Biomass Production, Nutrien Cycling And Energy Flow Of A Silvopastoral System

The silvopastoral system is an important type of the agroforestry system, which is widely used in the world. In recent years, increasing attention has been paid to silvopastoral system in our country to meet the needs of the great west explorition, eco-enviorment construction, foresty and stockbreeding development. Especially after the carrying out of the engineering of Returning Forestry to Farmland or Pasture (RFFP). It is realized as the most important management patterns in the RFFP area. But, most of the past studies have been constrained on techniques and benefits of tree-grass intercropping, non-timber forests and orchard grass covering. On the contrary, as an integrated system there are few studies of biomass production, nutrient cycle, energy transformation and utilization on the silvopastoral system, and even less on how to extend the industry chain by introducing the herbivorous stock and poultry to the system for the maximum ecological, economical and social benefits. In this dissertation, the silvopastoral system was constructed with apple, alfalfa and sheep, which were common in the dry and low mountainous areas in north China. With the guide of modern systematic ecology principles and agroforestry techniques, some modern techniques as sitefixed experiment method, ¹⁵N tracing technique are applied to quantify the characteristics of bio-mass production, nutrient cycle, energy transformation and utilization of the compound system. It is of great theoretical importance and practical value in exploring the intrinsic ecological relationships between different components of the system, quantifying its ecological process .And therefore, the optimum models of this silvopastoral system, with high efficiency and maximum ecological, economical and social benefits can be constructed. This dissertation was accomplished on the past 6a intensive study. The main conclusions were as follows:The apple-alfalfa-sheep system (AAS) affected the growth of alfalfas with shortening its individual height, increasing single leaf area and decreasing the specific leaf dry weight (SLW) and leaf: stem ratio. Compared to the CK2, the average photosynthesis rate of alfalfa below crown was decreased by 27.6%. As to the average biomass of 5-year alfalfas about 6rows, which blow or near crown were only 68.84% of CK2, while the middle 7rows of alfalfas had minor influences, with 97.64% of CK2's yields. The AAS had little effect on nutrition value of alfalfas. Thecrude protein content slightly decreased, while the content of acidic washing fiber and neutral washing fiber decreased too, which could increase digest rate of dry matter. And this indicated that the compound system can improve the digest quality of alfalfas, to some extent. Compared to CK1 of soil clean, the AAS with lm soil clean protective belt on both sides of apple tree, 100 leaves weight, SLW, Chlorophyll content and average photosynthesis rate of apple tree increased separately, individual yield of apple tree increased by 17.26%, average fruit weight by 7.93%, hardness by 10.24%, solid substance by 10.56%. Apple trees without soil clean protective belts (fully intercropped) showed consistent decrease in tree growth, fruit yield per tree and average fruit weight. Therefore, lm wide soil clean protective belt should be remained on both sides of apple trees in the AAS.In the 5-year AAS, above ground biomass (forage yield) of alfalfa reached 9402.95 kg-hm"2, which decreased merely by 2.54% compared to mono-culture (CK2), indicating comparatively high alfalfa productivity in the AAS. In the total primory productivity of 24496.6kg hm^-a"1 in the AAS, alfalfas occupy 44.68% and apple trees 55.32% separately. So that, the apple-alfalfa-sheep system could increase the primary productivity of apple orchard by 1.81 times.lkg gain of sheep generally requires alfalfa hay powder with dry matter of 16.62kg, crude protein of 2.57kg, and the metabolized energy of 130.72MJ. Every lhm2 apple-alfalfa compound system could support 15.5 young growing sheep or with-child mother sheep weighted 40 to 50kg each, with a daily gain of lOOg. The total second productivity of the compound system could reach 565.75kg hm^-a"1, the general biotic efficiency was 6.02%.From above results, an optimum model of apple-alfalfa-sheep system was proposed as: apple tree spacing 3mx4m, lm wide soil clean protective belts on both sides of apple trees, alfalfa row distance 30cm and 13 rows between two apple rows, each lhm2 could support 15.5 young growing sheep or with-child mother sheep weighted 40 to 50kg each, yearly gain 565.75kg.Compared with soil clean treatment, the AAS could increase the soil organic matter by 12.87% in the layer of 0⁴0cm.While, contents of total P, total K, available P and available K were consistently lower than that in the Control, which revealed the competitive use of P, K between apple trees and alfalfas, to some extent. In general, no large changes appeared in available N content, but in contrast to the CK1, a clearlyhigher NH4"1"—N content and a.lower NO3"—N content were in the AAS's. In the AAS, N, P, K in each apple tree organ separately higher than those in soil clean trees, while in alfalfas, N contents in the AAS were lower than mono-culture alfalfa system (CK2) with the exception of N content in hot summer.In the AAS, N, P, K return were separately 245.67 kghmV1, 17.71 kg-hm'V1 and 173.05 kghm^a"1, greatly exceeded to mono-culture systems. It showed that the AAS played an important role in accelerating nutrient cycling and rotation. In the AAS, N, P, K absorption coefficient separately were 5.76%, 1.03% and 0.17%, cycling coefficient separately were 62.14%, 29.65% and 62.35%, and remnant coefficient separately were 75.78%, 78.08% and 69.51%, nutrient utilization rate were separately 63.39, 419.66 and 90.30, recycle period cycle were separately 2.09a, 5.69a and 1.75a, most of them are between the apple tree mono-culture system and alfalfa mono-culture system. The apple-alfalfa-sheep system could improve the characteristics of mono-culture systems, by accelerating nutrient cycling and rotation in the system. Based on a N, P, K input-output budget analysis, N, P, K deficiency were found to be 47.19 kg-hnVV1, 10.57 kg-hm'V1 and 38.38 kg-hm'V1 in the AAS, A precise nutrient supply standard was put forward.Studies on sheep's utilization and transforming of nutrient elements indicated that N loss in feces occupied 30.83% of N take, N loss in urine occupied 51.12%, N digestion rate was 64.17%, N metabolizing remains were 13.05%; P digestion rate was 91.52%, P metabolizing remains were 87.43%; Kdigestion rate was 98.56%, K metabolizing remains were 31.27%? In this study,15 N isotopes were used to trace the N in sheep's body, soil and apple tree. By collecting feces, urine, the recovery rates of alfalfa N by sheep feces and urine were 25.07% and 35.18%. In the apple trees to which sheep feces and urine with labessed 15N were applied for over 10 months, the largest15 N content appeared on the new blades on the sheeting, and the following in turn were fine root>thin fruit branch> 1 a sheeting >2 a branch> thick root>trunk; 15N absorption of the apple tree was 632.08mg, 1-a branches occupied the largest distribution of 26.70%, and they were followed in turn by 2-a branches>new leaves on the sheeting > fine roots > leaves on fruits branches > fruits > thick roots > trunk. The total utilization of the apple tree was 10.53%, 1-a branches and 2-a branches stood for the first and second places, with the occupations separately were 2.81% and2.11%, they were followed in turn by new leaves on the sheeting>fine roots>leaves on fruits branches > thick roots > trunk. 15N remnant rate in 0⁶0cm soil layer was 78.03%, and loss rate was 11.44%. So, compared with other experiments to apply nitrogen, green manures, livestock fertilization for crops and trees, N cycling through sheep might not has a high utilization rate, but as far as its high rampancy and low loss were concerned, it could reduce N loss and increase the utilization efficiency.The annual solar radiation to the apple-alfalfa-sheep system summed up to 49868.65GJ-hm²a"1, photosynthetically active radiation was 24244.67 GJhm'^a'.The mean reflection rate of the AAS was 22.5%,which was higher than that of mono-culture orchard, and the overage transmission of the AAS was 18.0%, a little lower than that of mono-culture apple. Alfalfas,in the AAS, had a net fixed energy of 183.54 GJhm^a^and according to the total radiation, alfalfa powder solar energy efficiency was 0.335%, and according to photosynthe tically active radiation, it was 0.688%; The total, as a whole, processed a primary net energy production of AAS was 431.33 GJ-hm"2-a"\ in which apple trees occupied 57.45%, and alfalfas42.55%, which were slightly higher than that of mono-culture cultivated alfalfa and highly exceeded those of mono-culture apple. With respect to the total radiation, the primary produced solar energy dfficiency could reach 0.86%, and with reference to active radiation, 1.78%, which exceeded those of the mono-culture apple orchard by 41.86% and 42.70% separately, and exceeded the mono-culture alfalfa system by 8.14% and 8.43% separately.Feed merely on alfalfa hay powders, sheep's energy digestion rate could reach 59.08%, and energy assimilation efficiency was 50.74%, energy growing efficiency 10.28%, energy production efficiency was 19.86%, the secondary energy net production was 16.7632 GJhm^a1, the secondary energy efficiency was 10.05%.Combining the energy primary production with secondary production, the net energy production of the AAS was 448.09 GJhm^a"1, with reference to the total radiation, solar energy transforming efficiency was 0.90%, while according to photosynthe tically active radiation, it was 1.85%, which exceeded those of the mono-culture apple tree by 44.44% and 44.86%, and exceeded those of mono-culture alfalfa system by 12.22% and 11.89% separately. Therefore, the apple-alfalfa-sheep system could effectively improved the use of solar energy.Innovations of this paper are: for the first time, studied the apple-alfalfa-sheep...