Effects Of Nitrogen And Potassium Fertilizer Application On Yield, Protein Formation And Their Mechanism In Malting Barley

Based on field experiments in two sequential growth seasons in two eco-sties, the effects of nitrogen fertilizer application and combined potassium fertilizer application on grain yield, protein and their mechanism were studied. Here are the main results:1. Effects of nitrogen and potassium on grain yield and quality in malting barleyGrain yield of malting barley increased and then decreased with increasing N fertilizer rate and fraction of topdress N (FTN), showed a conic curve with N rate and FTN; and under225kg hm-2N level and300kg hm-2N level, grain yield were increased and then decreased with increasing K fertilizer rate. Increasing N rate and FTN improved contents of protein, albumin, gliadin and glutinin, and especially for gliadin content.1000kernels weight and starch content decreased by N. Thus, quality of malting barley was declined by N fertilization. Under N and K fertilizer application, thousand kernel weight and protein content followed the same change tendency with grain yield, but decreased gliadin content, and increased starch content, which could improve malting quality.2Effect of nitrogen and potassium on carbon metabolism in malting barleyEffect of nitrogen rate on carbon metabolism in malting barley Photosynthetic rate (Pn), the maximum photochemistry efficiency (Fv/Fm) and quanta yield (Φ PSⅡ) of the photosynthetic system Ⅱ (PSⅡ) and chlorophyll relative content (SPAD value) increased with raised N rate. However, these parameters decreased at further N fertilizer enhancement of300kg ha-1. Starch content decreased with raised N fertilizer rate. However, grain starch accumulation, accumulation rate and yield showed the same tendency with grain yield in response to varying N level. Moderae N rate application also improved activities of SST (sucrose:sucrose fructosyltransferase) and FFT (fructan:fructan fruc-tosyltransferase) to benefit accumulation of water soluble carbohydrates (WSC), so as to increase amount of water soluble carbohydrates (WSC) stored in vegetative organs before anthesis and the PSGS (percentage of total soluble sugar remobilization quantity to grain starch yield).Effect of fraction of topdressed nitrogen (FTN) on carbon metabolism in malting barley Pn, Fv/Fm and ΦPSⅡ increased with raising FTN from FTNo to FTN30, and then decreased with further topdressed N fertilizer fraction of40%and50%at the front and middle grain filling stage; but increased with raising FTN from0to50%of FTN at the later grain filling stage. Chlorophyll relative content (SPAD) decreased by raising FTN in the whole grain filling stage. Leaf area index (LAI) and light extinction coefficient (K) followed the same tendency with Pn, were highest at FTN30. proper FTN improved the quantity of carbohydrate stored in vegetative organs of barely before anthesis, and increased the PSGS (percentage of total soluble sugar remobilization quantity to grain starch yield). Post-anthesis fructan (DP=3and DP>3) content and sucrose content in stem and sheath increased with raising FTN from0to30%of FTN, then decreased from30to50%of FTN. Activities of SST (sucrose:sucrose fructosyltransferase), FFT (fructan: fructan fruc-tosyltransferase) and FEH (fructan exohydrolase) were followed the same changing tendency with fructan content. More, WSC content and translation were higher at proper FTN (FTN30). Consequently, proper FTN could improve Pn of leaves to offer more substrates for starch synthesis at grain filling process, which increased grain starch yield and grain yield.Effect of nitrogen combined with potassium on carbon metabolism in malting barley Proper potassium fertilizer improved water soluble carbohydrates (WSC) accumulation in stem and sheath, and the WSC accumulation was higher at150kg ha-1K than another two treatments, and all treatments at225kg ha-1N level were higher than the corresponding treatments at300kg ha-1N level. More, the WSC redistribution quantity and rate were higher at150kg ha-1K than than another two treatments at two N levels, and all treatments at300kg ha-1N level also were higher than the corresponding treatments at300kg ha-1N level. So, proper nitrogen and potassium could increase WSC accumulation and redistribution to improve grain starch accumulation and yield.3Effect of nitrogen and potassium on nitrogen metabolism in malting barleyEffect of nitrogen rate on nitrogen metabolism in malting barley Within N fertilizer rate range of0to225kg hm-2, N accumulation in plants before anthesis, and remobilization of pre-anthesis stored nitrogen to grain increased with N fertilizer rates, however, the increasing extent shrinked at a further N fertilizer rate of300kg hm-2. Remobilization efficiency of pre-anthesis store N and its contribution to grain protein showed a single peak curve with increasing N fertilizer rate. Acitivities of glutamine synthetase (GS) and glutamic pyruvic transaminase (GPT) in grain also increased with increasing N fertilizer rates, and subsequently improved grain protein content and yield. In addition, proper N rate was beneficial to improvement of N recovery efficiency (NRE) and N agronomic efficiency (AE), while N fertilizer redueced N physiological use efficiency (PE) and N harvest index (NHI).Effect of FTN on nitrogen metabolism in malting barley N accumulation in two malting barley before anthesis and after anthesis increased with raising FTN from0to30%of FTN, decreased from30to50%of FTN. Remobilization amount of N accumulated before anthesis (RNA) and remobilization efficiency of N accumulated before anthesis (REN) showed the same changing tendency under FTN, but RNA contribution to grain N (NCG) decreased with raising FTN, and was the highest at FTNo. Grain protein yield also first increased, then decreased, and was the highest at FTN30. But grain protein content and albumin, gliadin, glutinin content all increased with raising FTN. Moreover, Grain glutamine synthetase (GS) and glutamic pyruvic transaminase (GPT) activity increased with raising FTN, and subsequently improved grain protein content and yield. In addition, N recovery efficiency (NRE), N physiological use efficiency (PE) and N agronomic efficiency (AE) also first increased, then decreased. So, proper FTN was beneficial to improvement of N fertilizer recovery and use efficiency.Effect of nitrogen combined with potassium on nitrogen metabolism in malting barley At two high N levels, N accumulation in plants before anthesis and after anthesis of all treatments at300kg ha-1N level were higher than the corresponding treatments at225kg ha-1N level, and increased with from0to150kg ha-1K level, then decreased from150kg ha-1K level, to300kg ha-1K level, at both two N levels. Remobilization amount of N accumulated before anthesis (RNA), remobilization efficiency of N accumulated before anthesis (REN) and RNA contribution to grain N (NCG) showed the same tendency with N accumulation. Grain protein accumulation at middle filling stage and maturity and Grain protein yield at maturity followed the same change tendency with N remobilization with the highest value at150kg ha-1K level at both N levels. Thus, grain protein accumulation could be controlled by increasing potassium fertilizer at high N level. In addition, N physiological use efficiency (PE) and Nitrogen partial factor productivity (PFP) were higher at150kg ha-1K level than at another two K levels at both two N levels, but N harvest index (NHI) was decreased with raising potassium fertilizer.