Effect Of Soil Penetration Resistance On Growth And Water Relations Of Maize In Red Soil Of South Hubei

Seasonal drought is a key factor restricting the farming of the red soil area in South China. The physical nature of red soil is very important in the formation and development of drought. Due to its abundant clay particles and stable aggregates, red soil has high penetration resistance, which increases as the water content decreases. The soil resistance inhibited roots growth downward and water uptake. This may worsen the drought. On the contrary, it may reduce the root consumption and signal the plant to prevent an even worse drought. Therefore, the red soil resistance’s effects on the formation and development of seasonal drought can’t be overlooked. However, there are few researches on the effect of soil penetration resistance on crops during drought period. Thus we hardly know the role of soil penetration resistance plays in the drought of soil-crops. The significance, which reduces seasonal drought through controlling the red soil resistance by tillage, is also unclear. The objectives of this thesis were to study the change of soil penetration resistance with water and the effect of the soil penetration resistance on the crop growth, and analyzed the effect of the soil resistance on the soil-crop water relations. From the results, some scientific basis were provided for discussing the formation mechanism of seasonal drought and defending the seasonal drought in red soil area.The pot experiments were conducted several times from November,2011to May,2012. It used the dual-factor method of water content and soil bulk density, set three levels of soil bulk density (1.1、1.3、1.5g/cm3) and two water content disposals (continuous drought-D and sufficient watering-W). The field experiment was carried out in two lots, Plot A and Plot B, from June to September in2012. The Plot A regulated the soil penetration resistance by four tillage measures, which included deep tillage-D, conventional tillage-C, no tillage-N, and compaction-P. Each of the measures consisted of two water treatments (rainfall without irrigation for the whole growth period-I1and irrigation upon no rainfall for7days-I2). The Plot B regulated the soil resistance by long-term fertilizer from1998till now. It set four fertilizer treatments, including no fertilizer-CK, application of chemical fertilizer-NPK, application of manure-PCM and application of chemical fertilizer with straw returning-NPKM. There were without tillage. In both methods the red soil was from red clay and summer maize was planted. The drying method was used for water content. TYD-1micro-penetrometer (in pots) and SC900soil penetrometer (in fields) were used to measure the soil penetration resistance. The pot experiments measured the root morphology parameters, and the field experiment measured maize growth morphology parameters, root distribution, root water potential, leaf water content and the maize yield. The main findings are showed as follows:The relationship between red soil penetration resistance and water content was non-linear and negative significantly. The penetration resistance mostly surpassed the maximum resistance suitable for the root (2.0MPa) in mild and moderate droughts. And it was unimodal distribution in soil layer of0-40cm. In moderate drought, the biggest resistance of D was1.8MPa in the25cm layer and the P was3.3MPa in the12.5cm layer. The peak value of the Plot B occurred in the20cm layer. The CK was4.3MPa and the NPKM was3.7MPa. The penetration resistance difference was significant among tillage measures and fertilizer treatments, and enlarged as water content decreased. The result indicated that as for red soil, the effect of high penetration resistance which due to lowered water content on crops must be considered.In mild and moderate droughts, the maize growth was intensively affected by the red soil penetration resistance. The root morphology indicators except the root diameter, plant growth indicators and the yield were all negatively related to the soil penetration resistance. Difference of maize growth was significant among the resistance treatments. The orders were D1.1> D1.3> D1.5of root morphology indicators, D> C> N> P and NPKM> PCM> NPK> CK of the plant indicators and yield. The differences got bigger during drought period. The result showed that soil penetration resistance changed root growth and decreased plant growth and yield. Also, resistance stress occurred before drought stress to act on the maize.The red soil penetration resistance reduced drought-resistant ability of the maize. It limited the roots into0-10cm horizontally and0-20cm vertically, reducing the range of water uptake. The wilting point was positively correlated with soil penetration resistance, and it in maximum resistance was19.5%higher compared with in minimum resistance. In the same dry condition, crops in high soil resistance wilted ahead of time. The water use efficiency, root water potential and leaf water content were negatively correlated with soil penetration resistance. The water use efficiency of D was respectively28.3%and30.9%higher compared with N and P under non-irrigation. Then it was38.0%and29.5%higher respectively under irrigation. The regression analysis showed that effects of soil resistance on root water potential and leaf water content were bigger than water content in non-drought period.The water and resistance interaction of red soil in drought was complex. In mild and moderate droughts, soil penetration resistance affected crop before water stress, and played a more important role of maize growth. As the drought aggravated, soil resistance increased sharply, then it made the soil-crop water relation worse. Soil penetration resistance stress formed positive feedback with water stress, intensifying the harm of seasonal drought to crops. As to the red soil in this study, deep tillage reduced its penetration resistance remarkably. The application of manure and straw returning also were helpful to reduce soil penetration resistance, thus improved crop-water relations. On the other hand, no tillage practice resulted in the high soil penetration resistances, so it reduced the crop growth directly and was not helpful to reduce the seasonal drought.