Phu V. Nguyen

Influence of direction and distance from trees on wheat yield and photosynthetic photon flux density (Qp) in a Paulownia and wheat intercropping system

Abstract A Paulownia -winter wheat intercropping experiment with the object of quantifying photosynthetically active radiation (PAR) and its effect on wheat yield was conducted 60 km south of Zhengzhou (35°N 113°E), Henan Province, PR China, from September 1991 to July 1992 using a tree and crop interface approach. The middle row of three 240 m long rows of 11-year-old trees was studied for its effects on the yield of irrigated and fertilized winter wheat. Photosynthetic photon flux density ( Q p ) was quantified using a split-plot design with four blocks. There were four distance (subplot) treatments (2.5 m, 5 m, 10 m and 20 m) and two direction (main plot) treatments laid out to the east and west of a north-south tree line. Results showed no difference in direction effects but Q p did affect total grain weight ( P = 0.0047) between 2.5 m and 20 m. A regression equation was fit using the mean for each distance treatment: Y = 391.7 + 4.57 X with r 2 = 0.9310 indicating a yield increase of 4.57 g m −2 (45.7 kg ha −1 ) over a distance of 2.5 m to 20 m from the trees.

Quality and decomposition of black locust (Robinia pseudoacacia) and alfalfa (Medicago sativa) mulch for temperate alley cropping systems

Black locust and alfalfa mulch quality were characterized over a 9-week period of decomposition. Both mulch materials were harvested with a forage harvester. The black locust material was harvested from trees annually coppiced for four years, the alfalfa from a preflorescent second cutting. Two identical, adjacent experiments were conducted, one on each mulch source. A randomized complete block design was used with four replications for this single factor experiment. Fifty grams fresh weight of both mulch types were placed in litter bags, made of 98% shade cloth, a woven plastic with holes approximately 1×0.5 mm. The treatments included two placements of the mulch material, surface and buried. Sampling took place on weeks 0, 1, 3, 6, and 9.The incorporation of mulch materials appears to accelerate dry weight loss. From an initial dry weight of 44.25 g, the buried black locust mulch averaged 4.58 g, while the surface mulch averaged 7.41 g by week 6. The alfalfa mulch initially weighed 40.99g, with buried mulch averaging 1.75 g and surface mulch averaging 4.08 g by week 9.Carbon concentration of alfalfa mulch increased with time in both mulch placements from 43.6% to 57.6% and 51.8% in surface and buried mulch, respectively. Black locust, with an initial carbon concentration of 46.9% increased to 55.9% for the buried mulch and to 53.89% in surface mulch. Nitrogen concentrations increased as well in buried mulch. Lignin concentrations increased dramatically over time for both species of mulch. Black locust lignin concentrations rose from 13.11% to 51.0% (buried) and 32.9% (surface); alfalfa mulch lignin concentrations rose from 6.67% to 31.4% (buried) and 47.7% (surface).

Influence of orientation on wheat yield and photosynthetic photon flux density (Qp) at the tree and crop interface in a Paulownia—wheat intercropping system

Abstract An on-farm field research study to characterize wheat yield in plots oriented 2.5 m east (E), west (W), and north (N) from the canopy of a north-south row of 11-year-old Paulownia trees was conducted at Zhengzhou, Henan Province, PR China. Wheat yield was higher on the east orientation compared with the west and north as determined by total grain weight and 1000-grain weight. Measured photosynthetic photon flux density (Qp) was higher on E orientation during critical stages of wheat development. Soil pH, soil organic matter, available nitrogen, phosphorus, and air temperature parameters did not affect yield differences. In a second, related study, yield data from plots with and without plastic root barriers, placed to a depth of 1 m between the tree and winter wheat yield plots located 2.5 m E or W of the tree row, indicated that tree and crop root interaction had no effect on total grain weight or 1000-grain weight. However, there was a significant increase in yield of the E orientation as compared with the W.

Net assimilation and photosynthate allocation of Populus clones grown under short-rotation intensive culture: Physiological and genetic responses regulating yield

The overall objective of this project was to determine the differential responses of poplar clones from sections Tacamahaca and Aigeiros of the genus Populus to varying levels of applied water and nitrogen. Above- and below-ground phenology and morphology, photosynthate allocation, and physiological processes were examined. By manipulating the availability of soil resources, we have been able to separate inherent clonal differences from plastic responses, and to determine genotype-environment interactions. We also have been able to make some contrasts between trees grown from hardwood cuttings and coppice sprouts. Our overall hypothesis was that carbon allocation during growth is greatly influenced by interactions among moisture, nitrogen, and genotype, and that these interactions greatly influence yield in short-rotation plantations. As is true of any project, some of our original expectations were not realized, whereas other initially unforeseen results were obtained. The reduced funding from the Biofuels Feedstock Development Program (BFDP) during the last few years of the project slowed us down to some extent, so progress was not been as rapid as we might have hoped. The major problem associated with this funding shortfall was the inability to employ skilled and unskilled student labor. Nonetheless, we were able to accomplish most of our original goals. All of the principal investigators on this project feel that we have made progress in advancing the scientific underpinning of short-rotation woody biomass production.