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Soil phosphorus (P) is essential for plant growth and influences biological processes. Determining the amounts of available P to plants has been challenging, and many different approaches exist. The traditional Hedley sequential extraction method and its subsequent modification are applied to determine different soil P forms, which is critical for understanding its dynamics and availability. However, quantifying organic and inorganic P (Po & Pi) in different extracts is labor-intensive and rarely used with large sample numbers. As an alternative, near-infrared spectroscopy (NIRS) has been employed to determine different P fractions at reasonable costs in a short time. This study aimed to test whether the analysis of P fractions with NIRS is an appropriate method to disentangle the effects of P limitation on high-altitude grassland ecosystems, particularly with fertilizer amendments. We explored NIRS in soils from the grassland soil samples on the northern Tibetan Plateau. First, we extracted the P fractions of 191 samples from the Haibei Alpine Meadow Ecosystem Research Station at four depth increments (0–10 cm, 10–20 cm, 20–40 cm, and 40–70 cm), including nutrient additions of nitrogen (N) and P. We compared the results of the Hedley extraction with the laboratory-based NIRS model. The fractionation data were correlated with the corresponding NIRS soil spectra; the coefficient of determination (R2) of the NIRS calibrations to predict P in P fractions ranged between 0.12 and 0.90; the ratio of (standard error of) prediction to the standard deviation (RPD) ranged between 1.07 and 3.21; the ratio of performance to inter-quartile distance (RPIQ) ranged from 0.3 to 4.3; and the model prediction quality was higher for Po than Pi fractions, and decreased with fertilizer amendment. However, the external-validation results were not precise enough for the labile P fractions (RPD < 1.4) due to the limited number of samples. The results indicate that using NIRS to predict the more stable P pools, combined with Hedley fractionation focusing on the labile P pool, can be a promising approach for soils in alpine grasslands on the Tibetan Plateau. [ABSTRACT FROM AUTHOR]

Plastic‐film mulch significantly improves maize (Zea mays L.) productivity in hydrothermally limited areas, but there is a lack of understanding of how mulch affects the partitioning of dry matter and nutrients to grain. This study was conducted to investigate the effects of plastic‐film mulch on the remobilization of biomass and nutrients accumulated in the presilking stage to grain during the grain‐filling period. A 2‐yr field experiment was conducted with five maize hybrids in a cold semiarid environment. The vegetative biomass in all cultivars at maturity was generally greater than that at silking regardless of whether the soil was mulched or not, indicating that there was no translocation of presilking assimilates to the grain. The increased grain yield in plastic‐film mulched plots compared with those that were nonmulched was ascribed to their enhanced partitioning of postsilking assimilates to grain. Conversely, increased accumulation of nitrogen and phosphorus in grain at maturity under mulch relative to no mulch mainly was due to increased remobilization from presilking vegetative organs. The benefit of plastic‐film mulch in increasing the partitioning of postsilking assimilates and the remobilization of nutrients from presilking vegetative organs was greater in a drier than in a wetter year. The results of this study strongly support the conclusion that in hydrothermally limited environments, maize generally does not remobilize presilking assimilates but does remobilize presilking nitrogen and phosphorus in vegetative organs to the grain during grain filling. Further, plastic‐film mulched, relative to nonmulched, maize increases the translocation to the grain of postsilking assimilates and presilking nitrogen and phosphorus accumulated in vegetative organs. Core Ideas: Mulch increased grain yield through enhanced partitioning of postsilking assimilates to grain.Mulch increased N & P remobilization from vegetative organs to maintain the grain concentration.Mulching efficiently alleviates effects of unfavorable climates on grain formation. [ABSTRACT FROM AUTHOR]

Conversion of grassland to cropland affects microbial transformation of plant derived organic substances and the accumulation of microbially synthesized products in soil. We investigated long-term effects of agricultural use [more than 50 years' rotation with barley ( Hordeum vulgare ) and rapeseed ( Brassica rapa )] after conversion from grasslands (grazed in the winter season) on the contents and composition of non-cellulose sugars and amino sugars in a broad range of soils on the Tibetan Plateau. Soils from two types of croplands (barley or rapeseed) were compared to a reference grassland soil by detailed analysis of plant vs. microbial and bacterial vs. fungal biomarkers. Long-term cultivation decreased total soil organic matter (SOM), light SOM and total non-cellulose sugar contents in the 0–20 cm soil by 27%, 47–72% and 57%, respectively, reflecting decreased root biomass compared to grassland. The ratios of (galactose + mannose)/(arabinose + xylose) and (rhamnose + fucose)/(arabinose + xylose) were both 26% smaller in cropland than in grassland soils, while the ratios of hemicelluloses in shoots or roots were similar between native and cultivated plants. Consequently, net transformation of plant substances to microbially synthesized polysaccharides decreased in cultivated soils. The total amino sugars (muramic acid, glucosamine, mannosamine, galactosamine) in cropland soils decreased by 42% as did their contribution to the SOM pool by 22%, compared to grassland soils, but the ratio of glucosamine/muramic acid in cropland soils doubled when compared to the grassland soil. This shows a strong decrease in microbial residue under cultivation, with the magnitude of the decrease greater in the bacterial than in the fungal components. All the above results from the intensively sampled site were confirmed in seven other sites featuring lower sampling intensity. We concluded that the conversion of grassland to cropland strongly decreases microbial transformation of plant residues and accumulation of the resulting microbial compounds – necromass – in soil (i.e., reduction of microbial input to stable SOM). The conversion also leads to a shift in the composition of microbial compounds towards a decreasing contribution of bacterial compared to fungal necromass. [ABSTRACT FROM AUTHOR]

Plastic-film mulch is an agricultural technology widely used for maize ( Zea mays L.) production in northern China, but the effects of the interaction between cultivar and plastic-film mulch on the grain yield and biomass production have not been studied. Five maize hybrids, Jinsui 4; Jixiang 1; Pingyu 8; Xianyu 335 and Yuyuan 5, were assessed in 2014 and 2015 in plastic-film mulched and non-mulched ridge-furrow plots in a cold semiarid environment. In 2014, the grain yield of the five cultivars varied from 685 to 898 g m −2 with no mulch, and from 966 to 1228 g m −2 under mulch. In 2015 (drier and warmer than in 2014), the grain yield varied from 179 to 353 g m −2 without mulch, and from 548 to 1021 g m −2 with mulch. By incorporating the variation in grain yield over cultivars, mulch treatments and cropping years, Jixiang 1 was the highest yielding cultivar: in 2014 the grain yield reached 898 g m −2 under no mulch, compared to 1228 g m −2 under mulch, while in 2015 the grain yield was 329 g m −2 under no mulch compared to 1021 g m −2 under mulch. Cultivar and mulch independently affected the aboveground biomass and harvest index of maize. Jixiang 1 attained high yields as a result of average aboveground biomass, but high harvest index. Differences in maize water use efficiency (grain yield per unit of evapotranspiration) as affected by mulch and cultivar paralleled those of grain yield due to minor effects of mulch and cultivar on growing-season evapotranspiration. The effects of plastic-film mulch on maize root biomass in the upper 0.6 m soil profile and root/shoot ratio varied with cultivar. Averaging years and mulch treatments, Jixiang 1 had the smallest root biomass in the upper 0.6 m soil layer and Jixiang 1 and Jinsui 4 had smaller root/shoot ratios than the other three cultivars. We conclude that the effects of plastic-film mulch on the grain yield, root biomass and root/shoot ratio varied significantly with cultivar. A moderate aboveground biomass and high harvest index may give satisfactory grain yield in plastic-film mulched or non-mulched fields in hydrothermally-limited areas. A wide variation of root/shoot ratio with maize cultivar and cropping year indicated that using a fixed root/shoot ratio to estimate the root carbon input to the soil would induce large uncertainty. [ABSTRACT FROM AUTHOR]