太湖稻麦轮作区减施磷肥对土壤供磷和小麦吸收磷的影响

为了探究太湖稻麦轮作区土壤供磷能力,寻找适宜的减磷措施,通过田间减施磷肥试验,以稻麦季均施磷(PR+W)为对照,设置稻季施磷麦季不施磷(PR)、麦季施磷稻季不施磷(PW)、稻麦季均不施磷(Pzero)3种处理,于第7年测定土壤速效磷含量、梯度扩散薄膜技术(Diffusive Gradients in Thin films,DGT)提取态磷含量、小麦产量以及小麦磷吸收量,分析太湖稻麦轮作区减施磷肥对土壤供磷和小麦吸收磷的影响。结果表明:与PR+W处理相比,PW处理的土壤速效磷含量、小麦籽粒产量以及植株全磷含量均无显著降低;但PR处理显著(P0.05)降低了44.8%的土壤速效磷含量、32.8%的小麦籽粒产量以及27.9%的地上部植株吸收磷量。线性回归分析发现,利用DGT技术提取的磷与土壤速效磷有显著的正相关关系(P0.05,R2=0.42),且两者皆与小麦籽粒产量、地上部植株全磷含量及地下部植株全磷含量呈显著的正相关关系。可见,麦季施磷稻季不施磷的减磷措施能够保证土壤速效磷供应和小麦吸磷量,并维持小麦籽粒产量,但麦季不施磷的减磷措施会显著降低土壤速效磷含量、小麦吸磷量以及小麦籽粒产量,同时DGT提取磷可作为稻麦轮作系统土壤供磷与作物需磷动态关系研究的评价指标。     

成都平原周年耕作模式对稻茬小麦产量与品质性状的持续效应

【目的】小麦产量和品质性状除了受遗传因子控制外,还受到生态环境条件和耕作栽培措施等外部因子的影响。研究周年耕作模式对小麦产量和品质的持续效应可为优化区域耕作制度提供依据。【方法】基于2004年小麦秋播时建立的长期定位试验,研究成都平原稻麦轮作区耕作方式与秸秆还田两个因素的5种周年组合模式（麦免稻旋WZRR,麦免稻旋+秋菜WZRRV,麦稻双免WZRZ,麦稻双免垄作WRZB,周年旋耕无秸秆还田CK）对小麦生长发育、产量与品质性状的持续影响效应。【结果】所有耕作模式的小麦产量及产量构成因子在年际间均呈波动性变化,对照产量在多数年份都处于低值水平,7年平均较其它处理低3.0%-4.7%,随时间推延下降趋势明显,年均递减0.125 t•hm-2。所有处理的有效穗均无明显的时间变化趋势,但穗粒数下降趋势和千粒重上升趋势明显。7年平均,对照的有效穗显著低于其它处理,而穗粒数、单位面积粒数和千粒重在处理之间均无显著性差异。免耕与秸秆还田组合模式具有不同程度提高小麦主要生育阶段耕层土壤速效N、P、K含量和改善中后期个体与冠层质量的作用。WZRZ、WRZB处理的多数小麦品质性状与CK相当或略优,而WZRR、WZRRV处理有降低籽粒蛋白质含量、沉降值、面团稳定时间的趋势。【结论】免耕与秸秆还田利于稳定小麦产量和改善耕地质量,尤以周年免耕秸秆全量还田模式最好。     

Modeling the Impacts of Soil Organic Carbon Content of Croplands on Crop Yields in China

This study quantified the impacts of soil organic carbon （SOC） content on the grain yield of crops using a biogeochemical model （DNDC, denitrification-decomposition）. Data on climate, soil properties, and farming management regimes of cropping systems were collected from six typical agricultural zones （northeast, north, northwest, mid-south, east and southwest regions of China, respectively） and integrated into a GIS database to support the model runs. According to the model, if the initial SOC content in the cropland was increased by 1 g C kg^-1, the crop yield may be increased by 176 kg ha^-1 for maize in the northeast region, 454 kg ha^-1 for a maize-wheat rotation in the north region, 328 kg ha^-1 for maize in the northwest region, 185 kg ha^-1 for single-rice in the mid-south region, 266 kg ha^-1 for double-rice in east region, and 229 kg ha^-1 for rice and wheat rotation in southwest region. There is a great potential for enhancing the crop yield by improving the SOC content in each region of China.     

减氮覆膜下土壤有机碳组分含量的变化特征

【目的】明确长期优化施肥（减施氮肥）和减氮覆膜下土壤有机碳（SOC）与各组分有机碳含量特征及其对冬小麦籽粒产量的贡献,以期为黄土高原旱地土壤培肥和作物增产提供科学依据。【方法】依托山西省洪洞县7年定位试验,采集0—20 cm土层原状土样,利用连续物理分组方法进行分组,结合冗余分析,研究不同农田管理措施下冬小麦籽粒产量、SOC以及颗粒有机碳（POC）、矿质结合态有机碳（MOC）、轻组颗粒有机碳（Light-POC）和重组颗粒有机碳（Heavy-POC）含量特征,明确SOC含量与各组分有机碳含量的关系,量化其对冬小麦籽粒产量的贡献。试验共设农户施肥（FP）、测控施肥（MF）、垄膜沟播（RF）和平膜穴播（FH）4个处理。【结果】分析不同管理措施下冬小麦籽粒产量和SOC含量发现,FP处理的冬小麦平均产量最低,为3 070 kg·hm^-2,与FP相比,MF在减少氮肥用量的情况下并未造成小麦减产,而RF和FH可进一步显著提高小麦籽粒产量,增幅分别达到27.0%和46.4%;与试验初始（2012年）土壤相比,经连续7年采用不同管理措施后SOC含量均显著提高,提高幅度从小到大依次为11.8%（MF）、22.4%（RF）、25.5%（FP）和36.1%（FH）,即MF对试验地石灰性褐土SOC提升作用最小,但结合地膜覆盖会显著提升其培肥土壤的效果,FH对SOC含量提升的效果最佳。进一步分析不同处理下SOC组分的差异发现,与FP和MF相比,两种减氮覆膜措施不同程度提高了POC和Light-POC含量及Light-POC在SOC中的分配比例。结合SOC及其各组分有机碳含量与冬小麦籽粒产量的冗余分析、敏感性指数分析和SOC与各组分有机碳含量的相关性分析发现,各有机碳组分均以POC对小麦产量的贡献最大（达71.0%）并对SOC含量的变化和农田管理措施的响应最为敏感。因此,平膜穴播对作物产量和土壤肥力的提高主要是通过提高土壤有机碳中POC含量得以实现的。【结论】在减氮优化施肥的基础上进行平膜穴播,有利于提高黄土高原南部旱地褐土区土壤有机碳和活性有机碳含量,实现冬小麦可持续增产。     

农田土壤有机碳含量对作物产量影响的模拟研究

 【目的】探求土壤有机碳含量对作物产量的影响,以期为保障国家粮食安全和耕地持续利用与管理提供决策依据。【方法】利用农田生态系统生物地球化学模型DNDC,针对中国东北、华北、西北、中南、华东和西南6个典型农业区域,每个区域选择各自典型的种植模式和现行的农田管理措施,在各自特定的土壤和气候条件下,输入并运行模型,模拟考察在其它投入条件不变的情况下,改变土壤有机碳本底值对作物产量的影响。【结果】当土壤有机碳含量（SOC）增加1 g C?kg-1,东北地区玉米产量可增加176 kg?hm-2;华北地区夏玉米与冬小麦轮作,产量可增加约454 kg?hm-2;西北地区春玉米产量约可增加328 kg?hm-2;中南地区单季水稻产量可增加约185 kg?hm-2;华东地区双季稻产量可增加约266 kg?hm-2;西南地区水稻与冬小麦轮作产量可增加约229 kg?hm-2。【结论】在其它投入既定的条件下,全国各地区均存在通过提高耕地土壤有机碳含量来增加作物产量的潜力。保持较高水平的土壤有机碳含量对节本增效具有十分明显的作用。     

Inverse meta-modelling to estimate soil available water capacity at high spatial resolution across a farm

Geo-referenced information on crop production that is both spatially- and temporally-dense would be useful for management in precision agriculture (PA). Crop yield monitors provide spatially but not temporally dense information. Crop growth simulation modelling can provide temporal density, but traditionally fail on the spatial issue. The research described was motivated by the challenge of satisfying both the spatial and temporal data needs of PA. The methods presented depart from current crop modelling within PA by introducing meta-modelling in combination with inverse modelling to estimate site-specific soil properties. The soil properties are used to predict spatially- and temporally-dense crop yields. An inverse meta-model was derived from the agricultural production simulator (APSIM) using neural networks to estimate soil available water capacity (AWC) from available yield data. Maps of AWC with a resolution of 10 m were produced across a dryland grain farm in Australia. For certain years and fields, the estimates were useful for yield prediction with APSIM and multiple regression, whereas for others the results were disappointing. The estimates contain ‘implicit information’ about climate interactions with soil, crop and landscape that needs to be identified. Improvement of the meta-model with more AWC scenarios, more years of yield data, inclusion of additional variables and accounting for uncertainty are discussed. We concluded that it is worthwhile to pursue this approach as an efficient way of extracting soil physical information that exists within crop yield maps to create spatially- and temporally-dense datasets.     

淮北砂姜黑土地力贡献与培肥技术研究

对杨柳点长期定位培肥试验和相关小麦施肥试验资料进行分析,结果表明:地力贡献与小麦施肥产量、地力贡献率之间呈线性正相关,高产田块地力贡献在小麦施肥产量中占主要地位。砂姜黑土地力贡献主要受土壤有机质和速效磷含量的影响,速效钾含量尚不是限制因子。长期连续施肥条件下．不同的土壤养分指标受有机无机配比的影响不同。有机质和氮素养分含量偏低的土壤,要通过增施有机肥加以培肥,磷素或钾素养分偏低的土壤可以通过增施有机肥或化肥来培肥。     

The delineation of agricultural management zones with high resolution remotely sensed data

Remote sensing (RS) techniques have been widely considered to be a promising source of information for land management decisions. The objective of this study was to develop and compare different methods of delineating management zones (MZs) in a field of winter wheat. Soil and yield samples were collected, and five main crop nutrients were analyzed: total nitrogen (TN), nitrate nitrogen (NN), available phosphorus (AP), extractable potassium (EP) and organic matter (OM). At the wheat heading stage, a scene of Quickbird imagery was acquired and processed, and the optimized soil-adjusted vegetation index (OSAVI) was determined. A fuzzy k-means clustering algorithm was used to define MZs, along with fuzzy performance index (FPI), and modified partition entropy (MPE) for determining the optimal number of clusters. The results showed that the optimal number of MZs for the present study area was three. The MZs were delineated in three ways; based on soil and yield data, crop RS information and the combination of soil, yield and RS information. The evaluation of each set of MZs showed that the three methods of delineating zones can all decrease the variance of the crop nutrients, wheat spectral parameters and yield within the different zones. Considering the consistent relationship between the crop nutrients, wheat yield and the wheat spectral parameters, satellite remote sensing shows promise as a tool for assessing the variation in soil properties and yield in arable fields. The results of this study suggest that management zone delineation using RS data was reliable and feasible.     

Algorithms for sensor-based redistribution of nitrogen fertilizer in winter wheat

Several methods were developed for the redistribution of nitrogen (N) fertilizer within fields with winter wheat (Triticum aestivum L.) based on plant and soil sensors, and topographical information. The methods were based on data from nine field experiments in nine different fields for a 3-year period. Each field was divided into 80 or more subplots fertilized with 60, 120, 180 or 240 kg N ha⁻¹. The relationships between plot yield, N application rate, sensor measurements and the interaction between N application and sensor measurements were investigated. Based on the established relations, several sensor-based methods for within-field redistribution of N were developed. It was shown that plant sensors predicted yield at harvest better than soil sensors and topographical indices. The methods based on plant sensors showed that N fertilizer should be moved from areas with low and high sensor measurements to areas with medium values. The theoretical increase in yield and N uptake, and the reduced variation in grain protein content resulting from the application of the above methods were estimated. However, the estimated increases in crop yield, N-uptake and reduced variation in grain protein content were small.     

我国不同区域粮食作物产量对有机肥施用的响应差异

探明全国不同气候、土壤和作物类型条件下,化肥配施有机肥对产量的影响及其增产效果的主控因素,可为粮食增产和有机肥的合理施用提供重要的理论依据。本研究通过收集109篇已公开发表的文献,建立了包含不施肥（CK）、单施化肥（NPK）和化肥配施有机肥（NPKM）处理的402组作物产量的数据库。采用整合分析（Meta-analysis）方法分析了不同施肥处理对小麦、玉米和水稻产量的影响,以及不同土壤性质和气候条件下有机肥的增产差异;采用随机森林（Random forest）方法量化土壤和气候因素对有机肥增产效果影响的重要度。全国来看,与NPK相比,NPKM处理下作物的产量平均增幅4.7%,其中小麦、玉米和水稻的增产率分别为5.6%、7.6%和4.5%;作物的平均增产率在西北地区最高,东北和华北地区次之,南方和华东地区较低。配施有机肥对产量的提升作用在我国温带大陆性气候区和温带季风性气候区显著高于亚热带季风性气候区,其中年降雨量是影响小麦和水稻产量对有机肥响应的主要因素,年均温和无霜期是影响玉米产量对有机肥响应的主要因素。有机质和全氮含量是土壤性状中影响有机肥增产效果的主要因素,其中土壤有机质和全氮含量越低,配施有机肥后产量的增幅越高。总的来说,化肥配施有机肥可显著提高作物的产量,尤其在低温少雨、土壤养分含量较低的地区,可通过化肥配施有机肥来进行增产促产。     

免耕覆盖下土壤水分、团聚体稳定性及其有机碳分布对小麦产量的协同效应

[目的]基于山西运城8年(2008—2015)长期定位试验,研究免耕覆盖下土壤团聚体稳定性、团聚体活性有机碳分布特征、冬小麦水分利用效率和产量变化特征,分析土壤水分、土壤团聚体稳定性及其有机碳组分对小麦籽粒产量的协同关系,为选择适宜黄土高原旱作农业区最佳耕作模式提供理论依据.[方法]选取传统耕作秸秆翻耕还田(CT-SP...     

Effects of long-term full straw return on yield and potassium response in wheat-maize rotation

The effect of long-term straw return on crop yield, soil potassium(K) content, soil organic matter, and crop response to K from both straw and chemical K fertilizer(K_2SO_4) were investigated in a fixed site field experiment for winter wheat-summer maize rotation in 6 years for 12 seasons. The field experiment was located in northern part of North China Plain with a sandy soil in relatively low yield potential. Two factors, straw return and chemical K fertilizer, were studied with two levels in each factor. Field split design was employed, with two straw treatments, full straw return of previous crop(St) and no straw return, in main plots, and two chemical K fertilizer treatments, 0 and 60 kg K2 O ha~(–1), as sub-plots. The results showed that straw return significantly increased yields of winter wheat and summer maize by 16.5 and 13.2% in average, respectively, and the positive effect of straw return to crop yield showed more effective in lower yield season. Straw return significantly increased K absorption by the crops, with significant increase in straw part. In treatment with straw return, the K content in crop straw increased by 15.9 and 21.8% in wheat and maize, respectively, compared with no straw return treatment. But, straw return had little effect on K content in grain of the crops. Straw return had significant influences on total K uptake by wheat and maize plants, with an increase of 32.7 and 30.9%, respectively. There was a significant correlation between crop yield and K uptake by the plant. To produce 100 kg grain, the wheat and maize plants absorbed 3.26 and 2.24 kg K2 O, respectively. The contents of soil available K and soil organic matter were significantly affected by the straw return with an increase of 6.07 and 23.0%, respectively, compared to no straw return treatment. K_2SO_4 application in rate of 60 kg K2 O ha~(–1) showed no significant effect on wheat and maize yield, K content in crop straw, total K uptake by the crops, soil available K content, and soil organic matter. The apparent K utilization rate(percentage of applied K absorbed by the crop in the season) showed difference for wheat and maize with different K sources. In wheat season, the K utilization rate from K_2SO_4 was higher than that from straw, while in maize season, the K utilization rate from straw was higher than that from chemical fertilizer. In the whole wheat-maize rotation system, the K absorption efficiency by the two crops from straw was higher than that from K_2SO_4.     

Airborne hyperspectral imagery and linear spectral unmixing for mapping variation in crop yield

Spectral unmixing techniques can be used to quantify crop canopy cover within each pixel of an image and have the potential for mapping the variation in crop yield. This study applied linear spectral unmixing to airborne hyperspectral imagery to estimate the variation in grain sorghum yield. Airborne hyperspectral imagery and yield monitor data recorded from two sorghum fields were used for this study. Both unconstrained and constrained linear spectral unmixing models were applied to the hyperspectral imagery with sorghum plants and bare soil as two endmembers. A pair of plant and soil spectra derived from each image and another pair of ground-measured plant and soil spectra were used as endmember spectra to generate unconstrained and constrained soil and plant cover fractions. Yield was positively related to the plant fraction and negatively related to the soil fraction. The effects of variation in endmember spectra on estimates of cover fractions and their correlations with yield were also examined. The unconstrained plant fraction had essentially the same correlations (r) with yield among all pairs of endmember spectra examined, whereas the unconstrained soil fraction and constrained plant and soil fractions had r-values that were sensitive to the spectra used. For comparison, all 5151 possible narrow-band normalized difference vegetation indices (NDVIs) were calculated from the 102-band images and related to yield. Results showed that the best plant and soil fractions provided better correlations than 96.3 and 99.9% of all the NDVIs for fields 1 and 2, respectively. Since the unconstrained plant fraction could represent yield variation better than most narrow-band NDVIs, it can be used as a relative yield map especially when yield data are not available. These results indicate that spectral unmixing applied to hyperspectral imagery can be a useful tool for mapping the variation in crop yield.     

Field methods for making productivity classes for site-specific management of wheat

Reducing the decision-making unit to classes within fields can improve yields, efficiency in the use of nutrients and profitability of crops. The objectives were to compare methods for class delimitation in wheat (Triticum aestivum L.) crops based on apparent productivity levels and establish similarities among them in terms of spatial overlapping, productive attributes and the use of nitrogen. In three wheat fields, high and low apparent productivity classes (APC) were defined based on eight methodologies: yield maps, soil maps, gramineae vegetation index, rotation crop index, interpretation of satellite images, management records, elevation and integrated soil and yield maps. In each APC, soil and crop yield components were determined under five nitrogen fertilization levels. Among delimitation methodologies, the degree of coincidence varied from 1.4 to 81.7%. The differences in soil properties, nitrogen use efficiency and grain yields were greater among fields than among APC within each field. In each field, the delimitation methodologies identified different single factors that discriminated among the potential management classes and were partially associated with the crop grain yields. The wheat crops at the low APC yielded 39% less and 12% less than at the high APC, respectively. The nitrogen fertilization, at the rate for maximum productivity for each ACP, reduced the yield differences between contrasting APC. Nitrogen fertilization also modified clustering of classes based on expected yields. Making management classes for wheat based on expected productivity is more accurate when based on previous crop production information under similar nitrogen fertilization conditions than the targeted crop.

     

A Dynamic Knowledge Model for Nitrogen Fertilization in Wheat Management

By analyzing and extracting the research progress on nitrogen fertilization in wheat, a dynamic knowledge model for management decision-making on total nitrogen rate, ratios of organic to inorganic and of basal to dressing nitrogen under different environments and cultivars in wheat was developed with principle of nutrient balance and by integrating the quantitative effects of grain yield and quality targets, soil characters, variety traits and water management levels. Case studies on the nitrogen fertilization model with the data sets of different eco-sites, cultivars, soil fertility levels, grain yield and quality targets and water management levels indicate a good performance of the model system in decision-making and wide applicability.     

小麦栽培氮肥运筹的动态知识模型

 通过分析和提炼小麦氮肥管理方面的最新研究资料 ,以小麦产量和品质为目标 ,根据土壤理化特性、品种遗传特征和水分管理水平等 ,利用养分平衡原理 ,建立了系统化和广适性的小麦栽培氮肥运筹的动态知识模型。该模型可用于精确定量不同环境条件及不同小麦品种生产过程中的总施氮量、有机氮与无机氮的比例以及氮基肥与氮追肥的比例等。利用南京和徐州 2个不同生态点的不同土壤和品种资料、不同产量和品质目标 ,以及不同水分管理水平等对所建氮肥运筹知识模型进行了实例分析 ,表明所建知识模型具有较好的决策性和适用性。     

Estimation of the Importance of Spatially Variable Nitrogen Application and Soil Moisture Holding Capacity to Wheat Production

Crop growth modelling techniques were used to investigate the performance of a wheat crop over a range of weather conditions, nitrogen application rates and soil types. The data were used to predict long term benefits of using spatially variable fertilizer application strategies where fertilizer application rate was matched to the soil type, against a strategy of uniform fertilizer application. The model was also run with modified soil properties to determine the importance of soil moisture holding capacity in the variability of crop yield. It was found that the benefits of spatially variable nitrogen management when fertilizer was applied at the beginning of the season were modest on average. The range of results for different weather conditions was much greater than the average benefit. A large proportion of the variability of crop performance between soil types could be explained by differing soil moisture holding capacity. Devising techniques for managing this variability was concluded to be important for precision farming of cereals.Agricultural Engineering     

干旱胁迫对冬小麦生态、光合、产量及光谱特征的影响

利用2010—2011年度小区冬小麦干旱试验资料,研究不同干旱时长和保持不同土壤水分条件下冬小麦生理生态以及光谱的变化特征,为改善冬小麦田间管理和减少农业损失提供依据。从孕穗期开始,研究了受试品种(中优9507)株高、叶绿素、净光合速率、产量及光谱特征等指标的变化规律,并据此构建出冬小麦归一化植被指数(NDVI)和增强植被指数(EVI)同冬小麦减产率的相关模型。结果表明,受干旱胁迫后,冬小麦株高、叶绿素含量、光合作用能力显著下降,且下降幅度随着胁迫的加强而增大。NDVI和EVI同减产率能够建立很好的关系模型,可以为作物产量监测和干旱风险预测提供依据。     

有机-无机肥协同调控小麦-玉米两熟作物产量及土壤培肥效应

【目的】在小麦-玉米两季秸秆全还田条件下,探索不同有机-无机运筹模式对作物产量、氮效率和土壤养分的影响,为小麦-玉米一年两季种植合理利用有机养分资源和科学培肥地力提供理论支撑。【方法】通过设计化肥与不同用量有机肥配合并结合施用秸秆腐熟剂措施,研究不同有机无机运筹模式对产量构成、氮养分吸收、土壤有机质及团聚体等特征的影响。试验共设6个处理,分别为F处理(单施化肥),FA处理(化肥配秸秆腐熟剂),FM1处理(化肥配1 500 kg·hm-2有机肥),FM2处理(化肥配3 000 kg·hm-2有机肥),FM3处理(化肥配4 500 kg·hm-2有机肥),FAM2处理(化肥配3 000 kg·hm-2有机肥和秸秆腐熟剂)。【结果】(1)与单施化肥相比,施用不同用量有机肥和秸秆腐熟剂均可显著增加小麦-玉米籽粒产量,其中FM3处理产量最高,小麦增产20.6%,玉米增产10.6%,FAM2处理小麦增产19.5%,玉米增产8.2%。产量增加源于产量各构成要素的协同提高,小麦以公顷穗数和穗粒数增加较为显著,玉米以行粒数增加最为显著。(2)增施有机肥和秸秆腐熟剂可以促进氮素向籽粒运移,提高氮素收获指数...     

Spatial and Temporal Variability of Sorghum Grain Yield: Influence of Soil,Water, Pests,and Diseases Relationships

This study was conducted to determine relationships between biotic and abiotic factors and to generate information needed to improve the management of site-specific farming (SSF). The effects of water (80% evapotranspiration (ET) and 50% ET), hybrid (drought-tolerant and -susceptible), elevation, soil texture, soil NO₃--N, soil pH, and greenbugs (Schizaphis graminum) (Gb) on sorghum grain yield were investigated at Halfway, TX on geo-referenced locations on a 30-m grid in 1997, 1998, and 1999. Grain yields were influenced by interrelationships among many factors. Grain yields were consistently high under 80% ET treatment and in the upper slopes where the clay and silt fractions of the soil were high. Soil NO₃--N, rainfall, hybrid, and Gb effects on grain yields were seasonally unstable. Soil NO₃--N increased grain yield when water was abundant and depressed grain yields when water was limiting. Plant density effects on grain yield were confounded with hybrid responses to drought and Gb infestation. Managing seasonally unstable factors is a major challenge for farmers and better ways to monitor crop growth and diagnose causes of poor plant growth are needed. To improve the management of SSF, effects of the relationships between biotic and abiotic factors on crop yield must be integrated and evaluated as a system. Based on our study, information on seasonally stable factors like elevation and soil texture is useful in identifying management zones for water and fertilizer application. Water and fertilizers management should be complemented by in-season management of seasonally unstable factors like soil NO₃--N, rainfall, hybrid, and Gb effects on grain yield.