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We investigated the dynamics and factors influencing the N uptake capacity in two sub-root systems of maize seedlings under partial N stress. Maize seedlings were grown in split-root containers containing nutrient solutions. Two N application conditions prior to partial N stress (full-strength N (4.0 mM): CP; N stress: SP) were considered. Thus, two experiments were conducted: (A) four treatments: CPNc, CPN2, CPN1 and CPN0, in which half of the root system was exposed to 4.0 mM, 2 mM, 1 mM and 0 mM N (CPNc–c, CPN2–2, CPN1–1 and CPN0–0), respectively, and the other half received full-strength N (CPNc–c, CPN2–c, CPN1–c and CPN0–c); (B) four treatments: SPNc, SPN2, SPN1 and SPN0, in which both sub-root systems received 4.0 mM, 2 mM, 1 mM and 0 mM N for 6 days, respectively, after which half of the root system was maintained at original N level (SPNc–c, SPN2–2, SPN1–1 and SPN0–0) and the other half received full-strength N (SPNc–c, SPN2–c, SPN1–c and SPN0–c). At 0.25 days after treatment (DAT), CPN2–c and CPN1–c enhanced N inflow rates (Iroot), whereas CPN0–c decreased it by 27.3% compared with CPNc–c, Iroot in CPN2–c, CPN1–c and CPN0–c was uniformly enhanced at 1 DAT, but were only enhanced in CPN0–c at 5 DAT compared with CPNc–c. In contrast, SPN1–c had a significantly increased Iroot by 10.52% compared with SPNc–c, although other treatments showed a negative effect on Iroot at 0.25 DAT. At 1 and 5 DAT, Iroot in SPN2–c, SPN2–2, SPN1–c, SPN1–1 and SPN0–c were significantly lower than that in SPNc–c. Furthermore, CP significantly enhanced Iroot in non-stressed sub-roots compared with SP. Additionally, CPN2 improved shoot dry mass and N use efficiency even under SPN2. Thus, N uptake capacity in each sub-root zone varied not only depending on the severity and duration of the N stress, but was also related to the N status prior to partial N stress. Moreover, the occurrence and disappearance of the root compensatory effect were delayed with increasing N stress severity. A higher compensatory effect developed following CP, even under CPN0.

The influence mechanism of heterogeneous nutrient distribution on compensatory growth of maize seedlings is a key topic in the interaction between crops and soil environment. We evaluated the significance of root hydraulic conductance (Lp) and related parameter changes in water uptake and growth regulation of plants under different nitrogen (N) conditions. Maize seedlings were grown in split-root containers containing N solutions. Three N treatments were applied: (1) full-strength N (control: C), in which both sub-root systems received 4.0 mM N (each sub-root: C44); (2) partial N deficit (D), in which each sub-root system received 2.0 mM N (D42) or full-strength N (D44); and (3) partial N resupply (S), in which both sub-root systems received 2.0 mM N for six days, followed by 2.0 mM N (S22) or full-strength N (S24). The shoot dry mass in D increased gradually with early development, and was greater than that in C and S within 15–21 day, suggesting that the superiority of partial N deficit (D) in term of maize seedling growth was apparent and caused compensatory growth. Moreover, the slope and intercept in D44 and D42 between ΨL vs. Lp and shoot N content vs. Lp were obviously greater than that in C44, S24 and S22, indicating that higher plant dry mass in D might be attributable to the maintenance of a similar ΨL and improved shoot N content. In addition, the slopes and intercepts in D44 and D42 between Lp vs. root surface area and shoot N content vs. root surface area were higher than that in S24 and S22, suggesting that compared with partial N resupply, partial N deficit was more advantageous to root water uptake and N accumulation at the same level of root surface area, thus resulted in higher dry mass of maize seedlings. However, partial N resupply significantly increased root cortex thickness/diameter ratio and reduced root vessel diameter, which resulted in lower Lp, ΨL and shoot N content during 12–21 day. Unexpectedly, at 21 day, the shoot dry mass in S could recover to the level of control. The regulation mechanisms in partial N resupply will be the focus of future studies. Thus, when adopting the method of partial N application, it is necessary to consider the soil N condition before partial application.

International audience; Nitrogen (N) accumulation in plant reproductive organs during the post-anthesis growth phase of maize and wheat plays a crucial role in the formation of grain yield and quality. However, little is known about the effect of crop pre-anthesis and post-anthesis N status on ear N accumulation (NA(E)). This study endeavored to extend the crop N dilution theory already developed for vegetative growth period to determine ear critical N concentration (%Nc(E)) during post-anthesis period of crop growth for analyzing the difference of NA(E) under various N levels. The data including the weight of dry mass (W) and N concentration of entire plant and ear, post-anthesis plant N uptake (PAN(u)) from soil, grain number (GN), and grain weight (GW) were collected on wheat (two cultivars) and maize (three cultivars) from eight N rates (0-300 kg N ha(-1)) field experiments. The results revealed that the process of %N dilution exists in ear and it is plausible to extend the concept of %Nc(E) curve till crop post-anthesis period. The %Nc(E) curves as function of ear dry mass (W-E) of wheat (%Nc(E) = 2.85W(E) (.0.17)) and maize (% Nc(E) = 2.22W(E)(-0.26)) were lower than those developed in maize and wheat on whole plant basis. This study revealed that the ear has the potential to diagnose ear N status under different N conditions and the increases in ear N nutrition index (NNIE) during the post-anthesis period with increasing N rate were well synchronized with plant NNI (NNIp) at anthesis. GN and GW of maize and wheat showed significantly positive correlation with NNIp at anthesis and NNIE at maturity under N-limiting treatments, and GN and GW could keep relatively stable under non-N limiting treatments. NNI and NNIE showed the potential capacity to predict GN and GW of maize and wheat under N limiting condition. Ear critical N accumulation (NAcE) was calculated using ear N-c curve to investigate the differences mechanism of NA(E) under different N conditions. The difference of NAC(E) under different N treatments was deduced from the pre-anthesis N status of maize and wheat by determining GN. The ear N deficiency (ND E ) between NAC(E) and NA(E) was co-regulated by plant pre-anthesis and post-anthesis N status, which in turn have potential to explain the variance of GW at maturity in both crops. The significantly attenuated effect of pre-anthesis N deficiency on ear potential N demand in maize and wheat indicated that the postanthesis N management must consider the pre-anthesis N status and the corresponding reduction of the postanthesis N input to prevent N loss under N limiting treatment in both crops. Maize was more dependent on postanthesis N status while wheat was more reliant on pre-anthesis N status for satisfying ear growth and producing optimum GN owing to the differential values of PAN(U)/NA(E) in maize and wheat during post-anthesis period. This study provides a new viewpoint on post-anthesis N management of maize and wheat for enhancing N use efficiency and grain yield.

Exploring the interactive effect of water and fertilizer on yield, soil water and nitrate dynamics of young apple tree is of great importance to improve the management of irrigation and fertilization in the apple-growing region of semiarid northwest China. A two-year pot experiment was conducted in a mobile rainproof shelter of the water-saving irrigation experimental station in Northwest A&amp, F University, and the investigation evaluated the response of soil water and fertilizer migration, crop water productivity (CWP), irrigation water use efficiency (IWUE), partial factor productivity (PFP) of young apple tree to different water and fertilizer regimes (four levels of soil water: 75%&ndash, 85%, 65%&ndash, 75%, 55%&ndash, 65% and 45%&ndash, 55% of field capacity, designated W1, W2, W3 and W4, respectively, three levels of N-P2O5-K2O fertilizer, 30-30-10, 20-20-10 and 10-10-10 g plant&minus, 1, designated F1, F2 and F3, respectively). Results showed that F1W1, F2W1 and F3W1 had the highest average soil water content at 0~90 cm compared with the other treatments. When fertilizer level was fixed, the average soil water content was gradually increased with increasing irrigation amount. For W1, W2, W3 and W4, high levels of water content were mainly distributed at 50~80 cm, 40~70 cm, 30~50 cm and 10~30 cm, respectively. There was no significant difference in soil water content at all fertilizer treatments. However, F1 and F2 significantly increased soil nitrate-N content by 146.3%~246.4% and 75.3%~151.5% compared with F3. The highest yield appeared at F1W1 treatment, but there was little difference between F1W1 and F2W2 treatment. F2W2 treatment decreased yield by 7.5%, but increased IWUE by 11.2% compared with F1W1 treatment. Meanwhile, the highest CWP appeared at F2W2 treatment in the two years. Thus, F2W2 treatment (soil moisture was controlled in 65&ndash, 75% of field capacity, N-P2O5-K2O were controlled at 20-20-10 g&middot, tree&minus, 1) reached the best water and fertilizer coupling mode and it was the optimum combinations of water and fertilizer saving.

Effects of severity and duration of osmotic stress on partial root system were investigated on root hydraulic conductance (L p ) and growth in each sub-root system. The maize seedlings were raised in nutrient solution with the roots divided equally into two containers. At 12 days after transplanting, half of root system was subjected to osmotic stress of −0.2, −0.4 and −0.6 MPa using PEG 6000 added in the solution, and no PEG 6000 solution was taken as control (CK). L p and root growth in each sub-root system were measured at 0, 0.25, 0.5, 1, 3, 5, 7 and 9 days after treatment (DAT). Results show that compared to CK, −0.2 MPa treatment enhanced the hydraulic conductance per root area (L pr ) in non-stressed sub-root system by 12 % at 0.5 DAT. In −0.4 MPa treatment, L pr in non-stressed sub-root system was significantly increased at 9 DAT. But in −0.6 MPa treatment, significant decrease of 12–40 % was observed in non-stressed sub-root system during 0.5–3 DAT if compared to CK, indicating that the threshold of osmotic stress for the compensatory effect of water uptake in non-stressed sub-root system was between −0.2 and −0.4 MPa. In addition, the root area growth rate in non-stressed sub-root system was significantly higher than that in CK during 0.25–0.5, 1–3 and 5–7 DAT for −0.2, −0.4 and −0.6 MPa treatments, respectively. Similar trend also was observed for root length growth rate, indicating that osmotic stress could still stimulate the compensatory effect of root growth other than water uptake under partial root system. Moreover, the occurrence of such compensatory effect delayed with the increasing osmotic stress. Meanwhile, −0.2 MPa treatment had no significant effect on maize shoot growth but −0.4 and −0.6 MPa treatments inhibited shoot biomass accumulation, which resulted in higher root/shoot ratio in −0.4 and −0.6 MPa treatments. Thus root plasticity in hydraulic conductance and root growth in different root zones varied largely depending on the severity and duration of osmotic stress under partial root system.

In recent years,the quality and security of vegetables have being increasingly concerned by people and investigated by researchers.However,vegetable quality decline is very common due to excessive irrigation and irrational fertilization.The nitrate content is an important index which is used to evaluate vegetable quality.Although tomatoes have been grown successfully for many years in many parts of the world,there is no accurate formula or recipe on both the amount of irrigation and fertilizer levels to get high quality tomato fruit.Alternate partial root-zone irrigation(APRI) is a new water-saving technique and may improve crop water use efficiency and fertilizer use efficiency.To determine the effects of irrigation amount and fertilizer rates of nitrogen,phosphorus,potassium and manure on the nitrate content in tomato fruits under APRI,the quadratic orthogonal regressive rotation design with five factors was used in pot experiment,in which five rates were set for every experimental factor.A regression model on the amount of irrigation water and fertilizers and the nitrate content in tomato fruits was established.Based on the regression equation,the single,interactive and coupling effects of these five experimental factors on the nitrate content in tomato fruit were analyzed.The results showed that if other factors were zero codes,the nitrate content in tomato decreased firstly and then rose with irrigation water increase,while it showed a reverse trend with N and P fertilizer levels.The nitrate content in tomato increased gradually with manure amount,but it was not affected by K fertilizer level.The interactions on the nitrate content in tomato fruits between P fertilizer and manure levels,N and P fertilizer levels showed positive effects,while the interactions between irrigation amount and K fertilizer or manure level,as well as N and K fertilizer levels were negative effects.The coupling effects between two of these five experimental factors showed that the nitrate content in tomato fruits increased markedly with higher irrigation amount when no manure was applied,while it decreased firstly and then increased with irrigation amount for the other manure and all K fertilizer rates.The nitrate content in tomato decreased with K fertilizer or manure increase when irrigation amount was above the mid level.The nitrate content in tomato increased firstly and then decreased with N fertilizer increase for any P or K fertilizer rate.The nitrate content was less when P fertilizer rate was at the highest than any other level,and it was the lowest when P and N fertilizer rate were at the highest and the lowest,respectively,suggesting that lower N fertilizer and higher P fertilizer rates could decrease the accumulation of nitrate content in tomatoes.Interestingly,the situation was different for K fertilizer.Higher K fertilizer rate could reduce the nitrate content significantly only when the N fertilizer rate was above the mid level.The coupling effects of P fertilizer with manure rates on the nitrate content in tomato fruits indicated that increasing P fertilizer properly and decreasing manure application at the same time could greatly contribute to less nitrate content in tomato fruits.