDOM). Low levels of GC in sand with low amounts of added urea resulted in little NH3 loss. Ammonia loss increased as more N was applied at the low levels of GC. The loss was independent of urea application rates at high levels of GC. Ammonia losses were reduced more effectively at low EDOM and NOM in the presence of Ca. Incubation of sand with GC at low rates prior to urea addition increased NH 3 losses relative to high levels of non-incubated GC. For the above situation incubation for as high as 24 days resulted in equivalent NH 3 losses. The amount and state of decomposition of existing organic matter affected the degree ofNH 3 loss from surface placed urea and its control by added Ca-salts. Microbial decomposition of EDOM, such as might occur in the spring prior to urea addition, led to greater NH 3 losses. Greater loss of NH 3 from urea might be an indication of a larger ureolytic microbial population leading to increased urease production,

Growth and flower and nut production were monitored in shoots of mature ‘Moneymaker’ pecan [Carya illinoensis (Wang) K. Koch] trees for 3 years in Georgia. Highest yield per tree was found when 60% of the shoots were in a 7- to 18-cm range. Low production was due to a failure to produce pistillate flowers. Longer shoots consistently produced more flowers and retained more nuts. Shoots growing from 1-year-old wood that was previously vegetative produced 26% more flowers at bloom and 32% more nuts at harvest than those growing on former fruiting twigs. Nuts per cluster increased stepwise with shoot length. Long shoots that fruited had a markedly decreased production the following year compared to those which were vegetative. It is proposed that the combined stresses of increased cluster size and minimal leaf area per shoot increase above 30 cm length reduced reserves necessary for flower differentiation the following year.

No abstract