Fertilizer ^(15)N Accumulation, Recovery and Distribution in Cotton Plant as Affected by N Rate and Split

N fertilization of 300 kg N ha-1 is normally applied to cotton crops in three splits： pre-plant application （PPA, 30%）, first bloom application （FBA, 40%） and peak bloom application （PBA, 30%） in the Yangtze River Valley China. However, low fertilizer N plant recovery （NPR） （30-35%） causes problems such as cotton yield stagnation even in higher N rate, low profit margin of cotton production and fertilizer release to the environment. Therefore, it is questioned： Are these three splits the same significance to cotton N uptake and distribution？ An outdoor pot trial was conducted with five N rates and 15 N labeled urea to determine the recovery and distribution of 15N from different splits in cotton （Gossypium hirsutum L. cv. Huazamian H318） plant. The results showed that, cotton plant absorbed fertilizer 15N during the whole growing period, the majority during flowering for 18-20 d regardless of N rates （150-600 kg ha-1）. Fertilizer 15N proportion to the total N accumulated in cotton plant increased with N rates, and it was the highest in reproductive organs （88% averaged across N rates） among all the plant parts. FBA had the highest NPR （70%）, the lowest fertilizer N lose （FNL, 19%）, and the highest contribution to the fertilizer 15N proportion to the total N （46%） in cotton plant, whereas PPA had the reverse effect. It suggests that FBA should be the most important split for N absorption and yield formation comparatively and allocating more fertilizer N for late application from PPA should improve the benefit from fertilizer.

Use of Several Plant Materials and Chemicals to inhibit Soil Urease Activity and Increase Nitrogen Recovery Rate of Urea by Plant

Effects of residues of 9 plants, lemon eucalyptus (Eucalyptus citriodoraHook., P_1), robust eucalyptus (E. robusta Smith, P_2), Nepal camphortree (Cinnamomum glanduliferum(Wall.) Nees, P_3), tea (Camellia sinensis (Linn.) O. Ktze. f., P_4), oleander (Nerium indicum Mill,P_5), rape (Brassica campestris L., P_g), Chinese tallow tree (Sapium sebiferum L., P_7), tung(Vernicia fordii (Hemsl.), P_8), and croton (Croton tiglium L., P_9), 7 chemicals, boric acid (C_1),borax (C_2), oxalic acid (C_3), sodium oxalite (C_4), sodium dihydrogen phosphate (C_6), sodiumsilicate (C_7) and sodium citrate (C_8), and a natural organic substance, humic acid (C_5), onurease activity of a neutral purple soil and recovery of urea nitrogen by maize were studied throughincubation and pot experiments. Hydroquinone (HQ) was applied as the reference inhibitor. Afterincubation at 37℃ for 24 h, 7 inhibitors with higher ability to inhibit urease activity wereselected and then incubated for 14 days at 25℃. Results of the incubation experiments showed thatsoil urease activity was greatly inhibited by them, and the inhibition effect followed an order ofP_2>P_4>C_3>C_2>P_3>C_1>HQ>P_1. The 7 selected materials reduced the accumulative amounts of Nreleased from urea and the maximum urease activity by 11.7%～28.4% and 26.7%～39.7%, respectively,and postponed the N release peak by 2～4 days in the incubation period of 14 days under constanttemperature, as compared to the control (no inhibitor). In the pot experiment with the 7 materialsat two levels of addition, low (L) and high (H), the C_1 (H), C_3 (H), C_1 (L), P_4 (L) and C_2 (L)treatments could significantly increase the dry weights of the aboveground parts and the totalbiomass of the maize plants and the apparent recovery rate of urea-N was increased by 6.3%～32.4% ascompared to the control (no hibitor).

Recovery of fertility in quinestrol-treated or diethylstilbestroltreated mice:Implications for rodent management

Fertility control is an alternative strategy to traditional culling for the management of rodent pests.Previous studies have demonstrated that quinestrol is a potential contraceptive for male rodents,but the recovery of fertility in quinestrol-treated rodents has not been evaluated.This study used C57BL/6J mice to evaluate the recovery rate of male fertility after the administration of quinestrol.Diethylstilbestrol(DES),a non-steroid estrogenic compound,was used for comparison.Different groups of mice were treated with 1 mg/kg quinestrol,1 mg/kg DES,or castor oil separately for 7 days.These mice were then killed on days 8,22 and 50 respectively.Our results indicated that the weight of epididymides and seminal vesicles decreased significantly on days 8 and 22 in quinestrol/DES-treated mice,with extensive histological changes in the seminiferous tubules.Sperm concentrations in the cauda epididymal fluid were significantly reduced on days 8 and 22 in both quinestrol and DES treatment groups and on day 50 for the DES,but not the quinestrol group.Further analysis revealed that DES-treated mice exhibited a higher proportion of abnormal sperm accumulation in the epididymis,indicating that the normal sperm transportation to the cauda epididymis was blocked.Our results indicate that the anti-fertility effects on male mice given quinestrol were of shorter duration than for those receiving DES at the dose of 1 mg/kg body weight.