Effects of fertiliser applications on survival and recruitment of the apple snail,Pomacea canaliculata (Lamarck)

Since its introduction to Asia in the 1980s, the golden apple snail, Pomacea canaliculata (Lamarck), has represented a major constraint to the profitability of rice (Oryza sativa L.) farming by damaging rice seedlings during crop establishment. This study describes a series of experiments designed to determine the effects of nitrogenous fertilisers on snail fitness. We examined the possibility of a two-phase model of snail response to nitrogen, whereby fertilisers initially increase snail mortality through toxicity, but once assimilated into the rice ecosystem, eventually favour snail reproduction and survival. In experimental arenas, fertiliser had lethal effects: Complete fertiliser (14:14:14), urea, ammonium sulphate and organic fertilisers were associated with snail mortality, generally affecting adult snails more than juvenile snails, and with greater effects when applied to saturated soil that was subsequently flooded (as opposed to direct application to flooded soil). Snail mortality was found to decline considerably when snails were added to arenas one day after fertiliser application – this occurred in arenas with soil and water, but not in arenas with water only, suggesting that soil can reduce the toxic effects of fertilisers. In a field experiment, snail numbers declined in both fertilised and non-fertilised plots at the time of crop establishment. Numbers increased in all plots after rice tillering, with significantly more recruitment in plots with high nitrogen. Although the responses were generally weak in the field experiment, they did support the two-phase model. The consequences of fertiliser applications for snail management and ecosystem health are discussed.     

The Effect of Different Nitrogen Sources from Urea and Ammonium Sulfate on the Spikelet Number in Egyptian Spring Wheat Cultivars on Well Watered Pot Soils

Abstract

The spikelet number (SPN) is an important wheat yield component decided before anthesis. Our objective was to determinethe effect of nitrogen (N) from urea and ammonium sulfate split-applied at different rates before anthesis on the SPN in the recent Egyptian cultivars Sakha93 and Sakha94 and two commonly used cultivars in pots. The response of SPN to applied Nfrom ammonium sulfate was higher than that from urea in all four cultivars used. However, there was no difference in the responses of SPN to absorbed N from the two fertilizers in any of the cultivars. The SPN per applied and absorbed N was thehighest in Sakha94 among the four cultivars. These cultivar differences in the SPN were due to the difference in the spikenumber. The results suggested that the N from ammonium sulfate has a greater effect on SPN than that from urea in recent Egyptian cultivars.     

低毒脲醛胶用于杨木胶合板的研究

本文以五种杨木单板为试材研究了低毒不脱水脲醛树脂Ｐ２ＨＳ－５的胶合性能。无论采用相同或不同树种的杨木单板组坯制造胶合板均能得到理想的胶合强度。固化剂的用量对胶事强度影响较大，可根据杨木的树种作适当调整。     

尿素改性酚醛树脂胶粘剂的研究

利用尿素与苯酚和甲醛三元共缩聚的方法来提高酚醛树脂的固化速度。通过PF与PUF树脂的DSC分析表明,PUF在缩聚时放热峰的起始温度低于PF。PUF树脂在低于PF树脂25℃的固化温度下就能固化完全。在相同的固化温度下,PUF树脂的固化速度要快于PF。用PF和PUF制得的刨花板物理力学性能均达到德国建筑用刨花板标准DIN 68763 V100的要求,PUF刨花板的热压时间可以比普通酚醛胶刨花板缩短35％。当尿素替代苯酚量为25％-30％时,合成胶粘剂的成本可降低15％-20％。     

DDS改善胶合板用低摩尔比UF胶的预压性能

针对现在胶合板用低摩尔比的脲醛树脂胶(UF)预压性能差的问题进行了研究，试验结果表明，用DDS添加剂和RN阳离子表面活性剂的组合能明显改善UF胶的预压性能。     

添加物对粪肥堆腐过程中尿囊素含量的影响

研究表明,加入尿素、苜蓿根粉等含氮添加物,能显著提高粪肥中尿囊素（Ａｌｌ）的含量,幅度为１０．５％～２２．５％,并在堆腐后期减缓Ａｌｌ含量的降低速率。蛋白质和核酸的变化能影响Ａｌｌ的含量,通径分析表明,蛋白质对Ａｌｌ的累积直接贡献大,其直接作用系数均在０．９以上,核酸的直接作用较小,其直接作用系数在０．０５以下,两者的间接作用都小。加入含氮添加物能提高Ａｌｌ含量,主要是因为提高了微生物的活性,促进了Ａｌｌ的生物合成。     

不同水平尿素、氢氧化钙对玉米秸纤维含量的影响

为探讨不同水平尿素、氢氧化钙对玉米秸纤维含量的影响,本试验将尿素和氢氧化钙均按玉米秸风干重0%、2%、3%和4%的量分别添加,共16组,其中原玉米秸组为对照组,通过测定各组玉米秸的中性洗涤纤维和酸性洗涤纤维含量来确定尿素和氢氧化钙最适宜的添加水平。结果表明,试验组在中性洗涤纤维和酸性洗涤纤维含量上均极显著低于对照组(P<0.01),大部分试验组间也存在极显著或显著的差异(P<0.01或P<0.05)。在本试验设计条件下,尿素和氢氧化钙处理玉米秸时最适宜的添加水平分别为玉米秸风干重的4%和2%。     

施用尿素、有机-无机复混肥和包膜有机肥对几种水稻田土表水层pH的影响

采用不同类型的3种水稻田土壤进行模拟培养,研究施用尿素、有机-无机复混肥和包膜有机肥对土表水层pH变化的影响。实验表明:淹水培养5天以后土表水层pH变化趋势明显。水稻田土壤类型不同,培养期间土表水层pH变化差异显著。在培养后5～15天期间,不施肥对照、施用包膜有机肥处理和施用复混肥处理,红壤、灰潮土和盐碱土土表水层pH都明显上升;施用尿素处理在灰潮土和盐碱土上土表水层pH值略微下降,而在红壤上仍呈上升趋势。     

袋控缓释条件下硝态氮、铵态氮对桃尿素吸收、分配的影响

采用15N示踪技术,在袋控缓释条件下,研究不同形态氮素对当年生毛桃尿素态氮吸收分配的影响。结果表明:单独尿素处理、尿素与硝态氮混施、尿素与铵态氮混施,尿素与硝态氮、铵态氮按1∶1∶1混施4个处理15N利用率分别为13.81%、10.92%1、5.53%和15.78%,尿素与铵态氮混施、尿素与硝态氮、铵态氮1∶1∶1混施显著高于其它处理,均能提高植株对尿素态氮的吸收利用;而尿素与硝态氮混施,15N利用率显著低于其它处理,降低了植株对尿素态氮的吸收利用。从15N在植株不同器官的分配来看,各处理植株叶片的15N分配率最高,均占植株总吸收量的60%以上,其它依次为根主干枝梢。植株总吸氮量以尿素与铵态氮混施处理最高,但该处理表观生长量低于尿素与硝态氮混施处理。     

Effect of strategies regarding concentrate supplementation and day-time grazing on N utilization at both field and dairy cow level

N utilization at cow and field level was examined over two grazing periods of 30 days with 64 Holstein dairy cows. At cow and field level the effect of sward type (diploid vs. tetraploid perennial ryegrass, both mixed with white clover) and compressed sward height (6 vs. 10 cm) was examined. At dairy cow level the effect of urea supplementation (0 vs. 145 g/day) and energy supplementation strategy (soy hulls(am)/barley(pm) vs. barley(am)/soy hulls(pm)) was also examined. Cows grazed grass/clover swards for 7.5 h/day and were restrictively fed in the barn (3.2 kg dry matter (DM) in maize silage, 3.6 kg ground barley, 3.6 kg soy hulls per day). In none of the two periods were yield of milk (Period 1: 30.9 kg, Period 2: 25.4 kg), fat, protein and lactose significantly affected by sward type, sward height, urea supplementation or energy supplementation strategy. Urea supplementation increased the urea concentration in milk. Also low sward height and feeding soy hulls(am)/barley(pm) increased the urea concentration, probably due to a higher protein content in the sward and a higher grass intake, respectively. N utilization at cow level was highest with high sward height and no urea supplementation. Feeding soy hulls(am)/barley(pm) increased milk yield numerically but was counterbalanced by an equivalent increase in estimated grass intake, and supplementation strategy seemed therefore not to affect N utilization. At field level the N surplus was higher on diploid than on tetraploid swards (50 and 21 kg N/ha) due to a higher clover content in the diploid swards, whereas the difference in N surplus between sward heights was minimal (32 and 38 kg N/ha). Estimated N removal from the pasture in the grazing periods (intake minus excretion) increased by 5.2 kg N/ha when feeding soy hulls(am)/barley(pm), whereas with no urea supplementation the net N removal increased by only 2.5 kg N/ha. It was concluded that N utilization in dairy cows can be improved by decreasing N intake from both herbage and supplementary concentrate without compromising milk yield, and that N balance at field level could be improved by strategic barn feeding.