Research About Monitoring Cotton Growth Based On The Spatial Distribution Of Photosynthetically Active Radiation

To develop and master the monitoring technology which can quickly and accurately get the growth condition of crop is the premise for higher yield, higher quality and higher efficiency. After knowing the growth condition of crop, proper field management practices which are advantage for establishing suitable canopy structure and standardized growth could be adopted. Photosynthetically Active Radiation(PAR) is highly linear correlated with the yield of crop. The spatial distribution of PAR in crop canopy greatly affect the dynamic change of crop growth condition in different stages. Monitoring the growth condition of cotton based on the spatial distribution of PAR has very important practical significance and academic value for quickly and accurately monitoring the growth condition of crop and promoting the simple cultivation and mechanization. Thus field experiments were conducted in 2014 and 2015 at the experimental station of the Institute of Cotton Research of the Chinese Academy of Agricultural Sciences in Anyang, Henan, China(36° 06’ N and 114° 21’ E) using transgenic Bt SCRC28(Gossypium) as material with six plant population densities(15000、33000、51000、69000、87000、105000 plants/hm2)and three repetition. The PAR data were got using the spatial grid method and spatial local interpolation of spatial statistics. Then the spatial distribution of the interception rate of PAR(Ir) and its’ relationships with the growth condition of cotton were analyzed. Also new method to quickly acquire Ir was explored using digital images. The main results were as follows:(1) The semivrivances of Ir under different plant densities at preliminary stage of boll forming, mid-term of boll forming and boll opening stage show that there was good space structural and spatial correlation of Ir in cotton canopy. With the proceeding of growth the ranges of spatial correlation of Ir under stable plant population increased. The analysis of spatial distribution of Ir at different points, different profiles and zones at the three stages indicated that the Ir decreased with increasing height on vertical direction; On horizontal direction, the more close to the main stem the more higher the Ir was at the early or later stage of cotton growth. While the Ir changed little at the mid-stage of cotton growth on horizontal direction, especially the higher plant densities.(2) The Ir was exponentially related to the Leaf area index(LAI) under six plant densities. With the quickly develop of leaf area the Ir also increased quicky at early stage of cotton growht. When the LAI reached a certain degree the Ir increased slowly and finally got a stable level; From budding to flowering the low plant densities have a higher morphogenesis rate of fruit branches. And with the increase of accumulated Ir, the speed of morphogenesis rate of fruit branches first increase then decrease; The more accumulated PAR interception before the peak the more early the senescence happened, which can be indicated by the decresed of the days when nodes above first position white flowers(NAWF) was 5 and the increased percentage of pre-frost seed cotton yield; There was a positive linear relationship between accumulated Ir and dry mass of cotton. However, the linear relationship between the cotton seed yield and the total canopy accumulated Ir were not obvious, which may caused by the shedding or unsuitable spatial distribution of the reproductive organs of cotton canopy.(3) The spatial distribution of reproductive organs of cotton at preliminary stage of boll forming, mid-term of boll forming and boll opening stage show that with the increase in density the number of reproductive organs per plant decreased. A lot of reproductive organs shed before boll opening stage coming. And the shedding positions more and more close to the main nodes with the rising of fruit branch or with increase in density. The relationships between Ir and the probability of bolls, the probability of shedding in different zones indicated that the accumulated Ir in vertical zone 1, vertical zone 2 and external zone have higher negative relationship with the probability of boll in those zones; The accumulated in vertical zone 2 and inner zone have a close relationship which presented upward quadratic curves with the probability of shedding in those zones. So the growth condition of cotton can be got by acquring the Ir of cotton canopy.(4) The values of Red(R), Green(G), B(Blue), Intesity(I), Value(V), Y channel(Y), I channel(I2) and Q channel(Q) at six plant population densities presented upward quadratic curves during the entire growth period in two years; The values of hue(H and H2) under six plant population densities showed downward quadratic curves during the whole growth period in two years; The values of saturation(S and S2) had trends between those. However, only the quadratic curves for H and H2 yielded consistent results with R2 >0.8 which were similar with canopy Ir over the two years. Those findings indicated that the color attributes except hue were strongly affected by the outside environment; Regressions of Ir on the 12 color attributes revealed that the H and H2 values were significantly linearly correlated with LI. Thus, the H and H2 values could be used to quantify Ir. And the validation of the estimation model confirmed this hypothesis.In conclusion, Ir could be used to monitor the growth of cotton through the relationships between the Ir of canopy and cotton growth. The hue of cotton canopy digital images can reflect the Ir of canopy which provide a solid theoretical basis to conveniently, quickly and accurately monitor the growth codition of crop.