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The relationship between the leaf nitrogen content (LNC) and hyperspectral remote sensing imagery (HYP) was determined to construct an estimation model of the LNC of drip-irrigated sugar beets, aiming to [...]

To improve peanut yield under drip irrigation in Xinjiang, effect of potassium fertilizer application was investigated. Huayu 9610 (T1, a common cultivar in Xinjiang) and Heihua 5 (T2, a high yield cultivar) were used as materials at the Agricultural Meteorological Experiment Station in Wulanwusu, Xinjiang. Four potassium (K2O) fertilizer gradients were set as K0 (0 kg/hm²), K1 (150 kg/hm²), K2 (225 kg/hm²) and K3 (300 kg/hm²), and thus the potassium rates were at 15%, 40%, 30% and 15% at the seedling, pegging, podding and full fruit ripening stages respectively. Results showed that the main stem height and lateral branch length of Huayu 9610 and Heihua 5 changed parabolically with the increase of potassium application. The dry matter accumulation were the highest at K2 level, which were 84.37 g per plant and 89.37 g per plant, respectively. Compared with no potassium fertilizer, the main stem height and lateral branch length of K2 treatment increased by 17.91% and 16.56%, 7.4% and 12.31%, respectively. The number of nodules was the highest at podding stage, which was 42.0 per plant and 45.3 per plant respectively. The leaf area index increased with the increase of potassium fertilizer application, and reached the maximum at 90 days after emergence. The photosynthetic potential also changed in a parabolic shape with the increase of potassium fertilizer application rate, and reached the maximum value of 4.38 m2·d and 4.51 m2· d respectively after 75-90 days of K2 treatment. The fertilizer contribution rate and agronomic utilization rate of K2 treatment were the largest, which were 26.06% and 1.83 kg/kg (for Huayu 9610), 25.18% and 1.67 kg/kg (for Heihua 5), respectively, and the yields were 9628.38 kg/hm² and 10 368.35 kg/hm², respectively. The results showed that potassium application amount of 225 kg/hm² at K2 level could be used as reference for drip irrigation peanut in Xinjiang, China. [ABSTRACT FROM AUTHOR]

The adjustment of the C/N ratio by straw combined with fertilizer nitrogen (N) not only affects straw decomposition but also affects soil organic carbon (SOC) decomposition, i.e. the priming effects. Therefore, it is doubly important to study how the ratios of straw to N fertilizer influence the release of endogenous and exogenous C for greenhouse gas emission reduction and soil fertility improvement. We conducted a 32-week laboratory incubation experiment with 13 C labeled maize straw under different N levels in farmland soil collected from fields in Huantai County to investigate the effect of the ratios of straw to N fertilizer on straw decomposition and the priming effects. Four treatments were set up, including CK, corn straw (S), corn straw+low urea rates (SN1), and corn straw+high urea rates (SN2). Dynamic sampling was conducted during the early stage (0-10 d), the middle stage (11-43 d), and the later stage (44-224 d) of straw decomposition. The approach was based on using a two-source mixing model to differentiate two sources of soil CO 2 (straw and soil-derived C). With an increase in the incubation time, the contribution of SOC decomposition to soil CO 2 emissions first decreased and then increased. On the contrary, the contribution of straw mineralization to soil CO 2 emissions first increased and then decreased. By the end of the incubation time, the contribution of SOC and straw decomposition to soil CO 2 emissions was 0.84-0.86 and 0.14-0.16, respectively. Over the whole incubation period, the effects of N fertilization on straw decomposition first increased and then decreased. The promotion degree of high and low N fertilization on straw decomposition was up to 15.8% and 7.9%, respectively. Over the whole incubation period, the inhibition degree of low N fertilization reached up to 7.1%, while high N fertilization showed a slight promotion trend of 0.7%. Therefore, the regulation of C:N by straw combined with fertilizer N not only affected the contribution of exogenous straw to SOC but also influenced the decomposition of endogenous SOC, and then influenced soil C fixation. Over the whole incubation period, straw C retention could not compensate for CO 2 released by the priming effects, which led to a net loss of SOC.