Effects of Different Soil Preparation and Fertilizer Application Methods on the Growth and Yield of the Rice-Crayfish Rotation Direct Seeding Rice Nongxiang 32

DAI Li, TAO Shu-hua, HU Wen-bin, LIU Ye, LI Wen-zhong, FANG Bao-hua, ZHAO Zheng-hong

Hunan Rice Research Institute, Changsha 410125, PRC

Abstract In order to improve the yield and fertilizer utilization of the ricecrayfish rotation and direct seeding rice Nongxiang 32, the effects of different soil preparation and fertilizer application methods on the growth, yield and fertilizer utilization of the variety were studied. The results showed that, under the ricecrayfish rotation and direct seeding farming mode, the contributions of seed setting rate, 1 000-grain weight, yield, and fertilizer contribution rate to yield of Nongxiang 32 in the treatments with rotary tillage with base fertilizer, rotary tillage without base fertilizer and no-tillage with base fertilizer were relatively higher than those in the treatments with rotary tillage without fertilizer, no-tillage without fertilizer and notillage without base fertilizer, and there were no significant differences between the three treatments. Rotary tillage with base fertilizer and rotary tillage without base fertilizer significantly increased the total number of stems and tillers, total number of ears, and number of effective ears. Rotary tillage and application of base fertilizer also significantly increased the number of tillers, plant weight and weed suppression ability in the early stage of rice growth. Therefore, in the different soil preparation and fertilizer application methods, the application of base fertilizer with rotary tillage was the best, followed by rotary tillage without base fertilizer and no-tillage with base fertilizer.

Key words Rice-crayfish rotation; Direct seeding; Rotary tillage; No-tillage; Fertilization method

1. Introduction

Recently, rice-crayfish farming in paddy fields developed very quickly as a result of the attractive profits in crayfish breeding. As a new hybrid, ecological mode mainly in the middle and lower reaches of Yangtze river, rice-crayfish farming is conducive to the adjustment and optimization of agricultural and rural economic structure. The ricecrayfish mode mainly includes rice-crayfish integrated farming mode and rice-crayfish rotation farming mode. Rice-crayfish integrated farming means to grow rice and breed crayfish concurrently in the same paddy field; while rice-crayfish rotation farming means to breed crayfish in the vacant paddy field and then grow rice after the crayfish were fished out. This kind of rice with rotation is called ricecrayfish rotation rice.

As the economy boomed and rural labor decreased, simplified growing of rice has become an inevitable trend. In rice-crayfish rotation farming mode, the paddy fields are submerged in water for long periods, the surface is usually covered with a thick layer of mud, and weeds are rarely seen after drainage. Besides, as no plowing is needed for this kind of fields, the base fertilizer cannot be ploughed into the soil. Moreover, the mud surface also contains rich nutrients, hence no base fertilizer is required. Only tillering fertilizer and particle fertilizer are necessary during middle and late breeding periods. In this case, a simplified growing mode of “no-tillage+ base fertilizer-free + direct seeding” was therefore created. Obviously, this mode can save cost and time significantly, but seldom studies on this new mode were reported. This study systematically explored the growth, yield and fertilizer utilization of rice-crayfish rotation rice under different soil preparation and fertilizer application methods to find out the optimal soil preparation and fertilizer application method for rice-crayfish rotation rice, thus providing theoretical basis and technical support for high quality and efficient production of rice-crayfish rotation rice in Hunan Province.

2. Materials and Methods

2.1. Experimental materials

The experimental variety was Nongxiang 32, which was an upscale ricebred by Hunan Rice Research Institute and provided by Hunan Jin Se Nong Feng Seed Co., Ltd.

2.2. Experimental design

The experiment was conducted from June to October of 2020 in Nanshan, Nanzhou, Nanxian, Yiyang, Hunan Province. The seeds were sown on June 19after crayfish were netted. The seeding quantity was 75 kg/hm.

Split-plot design was adopted for the experiment. The primary plot used different soil preparation methods, and the subplot used different fertilizer application methods. The sizes of the primary plot and the subplot were 210 and 70 m, respectively. Totally 6 treatments with 3 repetitions were performed. The field ridge of subplot was covered with membrane for isolation. The soil preparation treatments include: rotary tillage P1 (mechanical rotary tillage at 15 cm depth from soil surface) and no-tillage P2. The fertilizer application treatments include: no fertilizer F1, no base fertilizer F2 (only topdressing) and base fertilizer F3. The amount and application method for F2 was: apply 240 kg/hmof both pure nitrogen and KO; topdress 450 kg/hmcompound fertilizer at tillering stage (N∶PO∶KO=17∶10∶17); topdress 150 kg/hmpotassium chloride after field drying; topdress 51 kg/hmurea and 108 kg/hmpotassium chloride respectively at panicle primordium differen- tiation stage. The amount and application method for F3 was: apply 225 kg/hmof both pure nitrogen and KO; apply 600 kg/hmcompound fertilizer for base fertilizer (N∶PO∶KO=17∶10∶17); topdress 150 kg/hmcompound fertilizer and 150 kg/hmurea at tillering stage; topdress 150 kg/hmpotassium chloride after field drying; topdress 60 kg/hmurea and 60 kg/hmpotassium chloride respectively at panicle primordium differentiation stage.

Conduct closed weeding after sowing. Other managements were the same as local mode.

2.3. Test items and methods

2.3.1. Seedling quality

Select 10 representative plants from each plot at the three-leaf stage and examine their leaf age, number of tillers per plant and stem base width; after each treatment, select 30 representative plants and examine the dry weight of the stem and leaf.

2.3.2. Inverted two-leaf SPAD value

Select 10 representative plants from each plot at the maximum tillering stage, panicle primordium differentiation stage II, initial heading stage and pustulation period respectively. Use SPAD-502 portable chlorophyll content tester to perform

in vivo

measurement of the inverted two-leaf SPAD value.

2.3.3. Accumulation of above-ground dry matter

Select 10 representative plants from each plot at the maximum tillering stage, panicle primordium differentiation stage II, initial heading stage and pustulation period respectively and measure the above-ground dry matter accumulation.

2.3.4. Number, fresh weight and dry weight of weed plants, stem and tiller number of rice, fresh weight and dry weight of rice, the ratio of weed dry weight and rice dry weight

Measure the number, fresh weight and dry weight of weed plants, stem and tiller number of rice, fresh weight and dry weight of rice, the ratio of weed dry weight and rice dry weight of 1 marea during the jointing stage.

2.3.5. Tiller, yield and components

Select 1 mplants from each plot at the maturing stage to investigate their number of effective ears, total number of ears, total number of stems and tillers, and stem-tiller percentage; randomly select 30 effective tillers from each plot to investigate the filled grain number per ear, empty grain number per ear, total number of grains per ear, setting rate, 1 000-grain weight and theoretical yield; randomly select 2 msamples from each plot to investigate the actual yield of rice, stem weight, harvest index and contribution rate of fertilizer to yield.

2.3.6. Lodging

Make lodging evaluation based on the actual lodging state and area during mature lodging period.

2.4. Data processing analysis

Apply Excel 2007 and DPS 17.10 to make statistical analysis and use LSD method to make multiple comparisons.

3. Results and Analysis

3.1. Effects of different soil preparation and fertilizer application methods on the growth of rice-crayfish rotation and direct seeding rice in its three-leaf stage

The results of this study were shown as Table 1. For different soil preparation methods, the difference between P1 and P2 was not significant in terms of leaf age and number of stems and tillers per plant. The stem base width of P2 was significantly smaller than that of P1, the leaf dry weight of P2 was extremely larger than that of P1, and the stem dry weights of P1 and P2 were close. For different fertilizer application methods, the leaf age, stem base width, stem dry weight and leaf dry weight of F3 were the largest, followed by F1 and F2. F3 was extremely different from F1 and F2, and the number of stems and tillers of F3 was slightly higher than those of F1 and F2. For combined treatment of soil preparation and fertilizer application, the leaf age, stem base width, stem dry weight and leaf dry weight of P1F3 and P2F3 were extremely different from other treatments. The results indicated that P1F3 was the best treatment for the growth of Nongxiang 32 in its seedling stage, followed by P2F3.

3.2. Effects of different soil preparation and fertilizer application methods on the inverted two-leaf SPAD value and above-ground dry weight of rice-crayfish rotation and direct seeding rice

According to Table 2, different soil preparation methods presented limited effects on the above-ground dry matter accumulation and inverted two-leaf SPAD value during the maximum tillering stage, panicle primordium differentiation stage II, initial heading stage and filling stage. The two soil preparation methods had no significant difference. For different fertilizer application methods, the above-ground dry matter of F3 was extremely different from that of F1 and F2 during the maximum tillering stage; the aboveground dry matter of F3 was extremely different from F1 during the panicle primordium differentiation stage II; the difference of the methods in the aboveground dry matter at the initial heading stage was not significant. For the above-ground dry matter at thefilling stage, it was shown a order of F3>F2>F1. F1 was significantly different from F3 and F2, while F2 and F3 had no significant difference. For the effect of different fertilizer application methods on inverted two-leaf SPAD value, F1 and F3 had no significant difference at the panicle primordium differentiation stage but were extremely different at other three stages; F2 and F1 had no significant difference at the panicle primordium differentiation stage and filling stage but were significant different at the maximum tillering stage and initial heading stage; F2 and F3 were significantly different at the filling stage but presented no significant difference at other three stages. For combined treatment of soil preparation and fertilizer application, P1F3 had the highest aboveground dry weight for all the 4 growth stages. P2F3 was weak at the filling stage but performed well at other three stages.

Table 1 Effects of different soil preparation and fertilizer application methods on the growth of rice-crayfish rotation and direct seeding rice in its seedling stage

Table 2 Effects of different soil preparation and fertilizer application methods on the inverted two-leaf SPAD value and above-ground dry weight of rice-crayfish rotation and direct seeding rice at different growing stages

3.3. Effects of different soil preparation and fertilizer application methods on the rice and weed growth at the jointing stage

As shown in Table 3, for soil preparation methods, P1 and P2 had no significant difference in terms of quantity and weight of field weeds during the jointing stage. But the number of stems and tillers and plant weight (fresh and dry weight) per square meter of P1 were significantly higher than those of P2. This indicated that P1 had limited effect on eradicating weeds but can improve the soil structure and promote the growth of rice at the early growing stage. For fertilizer application methods, F1 and F3 had no significant difference in weed quantity per square meter during the jointing stage. The fresh and dry weight of weeds per square meter and dry weight ratio of weed and rice of F2 were both smaller than F1 and F3. For the fresh and dry weight of rice plant, it was shown a order of F3>F2>F1, and F1 was extremely different from F3 and F2. This indicated that topdressing at the tillering stage and after field drying was conducive to the growing of direct seeding rice during tillering stage and jointing stage, which can strengthen the competition of rice against weeds and inhibit the growth of weeds. The above results showed that rotary tillage with base fertilizer was the best for the early growth of Nongxiang 32, which can win the rice more light and nutrients against weeds, and restrict the growing of weeds.

Table 3 Effects of different soil preparation and fertilizer application methods on the competition ability of rice-crayfish rotation direct seeding rice against weeds during the jointing stage

3.4. Effects of different soil preparation and fertilizer application methods on the tiller-earing and yield of rice-crayfish rotation direct seeding rice

As shown in Table 4, the setting rate, 1 000-grain weight and harvest index of P1 were higher than those of P2. The setting rate and 1 000-grain weight of the treatments were extremely different, and the harvest indexes were significantly different; the total number of ears, number of effective ears, stem-tiller percentage, total number of grains per ear, theoretical yield, actual yield and fertilizer contribution rate to yield of P1 were all higher than P2, but the difference between the two treatments was not significant; this indicated that no-tillage could lead to rampant growth of plants and nourishment waste, thus harming the effective production of rice. Therefore, rotary tillage is more beneficial to the high yield of direct seeding rice.

Table 4 Effects of different soil preparation and fertilizer application methods on the yield and fertilizer utilization of direct seeding rice Nongxiang 32

For the total number of ears, number of effective ears and 1 000-grain weight of different fertilizer treatments, it was shown a order of F2>F3>F1, and F2 was significantly different from F1. As for the setting rate, theoretical yield and actual yield of different fertilizer treatments, it was shown a order of F3>F2>F1, and F3 was significantly different from F1. For the total number of grains per ear and harvest index, the three fertilizer treatments had no significant differences. The setting rate, theoretical yield, actual yield and fertilizer contribution rate to yield of F3 were all slightly higher than those of F2. The number of effective ears, total number of ears and stem-tiller percentage of F2 was slightly higher than those of F3, indicating that topdressing without base fertilizer can promote tiller-earing and avoid the invalid rampant growth of plants.

The total number of ears and number of effective ears of Nongxiang 32 by P1F3 and P1F2 treatments were higher than those by other treatments, indicating that the combination of soil preparation and fertilizer application can construct high-yield group and achieve high-yield goals; the number of effective ears, stemtiller percentage, 1 000-grain weight, theoreticalyield, actual yield and fertilizer contribution rate to yield by P1F3, P1F2 and P2F3 were all higher than by other treatments; the number of effective ears, stem-tiller percentage, theoretical yield, actual yield and fertilizer contribution rate to yield between these three treatments had no significant difference, but the 1 000-grain weight of P1F2 was significantly higher than that of other two treatments, and the harvest index of P1F3 was significantly higher than that of other two treatments.

3.5. Effects of different soil preparation and fertilizer application methods on plant lodging of rice-crayfish rotation direct seeding rice at the maturing stage

As shown in Table 5, P1F3 had the poorest performance in lodging resistance for Nongxiang 32 probably due to its highest plant height compared with other treatments, followed by P2F2 treatment. Other treatments had no plant lodging.

Table 5 Effects of different soil preparation and fertilizer application methods on plant lodging of rice-crayfish rotation direct seeding rice

4. Discussion and Conclusion

Rotary tillage can significantly increase the number of stems and tillers and dry matter accumulation of plants during the early growing stage of rice. It can strengthen their ability in competing with weeds, restrict ineffective tillers and reduce rampant growing thus to construct high-yield population. By coordinating the relationship with source-sink-translocation, the method can improve the setting rate, 1 000-grain weight and harvest index of rice and achieve a goal of efficient product goals. Meanwhile, rotary tillage can effectively improve the fertilizer utilization (fertilizer contribution rate to yield) and realize high-yield goals. During the early growth stage, application of base fertilizer or topdressing can increase the number of stems and tillers and weight of plants, and enhance their abilities of inhibiting the growth of weeds. When applying the same total amount of fertilizer during the whole growth duration, the yield and fertilizer utilization rate of either samples applied with base fertilizer or applied with topdressing (without base fertilizer) were basically the same. For the combination of soil preparation and fertilizer application, the setting rate, 1 000-grain weight, yield and fertilizer contribution rate to yield of rotary tillage with base fertilizer, rotary tillage without base fertilizer and no-tillage with base fertilizer were relatively higher than those of other treatments, and the three treatments had no significant difference; rotary tillage with base fertilizer and rotary tillage without base fertilizer can increase the total number of ears and the number of effective ears, reduce invalid tillers, and lay a good basis for future high production. Meanwhile, rotary tillage with base fertilizer can improve the growth of ricecrayfish rotation rice during its early growth stage, and enhance their ability of competing with weeds for light and nutrients. Therefore, when adopting simplified plowing methods for rice-crayfish rotation direct seeding rice, rotary tillage with base fertilizer can have better performance than rotary tillage without base fertilizer and no-tillage method with base fertilizer.

The “no-tillage + base fertilizer-free + direct seeding” mode can save cost and labor, but the yield and fertilizer utilization rate were relatively lower than the modes of rotary tillage with base fertilizer, rotary tillage without base fertilizer and no-tillage method with base fertilizer. Hence, a simplified highyield culture technique was recommended based on the cropping system, ecology and specific varieties from the aspects of food security and environment protection. In addition, this study only compared the difference between rotary tillage and no-tillage method without considering the tillage processing, and the topdressing amount, topdressing times and period can be further optimized. Finally, whether long-term topsoil rotary tillage could reduce the thickness of tillage layer of rice-crayfish rotation rice fields and how long it will take to make a deep tillage needs further exploration.