现(xian)在越来越多的人在理(li)(li)(li)论(lun)上懂得了玉(yu)米适当(dang)晚收即可增产的道(dao)理(li)(li)(li)，但(dan)是在玉(yu)米生(sheng)产实(shi)践中却没有完全做(zuo)到，玉(yu)米晚收必须以延长活秆绿叶时间(jian)为(wei)前(qian)提，青枝绿叶活棵成熟才能实(shi)现(xian)玉(yu)米高产。玉(yu)米生(sheng)长中后期要(yao)加强肥水管理(li)(li)(li)，延长叶片的光合时间(jian)，防止早衰。同时要(yao)坚决杜绝成熟前(qian)削尖、打叶现(xian)象。

玉米只(zhi)有在完全成熟(shu)的情况下，粒重(zhong)最(zui)大，产量(liang)最(zui)高。收获偏(pian)早(zao)，成熟(shu)度差，粒重(zhong)低，产量(liang)下降。我(wo)县(xian)农民有早(zao)收的习惯，常在果(guo)穗(sui)苞叶(ye)刚(gang)变白时收获，此时千粒重(zhong)仅为完熟(shu)期(qi)的90%左右，一般减产10%左右，应予以纠正。

当前生产上应用的(de)紧凑型玉(yu)米(mi)品种多有“假熟(shu)”现象，即玉(yu)米(mi)苞叶提早变白而子粒尚(shang)未停止灌浆。这(zhei)些品种往往被提前收(shou)获。一(yi)(yi)般(ban)在(zai)授(shou)粉后40-45天(tian)，即乳线下移到1/2至3/4时已经收(shou)获，比(bi)完(wan)全(quan)生理(li)成熟(shu)要早8-10天(tian)，一(yi)(yi)般(ban)减产8%左右，中晚熟(shu)品种的(de)减产幅度则达到10%以上。

1．延长子(zi)粒(li)(li)灌(guan)(guan)浆(jiang)(jiang)时间(jian)(jian)(jian)，提(ti)高玉(yu)(yu)米(mi)产(chan)(chan)(chan)(chan)量(liang)(liang)玉(yu)(yu)米(mi)收获过(guo)早会(hui)导致生育期(qi)不足而减(jian)产(chan)(chan)(chan)(chan)。而生育期(qi)不足减(jian)产(chan)(chan)(chan)(chan)的(de)(de)(de)首要因素是缩短(duan)了(le)玉(yu)(yu)米(mi)的(de)(de)(de)灌(guan)(guan)浆(jiang)(jiang)时间(jian)(jian)(jian)，降低粒(li)(li)重(zhong)(zhong)。晚播或(huo)早收对玉(yu)(yu)米(mi)开(kai)花期(qi)以前的(de)(de)(de)生长时间(jian)(jian)(jian)影响(xiang)很小，主(zhu)要是减(jian)少(shao)了(le)子(zi)粒(li)(li)灌(guan)(guan)浆(jiang)(jiang)期(qi)的(de)(de)(de)时间(jian)(jian)(jian)，而玉(yu)(yu)米(mi)绝大部分(fen)的(de)(de)(de)子(zi)粒(li)(li)产(chan)(chan)(chan)(chan)量(liang)(liang)又是在灌(guan)(guan)浆(jiang)(jiang)期(qi)间(jian)(jian)(jian)形(xing)成的(de)(de)(de)。开(kai)花以前所占(zhan)的(de)(de)(de)时间(jian)(jian)(jian)虽(sui)然很长，但(dan)生产(chan)(chan)(chan)(chan)的(de)(de)(de)干(gan)物质通常不到(dao)最后总(zong)干(gan)重(zhong)(zhong)的(de)(de)(de)一半。开(kai)花前叶(ye)片的(de)(de)(de)光(guang)(guang)合(he)产(chan)(chan)(chan)(chan)物只是为了(le)后期(qi)的(de)(de)(de)子(zi)粒(li)(li)生产(chan)(chan)(chan)(chan)奠定(ding)基础，很少(shao)能够(gou)直接用于子(zi)粒(li)(li)生产(chan)(chan)(chan)(chan)。从开(kai)花到(dao)成熟的(de)(de)(de)时间(jian)(jian)(jian)虽(sui)短(duan)，但(dan)对产(chan)(chan)(chan)(chan)量(liang)(liang)形(xing)成却十(shi)分(fen)重(zhong)(zhong)要。此期(qi)叶(ye)片光(guang)(guang)合(he)产(chan)(chan)(chan)(chan)物大部分(fen)输(shu)送(song)到(dao)子(zi)粒(li)(li)中去形(xing)成产(chan)(chan)(chan)(chan)量(liang)(liang)，灌(guan)(guan)浆(jiang)(jiang)期(qi)间(jian)(jian)(jian)不但(dan)干(gan)物质生产(chan)(chan)(chan)(chan)的(de)(de)(de)数(shu)量(liang)(liang)大，而且主(zhu)要用于子(zi)粒(li)(li)建(jian)成，直接关(guan)系到(dao)经济(ji)系数(shu)的(de)(de)(de)高低。玉(yu)(yu)米(mi)80%-90%的(de)(de)(de)子(zi)粒(li)(li)产(chan)(chan)(chan)(chan)量(liang)(liang)来自(zi)于灌(guan)(guan)浆(jiang)(jiang)期(qi)间(jian)(jian)(jian)的(de)(de)(de)光(guang)(guang)合(he)产(chan)(chan)(chan)(chan)物，只有10%-20%是开(kai)花前贮藏在茎、叶(ye)鞘等器(qi)官内，到(dao)灌(guan)(guan)浆(jiang)(jiang)期(qi)再转运到(dao)子(zi)粒(li)(li)中来的(de)(de)(de)。因此，灌(guan)(guan)浆(jiang)(jiang)期(qi)越长，灌(guan)(guan)浆(jiang)(jiang)强度越大，玉(yu)(yu)米(mi)产(chan)(chan)(chan)(chan)量(liang)(liang)就(jiu)越高。

2．增加(jia)(jia)蛋白质(zhi)(zhi)(zhi)(zhi)(zhi)、氨(an)(an)(an)基(ji)酸(suan)(suan)数量(liang)，提高商(shang)品质(zhi)(zhi)(zhi)(zhi)(zhi)量(liang)玉(yu)米适(shi)当晚(wan)收不仅(jin)能增加(jia)(jia)子(zi)(zi)粒(li)中淀粉(fen)产量(liang)，其他营养(yang)物(wu)质(zhi)(zhi)(zhi)(zhi)(zhi)也(ye)随(sui)之(zhi)增加(jia)(jia)。玉(yu)米子(zi)(zi)粒(li)营养(yang)品质(zhi)(zhi)(zhi)(zhi)(zhi)主要取决于蛋白质(zhi)(zhi)(zhi)(zhi)(zhi)及(ji)氨(an)(an)(an)基(ji)酸(suan)(suan)的含(han)(han)量(liang)。子(zi)(zi)粒(li)营养(yang)物(wu)质(zhi)(zhi)(zhi)(zhi)(zhi)的积(ji)累(lei)是一个连(lian)续过(guo)程，随(sui)着子(zi)(zi)粒(li)的充实(shi)增重(zhong)，蛋白质(zhi)(zhi)(zhi)(zhi)(zhi)及(ji)氨(an)(an)(an)基(ji)酸(suan)(suan)等营养(yang)物(wu)质(zhi)(zhi)(zhi)(zhi)(zhi)也(ye)逐(zhu)渐积(ji)累(lei)，至完(wan)熟期(qi)达(da)最大值。玉(yu)米子(zi)(zi)粒(li)中蛋白质(zhi)(zhi)(zhi)(zhi)(zhi)及(ji)氨(an)(an)(an)基(ji)酸(suan)(suan)的相对(dui)含(han)(han)量(liang)随(sui)淀粉(fen)量(liang)的快速增加(jia)(jia)呈(cheng)(cheng)下降趋势，但绝对(dui)含(han)(han)量(liang)却随(sui)粒(li)重(zhong)增加(jia)(jia)呈(cheng)(cheng)明显上升趋势，完(wan)熟期(qi)达(da)到最高值。表明延期(qi)收获也(ye)能增加(jia)(jia)蛋白质(zhi)(zhi)(zhi)(zhi)(zhi)和氨(an)(an)(an)基(ji)酸(suan)(suan)数量(liang)。

此外(wai)，适期收获(huo)的玉米子粒(li)饱满(man)充(chong)实(shi)，子粒(li)比较均匀(yun)，小粒(li)、秕粒(li)明(ming)(ming)显(xian)减少(shao)，子粒(li)含(han)水量比较低，便于脱粒(li)和(he)储放(fang)，商品质量会(hui)有明(ming)(ming)显(xian)提高。

每一个玉米品种(zhong)在同一地区都有一个相对固定的生(sheng)育(yu)期，只有满足其生(sheng)育(yu)期要(yao)求，使(shi)玉米正常成(cheng)熟(shu)，才(cai)能(neng)实现高产优质(zhi)。判断玉米是否正常成(cheng)熟(shu)不能(neng)仅看(kan)外表，而是要(yao)着(zhe)重考察子粒灌浆是否停止，以生(sheng)理成(cheng)熟(shu)作为收获(huo)标准。

玉(yu)(yu)(yu)(yu)米(mi)(mi)子(zi)(zi)粒(li)生理成(cheng)(cheng)(cheng)熟(shu)(shu)的主要(yao)标志(zhi)有两个，一(yi)(yi)是(shi)(shi)(shi)子(zi)(zi)粒(li)基部(bu)黑(hei)色(se)(se)层(ceng)(ceng)(ceng)(ceng)形(xing)(xing)(xing)(xing)(xing)成(cheng)(cheng)(cheng)，二是(shi)(shi)(shi)子(zi)(zi)粒(li)乳(ru)(ru)(ru)线消(xiao)(xiao)(xiao)失(shi)(shi)。玉(yu)(yu)(yu)(yu)米(mi)(mi)成(cheng)(cheng)(cheng)熟(shu)(shu)时(shi)(shi)是(shi)(shi)(shi)否(fou)形(xing)(xing)(xing)(xing)(xing)成(cheng)(cheng)(cheng)黑(hei)色(se)(se)层(ceng)(ceng)(ceng)(ceng)，不(bu)(bu)同(tong)品种(zhong)之(zhi)间(jian)差别很大(da)。有的品种(zhong)成(cheng)(cheng)(cheng)熟(shu)(shu)以(yi)后(hou)再(zai)过一(yi)(yi)定时(shi)(shi)间(jian)才能看到(dao)明显的黑(hei)色(se)(se)层(ceng)(ceng)(ceng)(ceng)。玉(yu)(yu)(yu)(yu)米(mi)(mi)子(zi)(zi)粒(li)黑(hei)色(se)(se)层(ceng)(ceng)(ceng)(ceng)形(xing)(xing)(xing)(xing)(xing)成(cheng)(cheng)(cheng)受水分(fen)影响极(ji)大(da)，不(bu)(bu)管是(shi)(shi)(shi)否(fou)正常成(cheng)(cheng)(cheng)熟(shu)(shu)，子(zi)(zi)粒(li)水分(fen)降低到(dao)32%时(shi)(shi)都能形(xing)(xing)(xing)(xing)(xing)成(cheng)(cheng)(cheng)黑(hei)色(se)(se)层(ceng)(ceng)(ceng)(ceng)，所以(yi)黑(hei)色(se)(se)层(ceng)(ceng)(ceng)(ceng)形(xing)(xing)(xing)(xing)(xing)成(cheng)(cheng)(cheng)并(bing)不(bu)(bu)完全是(shi)(shi)(shi)玉(yu)(yu)(yu)(yu)米(mi)(mi)正常成(cheng)(cheng)(cheng)熟(shu)(shu)的可靠标志(zhi)。玉(yu)(yu)(yu)(yu)米(mi)(mi)子(zi)(zi)粒(li)乳(ru)(ru)(ru)线的形(xing)(xing)(xing)(xing)(xing)成(cheng)(cheng)(cheng)、下(xia)移、消(xiao)(xiao)(xiao)失(shi)(shi)是(shi)(shi)(shi)一(yi)(yi)个连续的过程(cheng)。生育期(qi)(qi)100天(tian)左(zuo)右(you)(you)的品种(zhong)授(shou)(shou)粉(fen)26天(tian)前后(hou)，子(zi)(zi)粒(li)顶部(bu)淀粉(fen)沉(chen)积(ji)、失(shi)(shi)水，成(cheng)(cheng)(cheng)为(wei)(wei)固(gu)(gu)体，形(xing)(xing)(xing)(xing)(xing)成(cheng)(cheng)(cheng)了(le)子(zi)(zi)粒(li)顶部(bu)为(wei)(wei)固(gu)(gu)体、中下(xia)部(bu)为(wei)(wei)乳(ru)(ru)(ru)液(ye)的固(gu)(gu)液(ye)界面，这个界面就是(shi)(shi)(shi)乳(ru)(ru)(ru)线，此(ci)时(shi)(shi)称为(wei)(wei)乳(ru)(ru)(ru)线形(xing)(xing)(xing)(xing)(xing)成(cheng)(cheng)(cheng)期(qi)(qi)。有时(shi)(shi)从子(zi)(zi)粒(li)外表看乳(ru)(ru)(ru)线不(bu)(bu)太(tai)明显，过1-2天(tian)以(yi)后(hou)才明显可见。乳(ru)(ru)(ru)线形(xing)(xing)(xing)(xing)(xing)成(cheng)(cheng)(cheng)期(qi)(qi)子(zi)(zi)粒(li)含水量(liang)51%-55%，粒(li)干(gan)重(zhong)为(wei)(wei)最大(da)值(zhi)的65%左(zuo)右(you)(you)。随着淀粉(fen)沉(chen)积(ji)量(liang)的增加(jia)，乳(ru)(ru)(ru)线向下(xia)推移，至授(shou)(shou)粉(fen)后(hou)40天(tian)左(zuo)右(you)(you)下(xia)移至子(zi)(zi)粒(li)中部(bu)，此(ci)期(qi)(qi)称为(wei)(wei)乳(ru)(ru)(ru)线中期(qi)(qi)。当子(zi)(zi)粒(li)含水量(liang)下(xia)降到(dao)40%左(zuo)右(you)(you)时(shi)(shi)，粒(li)重(zhong)达最大(da)值(zhi)的90%左(zuo)右(you)(you)，乳(ru)(ru)(ru)线上方坚硬(ying)，下(xia)方较硬(ying)，有弹(dan)性(xing)，此(ci)时(shi)(shi)为(wei)(wei)蜡(la)熟(shu)(shu)期(qi)(qi)。授(shou)(shou)粉(fen)后(hou)50天(tian)左(zuo)右(you)(you)乳(ru)(ru)(ru)线消(xiao)(xiao)(xiao)失(shi)(shi)，子(zi)(zi)粒(li)含水量(liang)30%左(zuo)右(you)(you)，此(ci)时(shi)(shi)子(zi)(zi)粒(li)干(gan)重(zhong)最大(da)，有的品种(zhong)出现(xian)明显黑(hei)色(se)(se)层(ceng)(ceng)(ceng)(ceng)，苞叶变(bian)白(bai)而(er)松散。也(ye)就是(shi)(shi)(shi)说玉(yu)(yu)(yu)(yu)米(mi)(mi)果穗下(xia)部(bu)子(zi)(zi)粒(li)乳(ru)(ru)(ru)线消(xiao)(xiao)(xiao)失(shi)(shi)，子(zi)(zi)粒(li)含水量(liang)30%左(zuo)右(you)(you)，果穗苞叶变(bian)白(bai)而(er)松散时(shi)(shi)收(shou)获(huo)粒(li)重(zhong)最高，玉(yu)(yu)(yu)(yu)米(mi)(mi)的产(chan)量(liang)最高，可以(yi)作为(wei)(wei)玉(yu)(yu)(yu)(yu)米(mi)(mi)适(shi)期(qi)(qi)收(shou)获(huo)的主要(yao)标志(zhi)。同(tong)时(shi)(shi)，玉(yu)(yu)(yu)(yu)米(mi)(mi)子(zi)(zi)粒(li)基部(bu)黑(hei)色(se)(se)层(ceng)(ceng)(ceng)(ceng)形(xing)(xing)(xing)(xing)(xing)成(cheng)(cheng)(cheng)也(ye)是(shi)(shi)(shi)适(shi)期(qi)(qi)收(shou)获(huo)的重(zhong)要(yao)参考(kao)指标。