Estimation of Soil Nitrogen Status in Intercropping Through Soil Solution

E s t i m a t i r ~ ~ soil nitrogen ( N ) status in cropping systems by sartrpling thtsoil follow~~d by extraction using KC1 or CaC12 h[ls b e ~ n researched t7xtettsizrely. H O Z O P ~ ~ E ~ , fezu S ~ N ~ ~ C S have been conducted to nrottitor soiland fertilizer-N dyttanrics in cropping systems rcsitt~ ceratt~ic porous cups. Nitrate-N (NO,?-N) in soil solution extracted by porous cups is point snmplirlg and collld better reflect a stmriy state betwren ntineralizntiott and plattt-N uptake than that extrrzcted usittg KC1 or CuCl? whiclt are commonly used to estinzate the az~ailability o f N to plattts. D t i r i n ~ a 3-year field study to motzitor the N-dynamics o f pi~qeonpe~~/sorgltutrt it~tercropping ott Alfisol, zue found tltat an NO3-N concentmtion qf 2 to 5 m M (ca. 100 k'y N / i d ) d~ t rc t rd in soil soliltioti at the otlset of tltc croppittg season disnppeareri frortt tlte soil sol~rtiott 30-40 days after sozuitlg ( D A S ) cornpart3ii zuitli basal application. Delayed N fertilizer application to tlte sor~lrunr restrlted i n a kiglter uptake of soil NO1-N . O u r data ittdicated that 80-90% of N detected in soil solutiori at t ime of planting wns not ~ctilized by crops. Tltere was no clear evidence of NO, -N leach in^ into the deep soil layers because the NO.?-N concetrtratic~t~s detected ill the deep soil layers ulere low. W e speculatt7 that an appreciable lzntotittt of NO,{-N d~.tt*cted it1 soil sol~rtiorr in tlte soil profile at the be~ir lr~ing of croppit~g seasoti is qtiickly immobilized, and/or incorporat~~ri into tht3 soil organic pool at the early crop grori~th stage rcrhen crop uptakr is IOU). The qtrestiort of whetlter or not thc N O I N itrcorporated ittto tlte soil ~ r ~ y a t t i c pool becomes available for crop uptake during tlte later ,grozirt/z stage, n ~ e d s firrtller irlvesti,gation. T /~ere f i~ re , sources and forms of available-N it1 the soil, the rates of availability atld n~i t~eral i za t ion ut the beginning o f t he season, artd the control by rainfall timitrg and atnotint, net~d t t t ud~ more attention in thefuture. Monitoring N-concentration in soil solution using porous cups provides a better insight in to soil-nutrient-plant interaction, attd enhances the probability of acclirately predicting thr amount offertilizer-N required by crops.