Comparison of multivariate models and variable selection algorithms for rapid analysis of the chemical composition of field crops

This study evaluates the use of visible and near-infrared spectroscopy for rapid prediction of total carbon, total nitrogen, and total phosphorus concentrations in field crop samples. Two multivariate models (partial least squares regression and support vector machine regression) were compared. In addition, four spectral variable selection algorithms (competitive adaptive reweighted sampling, genetic algorithm, uninformative variable elimination, and variable importance for projection) were applied with support vector machine regression to determine the most accurate predictions. The results showed that support vector machine regression performed better than partial least squares regression for predicting the three chemical compositions. The combination of competitive adaptive reweighted sampling and support vector machine regression outperformed the other models for the predictions of total carbon and total nitrogen with high coefficients of determination of 0.91 and 0.90, respectively. For the determination of total phosphorus, the prediction accuracy of competitive adaptive reweighted sampling was comparable with the best result obtained from genetic algorithm with the coefficients of determination of 0.73 and 0.77, respectively. In conclusion, the support vector machine regression combined with competitive adaptive reweighted sampling has great potential to accurately determine the chemical composition of field crops using the visible and near-infrared spectroscopy.     

Effects of nitrogen feeding for extraradical mycelium of Rhizophagus irregularis maize symbiosis incorporated with phosphorus availability

In terrestrial ecosystems, plants are frequently in symbiosis with arbuscular mycorrhizal fungi (AMF) with mineral nutrients and photosynthesis carbon exchanges in between. This research sought to identify the effects of phosphorus (P) levels on the nitrogen (N) uptake via extraradical mycelium (ERM) and the mycorrhizal growth response (MGR) of maize plants within the AMF symbiosis. Pots were separated into root compartments and hyphae compartments (HCs) with two layers of a 30‐μm mesh membrane and an air gap in between, where only hyphae could pass through, to avoid both N diffusion and root growth effects. Maize plants were inoculated with Rhizophagus irregularis with different N fertilization in HCs under two different P fertilization levels. Our results indicated that a strong increase in MGR with low‐P fertilization. The same tendency was not observed with high‐P fertilization, although both had a large increase in P concentration as a potential source of growth in shoot tissue of mycorrhizal plants. Substantial effects (10.5% more N) were observed in the case of high‐P availability for the host plants from ERM fed with N, whereas under low‐P conditions ERM may prioritize P uptake rather than N uptake. The AM fungi increase the uptake of N and P, which are most limiting in the soil with fewer forces from soil resources. In addition, there was still more P accumulated than N due to the high N for ERM with high‐P supply. Low N in HCs corresponded with a lower colonization rate in roots but with high hyphae density in HCs; this result suggest that N and P availability might change the ratio of extraradical to intraradical hyphae length.     

基于稻田控水减排的氮肥运筹试验研究

为改善江汉平原地区稻田水肥管理措施,采用田间小区试验,研究了常规淹灌(CF)和浅灌深蓄(SIDS)条件下,农民习惯施肥(FFP)、30%尿素+70%控释参混肥(30%N+70%CRF)和优化减氮施肥(OPT-N)对水稻各生育阶段稻田氮磷流失特征、养分吸收和土壤养分积累的影响。结果表明:与CF处理相比,SIDS处理田间灌溉水量、总用水量、径流量和渗漏量分别降低41.7%,18.5%,45.8%和21.9%,降雨利用率增加16.2%,TN和TP径流流失量分别降低32.6%~35.9%和36.4%~53.1%,渗漏流失量分别降低22.8%~32.0%和16.2%~33.3%,水稻返青期—拔节孕穗期分别占稻田氮磷径流和渗漏流失总量的70%以上。30%N+70%CRF处理、OPT-N处理较FFP处理,TN径流流失量分别降低19.7%~29.2%,15.1%~25.2%,渗漏流失量分别降低25.4%~51.7%,20.9%~26.4%,TP渗漏流失量分别降低18.4%~24.5%,20.4%~31.6%,但TP径流流失量差别很小。从水稻养分吸收和土壤养分积累来看,SIDS处理实际产量相对CF处理可增产4.4%,但对0—40cm土层氮磷养分累积影响不大,30%N+70%CRF处理和OPT-N处理相对FFP处理可增产5.6%和0.4%,且0—20cm土层速效态氮磷养分能维持在一个较高且相对稳定的水平。综上,浅灌深蓄结合30%N+70%CRF施用有利于稻田节水、减少氮磷流失、水稻增产以及土壤肥力改善。     

不同施肥处理对三峡库区柑橘园土壤氮磷淋失影响

在2017年8月利用原状土柱模拟淋溶试验对三峡库区秭归县柑橘园土壤的氮磷淋溶流失进行研究,探讨不同施肥处理对土壤氮、磷淋失的影响,为三峡库区农业面源污染的防控提供理论依据。试验设置6个处理,分别为不施肥处理(T0)、减量施肥(T1)、常量施肥(T2)、增量施肥(T3)、常量复合肥A施肥(T4)和常量复合肥B施肥(T5)。结果表明:(1)不同施肥处理下,柑橘园土壤淋滤液中总氮(TN)、总磷(TP)、硝态氮(NO_3~-—N)和铵态氮(NH_4~+—N)的淋溶浓度范围分别为37.16~163.07,0.61~6.69,27.54~79.38,2.37~7.10mg/L。(2)施肥量和施肥种类皆为土壤中氮磷淋溶的影响因素。在相同施肥种类下,土壤氮磷淋溶浓度随施肥量增加而显著增加,但施肥量高到一定程度后,淋溶浓度增长幅度会降低。在相同施氮量下,硝态氮的淋失受施肥种类影响最大,铵态氮最小。(3)在土壤淋滤液中,硝态氮为可溶性氮主要淋失形态,其淋失量占TN淋失量的比率为29.72%~46.18%,NH_4~+—N淋失量的比重为1.09%~2.05%。从研究结果推论,常量复合肥A施肥处理更有利于肥料氮向供植物吸收可溶性氮转化并降低施肥后土壤中氮素累积的风险。     

Changes in sorghum production,soil P forms and P use efficiency following long-term application of manure,compost and straw in a Ferric Lixisol

Low phosphorus availability in cultivated soils limits sustainable crop production in sub‐Saharan Africa. This study aimed at evaluating the effect of long‐term application of different types of organic amendments on soil P forms, P use efficiency and sorghum yields. A long term experiment established in 1980 at Saria in Burkina Faso, comparing the effects of manure, compost and sorghum straw was used. Manure and compost significantly increased organic P and resin‐P by about 35% and 64%, respectively after 10 and 32 years of sorghum cultivation, and HCl‐P after 32 years of cultivation compared to the control. Manure significantly increased NaHCO₃-Pi and NaOH-Pi by 63% and 26%, respectively compared to the control. Sorghum straw had little effect on measured soil P forms. Manure and compost were the best in increasing sorghum grain yield, which effect were strongly correlated to soil pH, carbon and nitrogen. The partial factors productivities of P resulting from the application of studied organic amendments were similar and low, but significantly higher than that of the control treatment. Organic amendments with high P content, maintaining soil carbon and pH could be used to improve soil P availability, sorghum yield and reduce the demand for mineral phosphorus fertilizers.     

亚热带2种针叶林土壤碳氮磷储量及化学计量比对混交的响应

针叶林混交阔叶树是改善土壤肥力、增强林地养分循环的重要措施,而混交效应受到针叶树种自身特性的影响,马尾松(Pinus massoniana)和湿地松(P.elliottii)是亚热带地区广泛种植的针叶树种,但目前2种针叶林对阔叶树混交的响应特征还不清楚。选取马尾松、湿地松纯林以及木荷(Schima superba)补植后形成的马尾松—木荷和湿地松—木荷混交林为研究对象,采集剖面土壤样品,测定土壤容重、有机碳(OC)、全氮(TN)和全磷(TP)含量,计算碳氮磷储量及化学计量特征,比较不同森林类型间的异同。混交阔叶树显著增加了马尾松林0—60cm各土层OC含量,而湿地松纯林与其混交林间OC含量无显著差异。同时,混交增加了2种针叶林土壤TN含量。马尾松林混交后0—60cm土层碳储量显著增加95.8%,而混交阔叶树对湿地松林土壤碳储量无显著影响。混交阔叶树后马尾松和湿地松林0—60cm土壤总氮储量分别增加了15.8%和28.4%,但混交对土壤磷储量无显著影响。混交显著增加了马尾松林0—40cm各土层C/N,而降低了湿地松林0—10cm土层C/N。混交阔叶树后马尾松林0—20cm土层C/P和0—10cm土层N/P显著增加,而混交仅增加湿地林0—10cm土层N/P。混交阔叶树增加了针叶林土壤氮储量,但对磷储量无显著影响,同时混交改变了土壤碳氮磷生态化学计量特征。与湿地松林相比,马尾松林土壤养分含量、储量及其化学计量特征对混交的响应更敏感。     

退化红壤植被恢复团聚体及化学计量特征

为了探究不同植被恢复模式对土壤碳(C)、氮(N)、磷(P)分配格局及其生态化学计量特征的影响,为红壤侵蚀区的植被恢复措施及生态治理模式优化提供科学依据,以江西省泰和县红壤严重退化地为研究对象,对研究区马尾松纯林、湿地松纯林、木荷纯林、马尾松木荷混交林(马木混交林)以及湿地松木荷混交林(湿木混交林)5种植被恢复模式0—20,20—40cm土层不同粒径水稳性团聚体C、N、P分配格局及其化学计量特征进行了研究。结果表明:(1)0—40cm不同粒径团聚体分别占总重56.34%(>2mm),30.01%(0.25~2mm),7.14%(0.053~0.25mm),6.54%(<0.053mm),各植被恢复模式土壤水稳性团聚体含量随着粒径的减小而降低,且差异显著(p<0.05),马木混交林>2mm土壤水稳性团聚体含量显著高于其他恢复模式(p<0.05);(2)各植被恢复模式土壤C、N、P含量以马木混交林及湿地松纯林较高,水稳性团聚体C、N、P的含量总体随着粒径减小呈升高的趋势,以较小粒级养分含量较高,且存在显著差异(p<0.05);土层间C、N含量差异显著,P无显著差异,C∶N、C∶P及N∶P存在显著差异(p<0.05);粒径间C∶N、C∶P及N∶P存在显著差异;土壤团聚体C、N与C∶N、C∶P、N∶P均呈极显著相关关系,N∶P值较高且P与N∶P存在显著负相关性(p<0.05);(3)土壤C、N与土壤团聚体C、N含量显著相关(p<0.05),土壤团聚体C、N与土壤容重及含水率存在极显著相关性(p<0.01)。研究结果表明,不同植被恢复模式对土壤养分的改善作用主要集中于表层土壤;土壤团聚体养分对土壤养分状况具有指示作用,且土壤团聚体养分保持能力与土壤物理性质有关;研究区植被生长限制因素以P限制为主且大团聚体和微团聚体受P限制作用更严重;马木混交林较其它植被恢复模式对土壤质量和结构提升均具有显著作用。     

狗牙根与空心莲对水库消落带土壤氮磷释放影响的模拟

通过水库水位涨落室内模拟试验,探究丹江口库区消落带优势物种狗牙根和空心莲2种草本植物对土壤氮磷释放过程影响。结果表明:(1)水淹结束后(32天),空心莲子草土壤TN、TP分别降低11.75%,25.28%,狗牙根分别降低3.62%,25.77%。(2)干湿交替环境主要影响土壤中NH_4~+-N、NO_3~--N和AP的含量的变化,对土壤中的TN、TP含量的影响较小。(3)狗牙根的死亡增加土壤TN、NH_4~+-N、TP量,即不耐淹植被过滤带虽然能净化径流中N、P等污染物,但截留的污染物和植物吸收的养分随着植物体的分解再次进入水体或土壤,无法达到有效防控农业面源污染的目的。该研究为丹江口水库利用植被缓冲带防控水体富营养化提供一定理论依据。     

西瓜根系分泌酸性磷酸酶对有机肥营养的响应

有机肥营养对西瓜品质具有提升效果,但根系对有机肥中养分的吸收机制尚不完全清楚,尤其对磷素的利用机制。本研究关注西瓜根系分泌酸性磷酸酶活性对有机肥施用的响应。采用模拟西瓜根系分泌物的方法研究有机酸对有机肥中可溶性全磷和有效磷含量的影响;采用砂培的方法,研究有机肥中的磷替代化肥磷时西瓜根系分泌酸性磷酸酶活性的响应;采用田间试验研究有机肥替代化肥以及有机肥不同施用量对西瓜根际酸性磷酸酶活性、西瓜磷营养、产量和品质的影响。结果表明,有机肥中水浸提可溶性全磷含量为6.9 g?kg~(-1),可溶性无机磷含量为525.1 mg?kg~(-1),可溶性全磷中无机磷占7.6%,有机磷占92.4%,可溶性有机磷需经过水解后才能被根系吸收。有机肥中磷替代化肥磷时,西瓜根系和根际土壤酸性磷酸酶活性均显著提高,西瓜茎、叶中磷含量提高。施用三倍有机肥时西瓜根际土壤有效磷含量和西瓜产量提高。因此,有机肥中磷替代化肥磷时,西瓜通过提高根系分泌酸性磷酸酶的活性而提高利用有机磷的能力。     

稻虾共作模式氮和磷循环特征及平衡状况

稻虾共作模式是我国长江中下游地区一种新兴的稻田复合种养生态模式,研究稻虾共作系统中氮（N）和磷（P）的循环特征及盈亏状况,对合理调控稻虾共作系统养分循环和平衡,指导系统N和P优化管理具有重要的意义。本文通过田间试验,采用投入产出法,以中稻单作模式作为对照,研究了稻虾共作模式下N和P的循环特征及平衡状况。结果表明：克氏原螯虾子系统N和P的输出/输入比分别为0.62和0.44,且子系统中N和P以饲料输入最大,占总输入的92.9%和96.4%,以成虾N和P输出最大,分别占总输出的53.3%和59.5%;在目前投入水平下,两种模式土壤子系统中N和P表观平衡均出现盈余,且稻虾共作模式土壤子系统N的盈余量高于中稻单作模式,而P的盈余量则低于中稻单作模式;稻虾共作模式和中稻单作模式的N和P输出/输入比均小于1,且稻虾共作模式的N和P输出/输入比均小于中稻单作模式;稻虾共作模式增加了土壤截存的N和P量,其土壤截存的N和P量较中稻单作模式分别提高49.2 kg·hm^-2和9.1 kg·hm^-2;稻虾共作模式提高了系统N和P表观损失量,其系统N和P表观损失量较中稻单作模式分别提高10.2 kg·hm^-2和1.0 kg·hm^-2。可见稻虾共作模式降低了N和P输出/输入比,促进了土壤中N和P的累积,但增加了系统N和P表观损失量。